94. Dierauer, JR; Allen, DM; Whitfield, PH.Snow Drought Rick and Susceptibility in the Western United States and Southwestern Canada.Water Resour. Res., 2019, 55: 3076-3091 Snow Drought Rick and Susceptibility in the Western United States and Southwestern Canada
In western North America (WNA), mountain snowpack supplies much of the water used for irrigation, municipal, and industrial uses. Thus, snow droughts (a lack of snow accumulation in winter) can have drastic ecological and socioeconomic impacts. In this study, the historical (1951-2013) frequency, severity, and risk (frequency x severity) of dry, warm, and warm and dry snow droughts are quantified at the grid-cell and ecoregion scale for snow-dominated regions in the western United States and southwestern Canada (sWNA). Based on multiple linear regression analysis, relationships between mean winter temperature, snow drought risk, and snow water equivalent sensitivity are explored. Piecewise linear regression is used to identify temperature thresholds for mapping temperature-related snow drought susceptibility. Results highlight spatial differences in snow drought regimes across sWNA and reveal that temperature thresholds exist at -3.1 degrees C (+/- 0.3 degrees C) and 1.4 degrees C (+/- 0.3 degrees C), above which the warm snow drought risk increases more rapidly. Approximately 3% of the nonglaciated snow storage in this region has high susceptibility to temperature-related snow drought, representing 11 km(3) of water, or approximately one third the capacity of Lake Mead. Under a +2 degrees C climate scenario, an additional 8% (28 km(3)) of this snow storage volume will transition to high susceptibility. Plain Language Summary In western North America, mountain snowpack fills reservoirs for agricultural, municipal, and industrial uses and sustains streamflow in summer when ecosystem needs are high. Thus, snow droughts (a lack of snow accumulation in winter) can have large social, economic, and environmental impacts. An analysis of the frequency and severity of past snow droughts shows that warm and dry winter conditions occurring together produce the most severe snow droughts, while warm winter conditions alone produce the least severe snow droughts. The severity and frequency of warm snow droughts, however, is dependent on mean winter temperature, and the risk of warm snow droughts is substantially higher for locations with mean winter temperatures above -3.1 degrees C (+/- 0.3 degrees C). Approximately 3% of the volume of the western United States' and southwestern Canada's nonglaciated snowpack is highly susceptible to warm snow droughts, and an additional 24% exhibits medium susceptibility. DOI
93. Morgan, SE; Allen, DM; Kirste, D; Salas, CJ.Investigating the hydraulic role of a large buried valley network on regional groundwater flow.Hydrogeol. J., 2019, 27: 2377-2397 Investigating the hydraulic role of a large buried valley network on regional groundwater flow
Buried valley aquifers; Geophysical methods; Petrel; Groundwater modeling; Canada
An understanding of the three-dimensional hydrostratigraphic architecture of a buried valley network, in particular the continuity of permeable units within their fill, is needed to evaluate the resource potential and role of buried valley aquifers in regional groundwater flow. In this study, a facies modeling algorithm within the exploration and production software Petrel was used to construct a geological model of a buried valley network located in the central Peace Region in Northeast British Columbia, Canada. Facies were interpreted using resistivity inversion results from an airborne electromagnetic survey (SkyTEM) and borehole gamma-ray and lithology logs. This detailed geological model and a simplified geological model of the buried valley network were used to develop two interpretive numerical groundwater flow models in MODFLOW. Calibration was performed using baseflow estimates derived using a novel approach whereby upper and lower bounds for baseflow indices were combined with streamflow estimates from the Northeast Water Tool (NEWT), a hydrological modeling tool developed for water allocation for industrial use by the British Columbia Oil and Gas Commission. The modeling results suggest that permeable deposits exist within the buried valleys, but are not regionally connected throughout the whole network, and thus do not play a significant role in the regional groundwater flow regime. However, locally extensive permeable deposits occur within the buried valleys and may offer viable water sources for domestic use or to replace existing surface-water licenses for industrial use. DOI
92. Dierauer, JR; Whitfield, PH; Allen, DM.Climate Controls on Runoff and Low Flows in Mountain Catchments of Western North America.Water Resour. Res., 2018, 54: 7495-7510 Climate Controls on Runoff and Low Flows in Mountain Catchments of Western North America
In the mountainous regions of western North America, snowmelt recharges groundwater and provides ecosystem-sustaining base flow during low-flow periods. Continued warming is expected to have large impacts on snowmelt hydrology and on low-flow regimes, but the relative impact of temperature and precipitation on low flows is unclear. To address this knowledge gap, the dominant climate controls on summer and winter season low flows in 63 near-natural catchments in mountainous ecoregions of western North America are identified with correlation analysis, and low-flow sensitivity to temperature and precipitation is quantified with multiple linear regression analysis. Results show that precipitation is the dominant control on the interannual variability of annual runoff and on the duration and severity of summer and winter low flows. The temperature sensitivity of low flows, however, can be as much as twice that of annual runoff. Warm winters correspond to significantly lower runoff; significantly longer, more severe summer low flows; and significantly shorter winter low flows. This highlights the importance of winter climate conditions for runoff and low flows in these mountain catchments and provides another line of evidence regarding the impacts of climate change on snowmelt hydrology. Plain Language Summary In the mountains of western North American, snowmelt is an important component of streamflow. Precipitation that falls during the winter season is stored as snowpack, and melting of this snowpack generates streamflow. During spring when the snowpack is melting rapidly, streamflow peaks, but during the winter and summer months the contribution of snowmelt to streamflow diminishes, and streamflow is largely sourced from groundwater discharge. These periods correspond to low-flow periods. Continued warming is expected to have large impacts on the timing and magnitude of snowmelt and thus large impacts on the duration and severity of low-flow periods. The relative impact of precipitation and temperature on low flows is currently unclear. Analysis of streamflow and climate data from 63 mountain catchments shows that precipitation is the dominant control on total annual streamflow and on the duration and severity of low flows. Compared to annual streamflow, however, low flows are up to 2 times more sensitive to temperature, particularly winter temperatures above 0 degrees C. With no change in precipitation, continued warming in these mountain catchments will likely yield longer, more severe summer low flows, shorter winter low flows, and an overall decrease in annual streamflow. DOI
91. Hund, SV; Allen, DM; Morillas, L; Johnson, MS.Groundwater recharge indicator as tool for decision makers to increase socio-hydrological resilience to seasonal drought.J. Hydrol., 2018, 563: 1119-1134 Groundwater recharge indicator as tool for decision makers to increase socio-hydrological resilience to seasonal drought
Groundwater recharge; Socio-hydrology; Resilience; Drought; Wet-dry tropics; Adaptation
Communities in regions with seasonal rainfall face annual dry seasons, during which water shortages and conflicts between different water use sectors may erupt. These difficulties increase following wet seasons with low rainfall, such as in relation to El Nino events in the wet-dry tropics of Central America. Hydrologic data are typically scarce in this region, making the development of drought adaptation strategies challenging. Many communities in the region depend on groundwater as their primary water source. For instance in the Province of Guanacaste in Costa Rica, groundwater supplied 78% of the total domestic water demand in 2015 and groundwater recharge from the wet season provides the primary water supply for the subsequent dry season. In this research we present a 'groundwater recharge indicator' that can support water managers in preparing for seasonal droughts. We developed this tool for an aquifer in northwestern Costa Rica where we conducted hydrological monitoring of streams and groundwater levels for 2.5 years, obtained further hydrological data (groundwater levels from 2005 to 2016), and worked with communities to assemble water use data. We combined these datasets in a hydrologic model (the Water Evaluation And Planning system, WEAP) and modelled groundwater recharge from 2005 to 2016, permitting a characterization of the relationship between rainfall and groundwater recharge. The groundwater recharge indicator is based on this relationship, and allows estimating total groundwater recharge for a wet season from cumulative rainfall measured to date. The indicator permits water managers to assess if the current year will likely fall into a low recharge category prior to the end of the wet season. This information can then be used to trigger short-term adaptation strategies with the goal to 'bank' groundwater while surface water sources are still available in the wet season. This indicator-based tool was refined through feedback provided in local stakeholder workshops. We also assessed the overall accuracy of predicting end-of-wet-season groundwater recharge with cumulative rainfall to date, and found that after the first 2-3 months of the wet season, prediction accuracies are high, leaving 5-6 months of wet season to respond adaptively to the prediction. The indicator can help water managers to plan ahead, and communicate the need for water conservation (demand management) and consideration of other water sources such as rain and surface water (supply management). This idea is transferable to other communities in regions with seasonal rainfall, and can support decision makers in increasing the socio-hydrological resilience of communities to seasonal droughts. DOI
90. Rathay, SY; Allen, DM; Kirste, D.Response of a fractured bedrock aquifer to recharge from heavy rainfall events.J. Hydrol., 2018, 561: 1048-1062 Response of a fractured bedrock aquifer to recharge from heavy rainfall events
Groundwater recharge; Heavy rainfall; Fractured rock; Groundwater seepage; Thermal infrared imagery; Stable isotopes of water
Climate change is predicted to lead to an increased frequency of high intensity rainfall events. The impact on groundwater resources, particularly in areas of fractured bedrock aquifer systems, requires knowledge of how recharge is affected. In this study, the response of a fractured bedrock aquifer to heavy rainfall events is characterized. The study area is the Gulf Islands, a temperate region in British Columbia, Canada. Of the 14 provincial observation wells with hourly groundwater level data, only three showed pronounced responses to heavy rain events and were analyzed in detail. A detailed analysis at one well suggests rises in groundwater level were better correlated to all rain events than exclusively heavy rain during summer. The strength of the correlation decreased as the rainfall intensity increased. Solution of the Green-Ampt equation for rainfall events of varying magnitude indicated that an increase in rainfall intensity leads to more surface ponding and overland flow. Thus, the occurrence of more frequent heavy rain events in the future may result in lower net recharge. Thermal infrared images in seepage areas and the delta O-18 and delta H-2 composition for precipitation and seepage suggest rapid seepage responses to heavy rain events and rapid seepage dissipation rates. The overall rapid response of the fractured bedrock was advantageous for studying the response of the system to heavy rain events. (C) 2017 Elsevier B.V. All rights reserved. DOI
89. Alessi, DS; Zolfaghari, A; Kletke, S; Gehman, J; Allen, DM; Goss, GG.Comparative analysis of hydraulic fracturing wastewater practices in unconventional shale development: Water sourcing, treatment and disposal practices.Can. Water Resour. J., 2017, 42: 105-121 Comparative analysis of hydraulic fracturing wastewater practices in unconventional shale development: Water sourcing, treatment and disposal practices
This paper is the first of a two-part series designed to assess and summarize extant knowledge regarding hydraulic fracturing water and wastewater management practices using a comparative, multidisciplinary approach. To provide context for both papers, the water and wastewater practices are summarized for the four focus plays: Montney, Duvernay, Barnett, and Marcellus. In Alberta and British Columbia, which host the less-studied Duvernay and Montney plays, play-scale unconventional water and wastewater data are extracted and combined from three databases: FracFocus. ca, geoSCOUT, and AccuMap. A reasonable picture of hydraulic fracturing water use and practices in western Canada emerges from the over 4,000 wells studied. From late 2011 to early 2014, the average number of fracturing stages reported increased from 7 to over 14, while reported cumulative water use approached approximately 15 million m(3) in 2013, the first year for which full data in all three databases was available. The majority of wells consuming 10,000 to 50,000 m(3) of water are slickwater type, located largely in the two target plays; however, several wells using >50,000 m(3) of water appear in the Horn River Formation in BC. While it is possible to identify in the databases wastewater treatment facilities and deep wastewater injection wells, it is at present difficult to constrain wastewater disposal practices and chemistry in Alberta and British Columbia. The analysis points to the need for further coordination between academics, industry, and governmental agencies to develop publicly available, searchable databases that carefully document water sourcing, wastewater recycling/reuse/disposal, and chemistry, in order to properly form hydraulic fracturing water management strategies. DOI
88. Dierauer, JR; Whitfield, PH; Allen, DM.Assessing the suitability of hydrometric data for trend analysis: The 'FlowScreen' package for R.Can. Water Resour. J., 2017, 42: 269-275 Assessing the suitability of hydrometric data for trend analysis: The 'FlowScreen' package for R
FlowScreen is an R package primarily developed for assessing the suitability of daily hydrometric data for trend analysis. It also contains tools for plotting and calculating other streamflow metrics. The package can be used to produce summary screening plots showing change-points and significant temporal trends for high flow, low flow and/or baseflow statistics, or it can be used to perform more detailed hydrological time series analyses. The package was designed for screening daily streamflow time series from Water Survey Canada and the United States Geological Survey but will also work with streamflow time series from many other agencies. DOI
87. Hsieh, AI; Allen, DM; MacEachern, JA.Upscaling permeability for reservoir-scale modeling in bioturbated, heterogeneous tight siliciclastic reservoirs: Lower Cretaceous Viking Formation, Provost Field, Alberta, Canada.Mar. Pet. Geol., 2017, 88: 1032-1046 Upscaling permeability for reservoir-scale modeling in bioturbated, heterogeneous tight siliciclastic reservoirs: Lower Cretaceous Viking Formation, Provost Field, Alberta, Canada
Bioturbation; Permeability; Upscaling; Numerical flow modeling; Siliciclastic
Variations in bed-and bedset-scale permeability in bioturbated siliciclastic rocks result in heterogeneity that is difficult to model at a reservoir scale. This paper presents a technique to upscale permeability, such that the permeabilities of the bioturbated zones are explicitly included in the upscaled values. Study of 28 cored wells of the Lower Cretaceous Viking Formation in the Provost Field, Alberta, Canada integrated sedimentologic and ichnologic features to define recurring bed-/bedset-scale hydrofacies (HFs) characterized by a geometric mean permeability derived from plug samples. Permeability was upscaled by calculating equivalent vertical and horizontal permeabilities for composite hydrofacies (CHFs) using expressions for layered media. The equivalency of the vertical and horizontal permeability values assigned to the CHFs against those of the HFs was evaluated using a simple numerical flow model. Reservoir-scale flow was then simulated along a hydrogeological cross-section that was constructed using the CHFs. The resulting flow regime was consistent with flows simulated using published permeability estimates from tight reservoir units of the Viking Formation. This approach has the potential, therefore, for upscaling permeability for reservoir-scale modeling in tight oil and gas reservoirs, and more broadly in reservoirs where permeability is highly variable at the bed bedset scale. (C) 2017 Elsevier Ltd. All rights reserved. DOI
86. Klassen, J; Allen, DM.Assessing the risk of saltwater intrusion in coastal aquifers.J. Hydrol., 2017, 551: 730-745 Assessing the risk of saltwater intrusion in coastal aquifers
Saltwater intrusion; Risk assessment; Sea level rise; Storm overwash; Pumping; Economics
In coastal regions, the quality of groundwater can be compromised due to saltwater intrusion (SWI) caused by natural (sea level rise (SLR) and storm surge) and anthropogenic (pumping) hazards. The goal of this research was to develop and test an approach for assessing the risk of SWI in coastal aquifers. The Gulf Islands in British Columbia (BC) was the case study area. The vulnerability of the bedrock aquifers to SWI was assessed spatially by mapping hazards in combination with the aquifer susceptibility. Climate change related hazards, including SLR and storm surge overwash, were integrated into floodplain maps for each island using projected SLR data for 2100 in combination with estimated storm surge levels based on data collected over a forty year period. When combined with maps showing the density of pumping wells, coastal zones that may be at higher risk of SWI were identified for this particular coastal area of BC. Hazards due to pumping have the greatest influence on the vulnerability. Risk was evaluated spatially using an economic valuation of loss - here replacement of a water supply. The combination of chemical indicators of SWI and risk assessment maps are potentially useful tools for identifying areas vulnerable to SWI, and these tools can be used to improve decision-making related to monitoring and community development for coastal areas, thereby increasing resilience. (C) 2017 Elsevier B.V. All rights reserved. DOI
85. Notte, C; Allen, DM; Gehman, J; Alessi, DS; Goss, GG.Comparative analysis of hydraulic fracturing wastewater practices in unconventional shale developments: Regulatory regimes.Can. Water Resour. J., 2017, 42: 122-137 Comparative analysis of hydraulic fracturing wastewater practices in unconventional shale developments: Regulatory regimes
This paper is the second in a two-part series that assesses and summarizes extant knowledge regarding hydraulic fracturing wastewater management using a comparative, multidisciplinary approach. This study compares the regulatory regimes related to wastewater handling (storage and transport), treatment and disposal practices as they apply to the hydraulic fracturing industry in four unconventional shale plays in North America: the Montney in British Columbia (BC), the Duvernay in Alberta (AB), the Marcellus in the northeastern United States (US) and the Barnett in Texas. In North America, handling, treatment and disposal practices in the regulation of oil and gas wastewater is complex and multifaceted due to shared jurisdiction over many aspects across provincial or state lines, and/or across provincial/state and federal levels. All jurisdictions considered in this assessment have highly specific regulations for many elements of wastewater handling, treatment and disposal. However, much of the guidance for these practices comes from other legislation that makes provisions for environmental or safety performance, or prohibitions against pollution. The research suggests that knowledge gaps exist in the areas of regulatory outcomes, and compliance and best management practices, particularly in how those factors enable and constrain environmentally sustainable practices. BC's area-based-management model and AB's play-based-regulation pilot project are examples of attempted cumulative effects assessment and management noticeably absent from the Marcellus or Barnett plays. DOI
84. S. Holding, D.M. Allen, C. Notte, N. Olewiler.Enhancing water security in a rapidly developing shale gas region.Journal of Hydrology - Regional Studies. Special Volume on the Water-Energy Nexus, 2017, 11: 266-277 Enhancing water security in a rapidly developing shale gas region
Study region
This study is based in the rapidly developing shale gas region of Northeast British Columbia, Canada.
Study focus
Water security is central to decision-making within a water–energy nexus. In areas where energy resources, such as shale gas, are undergoing rapid development, water security and the associated risks to water quality and quantity are of paramount concern. However, in many regions there is a lack of understanding and data on the hydrologic system, particularly its vulnerability to hazards. The data and knowledge gap poses challenges for effective regulation of the shale gas activities and management of water resources. This paper describes initiatives that are addressing concerns surrounding water security in Northeast British Columbia.
New hydrological insights for the region
Initiatives and tools enhancing water security in the region include strategic partnerships and stakeholder collaborations, policy and regulation development, and data collection and distribution efforts. The contributions and limitations of each of these are discussed. A vulnerability mapping framework is presented which addresses data gaps and provides a tool for decision-making surrounding risk to water quality from various hazards. An example vulnerability assessment was conducted for wastewater transport along pipeline and trucking corridors.PDF DOI
83. Buttle, JM; Allen, DM; Caissie, D; Davison, B; Hayashi, M; Peters, DL; Pomeroy, JW; Simonovic, S; St-Hilaire, A; Whitfield, PH.Flood processes in Canada: Regional and special aspects.Can. Water Resour. J., 2016, 41: 7-30 Flood processes in Canada: Regional and special aspects
This paper provides an overview of the key processes that generate floods in Canada, and a context for the other papers in this special issue - papers that provide detailed examinations of specific floods and flood-generating processes. The historical context of flooding in Canada is outlined, followed by a summary of regional aspects of floods in Canada and descriptions of the processes that generate floods in these regions, including floods generated by snowmelt, rain-on-snow and rainfall. Some flood processes that are particularly relevant, or which have been less well studied in Canada, are described: groundwater, storm surges, ice-jams and urban flooding. The issue of climate change-related trends in floods in Canada is examined, and suggested research needs regarding flood-generating processes are identified. DOI
82. Gehman, J; Thompson, DY; Alessi, DS; Allen, DM; Goss, GG.Comparative Analysis of Hydraulic Fracturing Wastewater Practices in Unconventional Shale Development: Newspaper Coverage of Stakeholder Concerns and Social License to Operate.Sustainability, 2016, 8 Comparative Analysis of Hydraulic Fracturing Wastewater Practices in Unconventional Shale Development: Newspaper Coverage of Stakeholder Concerns and Social License to Operate
social license to operate; hydraulic fracturing; oil and gas industry; sustainability; stakeholder management; corporate social responsibility; cumulative effects management
In this article we review prior literature regarding the concept of social license to operate, and related concepts, including corporate social responsibility, sustainable development, stakeholder management and cumulative effects. Informed by these concepts, we search for newspaper articles published in North American provinces and states where the Barnett, Duvernay, Marcellus and Montney shale plays are located. Using these data, we tabulate coverage of stakeholder concerns related to hydraulic fracturing and wastewater practices, and compare the extent to which these concerns vary over place and time. Our vocabulary analyses identify differences in the types and quantities of newspaper coverage devoted to concerns regarding hydraulic fracturing activities in general and wastewater practices in particular. We interpret these differences as suggesting that obtaining a social license to operate is likely not a one size fits all proposition. By understanding which stakeholder concerns are most salient in particular places and times, oil and gas operators and regulators can better tailor their strategies and policies to address local concerns. In other words, the findings from this study indicate that conventional understandings of risk as a technical or economic problem may not be adequate for dealing with unconventional resource challenges such as hydraulic fracturing. Operators and regulators may also need to manage social and cultural risks. DOI
81. Holding, S; Allen, DM.Risk to water security for small islands: an assessment framework and application.Reg. Envir. Chang., 2016, 16: 827-839 Risk to water security for small islands: an assessment framework and application
Small islands; Water security; Risk assessment; Climate change; Land use
The freshwater resources of small islands are particularly vulnerable to the impacts of climate change and human stressors due to their limited extent and adaptive capacity. A water security approach is useful for effective management of the water resources; however, understanding risk to water security is critical in order to effectively plan and adapt to future changes. Currently available assessment tools generally do not incorporate risk and are not suitable for application on small islands, where the hydrogeological setting has unique vulnerabilities. The aim of this work is to provide a framework to characterize risk to water security for small islands. The risk assessment was developed using Andros Island, the Bahamas, as a case study area. Numerical modelling characterizes the response of the water system to potential future stressors related to climate change and human development, the results of which are integrated into the assessment framework. Based on risk assessment principles, indicators are determined for susceptibility, hazard threat, vulnerability and loss, in order to define the risk to water security. The resulting indicators are presented in geospatial maps that rank areas of risk to water security. These maps were provided to local water managers and policy-makers in the Bahamas as a tool to identify high-risk areas for near-term action and to inform long-term planning. The maps have also been used as a platform to engage local residents and raise awareness about the impact climate change and land-use activities may have on water security. DOI
80. Holding, S; Allen, DM; Foster, S; Hsieh, A; Larocque, I; Klassen, J; Van Pelt, SC.Groundwater vulnerability on small islands.Nat. Clim. Chang., 2016, 6: 1100-+ Groundwater vulnerability on small islands
The majority of naturally occurring freshwater on small islands is groundwater, which is primarily recharged by precipitation(1). Recharge rates are therefore likely to be impacted by climate change(2). Freshwater resources on small islands are particularly vulnerable to climate change because they are limited in size and easily compromised(3-5). Here we have compiled available aquifer system characteristics and water-use data for 43 small island developing states distributed worldwide, based on local expert knowledge, publications and regional data sets. Current vulnerability was assessed by evaluating the recharge volume per capita. For future vulnerability, climate change projections were used to estimate changes in aquifer recharge. We find that 44% of islands are in a state of water stress, and while recharge is projected to increase by as much as 117% on 12 islands situated in the western Pacific and Indian Ocean, recharge is projected to decrease by up to 58% on the remaining 31 islands. Of great concern is the lack of enacted groundwater protection legislation for many of the small island developing states identified as highly vulnerable to current and future conditions. Recharge indicators, shown alongside the state of legal groundwater protections, provide a global picture of groundwater supply vulnerability under current and future climate change conditions. DOI
79. Meixner, T; Manning, AH; Stonestrom, DA; Allen, DM; Ajami, H; Blasch, KW; Brookfield, AE; Castro, CL; Clark, JF; Gochis, DJ; Flints, AL; Neff, KL; Niraula, R; Rodell, M; Scanlon, BR; Singha, K; Walvoord, MA.Implications of projected climate change for groundwater recharge in the western United States.J. Hydrol., 2016, 534: 124-138 Implications of projected climate change for groundwater recharge in the western United States
Groundwater recharge; Recharge mechanisms; Climate change; Western United States
Existing studies on the impacts of climate change on groundwater recharge are either global or basin/location-specific. The global studies lack the specificity to inform decision making, while the local studies do little to clarify potential changes over large regions (major river basins, states, or groups of states), a scale often important in the development of water policy. An analysis of the potential impact of climate change on groundwater recharge across the western United States (west of 100 longitude) is presented synthesizing existing studies and applying current knowledge of recharge processes and amounts. Eight representative aquifers located across the region were evaluated. For each aquifer published recharge budget components were converted into four standard recharge mechanisms: diffuse, focused, irrigation, and mountain-systems recharge. Future changes in individual recharge mechanisms and total recharge were then estimated for each aquifer. Model-based studies of projected climate-change effects on recharge were available and utilized for half of the aquifers. For the remainder, forecasted changes in temperature and precipitation were logically propagated through each recharge mechanism producing qualitative estimates of direction of changes in recharge only (not magnitude). Several key patterns emerge from the analysis. First, the available estimates indicate average declines of 10-20% in total recharge across the southern aquifers, but with a wide range of uncertainty that includes no change. Second, the northern set of aquifers will likely incur little change to slight increases in total recharge. Third, mountain system recharge is expected to decline across much of the region due to decreased snow pack, with that impact lessening with higher elevation and latitude. Factors contributing the greatest uncertainty in the estimates include: (1) limited studies quantitatively coupling climate projections to recharge estimation methods using detailed, process-based numerical models; (2) a generally poor understanding of hydrologic flowpaths and processes in mountain systems; (3) difficulty predicting the response of focused recharge to potential changes in the frequency and intensity of extreme precipitation events; and (4) unconstrained feedbacks between climate, irrigation practices, and recharge in highly developed aquifer systems. (C) 2016 The Authors. Published by Elsevier B.V. DOI
78. Middleton, M; Allen, DM; Whitfield, PH.Comparing the groundwater contribution in two groundwater-fed streams using a combination of methods.Can. Water Resour. J., 2016, 41: 554-571 Comparing the groundwater contribution in two groundwater-fed streams using a combination of methods
Groundwater contributions to streams often vary both spatially and temporally. In this study, the relative contributions of groundwater to Fishtrap and Bertrand Creeks in the Lower Fraser Valley are compared during the summer and annually using a combination of methods. The streams drain watersheds that have a similar climate, area and topographic relief. However, the geological substrate differs, with finer grained material underlying Bertrand Creek. A simplified heat budget model is first used to estimate temperature at the air-water interface. Then, the correlation between the air-water and bed-water (interface) temperatures is compared for both annual and summer periods in each stream. The air temperature explains similar to 30% of the variance in the summer interface temperature in Fishtrap Creek, but more than 75% in Bertrand Creek. This difference suggests that factors at the bed-water interface influence the heat budgets, and that these factors differ between the two sites. The measured groundwater flux during the summer periods was higher in Fishtrap Creek than in Bertrand Creek, due to a higher vertical hydraulic gradient into the stream and higher aquifer sediment permeability. Thus, the larger groundwater contribution to Fishtrap Creek moderates stream temperature and stream discharge during the summer periods, whereas Bertrand Creek has greater potential for elevated stream temperatures and lower flows during the critical summer period The combination of methods used in this study strengthens the interpretations given the wide range of uncertainty in measurements. DOI
77. Mundy, EM; Dascher-Cousineau, K; Gleeson, T; Rowe, CD; Allen, DM.Complexity of hydrogeologic regime around an ancient low-angle thrust fault revealed by multidisciplinary field study.Geofluids, 2016, 16: 673-687 Complexity of hydrogeologic regime around an ancient low-angle thrust fault revealed by multidisciplinary field study
Champlain Thrust; fault zone; hydrogeology; outcrop mapping; pumping tests; thrust fault
Co-located and integrated observation of the surface and subsurface is necessary to characterize fault zone hydrogeology. The spectacular cliff-face exposure of the Champlain Thrust fault at Lone Rock Point, Vermont, and a nearby well-field site provides the opportunity for co-located structural and hydrogeologic field observations. We mapped the prominent structural features of the Champlain Thrust fault and discrete groundwater seeps in outcrop, and also drilled through the fault near the outcrop and determined aquifer parameters from aquifer pumping tests. In outcrop, the fault core thickness varies on the meter scale, splays out into multiple strands, and is offset by a minor normal fault. Groundwater seeps are prevalent in the heavily fractured footwall, but limited in the fault core and hanging wall, suggesting that at the cliff face the water table is generally near the fault core and groundwater flow in the hanging wall is limited. Enrichment of more soluble minerals in cemented fault rock associated with older strands of the fault system may play an important role in localizing karst features in the hanging wall. At the well-field site, the Champlain Thrust fault is offset significantly by a high-angle normal fault, the water table is near the surface, and aquifer pumping tests reveal a complex hydrogeologic system, with karst and steep fractures as strong hydraulic conduits in the hanging wall and fault core. The most salient features of the fault zone hydrogeology in the surface and subsurface data are different, but can be integrated into a preliminary conceptual model. Together, the surface and subsurface methods underscore and emphasize the complexity and heterogeneity of the hydrogeology of this low-angle sedimentary fault. DOI
76. Antonellini, M; Allen, DM; Mollema, PN; Capo, D; Greggio, N.Groundwater freshening following coastal progradation and land reclamation of the Po Plain, Italy.Hydrogeol. J., 2015, 23: 1009-1026 Groundwater freshening following coastal progradation and land reclamation of the Po Plain, Italy
Land reclamation; Groundwater freshening; Coastal aquifers; Numerical modeling; Italy
Many coastal areas historically were inundated by seawater, but have since undergone land reclamation to enable settlements and farming. This study focuses on the coastal unconfined aquifer in the Po Plain near Ravenna, Italy. Freshwater is present as isolated thin (1-5 m) lenses on top of brackish to saline water. Historical maps show large areas of sea inundation until approximately 150-200 years ago when coastal progradation and construction of the drainage canals began. Since then, the aquifer has been freshening from recharge. A three-dimensional SEAWAT model is used to simulate a 200-year freshening history, starting with a model domain that is saturated with seawater, and applying recharge across the top model layer. Calibration to the observed concentrations for discrete depths within many monitoring wells is remarkably good. The current distribution of freshwater is largely controlled by the drainage network. Within and adjacent to the drains, the groundwater has high salinity due to up-coning of salt water. Between drains, the surface layers of the aquifer are fresh due to the flushing action of recharge. The modeling results are consistent with cation exchange processes revealed in the groundwater chemistry and with freshwater lenses identified in electrical resistivity soundings. DOI
75. Foster, SB; Allen, DM.Groundwater-Surface Water Interactions in a Mountain-to-Coast Watershed: Effects of Climate Change and Human Stressors.Adv. Meteorol., 2015, Groundwater-Surface Water Interactions in a Mountain-to-Coast Watershed: Effects of Climate Change and Human Stressors
Watersheds located within a mountain to coast physiographic setting have been described as having a highly interconnected surface water and groundwater environment. The quantification of groundwater-surface water interactions at the watershed scale requires upscaling. This study uses MIKE SHE, a coupled numerical model, to explore the seasonally and spatially dynamic nature of these interactions in the Cowichan Watershed on Vancouver Island, British Columbia, Canada. The calibrated model simulates a transition of the Cowichan River from mostly gaining within the valley, to losing stream near the coast where groundwater extraction is focused. Losing and gaining sections correlate with geological substrate. Recharge across the watershed accounts for 17% of precipitation. Climate change is projected to lessen snowpack accumulation in the high alpine and alter timing of snowmelt, resulting in higher spring and winter river discharge and lower summer flows. DOI
74. Galway, LP; Allen, DM; Parkes, MW; Li, L; Takaro, TK.Hydroclimatic variables and acute gastro-intestinal illness in British Columbia, Canada: A time series analysis.Water Resour. Res., 2015, 51: 885-895 Hydroclimatic variables and acute gastro-intestinal illness in British Columbia, Canada: A time series analysis
epidemiology; acute gastro-intestinal illness; hydroclimatology; climate change; time series analysis
Using epidemiologic time series analysis, we examine associations between three hydroclimatic variables (temperature, precipitation, and streamflow) and waterborne acute gastro-intestinal illness (AGI) in two communities in the province of British Columbia (BC), Canada. The communities were selected to represent the major hydroclimatic regimes that characterize BC: rainfall-dominated and snowfall dominated. Our results show that the number of monthly cases of AGI increased with increasing temperature, precipitation, and streamflow in the same month in the context of a rainfall-dominated regime, and with increasing streamflow in the previous month in the context of a snowfall-dominated regime. These results suggest that hydroclimatology plays a role in driving the occurrence and variability of AGI in these settings. Further, this study highlights that the nature and magnitude of the effects of hydroclimatic variability on AGI are different in the context of a snowfall-dominated regime versus a rainfall-dominated regimes. We conclude by proposing that the watershed may be an appropriate context for enhancing our understanding of the complex linkages between hydroclimatic variability and waterborne illness in the context of a changing climate. DOI
73. Graham, G; Allen, DM; Finkbeiner, B.Climate controls on nitrate concentration variability in the Abbotsford-Sumas aquifer, British Columbia, Canada.Environ. Earth Sci., 2015, 73: 2895-2907 Climate controls on nitrate concentration variability in the Abbotsford-Sumas aquifer, British Columbia, Canada
Nitrate contamination; Climate variability; Groundwater; Monitoring
Understanding the linkage between temporal climate variability and groundwater nitrate concentration variability in monitoring well records is key to interpreting the impacts of changes in land-use practices and assessing groundwater quality trends. This study explores the coupling of climate variability and groundwater nitrate concentration variability in the Abbotsford-Sumas aquifer. Over the period of 1992-2009, the average groundwater nitrate concentration in the aquifer remained fairly steady at approximately 15 mg/L nitrate-N. Normalized nitrate data for 19 individual monitoring wells were assessed for a range of intrinsic factors including precipitation, depth to water table, depth below water table, and apparent groundwater age. At a broad scale, there is a negative correlation between nitrate concentration and apparent groundwater age. Each dedicated monitoring well shows unique, non-uniform cyclical variability in nitrate concentrations that appears to correspond with seasonal (1 year) cycles in precipitation as well as longer-period cycles (5 years), possibly due to ENSO (El Nio Southern Oscillation) or the Pacific North American (PNA) pattern. These precipitation cycles appear to influence nitrate concentrations by approximately +/- 30 % of the critical concentration (10 mg/L NO3-N). Not all wells show direct correlation due to many complex local-scale factors that influence nitrate leaching including spatially and temporally variable nutrient management practices and soil/crop nitrogen dynamics (anthropogenic and agronomic factors). DOI
72. Holding, S; Allen, DM.Wave overwash impact on small islands: Generalised observations of freshwater lens response and recovery for multiple hydrogeological settings.J. Hydrol., 2015, 529: 1324-1335 Wave overwash impact on small islands: Generalised observations of freshwater lens response and recovery for multiple hydrogeological settings
Small islands; Freshwater lens; Overwash; Storm surge; Island classification; Numerical modelling
Wave overwash events have the potential to result in severe consequences to the freshwater resources of small islands as a result of salt contamination of the aquifer. Due to the significant impact of overwash, it is important to characterise the susceptibility of small islands to these events. This study uses numerical modelling to evaluate the freshwater lens response and recovery to overwash events for various island hydrogeological settings (island types) observed worldwide. Models were developed for an example of each island type using a fully coupled surface-subsurface, density-dependent flow and solute transport modelling code. A theoretical overwash event was simulated, and the response and recovery of the freshwater lens were observed for 20 years. The freshwater lens response (degree of aquifer contamination) was largely determined by the vadose zone thickness. Lens recovery ranged from 1 to 19 years for the different island types, and was strongly affected by recharge rate. However, the recovery of potable water in the lens (and restoration of a water supply) was dominantly influenced by geological heterogeneities. The model results demonstrate the cumulative impact of the different factors affecting the freshwater lens response and recovery to the overwash event for each island type, and provide a generalised assessment of island susceptibility to overwash on a global scale, despite limited data availability for many small islands. (C) 2015 Elsevier B.V. All rights reserved. DOI
71. Holding, S; Allen, DM.From days to decades: numerical modelling of freshwater lens response to climate change stressors on small low-lying islands.Hydrol. Earth Syst. Sci., 2015, 19: 933-949 From days to decades: numerical modelling of freshwater lens response to climate change stressors on small low-lying islands
Freshwater lenses on small islands are vulnerable to many climate change-related stressors, which can act over relatively long time periods, on the order of decades (e.g., sea level rise, changes in recharge), or short time periods, such as days (storm surge overwash). This study evaluates the response of the freshwater lens on a small lowlying island to various stressors. To account for the varying temporal and spatial scales of the stressors, two different density-dependent flow and solute transport codes are used: SEAWAT (saturated) and HydroGeoSphere (unsaturated/saturated). The study site is Andros Island in the Bahamas, which is characteristic of other low-lying carbonate islands in the Caribbean and Pacific regions. In addition to projected sea level rise and reduced recharge under future climate change, Andros Island experienced a storm surge overwash event during Hurricane Francis in 2004, which contaminated the main wellfield. Simulations of reduced recharge result in a greater loss of freshwater lens volume (up to 19 %), while sea level rise contributes a lower volume loss (up to 5 %) due to the flux-controlled conceptualization of Andros Island, which limits the impact of sea level rise. Reduced recharge and sea level rise were simulated as incremental instantaneous shifts. The lens responds relatively quickly to these stressors, within 0.5 to 3 years, with response time increasing as the magnitude of the stressor increases. Simulations of the storm surge overwash indicate that the freshwater lens recovers over time; however, prompt remedial action can restore the lens to potable concentrations up to 1 month sooner. DOI
70. Hsieh, AI; Allen, DM; MacEachern, JA.Statistical modeling of biogenically enhanced permeability in tight reservoir rock.Mar. Pet. Geol., 2015, 65: 114-125 Statistical modeling of biogenically enhanced permeability in tight reservoir rock
Bioturbation; Hydrofacies; Statistical modeling; Markov chain; Permeability
Bioturbation is generally perceived to be detrimental to bulk permeability by reducing primary grain sorting, homogenizing sediment, and introducing mud as burrow linings and feces. Recent studies show, however, that some ichnogenera and biogenic fabrics serves to increase porosity and permeability. In tight hydrocarbon reservoirs, subtle changes in sand and silt distributions, such as may be generated by bioturbation, can greatly affect the resulting porosity and permeability distribution. Despite this, permeability across unfractured sedimentary reservoirs is commonly assessed solely on the basis of average grain size. This study of the Lower Cretaceous Viking Fm integrates sedimentary and ichnologic features to define recurring "hydrofacies" that possess distinct permeability grades. Grain size, lithology, bioturbation index, and trace fossil suites were described from a cored section of well 14-30-22-16W4. The k(max) values from small plugs and full-diameter core samples were used to represent each hydrofacies. Hydrofacies were qualitatively defined at the bed/bedset scale, based on sedimentary, ichnological and permeability attributes, all of which affect flow pathways in heterolithic facies. The Markov chain method was employed to compare the vertical transitions of permeability (k(max)) within a borehole against grain size and hydrofacies at the bed to bedset scale. This provided an intuitive framework for interpreting facies relationships such as coarsening-upwards successions. The results show that in the studied core, grain size only correlates to permeability in homogeneous rock units. The transiograms show that the volumetric proportions of different kmax classes show a 15% correlation with grain size, compared to a 97% correlation with the hydrofacies, indicating that variations in permeability down the well are strongly related to variations in the hydrofacies. The hydrofacies approach potentially can be used as a conceptual framework for the spatial modeling of permeability in tight hydrocarbon reservoirs, where grain size may not be the primary factor on permeability distributions. (C) 2015 Elsevier Ltd. All rights reserved. DOI
69. Middleton, MA; Whitfield, PH; Allen, DM.Independent component analysis of local-scale temporal variability in sediment-water interface temperature.Water Resour. Res., 2015, 51: 9679-9695 Independent component analysis of local-scale temporal variability in sediment-water interface temperature
Temperature recorded at the sediment-water interface has been identified as a valuable tracer for understanding groundwater-surface water interactions. However, factors contributing to the variability in temperatures can be difficult to distinguish. In this study, the temporal variability in daily temperatures at the sediment-water interface is evaluated for a 40 m reach of a coastal stream using Independent Component Analysis (ICA). ICA separation is used to identify three independent temperature components within the reach for each of four summer periods (2008-2011). Extracted temperature signals correlate with stream discharge, estimated streambed temperature, and groundwater level, but the strength of the correlations varies from summer to summer. Overall, variations in the temperature signals have clearer separation in summers with lower stream discharge and greater stream temperature ranges. Surface heating from solar radiation is the dominant factor influencing the sediment-water interface temperature in most years, but there is evidence that thermal exchanges are taking place other than at the air-water interface. These exchanges take place at the sediment-water interface, and the correlation with groundwater levels indicates that these heat exchanges are associated with groundwater inflow. This study demonstrates that ICA can be used effectively to aid in identifying component signals in environmental applications of small spatial scale. DOI
68. Afsin, M; Allen, DM; Kirste, D; Durukan, UG; Gurel, A; Oruc, O.Mixing processes in hydrothermal spring systems and implications for interpreting geochemical data: a case study in the Cappadocia region of Turkey.Hydrogeol. J., 2014, 22: 7-23 Mixing processes in hydrothermal spring systems and implications for interpreting geochemical data: a case study in the Cappadocia region of Turkey
Hydrothermal springs; Thermal conditions; Hydrogeochemistry; Isotopes; Turkey
Mixing is a dominant hydrogeological process in the hydrothermal spring system in the Cappadocia region of Turkey. All springs emerge along faults, which have the potential to transmit waters rapidly from great depths. However, mixing with shallow meteoric waters within the flow system results in uncertainty in the interpretation of geochemical results. The chemical compositions of cold and warm springs and geothermal waters are varied, but overall there is a trend from Ca-HCO3 dominated to Na-Cl dominated. There is little difference in the seasonal ionic compositions of the hot springs, suggesting the waters are sourced from a well-mixed reservoir. Based on delta O-18 and delta H-2 concentrations, all waters are of meteoric origin with evidence of temperature equilibration with carbonate rocks and evaporation. Seasonal isotopic variability indicates that only a small proportion of late spring and summer precipitation forms recharge and that fresh meteoric waters move rapidly into the flow system and mix with thermal waters at depth. H-3 and percent modern carbon (pmC) values reflect progressively longer groundwater pathways from cold to geothermal waters; however, mixing processes and the very high dissolved inorganic carbon (DIC) of the water samples preclude the use of either isotope to gain any insight on actual groundwater ages. DOI
67.Allen, DM; Bayer, P; Ferguson, G; Blum, P.Preface: Hydrogeology of shallow thermal systems.Hydrogeol. J., 2014, 22: 1-6 Preface: Hydrogeology of shallow thermal systems
Shallow thermal systems; Thermal conditions; Springs; Basins; Geo-exchange systems
DOI
66.Allen, DM; Stahl, K; Whitfield, PH; Moore, RD.Trends in groundwater levels in British Columbia.Can. Water Resour. J., 2014, 39: 15-31 Trends in groundwater levels in British Columbia
The relations between groundwater level fluctuations and past climatic variations are explored using available data from the provincial observation well network, climate data and hydrometric data from the two major hydro-climatic zones of British Columbia. The majority of these well records start in the late 1970s or 1980s, providing only 20 to 30 years of record at most, and only a few of these wells monitor aquifers in "pristine" areas that reflect natural variability; the others have been influenced by human activity. Mean monthly groundwater levels were used to manually classify the wells into rainfall- and snowmelt-dominated seasonal cycles. Temporal trends of groundwater levels and a simple recharge measure were calculated using the non-parametric Spearman's rank correlation coefficient over a common period from 1976-1999. This period was selected to coincide with the positive phase of the Pacific Decadal Oscillation (PDO) so as to eliminate the potential impact a shift in the PDO might have on groundwater levels and recharge trends. Overall, late summer groundwater levels appear to have lowered across the province. Trends in recharge were more variable with both positive and negative trends. However, most of the trend results were non-significant. This assessment was complicated by the varied nature of the climate in different parts of the province, which determines the hydrologic regime (pluvial, nival, glacierized, mixed), the complexity of the groundwater system as it relates to the connection between groundwater and surface water, and the remote sources of many rivers in the mountainous regions of the province. DOI
65. Bridger, DW; Allen, DM.Influence of geologic layering on heat transport and storage in an aquifer thermal energy storage system.Hydrogeol. J., 2014, 22: 233-250 Influence of geologic layering on heat transport and storage in an aquifer thermal energy storage system
Thermal conditions; Aquifer thermal energy storage; Numerical modeling; Heat transport; Canada
A modeling study was carried out to evaluate the influence of aquifer heterogeneity, as represented by geologic layering, on heat transport and storage in an aquifer thermal energy storage (ATES) system in Agassiz, British Columbia, Canada. Two 3D heat transport models were developed and calibrated using the flow and heat transport code FEFLOW including: a "non-layered" model domain with homogeneous hydraulic and thermal properties; and, a "layered" model domain with variable hydraulic and thermal properties assigned to discrete geological units to represent aquifer heterogeneity. The base model (non-layered) shows limited sensitivity for the ranges of all thermal and hydraulic properties expected at the site; the model is most sensitive to vertical anisotropy and hydraulic gradient. Simulated and observed temperatures within the wells reflect a combination of screen placement and layering, with inconsistencies largely explained by the lateral continuity of high permeability layers represented in the model. Simulation of heat injection, storage and recovery show preferential transport along high permeability layers, resulting in longitudinal plume distortion, and overall higher short-term storage efficiencies. DOI
64. Galway, LP; Allen, DM; Parkes, MW; Takaro, TK.Seasonal variation of acute gastro-intestinal illness by hydroclimatic regime and drinking water source: a retrospective population-based study.J. Water Health, 2014, 12: 122-135 Seasonal variation of acute gastro-intestinal illness by hydroclimatic regime and drinking water source: a retrospective population-based study
acute gastro-intestinal illness; climate change; ecological determinants; seasonality
Acute gastro-intestinal illness (AGI) is a major cause of mortality and morbidity worldwide and an important public health problem. Despite the fact that AGI is currently responsible for a huge burden of disease throughout the world, important knowledge gaps exist in terms of its epidemiology. Specifically, an understanding of seasonality and those factors driving seasonal variation remain elusive. This paper aims to assess variation in the incidence of AGI in British Columbia (BC), Canada over an 11-year study period. We assessed variation in AGI dynamics in general, and disaggregated by hydroclimatic regime and drinking water source. We used several different visual and statistical techniques to describe and characterize seasonal and annual patterns in AGI incidence over time. Our results consistently illustrate marked seasonal patterns; seasonality remains when the dataset is disaggregated by hydroclimatic regime and drinking water source; however, differences in the magnitude and timing of the peaks and troughs are noted. We conclude that systematic descriptions of infectious illness dynamics over time is a valuable tool for informing disease prevention strategies and generating hypotheses to guide future research in an era of global environmental change. DOI PubMed
63. Mayer, JM; Allen, DM; Gibson, HD; Mackie, DC.Application of statistical approaches to analyze geological, geotechnical and hydrogeological data at a fractured-rock mine site in Northern Canada.Hydrogeol. J., 2014, 22: 1707-1723 Application of statistical approaches to analyze geological, geotechnical and hydrogeological data at a fractured-rock mine site in Northern Canada
Fractured rocks; Hydraulic testing; Geotechnical data; Statistical modeling; Canada
Mine site characterization often results in the acquisition of geological, geotechnical and hydrogeological data sets that are used in the mine design process but are rarely co-evaluated. For a study site in northern Canada, bivariate and multivariate (hierarchical) statistical techniques are used to evaluate empirical hydraulic conductivity estimation methods based on traditional rock mass characterisation schemes, as well as to assess the regional hydrogeological conceptual model. Bivariate techniques demonstrate that standard geotechnical measures of fracturing are poor indicators of the hydraulic potential of a rock mass at the study site. Additionally, rock-mass-permeability schemes which rely on these measures are shown to be poor predictors of hydraulic conductivity in untested areas. Multivariate techniques employing hierarchical cluster analysis of both geotechnical and geological data sets are able to identify general trends in the data. Specifically, the geological cluster analysis demonstrated spatial relationship between intrusive contacts and increased hydraulic conductivity. This suggests promise in the use of clustering methods in identifying new trends during the early stages of hydrogeological characterization. DOI
62. Simpson, MWM; Allen, DM; Journeay, MM.Assessing risk to groundwater quality using an integrated risk framework.Environ. Earth Sci., 2014, 71: 4939-4956 Assessing risk to groundwater quality using an integrated risk framework
Source-water protection; Risk assessment; Groundwater; Aquifer vulnerability; Groundwater contamination; Canada
Source-water protection strategies are ideally focused where the greatest amount of harm reduction can occur. This process of risk management requires an assessment of the spatial variability of risk to water. The assessment methodology presented herein combines aquifer susceptibility with a hazard threat inventory and an analysis of the consequence of contamination to assess the risk to water quality. Aquifer susceptibility combines the intrinsic susceptibility of the physical system with anthropogenic features that locally increase susceptibility. Hazard threats are assessed based on the properties of the chemicals (toxicity and environmental fate), the potential magnitude (extent and quantity of release) and the likelihood of release. The consequence is herein considered as the financial costs of the loss of the resource, including the replacement of a water source and the economic loss where water intensive businesses are lost. A second scenario is included that analyses health issues related to pathogen sources as well as the financial impact to the community where people fall ill and present a financial burden to the public health care system. The risk assessment methodology is applied to the Township of Langley, in southwestern British Columbia, Canada. The results outline the most vulnerable areas as those where susceptible aquifers coexist with potential chemical and biological threats. The risk is greatest where these vulnerable areas coincide with those with the greatest potential for financial loss: within the capture zones of major municipal production wells and where private wells serve agricultural operations with high annual farm sales. DOI
61. Spry, CM; Kohfeld, KE; Allen, DM; Dunkley, D; Lertzman, K.Characterizing Pineapple Express storms in the Lower Mainland of British Columbia, Canada.Can. Water Resour. J., 2014, 39: 302-323 Characterizing Pineapple Express storms in the Lower Mainland of British Columbia, Canada
Pineapple Express (PE) storms are subtropical winter storm systems that are known to trigger precipitation-induced natural hazards. However, they have not previously been well characterized in the Lower Mainland of British Columbia. This study uses an established chronology of PE storms to identify and compare PE and non-PE storms, using (1) meteorological variables recorded at meteorological stations from the Vancouver International Airport and Capilano watershed, (2) streamflow variables from a hydrometric station in Capilano watershed and (3) precipitation samples collected for oxygen isotope analysis from 27 recent storms identified as PE or non-PE storms using satellite imagery. Historical trends in PE storms were then estimated using records of PE storm magnitude (as recorded at Vancouver International Airport) and frequency (as determined from the subset of PE storms that made landfall between 47.5 and 52.5 degrees N) for the period of 1948 to 2011. Results from a Mann-Whitney U-test suggest that median precipitation values of PE storms are significantly higher than those of non-PE storms at the Capilano watershed. Comparisons of the 75th, 80th, 85th, 90th and 95th quantiles suggest that both precipitation and streamflow rates at stations in the Capilano watershed were significantly higher for PE storms than for non-PE storms. Precipitation samples from three PE storms identified with satellite imagery exhibited substantially less-depleted oxygen isotope ratios compared with non-PE storms, consistent with a subtropical water vapour source inferred from satellite images. In effect, from 1948-2007, Vancouver experienced 0-7 days/year that are classified as PE storm days, and these storm days contributed an average of 11 and 17% to annual precipitation and stream discharge totals, respectively. Annual PE storm maxima (i.e. total precipitation for the largest PE storm day in a given year) show significant correlations with both storm frequency and annual average temperature, suggesting that the largest PE storms tend to occur in warmer years with increased storm activity. The study also suggests an inverse relationship between the percent contribution of PE storms to annual precipitation and the Madden-Julian Oscillation (MJO) index. These results suggest that water years (1 October-30 September) with substantial PE precipitation are correlated with the negative phase of the MJO when convection is enhanced in the western Pacific Ocean. DOI
60. Voeclder, HM; Allen, DM; Alila, Y.Modeling coupled surface water - Groundwater processes in a small mountainous headwater catchment.J. Hydrol., 2014, 517: 1089-1106 Modeling coupled surface water - Groundwater processes in a small mountainous headwater catchment
Headwater catchment modeling; Recharge to deep bedrock; Steep mountainous terrain; MIKE SHE
Hydrological models for headwater catchments have typically excluded deep groundwater flow based on the assumption that it is a negligible component of the water budget. This study tests this assumption using a coupled surface water-groundwater model to explore the potential contribution of deep groundwater recharge to the bedrock in a snowmelt-dominated headwater catchment (Upper Penticton Creek 241) in the Okanagan Basin, British Columbia. Recharge to the bedrock is estimated at similar to 27% of the annual precipitation over the period 2005-2010, recognizing the uncertainty in this estimate due to data limitations, parameter uncertainty and calibration errors. A specified outward flux from the catchment boundary within the saturated zone, representing similar to 2% of the annual water budget, was also included in the model. This outward flux contributes to cross-catchment flow and, ultimately, to groundwater inflow to lower elevation catchments in the mountain block. This modeling exercise is one of the first in catchment hydrologic modeling within steep mountainous terrain in which the bedrock is not treated as impermeable, and in which recharge to the bedrock and discharge to the surrounding mountain block were estimated. (C) 2014 Elsevier B.V. All rights reserved. DOI
59. Welch, LA; Allen, DM.Hydraulic conductivity characteristics in mountains and implications for conceptualizing bedrock groundwater flow.Hydrogeol. J., 2014, 22: 1003-1026 Hydraulic conductivity characteristics in mountains and implications for conceptualizing bedrock groundwater flow
Conceptual models; Crystalline rock; Hydraulic conductivity; Numerical modelling; Mountain topography
Influences of hydraulic conductivity (K) heterogeneities on bedrock groundwater (BG) flow systems in mountainous topography are investigated using a conceptual 2D numerical modelling approach. A conceptual model for K heterogeneity in crystalline bedrock mountainous environments is developed based on a review of previous research, and represents heterogeneities due to weathering profile, bedrock fracture characteristics, and catchment-scale (similar to 0.1-1 km) structural features. Numerical groundwater modelling of K scenarios for hypothetical mountain catchment topography indicates that general characteristics of the BG flow directions are dominated by prominent topographic features. Within the modelled saturated BG flow system, similar to 90 % or more of total BG flux is focussed within a fractured bedrock zone, extending to depths of similar to 100-200 m below the ground surface, overlying lower-K bedrock. Structural features and heterogeneities, represented as discrete zones of higher or lower K relative to surrounding bedrock, locally influence BG flow, but do not influence general BG flow patterns or general positions of BG flow divides. This result is supported by similar BG transit-time distribution shapes and statistics for systems with and without structural features. The results support the development of topography-based methods for predicting general locations of BG flow-system boundaries in mountain regions. DOI
58. de Albuquerque, RC; Allen, DM; Kirste, D.A methodology for spatially representing the likelihood of occurrence of natural contaminants in groundwater.Environ. Earth Sci., 2013, 68: 1863-1875 A methodology for spatially representing the likelihood of occurrence of natural contaminants in groundwater
Groundwater quality; Arsenic; Aquifer mapping; Hydrogeochemistry; Canada
This paper presents a novel method of spatially representing the likelihood of occurrence of a contaminant in groundwater at the scale of a municipality or watershed. The specific contaminant of concern in the case study area is arsenic, which is variably present in groundwater at concentrations exceeding the 10 A mu g/l drinking water guideline. The method used to produce the likelihood of occurrence map incorporates confidence of geochemical interpretation based on availability of information and data on each aquifer. While demonstrated using arsenic as the contaminant of interest, the approach is readily adapted to other groundwater constituents. The final map is intended to be of use to water managers as it provides a spatial representation of aquifers of concern and identifies areas where further sampling or monitoring may be needed. DOI
57. Norman, ES; Dunn, G; Bakker, K; Allen, DM; de Albuquerque, RC.Water Security Assessment: Integrating Governance and Freshwater Indicators.Water Resour. Manag., 2013, 27: 535-551 Water Security Assessment: Integrating Governance and Freshwater Indicators
Water security; Governance; Environment; Indicators; Assessment; Framework; Canada
A new approach is developed for assessing water security status: the Water Security Status Indicators (WSSI) assessment method. The WSSI has four innovative aspects which address important gaps in the literature. First, it was developed in cooperation with end-users, whose participation enabled the design of a user-friendly assessment method. Second, this method is designed to be implemented at the local scale (small scale watershed or sub-watershed). Third, the WSSI is multivariate: it integrates variables pertaining to water quality and water quantity as they relate to aquatic ecosystems and human health. Fourth, the method provides concrete outputs for incorporation into water decision-making processes. In this paper, we document the WSSI assessment method and its application in a community in British Columbia (Canada), including the incorporation of community input into the development and application of the WSSI, and the integration of WSSI results into community water governance. DOI
56. Taylor, RG; Scanlon, B; Doll, P; Rodell, M; van Beek, R; Wada, Y; Longuevergne, L; Leblanc, M; Famiglietti, JS; Edmunds, M; Konikow, L; Green, TR; Chen, JY; Taniguchi, M; Bierkens, MFP; MacDonald, A; Fan, Y; Maxwell, RM; Yechieli, Y; Gurdak, JJ; Allen, DM; Shamsudduha, M; Hiscock, K; Yeh, PJF; Holman, I; Treidel, H.Ground water and climate change.Nat. Clim. Chang., 2013, 3: 322-329 Ground water and climate change
As the world's largest distributed store of fresh water, ground water plays a central part in sustaining ecosystems and enabling human adaptation to climate variability and change. The strategic importance of ground water for global water and food security will probably intensify under climate change as more frequent and intense climate extremes (droughts and floods) increase variability in precipitation, soil moisture and surface water. Here we critically review recent research assessing the impacts of climate on ground water through natural and human-induced processes as well as through groundwater-driven feedbacks on the climate system. Furthermore, we examine the possible opportunities and challenges of using and sustaining groundwater resources in climate adaptation strategies, and highlight the lack of groundwater observations, which, at present, limits our understanding of the dynamic relationship between ground water and climate. DOI
55. Chesnaux, R; Allen, DM; Simpson, MWM.Comparing isotopic groundwater age measurements with simulated groundwater ages: example of the Abbotsford-Sumas Aquifer (USA and Canada) and application.Water Environ. J., 2012, 26: 30-37 Comparing isotopic groundwater age measurements with simulated groundwater ages: example of the Abbotsford-Sumas Aquifer (USA and Canada) and application
groundwater; isotopic age dating; numerical modelling; particle tracking
Elevated nitrate concentrations have been documented since the 1970s within the trans-national AbbotsfordSumas aquifer, situated in the central Fraser Valley of southern British Columbia, Canada, and northern Washington State, United States. Nitrate concentrations in excess of 10 mg/L NO3N are commonly observed in the monitoring wells. A groundwater model is used in this study to conduct a particle tracking analysis to estimate groundwater travel times and compare these with groundwater ages determined from 3H/3He concentrations measured in several monitoring wells. Groundwater ages estimated from particle tracking show excellent agreement with measured ages (slope=1), although there is scatter (R2=0.76), reflecting the complexity of the travel pathways and ambiguities in groundwater ages because of mixing. An assessment of the efficacy of recommended nutrient management practices, which were implemented in 1992 to reduce nitrogen loading, suggests that wells shallower than about 20 m should be monitoring a decrease in nitrate concentration. However, persistent elevated nitrate concentrations even at shallow depths point to the lingering effects of a remnant manurenitrate signature in combination with continued high loading. DOI
54. Gleeson, T; Allen, DM; Ferguson, G.Teaching hydrogeology: a review of current practice.Hydrol. Earth Syst. Sci., 2012, 16: 2159-2168 Teaching hydrogeology: a review of current practice
Hydrogeology is now taught in a broad spectrum of departments and institutions to students with diverse backgrounds. Successful instruction in hydrogeology thus requires a variety of pedagogical approaches depending on desired learning outcomes and the background of students. We review the pedagogical literature in hydrogeology to highlight recent advances and analyze a 2005 survey among 68 hydrogeology instructors. The literature and survey results suggest there are only similar to 15 topics that are considered crucial by most hydrogeologists and > 100 other topics that are considered crucial by some hydrogeologists. The crucial topics focus on properties of aquifers and fundamentals of groundwater flow, and should likely be part of all undergraduate hydrogeology courses. Other topics can supplement and support these crucial topics, depending on desired learning outcomes. Classroom settings continue to provide a venue for emphasizing fundamental knowledge. However, recent pedagogical advances are biased towards field and laboratory instruction with a goal of bolstering experiential learning. Field methods build on the fundamentals taught in the classroom and emphasize the collection of data, data uncertainty, and the development of vocational skills. Laboratory and computer-based exercises similarly build on theory, and offer an opportunity for data analysis and integration. The literature suggests curricula at all levels should ideally balance field, laboratory, and classroom pedagogy into an iterative and integrative whole. An integrated, iterative and balanced approach leads to greater student motivation and advancement of theoretical and vocational knowledge. DOI
53. Gleeson, T; Alley, WM; Allen, DM; Sophocleous, MA; Zhou, YX; Taniguchi, M; VanderSteen, J.Towards Sustainable Groundwater Use: Setting Long-Term Goals, Backcasting, and Managing Adaptively.Ground Water, 2012, 50: 19-26 Towards Sustainable Groundwater Use: Setting Long-Term Goals, Backcasting, and Managing Adaptively
The sustainability of crucial earth resources, such as groundwater, is a critical issue. We consider groundwater sustainability a value-driven process of intra-and intergenerational equity that balances the environment, society, and economy. Synthesizing hydrogeological science and current sustainability concepts, we emphasize three sustainability approaches: setting multigenerational sustainability goals, backcasting, and managing adaptively. As most aquifer problems are long-term problems, we propose that multigenerational goals (50 to 100 years) for water quantity and quality that acknowledge the connections between groundwater, surface water, and ecosystems be set for many aquifers. The goals should be set by a watershed-or aquifer-based community in an inclusive and participatory manner. Policies for shorter time horizons should be developed by backcasting, and measures implemented through adaptive management to achieve the long-term goals. Two case histories illustrate the importance and complexity of a multigenerational perspective and adaptive management. These approaches could transform aquifer depletion and contamination to more sustainable groundwater use, providing groundwater for current and future generations while protecting ecological integrity and resilience. DOI PubMed
51. Voeckler, H; Allen, DM.Estimating regional-scale fractured bedrock hydraulic conductivity using discrete fracture network (DFN) modeling.Hydrogeol. J., 2012, 20: 1081-1100 Estimating regional-scale fractured bedrock hydraulic conductivity using discrete fracture network (DFN) modeling
Crystalline rocks; Fractured rocks; Numerical modeling; Hydraulic conductivity; Canada
Estimating bedrock hydraulic conductivity of regional fractured aquifers is challenging due to a lack of aquifer testing data and the presence of small and large-scale heterogeneity. This study provides a novel approach for estimating the bedrock hydraulic conductivity of a regional-scale fractured bedrock aquifer using discrete fracture network (DFN) modeling. The methodology is tested in the mountainous Okanagan Basin, British Columbia, Canada. Discrete fractures were mapped in outcrops, and larger-scale fracture zones (corresponding to lineaments) were mapped from orthophotos and LANDSAT imagery. Outcrop fracture data were used to generate DFN models for estimating hydraulic conductivity for the fractured matrix (K (m)). The mountain block hydraulic conductivity (K (mb)) was estimated using larger-scale DFN models. Lineament properties were estimated by best fit parameters for a simulated pumping test influenced by a fracture zone. Unknown dip angles and directions for lineaments were estimated from the small-scale fracture sets. Simulated K (m) and K (mb) values range from 10(-8) to 10(-7) m/s and are greatest in a N-S direction, coinciding with the main strike direction of Okanagan Valley Fault Zone. K (mb) values also decrease away from the fault, consistent with the decrease in lineament density. Simulated hydraulic conductivity values compare well with those estimated from pumping tests. DOI
50. Welch, LA; Allen, DM.Consistency of groundwater flow patterns in mountainous topography: Implications for valley bottom water replenishment and for defining groundwater flow boundaries.Water Resour. Res., 2012, 48 Consistency of groundwater flow patterns in mountainous topography: Implications for valley bottom water replenishment and for defining groundwater flow boundaries
Topographic influences on groundwater flow processes that contribute to baseflow and mountain block recharge (MBR) are conceptually investigated using three-dimensional numerical models of saturated groundwater flow. Model domains for conceptual and real topographies are developed as "mountain groundwatershed units'' (MGUs) to represent regional-scale watershed systems. Results indicate regularity in groundwater flow patterns that reflect consistency of prominent topographic features, providing a basis for conceptualizing three-dimensional groundwater flow. Baseflow is generated mainly from recharge within the watershed area. MBR is produced primarily from recharge that is focused across triangular facets near the mountain front (similar to 73%-97% of total MBR), with additional contributions originating within the watershed (up to similar to 27% of MBR). MBR contributions originating from recharge near the highest-elevation watershed boundaries are minimal but are greater for topography with less stream incision. With orographic influences, more MBR originates within the watershed. MBR rates are relatively consistent between models because of similarities in mountain front topography, while baseflow is variable. Gains and losses to systems via cross-watershed groundwater flux, generated because of topographic differences between adjacent watersheds, cause baseflow to vary by up to similar to 10% but do not significantly influence MBR. In data-sparse regions such as mountains, a basic numerical modeling approach, using the MGU concept with topography data and mapped watershed boundaries, can be used to develop site-specific conceptual models to constrain water budgets, to delineate recharge areas, and to guide further investigation and data collection. DOI
49. Welch, LA; Allen, DM; van Meerveld, HJ.Topographic Controls on Deep Groundwater Contributions to Mountain Headwater Streams and Sensitivity to Available Recharge.Can. Water Resour. J., 2012, 37: 349-371 Topographic Controls on Deep Groundwater Contributions to Mountain Headwater Streams and Sensitivity to Available Recharge
An important, yet poorly understood, influence on the hydrologic behaviour of mountain headwater streams is deep groundwater (DG) flow, which circulates at depth through the bedrock system and discharges to surface water or shallow groundwater at stream valleys. In this study, two- and three-dimensional hydrogeological models were generated for both generic and real topography. DG contribution areas were delineated using groundwater pathline analysis, and the sensitivity of DG discharge at headwater stream valleys due to changes in applied recharge was investigated. For some streams, the 3-D nested nature of topographically-driven DG flow results in groundwater that is recharged within one headwater stream catchment bypassing the associated stream valley and emerging as DG discharge in a different, relatively deeper stream valley. Contributing areas of DG to headwater streams are thus more complex than would be predicted based on catchment boundaries alone. Differences in DG discharge and DG contributing areas in response to changes in applied recharge are a reflection of differences in topography and suggest that headwater streams within the same watershed differ in their sensitivity to changes in recharge. A small, but significant, temporal response of DG discharge to a change in recharge is found to occur within a 1 to 3 year timeframe, highlighting the importance of variations in DG discharge for stream hydrology. The modelling approach used in this study requires only digital elevation model data, and thus can be used in regions of limited data and in ungauged basins to provide a preliminary indication of relative stream sensitivity to long-term changes in recharge as a result of climate change, forest management practices, or groundwater extraction. DOI
48. Green, TR; Taniguchi, M; Kooi, H; Gurdak, JJ; Allen, DM; Hiscock, KM; Treidel, H; Aureli, A.Beneath the surface of global change: Impacts of climate change on groundwater.J. Hydrol., 2011, 405: 532-560 Beneath the surface of global change: Impacts of climate change on groundwater
Adaptation; Climate change; Global change; Groundwater; Soil water; Vadose zone
Global change encompasses changes in the characteristics of inter-related climate variables in space and time, and derived changes in terrestrial processes, including human activities that affect the environment. As such, projected global change includes groundwater systems. Here, groundwater is defined as all subsurface water including soil water, deeper vadose zone water, and unconfined and confined aquifer waters. Potential effects of climate change combined with land and water management on surface waters have been studied in some detail. Equivalent studies of groundwater systems have lagged behind these advances, but research and broader interest in projected climate effects on groundwater have been accelerating in recent years. In this paper, we provide an overview and synthesis of the key aspects of subsurface hydrology, including water quantity and quality, related to global change. Adaptation to global change must include prudent management of groundwater as a renewable, but slow-feedback resource in most cases. Groundwater storage is already over-tapped in many regions, yet available subsurface storage may be a key to meeting the combined demands of agriculture, industry, municipal and domestic water supply, and ecosystems during times of shortage. The future intensity and frequency of dry periods combined with warming trends need to be addressed in the context of groundwater resources, even though projections in space and time are fraught with uncertainty. Finally, potential impacts of groundwater on the global climate system are largely unknown. Research to improve our understanding of the joint behaviors of climate and groundwater is needed, and spin-off benefits on each discipline are likely. Published by Elsevier B.V. DOI
47. Henry, CM; Allen, DM; Huang, JL.Groundwater storage variability and annual recharge using well-hydrograph and GRACE satellite data.Hydrogeol. J., 2011, 19: 741-755 Groundwater storage variability and annual recharge using well-hydrograph and GRACE satellite data
GRACE satellite; Groundwater storage; Groundwater recharge; Mali; Africa
Most studies using GRACE (Gravity Recovery and Climate Experiment) data for examining water storage anomalies have rich hydrogeological databases. Here, GRACE data are analyzed for southern Mali, Africa, a region with sparse hydrogeological data. GRACE data (2002-2008) did not overlap with observed groundwater-level data (1982-2002). Terrestrial water storage from GRACE was corrected for soil moisture using the Global Land Data Assimilation System (GLDAS) model to obtain monthly groundwater storage anomalies and annual net recharge. Historical storage anomalies and net recharge were determined using the water-table fluctuation method for available observation wells. Average annual net recharge averaged 149.1 mm (or 16.4% of annual rainfall) and 149.7 mm (14.8%) from historical water level and GRACE data, respectively. Monthly storage anomaly lows and peaks were observed in May and September, respectively, but have a shift in peak to November using the corrected GRACE data, suggesting that the GLDAS model may poorly predict the timing of soil-water storage in this region. Notwithstanding problems with the GLDAS model, the soil moisture-corrected GRACE data accurately predict the relative timing and magnitude of groundwater-storage changes, suggesting that GRACE data are valuable for identifying long-term regional changes in groundwater storage in areas with sparse hydrogeological data. DOI
46. Liggett, JE; Allen, DM.Evaluating the sensitivity of DRASTIC using different data sources, interpretations and mapping approaches.Environ. Earth Sci., 2011, 62: 1577-1595 Evaluating the sensitivity of DRASTIC using different data sources, interpretations and mapping approaches
DRASTIC; Aquifer vulnerability; Source water protection; Okanagan Basin
When used in a comprehensive risk assessment framework, aquifer vulnerability maps are a tool to identify the relative susceptibility of the groundwater from sources of contamination at the land surface. The DRASTIC method was designed for use over large areas with a wide variety of geological and hydrogeologic settings as a screening tool in groundwater protection and management. In this study, a series of vulnerability maps were made for the Greater Oliver area, in south central Okanagan, British Columbia, Canada, to test the sensitivity of the methodology to changes in input data type, interpretation, and mapping approaches. The study also illustrates how DRASTIC can be modified for use in areas of limited geological variability, where it may be important for smaller-scale changes in vulnerability to be recognized. Maps were produced using the original DRASTIC rating tables, a set of expanded tables using the original properties but modified ranges to accommodate the variability of data in the valley bottom region, and alternate tables, with modified properties and ranges. Differences in vulnerability rating for the maps using selected combinations and data interpretations are compared to the map using original DRASTIC rating tables using visual and statistical methods. One map was generated using expert hydrological knowledge. The modified tables allowed a greater amount of variability to be expressed in the valley bottom area compared to using the original tables and methods, and could provide a reasonable approach for assessing local scale variability for source water protection planning. DOI
45. McArthur, SAQ; Allen, DM; Luzitano, RD.Resolving scales of aquifer heterogeneity using ground penetrating radar and borehole geophysical logging.Environ. Earth Sci., 2011, 63: 581-593 Resolving scales of aquifer heterogeneity using ground penetrating radar and borehole geophysical logging
Ground penetrating radar; Borehole logging; Aquifer heterogeneity; Scale
Accurate and reliable characterization of aquifer heterogeneity remains one of the foremost problems in hydrogeology. In this study, ground penetrating radar (GPR) and borehole geophysical logging are used to investigate scales of heterogeneity present locally (< 500 m laterally) within an outwash deposit comprised of inter-bedded and cross-bedded sands and gravels of glaciofluvial origin. At a small scale (< 15 m laterally), gamma log data in adjacent boreholes show evidence of fining upward sequences, occasional coarsening upward sequences, and abrupt changes in grain sizes, which appear to be laterally continuous at scales of 10 m. At the site scale (< 500 m laterally), GPR profiles show a strong reflection interpreted as the water table. Reflectors in the unsaturated zone are more clearly defined than those beneath the water table due to signal attenuation within the saturated sediments. Undulating to discontinuous reflectors at scales of 10-15 m are interpreted to result from interbedded and cross-bedded sands and gravels. A few laterally continuous horizontal to sub-horizontal reflectors, which extend at least up to 360 m, are interpreted as unconformities, based on evidence of gravel bars, truncation of underlying units, as well as scour and fill features in a nearby gravel pit exposure. Overall, the integration of these two geophysical methods provided evidence of unit correlation at the two scales of investigation. DOI
44.Allen, DM; Cannon, AJ; Toews, MW; Scibek, J.Variability in simulated recharge using different GCMs.Water Resour. Res., 2010, 46 Variability in simulated recharge using different GCMs
Variations in the prediction of recharge is addressed by comparing recharge simulated using climate data generated using a state-of-the-art downscaling method, TreeGen, with a range of global climate models (GCMs). The study site is the transnational Abbotsford-Sumas aquifer in coastal British Columbia, Canada and Washington State, USA, and is representative of a wet coastal climate. Sixty-four recharge zones were defined based on combinations of classed soil permeability, vadose zone permeability, and unsaturated zone depth (or depth to water table) mapped in the study area. One-dimensional recharge simulations were conducted for each recharge zone using the HELP hydrologic model, which simulates percolation through a vertical column. The HELP model is driven by mean daily temperature, daily precipitation, and daily solar radiation. For the historical recharge simulations, the climate data series was generated using the LARS-WG stochastic weather generator. Historical recharge was compared to recharge simulated using climate data series derived from the TreeGen downscaling model for three future time periods: 2020s (2010-2039), 2050s (2040-2069), and 2080s (2070-2099) for each of four GCMs (CGCM3.1, ECHAM5, PCM1, and CM2.1). Recharge results are compared on an annual basis for the entire aquifer area. Both increases and decreases relative to historical recharge are simulated depending on time period and model. By the 2080s, the range of model predictions spans -10.5% to +23.2% relative to historical recharge. This variability in recharge predictions suggests that the seasonal performance of the downscaling tool is important and that a range of GCMs should be considered for water management planning. DOI
43.Allen, DM; Whitfield, PH; Werner, A.Groundwater level responses in temperate mountainous terrain: regime classification, and linkages to climate and streamflow.Hydrol. Process., 2010, 24: 3392-3412 Groundwater level responses in temperate mountainous terrain: regime classification, and linkages to climate and streamflow
groundwater levels; streamflow; groundwater-surface water interaction; climate; mountainous regions; aquifer characteristics
Groundwater responses in temperate mountainous terrain are assessed using groundwater, hydrometric and climatic data from southern British Columbia, Canada. Well and stream hydrographs are analysed using a series of diagnostic tools including time series plots, hysteresis plots, and cross-correlation plots. Characterizing the seasonal timing of the response requires consideration of the hydroclimatology of the region: rainfall-dominated (pluvial), snowmelt-dominated (nival) or hybrid (mixture of rain and snow). The magnitude and timing of the recharge and discharge response of the groundwater system was shown to depend on the storage and permeability characteristics of the aquifer and whether the system is stream-driven or recharge-driven. These two dominant stream-aquifer system types were defined based on classifying different aquifer types found in the southwest portion of the province. The classification scheme and diagnostic tools have the potential to provide a framework for evaluating the responses of wells in other mountainous regions. Using this framework, the potential consequences of future climate change may then be better understood based on the interactions between the hydrogeological and hydroclimatic settings of these aquifers. Copyright (C) 2010 Her Majesty the Queen in right of Canada. Published by John Wiley & Sons. Ltd DOI
42. Bridger, DW; Allen, DM.Heat transport simulations in a heterogeneous aquifer used for aquifer thermal energy storage (ATES).Can. Geotech. J., 2010, 47: 96-115 Heat transport simulations in a heterogeneous aquifer used for aquifer thermal energy storage (ATES)
Une etude de modelisation a ete effectuee afin d'evaluer l'influence de l'heterogeneite d'un aquifere, representee par differentes couches geologiques, sur le transport et l'entreposage de chaleur dans un aquifere utilise pour l'entreposage d'energie thermique (<< aquifer thermal energy storage, ATES >>). Un systeme ATES existant, situe a Agassiz, Colombie-Britannique, Canada, a ete utilise pour l'etude de cas. Le systeme comporte quatre puits de production, dans un aquifere heterogene non confine fait de sables et graviers intercales. Un autre puits a ete installe pour permettre la dissipation de la chaleur durant les periodes de refroidissement intense. Trois puits de suivi et les puits de production ont ete instrumentes pour mesurer la temperature periodiquement durant la premiere 1,5 ans d'operation. Un modele en trois dimensions de l'ecoulement de l'eau et du transport de chaleur a ete developpe avec FEFLOW. Les resultats des simulations indiquent que l'energie thermique se deplace de facon preferentielle dans les zones discretes de l'aquifere, ou du moins, penetre les puits sur des intervalles discrets. Les donnees du suivi sur le terrain concordent avec les resultats de la modelisation, mais montrent que l'entreposage de chaleur s'est bien fait malgre que l'operation se soit refroidie de facon significative durant la premiere annee. DOI
41. de Albuquerque, RC; Kirste, D; Allen, DM.Arsenic mobilization in confined aquifers formed in glaciomarine deposits., 2010, : 703-706 Arsenic mobilization in confined aquifers formed in glaciomarine deposits
Arsenic mobilization processes are investigated in confined aquifers formed by glaciomarine sediments in a temperate coastal region. The chemistry of groundwater in the studied aquifers is interpreted as being controlled by mineral weathering and cation exchange which caused these waters to be of a Na-HCO3 type. Mixing with connate seawater trapped in pore space appears to be occurring in one of the aquifers, resulting in a Na-Cl type groundwater. The groundwater with elevated arsenic is at a lower redox state and has basic pH, which are both conditions that favor arsenic mobilization. Arsenic is interpreted as being mobilized through desorption of anionic arsenic species at basic pH, reduction of arsenate to arsenite and dissolution of iron oxides and oxyhydroxides minerals. These processes are evidenced through observed positive relationships of arsenic with pH and iron. Mixing with connate seawater does not appear to contribute to arsenic mobilization.
39. Liggett, JE; Allen, DM.Comparing approaches for modeling spatially distributed direct recharge in a semi-arid region (Okanagan Basin, Canada).Hydrogeol. J., 2010, 18: 339-357 Comparing approaches for modeling spatially distributed direct recharge in a semi-arid region (Okanagan Basin, Canada)
Groundwater recharge/water budget; HELP; MIKE-SHE; Semi-arid; Canada
Spatially distributed recharge is compared at two different scales using three different modeling approaches within the semi-arid Okanagan Basin, British Columbia, Canada. Regional recharge was modeled by mapping results for one-dimensional soil columns from the water-balance code HELP (Hydrologic Evaluation of Landfill Performance, V3.80D). The regional model was then compared to two, independently derived, local-scale models to ensure local trends were captured in the regional model, and to compare modeling methods. Average annual recharge, predicted by the regional model, varied from no recharge to 186 mm/yr. For the north Okanagan (Vernon area), regional estimates were compared to Richards' equation-based MIKE-SHE (V2007) estimates, which showed a significant difference in average annual recharge: 7 mm/yr (MIKE-SHE) and 109 mm/yr (HELP). In the south Okanagan (Oliver area), regional estimates were compared to high-resolution, local HELP estimates. Similar values of average annual recharge were obtained: 34 mm/yr (local) and 42 mm/yr (regional). A comparison with measured actual evapotranspiration data in the north Okanagan, showed HELP over-predicted recharge compared to MIKE-SHE by under-predicting evapotranspiration during summer months. Thus, the use of HELP in semi-arid areas may be limited if accurate estimates of recharge are needed. However, results may give satisfactory groundwater model calibrations results because of high uncertainty in hydraulic properties. DOI
38. Ostry, A; Ogborn, M; Bassil, KL; Takaro, TK; Allen, DM.Climate Change and Health in British Columbia: Projected Impacts and a Proposed Agenda for Adaptation Research and Policy.Int. J. Environ. Res. Public Health, 2010, 7: 1018-1035 Climate Change and Health in British Columbia: Projected Impacts and a Proposed Agenda for Adaptation Research and Policy
climate change; British Columbia; health; adaptation
This is a case study describing how climate change may affect the health of British Columbians and to suggest a way forward to promote health and policy research, and adaptation to these changes. After reviewing the limited evidence of the impacts of climate change on human health we have developed five principles to guide the development of research and policy to better predict future impacts of climate change on health and to enhance adaptation to these change in BC. We suggest that, with some modification, these principles will be useful to policy makers in other jurisdictions. DOI PubMed
37. Pruneda, EB; Barber, ME; Allen, DM; Wu, JQ.Use of stream response functions to determine impacts of replacing surface-water use with groundwater withdrawals.Hydrogeol. J., 2010, 18: 1077-1092 Use of stream response functions to determine impacts of replacing surface-water use with groundwater withdrawals
Groundwater/surface-water relations; Stream response functions; Water-resources conservation; Numerical modeling; Canada; USA
A regional-scale numerical groundwater model is used to study the impacts of replacing surface-water use with groundwater wells to improve low-flow stream conditions for endangered species within the Bertrand and Fishtrap watersheds, southern British Columbia, Canada and Washington, USA. Stream response functions ranging from 0 to 1.0 were calculated for individual wells placed within a steady-state groundwater flow model at varying distances from the streams to determine the impact that these replacement wells, operating under sustained pumping rates, would have on summer instream flows. Lower response ratios indicate groundwater pumping will have less of an impact on streamflow than taking an equivalent amount of water directly from a surface-water source. Results show that replacing surface-water use with groundwater withdrawals may be a viable alternative for increasing summer streamflows. Assuming combined response factors should be a parts per thousand currency sign0.5 for irrigators to undergo the expense of installing new wells, similar to 57% of the land area within 0.8 km of Bertrand Creek would be suitable for replacement wells. Similarly, 70% of the land area within 0.8 km of Fishtrap Creek was found to be appropriate. A visual analysis tool was developed using STELLA to allow stakeholders to quickly evaluate the impact associated with moving their water right. DOI
36. Smerdon, BD; Allen, DM; Neilsen, D.Evaluating the use of a gridded climate surface for modelling groundwater recharge in a semi-arid region (Okanagan Basin, Canada).Hydrol. Process., 2010, 24: 3087-3100 Evaluating the use of a gridded climate surface for modelling groundwater recharge in a semi-arid region (Okanagan Basin, Canada)
climate surface; semi-arid; recharge; mountain; MIKE-SHE
Spatially distributed groundwater recharge was simulated for a segment of a semi-arid valley using three different treatments of meteorological input data and potential evapotranspiration (PET). For the same area, timeframe, land cover characteristics and soil properties, groundwater recharge was estimate using (i) single-station climate data with monthly PET calculated by the Thornthwaite method; (ii) single-station climate data with daily PET calculated by the Penman-Monteith method; and (iii) daily gridded climate data with spatially distributed PET calculated using the Penman-Monteith method. For each treatment, the magnitude and distribution of actual evapotranspiration (AET) for summer months compared well with those estimated for a 5-year crop study, suggesting that the near-surface hydrological processes were replicated and that subsequent groundwater recharge rates are realistic. However, for winter months, calculated AET was near zero when using the Thornthwaite PET method. Mean annual groundwater recharge varied from similar to 3.2 to 10.0 mm when PET was calculated by the Thornthwaite method, and from similar to 1.8 to 7.5 mm when PET was calculated by the Penman-Monteith method. Comparisons of bivariate plots of seasonal recharge rates estimated from single-station versus gridded surface climate reveal that there is greater variability between the different methods for spring months, which is the season of greatest recharge. Furthermore, these seasonal differences are shown to provide different results when compared to the depth to water table, which could lead to different results of evaporative extinction depth. These findings illustrate potential consequences of using different approaches for representing spatial meteorological input data, which could provide conflicting predictions when modelling the influence of climate change on groundwater recharge. Copyright (C) 2010 John Wiley & Sons, Ltd. DOI
35. Chesnaux, R; Allen, DM; Jenni, S.Regional fracture network permeability using outcrop scale measurements.Eng. Geol., 2009, 108: 259-271 Regional fracture network permeability using outcrop scale measurements
Groundwater modeling; Fractured rock aquifers; Discrete fracture network (DFN); Fracture scanline; Hydraulic conductivity tensor
Estimating the hydraulic properties of fractured aquifers is challenging due to the complexity of structural discontinuities that can generally be measured at a small scale, either in core or in outcrop, but influence groundwater flow over a range of scales. This modeling study uses fracture scanline data obtained from surface bedrock exposures to derive estimates of permeability that can be used to represent the fractured rock matrix within regional scale flow models. The model is developed using PETREL, which traditionally benefits from high resolution data sets obtained during oil and gas exploration, including for example seismic data, and borehole logging data (both lithological and geophysical). The technique consists of interpreting scanline fracture data, and using these data to generate representative Discrete Fracture Network (DFN) models for each field set. The DFN models are then upscaled to provide an effective hydraulic conductivity tensor that represents the fractured rock matrix. For each field site, the upscaled hydraulic conductivities are compared with estimates derived from pumping tests to validate the model. A hydraulic conductivity field is generated for the study region that captures the spatial variability of fracture networks in pseudo-three dimensions from scanline data. Hydraulic conductivities estimated using this approach compare well with those estimated from pumping test data. The study results suggest that such an approach may be feasible for taking small scale fracture data and upscaling these to represent the aquifer matrix hydraulic properties needed for regional groundwater modeling. (C) 2009 Elsevier B.V. All rights reserved. DOI
34. Shirazi, T; Allen, DM; Quinton, WL; Pomeroy, JW.Estimating soil thaw energy in sub-Alpine tundra at the hillslope scale, Wolf Creek, Yukon Territory, Canada.Hydrol. Res., 2009, 40: 1-18 Estimating soil thaw energy in sub-Alpine tundra at the hillslope scale, Wolf Creek, Yukon Territory, Canada
frozen soils; hillslope drainage; net radiation; permafrost; snowmelt energy; soil thaw energy
Accurate representations of subsurface flow in hydrologic models of permafrost terrain during spring thaw require an understanding of soil thaw and soil thaw rates. Field data, including daily photographs for snowcover estimation and meteorological measurements, and measurements of soil thaw depth, soil temperature and soil moisture content, were acquired on an organic-covered hillslope in Granger Basin, Yukon Territory, to quantify relationships between net radiation and soil thaw energy. The infiltration and freezing of meltwater into the soil likely contributes to pre-thaw warming. When this energy (1.82 MJm(-2) d(-1)) is taken into consideration, the daily mean contribution to soil thaw from net radiation is approximately 9%. Accounting for a period of refreezing that occurred during the study period and distributing the energy across the hillslope, the measured and estimated soil thaw depths compared well (R-2 = 0.92 and slope = 1.09). This research contributes to the understanding of active layer development, sheds insight into the role of infiltrating and freezing meltwater on soil thaw and provides an approach for the estimation of soil thaw based on a direct link between surface net radiation and the subsurface energy regime. DOI
33. Smerdon, BD; Allen, DM; Grasby, SE; Berg, MA.An approach for predicting groundwater recharge in mountainous watersheds.J. Hydrol., 2009, 365: 156-172 An approach for predicting groundwater recharge in mountainous watersheds
Recharge; Modelling; Semi-arid; Stable isotopes; MIKE-SHE; Mountainous terrain
Predicting groundwater supply for an entire watershed in mountainous terrain required an approach that considered a wide range in data availability between valley bottom and headwater areas, large change in elevation, and steep topography. The methodology utilized the MIKE-SHE numerical code to simulate overland flow. actual evapotranspiration and recharge for data-rich areas, and a simpler, seasonal water budget for data-limited areas. Recharge estimates were combined to form spatially variable recharge boundary conditions for a larger-scale groundwater flow model of the entire mountainous watershed. Research focused on the BX Creek watershed. located in the north Okanagan Basin in British Columbia, one of Canada's fastest growing and most water-limited regions. Groundwater recharge was found to vary from 0 to 20 mm/yr at lower elevations, and from 20 to 50 mm/yr at higher elevations. Simulation of the whole flow system illustrated that 58% of the groundwater flux from upland areas occurs through a relatively narrow alluvial fan aquifer that extends to the valley bottom, and the remaining recharge is nearly equally divided between groundwater flow through the mountain block (20%) and direct recharge (22%). Geochemical data from domestic water wells within the watershed suggest that water in the alluvial aquifer and bedrock are generally similar (i.e., common origin); however, stable isotope data indicate that groundwater in the alluvial aquifer may be derived from snowmelt recharge at a different time and elevation than snowmelt recharge to the bedrock. The combination of modelling results and complimentary geochemical and isotopic analyses of surface water and groundwater, provide an adequate first-order approximation of groundwater flow in the watershed. (c) 2008 Elsevier B.V. All rights reserved. DOI
32. Toews, MW; Allen, DM.Evaluating different GCMs for predicting spatial recharge in an irrigated arid region.J. Hydrol., 2009, 374: 265-281 Evaluating different GCMs for predicting spatial recharge in an irrigated arid region
Recharge modelling; Climate change; Irrigation; GCM; Downscaling; Okanagan
Groundwater systems in and regions will be particularly sensitive to climate change owing to the strong dependence of rates of evapotranspiration on temperature, and shifts in the precipitation regimes. Irrigation use in these arid regions is typically a large component of the water budget, and may increase due to changes in soil Moisture resulting from higher temperatures and changes in the timing of precipitation events. In this study, future predicted climate change scenarios from three global climate models (CGCM1 GHG+A1, CGCM3.1 A2, and HadCM3 A2) are used to determine the sensitivity of recharge to different climate models in an irrigated agricultural region. The arid Oliver region (annual precipitation similar to 300 mm) in the Okanagan Basin, British Columbia, is used to demonstrate the approach. Irrigation return flow, as a contribution to total diffuse recharge, is simulated by calculating the daily applied irrigation based on estimates of seasonal crop water demand and the forecasted precipitation and evaporation data. The relative contribution of irrigation return flow to groundwater recharge under current and future climate conditions is modelled. Temperature data were downscaled using Statistical Downscaling Model (SDSM), while precipitation and solar radiation changes were estimated directly from the GCM data. Shifts in climate, from present to future predicted, were applied to a stochastic weather generator, and used to force a one-dimensional hydrologic model, HELP 3.80D. Results were applied spatially, according to different soil profiles, slope and vegetation, over a 22.5 km by 8.6 km region. Changes to recharge in future time periods for each GCM result in modest increases of recharge with the peak recharge shifting from March to February. Lower recharge rates and higher potential evapotranspiration rates are similarly predicted by all three models for the summer months. All scenarios show that the potential growing season will expand between 3 and 4 weeks due to increases in temperature. However, the magnitude of the change varies considerably between models. CGCM3.1 has the largest increases of recharge rates, CGCM1 has very minor increases, and HadCM3 is relatively stable (as indicated by the near-zero changes between climate states). The significant differences between these three models indicate that prediction of future recharge is highly dependent on the model selected. The minor increase of annual recharge in future predicted climate states is due the shift of peak recharge from increased temperature. Irrigation rates dominate total recharge during the summer months in this arid area. Recharge in irrigated areas is significantly higher than natural recharge, with irrigation return flow between 25% and 58%. A comparison of recharge results for the least efficient and the most efficient irrigation systems indicates that the latter are more sensitive to choice of GCM. (C) 2009 Elsevier B.V. All rights reserved. DOI
31. Toews, MW; Allen, DM.Simulated response of groundwater to predicted recharge in a semi-arid region using a scenario of modelled climate change.Environ. Res. Lett., 2009, 4 Simulated response of groundwater to predicted recharge in a semi-arid region using a scenario of modelled climate change
groundwater modelling; recharge modelling; irrigation; climate change
Groundwater systems in arid regions will be particularly sensitive to climate change owing to the strong dependence of rates of evapotranspiration on temperature, and shifts in the precipitation regimes. In agricultural areas, such changes in climate may require increased irrigation, putting stress on existing water supplies. In this study, a regional-scale numerical groundwater model was developed for the Oliver region of the south Okanagan, British Columbia, Canada, to simulate the impacts of future predicted climate change on groundwater. In future time periods (the 2050s and 2080s), the most noticeable change in the water budget is the increased contribution of recharge to the annual water budget, estimated at 1.2% (2050s) and 1.4% (2080s) of the total annual budget relative to the current conditions. This increase is related primarily to increases to irrigation return flow resulting from higher irrigation needs under warmer temperatures and a longer growing season. Increases in recharge and irrigation return flow will result in higher water tables with future climate conditions, particularly in the irrigation districts. Median value increases in groundwater level of up to 0.7 m by the 2080s are estimated. DOI
30. Toews, MW; Allen, DM; Whitfield, PH.Recharge sensitivity to local and regional precipitation in semiarid midlatitude regions.Water Resour. Res., 2009, 45 Recharge sensitivity to local and regional precipitation in semiarid midlatitude regions
The influence of regional, local, and total precipitation on groundwater recharge in a semiarid region is investigated through modeling. Daily precipitation data at two meteorological stations within Okanagan Basin, British Columbia, Canada, are classified into regional (similar to 60% of annual) and local (similar to 40% of annual) precipitation. The classified daily precipitation data are used as inputs to a one-dimensional unsaturated zone recharge model, HELP 3.80 D. The recharge response is calculated at the base of the similar to 1.2 m soil columns for 86 soil profiles typical of the region. Results suggest that local precipitation events contribute insignificant amounts of recharge compared to regional events. Precipitation data from global climate models that cannot simulate local events accurately may therefore still provide reasonable estimates of groundwater recharge. DOI
29.Allen, DM; Schuurman, N; Deshpande, A; Scibek, J.Data integration and standardization in cross-border hydrogeological studies: a novel approach to hydrostratigraphic model development.Environ. Geol., 2008, 53: 1441-1453 Data integration and standardization in cross-border hydrogeological studies: a novel approach to hydrostratigraphic model development
hydrostratigraphic model; GIS; semantic standardization; aquifer heterogeneity; data integration; groundwater modelling
Data integration-or the merging of multiple source data sets-is central to hydrogeological studies. In cross-border situations, data heterogeneities are the source of most integration problems. Semantic integration of the subsurface geological terms is undertaken for the Abbots-ford-Sumas aquifer, a cross-border (trans-national) aquifer, which is equally shared by British Columbia (Canada) and Washington State (US). Subsurface information is largely derived from water well information submitted to the respective governments. Use of this information is constrained due to inconsistent use of geological terms in water well reports. Lack of standardized methodology resulted in 6,000 unique geological descriptions for the aquifer alone. Semantic standardization of geological descriptions progressed from database interpretation to domain expert interpretation. Despite the poor quality of water well information, trends were observed that facilitated the development of a hydrostratigraphic model that honors the generalized early conceptual models of the aquifer, but provides a much higher degree of resolution in the stratigraphy necessary for groundwater flow modeling. The standardization protocols introduced support the model creation despite the constraint of poor quality data. DOI
28. Chesnaux, R; Allen, DM.Simulating Nitrate Leaching Profiles in a Highly Permeable Vadose Zone.Environ. Model. Assess., 2008, 13: 527-539 Simulating Nitrate Leaching Profiles in a Highly Permeable Vadose Zone
Nitrate leaching; Vadose zone; Abbotsford-Sumas aquifer; Unsaturated flow; Infiltration front; Characteristic curves
An approach is developed to simulate leaching of a dissolved chemical constituent in the vadose zone of an aquifer. Specifically, nitrate loading at the water table for different water table depths, for a range of aquifer permeability values, and for different cases of heterogeneity of the aquifer, are considered. Models from the literature are first used to derive soil-water characteristic curves (water retention and hydraulic conductivity) from a grain size distribution curve for unsaturated conditions. Given infiltration from the surface, the initial conditions for the chemical concentration, and the water content profile, leaching of the chemical in the vadose zone is simulated as a function of both time and depth. The methodology is illustrated for a permeable aquifer. Simulations are undertaken using a finite element code for saturated and unsaturated flow. Different scenarios are simulated depending on the heterogeneity of the aquifer and the depth of the water table. Modeling results show that in the example case studied, nitrate concentration loading at the water table does not depend strongly on the position of the water table, but rather on the material properties of the aquifer. The contribution of this endeavor resides in the methodology which allows a prediction of nitrate leaching using only the grain size property of the aquifer. It allows practitioners to obtain a first assessment of leaching with limited data. DOI
27. Chesnaux, R; Allen, DM.Groundwater travel times for unconfined island aquifers bounded by freshwater or seawater.Hydrogeol. J., 2008, 16: 437-445 Groundwater travel times for unconfined island aquifers bounded by freshwater or seawater
analytical solutions; groundwater flow; unconfined aquifer; islands; salt-water/fresh-water relations
Analytical solutions for calculating groundwater travel times within unconfined island aquifers are given for cases of both a freshwater-bounded island (island located in a fresh water lake) and an oceanic island (freshwater contained above intrusive saltwater). The solutions apply for homogenous aquifers recharged by surface infiltration and discharged by a down-gradient, fixed-head boundary, under steady-state conditions. The solutions are given for two simple island geometries: circular islands and strip islands. A technique is also provided for comparing travel times in inland islands and oceanic islands. Travel times in oceanic islands are found to be shorter than travel times in inland islands, and travel times in circular islands are found to be longer than travel times in strip islands. DOI
26. Schuurman, N; Deshpande, A; Allen, DM.Data integration across borders: A case study of the Abbotsford-Sumas Aquifer (British Columbia/Washington State).J. Am. Water Resour. Assoc., 2008, 44: 921-934 Data integration across borders: A case study of the Abbotsford-Sumas Aquifer (British Columbia/Washington State)
interoperability; data integration; cross-border studies; ground water
Integrating spatial datasets from diverse sources is essential for cross-border environmental investigations and decision-making. This is a little investigated topic that has profound implications for the availability and reliability of spatial data. At present, ground-water hydrostratigraphic models exist for both the Canadian or for the United States (U.S.) portion of the aquifer but few are integrated across the border. In this paper, we describe the challenges of integrating multiple source, large datasets for development of a groundwater hydrostratigraphic model for the Abbotsford-Sumas Aquifer. Growing concerns in Canada regarding excessive withdrawal south of the border and in the U.S. regarding nitrate contamination originating north of the border make this particular aquifer one of international interest. While much emphasis in GIScience is on theoretical solutions to data integration, such as current ontology research, this study addresses pragmatic ways of integrating data across borders. Numerous interoperability challenges including the availability of data, metadata, data formats and quality, database structure, semantics, policies, and cooperation are identified as inhibitors of data integration for cross-border studies. The final section of the paper outlines two possible solutions for standardizing classification schemes for ground-water models - once data heterogeneity has been addressed. DOI
25. Scibek, J; Allen, DM; Whitfield, PH.Quantifying the impacts of climate change on groundwater in an unconfined aquifer that is strongly influenced by surface water., 2008, 288: 79-98 Quantifying the impacts of climate change on groundwater in an unconfined aquifer that is strongly influenced by surface water
A three-dimensional transient groundwater flow model, implemented in MODFLOW, is used to quantify the impacts of climate change on groundwater in an unconfined aquifer with demonstrated strong connection to surface water (Kettle and Granby Rivers). The Grand Forks aquifer is located in a semi-arid region of south-central British Columbia, Canada. Distributed recharge is modelled using HELP, driven by the LARS-WG stochastic weather generator, and stage-discharge curves for rivers are modelled using BRANCH and calibrated to historical data. For recharge modelling, three year-long climate scenarios were run, each representing one typical year in the present, and future (2020s and 2050s), by perturbing the historical weather according to the downscaled CGCM1 global climate model results. By the 2050s the largest increase in recharge relative to present occurs in late spring, by a factor of three or more, a 50% increase in summer months in most areas of the aquifer, a 10-25% increase in autumn, and a reduction in recharge in winter. CGCM1 downscaling was also used to predict basin-scale runoff for the Kettle River. Future climate scenarios suggest a shift in the hydrograph peak to an earlier date, although the peak flow remains the same, and baseflow level is lower and of longer duration. Groundwater levels near the river floodplain are predicted to be higher earlier in the year due to an earlier onset of peak flow, but considerably lower during the summer months. Away from rivers, groundwater levels increase slightly due to the predicted increase in recharge. DOI
24. Surrette, M; Allen, DM; Journeay, M.Regional evaluation of hydraulic properties in variably fractured rock using a hydrostructural domain approach.Hydrogeol. J., 2008, 16: 11-30 Regional evaluation of hydraulic properties in variably fractured rock using a hydrostructural domain approach
heterogeneity; fractured rocks; hydraulic properties; tectonics; Canada
A hydrostructural domain approach was tested and validated in fractured bedrock aquifers of the Gulf Islands, British Columbia (BC), Canada. Relative potential hydraulic properties for three hydrostructural domains in folded and faulted sedimentary rocks were derived using stochastically generated fracture data and hybrid discrete fracture network-equivalent porous media (DFN-EPM) modelling. Model-derived relative potential transmissivity values show good spatial agreement with transmissivity values obtained from pumping tests at selected sites. A spatial pattern of increasing transmissivity towards the southeast along the island chain is consistent between both datasets. Cluster analysis on relative potential permeability values obtained from a larger dataset for the region identified four clusters with geometric means of 9 x 10(-13), 4 x 10(-13), 2 x 10(-13), and 3 x 10(-14) m(2). The general trend is an increase in relative potential permeability toward the southeast, emulating the trends identified in the site-specific analyses. Relative potential permeability values increase with proximity to the hinge line of a regional northwest-trending asymmetric fault propagation fold structure, and with proximity to superimposed high-angle north- and northeast-trending brittle faults. The results are consistent with documented patterns of structurally controlled fluid flow and show promise for use in regional characterization of fractured bedrock aquifers. DOI
23. Surrette, MJ; Allen, DM.Quantifying heterogeneity in variably fractured sedimentary rock using a hydrostructural domain.Geol. Soc. Am. Bull., 2008, 120: 225-237 Quantifying heterogeneity in variably fractured sedimentary rock using a hydrostructural domain
faults; fractures; aquifers; ground-water; discrete fracture-network modeling
Characterizing permeability at a regional scale where fracture distributions are heterogeneous can be aided by defining hydrostructural domains. A hydrostructural domain approach is applied to a fracture data set for Mayne Island, one of the Gulf Islands in British Columbia, Canada. Fracture domains were defined using changes in fracture intensity, and are represented and modeled using a stochastic, discrete fracture-network approach. Models that statistically honor field data were constructed for representative stations for three hydraulically distinct, hydrostructural domains: "highly" fractured, interbedded mudstone and sandstone (IBMS-SS) (< 10-cm spacing), "less" fractured sandstone (LFSS) (> 1.0-m spacing), and fault and fracture zones (FZ). The highly fractured IBMS-SS and FZ domains have a greater potential porosity compared to the LFSS domain due largely to greater fracture intensities. The two highly fractured domains (IBMS-SS and FZ) have an average permeability, on the order of 10(-13) m(2), due to enhanced fracture-network connectivity. In contrast, the LFSS domain has an average permeability of 10(-14) m(2). The possibility of increased infiltration rates within FZ domains, coupled with a high-storage potential relative to the other domains suggests that fault zones with similar characteristics are likely zones of recharge. As a result, these recharge zones have an increased capacity to store and transmit infiltrated water throughout the interconnected fracture network. This study demonstrates that hydrostructural domain modeling provides a good foundation upon which to simulate flow and transport in regional groundwater resource studies. DOI
22.Allen, DM; Schuurman, N; Zhang, Q.Using fuzzy logic for modeling aquifer architecture.J. Geogr. Syst., 2007, 9: 289-310 Using fuzzy logic for modeling aquifer architecture
Modeling the geologic architecture of an aquifer and visualizing its three-dimensional structure require lithologic data recorded during well drilling. Uncertainties in layer boundaries arise due to questionable quality of drilling records, mixing during the drilling process, which results in blurred contacts, and natural heterogeneity of the geologic materials. An approach for modeling and visualizing the spatial distribution of aquifer units three-dimensionally based on fuzzy set theory is developed. An indicator is defined for evaluating the possibility of aquifer existence based on fuzzy set theory and probability principles. A specific interpolation method for aquifer 3D spatial distribution requiring only very basic borehole log data is proposed. A 3D modeling and visualization system for aquifers is also developed, which can implement basic GIS functions, like borehole identification and cross-section creation. The methodology developed is tested using real borehole lithology data available for an aquifer in British Columbia, Canada. DOI
21. Chesnaux, R; Allen, DM; Graham, G.Assessment of the impact of nutrient management practices on nitrate contamination in the abbotsford-sumas aquifer.Environ. Sci. Technol., 2007, 41: 7229-7234 Assessment of the impact of nutrient management practices on nitrate contamination in the abbotsford-sumas aquifer
The impact of recent changes to nutrient management practices in raspberry fields on the loading and subsequent transport of nitrate through the vadose zone of the Abbotsford-Sumas aquifer is investigated numerically. Previous studies have shown that nitrate concentrations in the aquifer have remained relatively stable despite a shift in nutrient management practices. Using an estimate of net annual available nitrogen in fields that are fertilized using synthetic fertilizer, nitrate concentrations as a function of time and depth through the vadose zone are simulated from spring to late fall. Results indicate rapid leaching of nitrate owing to the permeable nature of the aquifer and suggest that nitrate loading to the water table may occur earlier than previously thought, possibly due to spring rains. For an average fertilizer application rate of 90 kg of N/ha, the simulated nitrate concentration on Oct 1 within the top I m of soil is 33 mg of N/kg, while the residual soil nitrate measured in late September was 37 mg of N/kg. Taking into account the effects of dilution within the saturated zone,the simulated peak nitrate concentration is similar to average observed peak concentrations in a shallow monitoring well. A solution is offered for estimating nitrate concentration at the water table as a function of the rate of synthetic fertilizer applied to raspberry fields. DOI PubMed
20. Denny, SC; Allen, DM; Journeay, JM.DRASTIC-Fm: a modified vulnerability mapping method for structurally controlled aquifers in the southern Gulf Islands, British Columbia, Canada.Hydrogeol. J., 2007, 15: 483-493 DRASTIC-Fm: a modified vulnerability mapping method for structurally controlled aquifers in the southern Gulf Islands, British Columbia, Canada
DRASTIC; aquifer vulnerability; fractured rocks; faults; Gulf Islands; British Columbia; Canada
DRASTIC, the methodology for mapping the intrinsic vulnerability of aquifers, is modified to incorporate the structural characteristics of fractured bedrock aquifers. In these aquifers, groundwater flow is predominantly through fractures, with large-scale fracture zones and faults acting as primary conduits for flow at the regional scale. The methodology is applied to the southern Gulf Islands region of southwestern British Columbia, Canada. Bedrock geology maps, soil maps, structural measurements, mapped lineaments, water-well information and topographic data, assembled within a comprehensive GIS database, form the basis for assigning traditional DRASTIC indices, while adding the structural indices necessary for capturing the importance of regional structural elements in recharge and well capture zone determinations. DOI
19. Rayner, SF; Bentley, LR; Allen, DM.Constraining aquifer architecture with electrical resistivity Imaging in a fractured hydrogeological setting.J. Environ. Eng. Geophys., 2007, 12: 323-335 Constraining aquifer architecture with electrical resistivity Imaging in a fractured hydrogeological setting
Two-dimensional and three-dimensional electrical resistivity imaging (ERI) surveys were conducted on the southern part of Saturna Island, British Columbia, and interpreted using a lithology- and structure-based hydrogeological conceptual model. Highly resistive sections of the images are interpreted as lightly fractured sandstone units of the Protection Formation. More conductive regions of the images are interpreted as the mudstones of the Cedar District Formation. The two-dimensional (2-D) cross sections contain sub-vertical zones of decreased resistivity that cut across the sub-horizontal formations. The three-dimensional (3-D) image displays a resistive formation on the western side of the image that is separated from a more conductive region by a sub-vertical contact. The sub-vertical contact in the 3-D image and the sub-vertical low resitivity zones in the 2-D images are aligned, and the low resistivity zones are interpreted as the intensely fractured Harris Fault zone. By interpreting the 2-D and 3-D ERI results using a hydrogeological conceptual model, and verifying the results against outcrop observations and previously-collected borehole video and geophysical data, the aquifer architecture can be accurately constrained at a sub-regional scale. DOI
18. Scibek, J; Allen, DM; Cannon, AJ; Whitfield, PH.Groundwater-surface water interaction under scenarios of climate change using a high-resolution transient groundwater model.J. Hydrol., 2007, 333: 165-181 Groundwater-surface water interaction under scenarios of climate change using a high-resolution transient groundwater model
hydrologic modeling; climate change; groundwater-surface water interaction; groundwater modeling
A three-dimensional transient groundwater flow model is used to simulate three climate time periods (1960-1999, 2010-2039, 2040-2069) for estimating future impacts of climate change on groundwater-surface water interactions and groundwater levels within the unconfined Grand Forks aquifer in south-central British Columbia, Canada. One-year long climate scenarios were run, each representing a typical year in the present and future (2020 s and 2050 s), by perturbing the historical weather according to the downscaled Canadian Coupled Global Model 1 (CGCM1) general circulation model results. CGCM1 downscaling was used to predict basin-scale runoff for the Kettle River upstream of Grand Forks. These results were converted to river discharge along the Kettle and Granby River reaches. Future climate scenarios indicate a shift in river peak flow to an earlier date in a year; the shift for the 2040-2069 climate is larger than for the 2010-2039, although the overall hydrograph shape remains the same. Aquifer water levels shift by the same interval, when compared on the same day of the year. Distal from the river, modeled water level differences are less than 0.5 m, but were found to be greater than 0.5 m near the river. The maximum groundwater levels associated with the peak hydrograph are very similar to present climate because the peak discharge is not predicted to change, only the timing of the peak. (c) 2006 Elsevier B.V. All rights reserved. DOI
17. Toews, MW; Whitfield, PH; Allen, DM.Seasonal statistics: The 'seas' package for R.Comput. Geosci., 2007, 33: 944-951 Seasonal statistics: The 'seas' package for R
seasonal; normals; climatology; descriptive statistics; graphics; R programming language
The seas package for the R programming environment is capable of conveying descriptive statistics and graphics for seasonal variables, as found in climatology, hydrology and ecology. Seasonal variables can be continuous (e.g., temperature) or discontinuous (e.g., precipitation). An annum can be partitioned into many arbitrary divisions, or seasonal components, such as by month or into other fixed intervals. Boxplots are used to describe the seasonal distributions of continuous variables. Discontinuous variables need to be summed over time to smooth the irregularities before the variable can be evaluated and visualized. Statistics, such as precipitation normals, may be derived from the summed variables, using the mean or median methods. Other tools and utilities provided in the package can calculate precipitation interarrivals, cumulative precipitation departures, find changes between two normals and import data from archive formats. (C) 2007 Elsevier Ltd. All rights reserved. DOI
16.Allen, DM; Grasby, SE; Voormeij, DA.Determining the circulation depth of thermal springs in the southern Rocky Mountain Trench, south-eastern British Columbia, Canada using geothermometry and borehole temperature logs.Hydrogeol. J., 2006, 14: 159-172 Determining the circulation depth of thermal springs in the southern Rocky Mountain Trench, south-eastern British Columbia, Canada using geothermometry and borehole temperature logs
thermal springs; hot springs; geothermometry; geothermal gradient heat flow; Rocky Mountain Trench; British Columbia; Canada
Geochemical data for thermal spring waters along the southern Rocky Mountain Trench in British Columbia, Canada were examined. The range of equilibration temperatures for the thermal springs is between 24 and 59 degrees C, assuming that there is minimal mixing with colder shallow waters that might lead to a lowering of the calculated equilibration temperature. The chalcedony geothermometer is found to be the most appropriate given the carbonate host rocks. Temperature logs from 11 boreholes in the vicinity were used to calculate representative geothermal gradients, which range from 23.8 to 55.7 degrees C/km with an average of 24.8 +/- 8.0 degrees C/km. Using the average gradient and the range of equilibration temperatures calculated for each spring, the minimum range for the depth of origin of the thermal waters is 0.9-2.2 km. Heat flow values range from 90.3 to 155 mW/m(2), with an average of 109.1 +/- 21.0 mW/m(2). The moderate to high heat flow and heat generation result in generally higher temperatures at shallow depths, thus offering an explanation for the occurrence of thermal springs. The alignment of the thermal springs likely relates to the preferred northwest-southeast orientation for major thrust faults along the Rocky Mountain Trench, and with waters routed from depth along deep faults. DOI
15. Bridger, DW; Allen, DM.An investigation into the effects of diffusion on salinity distribution beneath the Fraser River Delta, Canada.Hydrogeol. J., 2006, 14: 1423-1442 An investigation into the effects of diffusion on salinity distribution beneath the Fraser River Delta, Canada
salinization; diffusion; numerical modeling; Fraser River Delta; Canada
Electrical conductivity (EC) and geochemical data were interpreted to determine the nature, origin and distribution of salinity in pore waters of sediments in a deltaic environment. The role of diffusion as a mechanism for transporting saline water within lower permeability prodelta and delta slope sediments is specifically investigated. Characteristic vertical salinity profiles at several different regions of the Fraser River Delta, British Columbia (Canada) are identified, including relatively shallow salinity zones in areas currently and historically near main river channels, and deeper salinity zones reaching up to 300 m depth in delta-front and inland areas. Comparison of salinity profiles with the results of a simple salt transport model suggests that diffusion may be a significant mechanism controlling the observed distribution of salinity in current or former estuarine areas of the delta. Density-effects were found not to be significant given the low permeability of the silt through which the salt is diffusing; however, in similar environments with higher permeability sediments, density effects may be significant. In inland and delta front areas, salinity extends to a considerable depth in the silts, beyond what would appear to be possible by diffusion alone, and points to a connate origin. DOI
14. Scibek, J; Allen, DM.Modeled impacts of predicted climate change on recharge and groundwater levels.Water Resour. Res., 2006, 42 Modeled impacts of predicted climate change on recharge and groundwater levels
A methodology is developed for linking climate models and groundwater models to investigate future impacts of climate change on groundwater resources. An unconfined aquifer, situated near Grand Forks in south central British Columbia, Canada, is used to test the methodology. Climate change scenarios from the Canadian Global Coupled Model 1 (CGCM1) model runs are downscaled to local conditions using Statistical Downscaling Model (SDSM), and the change factors are extracted and applied in LARS-WG stochastic weather generator and then input to the recharge model. The recharge model simulated the direct recharge to the aquifer from infiltration of precipitation and consisted of spatially distributed recharge zones, represented in the Hydrologic Evaluation of Landfill Performance (HELP) hydrologic model linked to a geographic information system (GIS). A three-dimensional transient groundwater flow model, implemented in MODFLOW, is then used to simulate four climate scenarios in 1-year runs (1961-1999 present, 2010-2039, 2040-2069, and 2070-2099) and compare groundwater levels to present. The effect of spatial distribution of recharge on groundwater levels, compared to that of a single uniform recharge zone, is much larger than that of temporal variation in recharge, compared to a mean annual recharge representation. The predicted future climate for the Grand Forks area from the downscaled CGCM1 model will result in more recharge to the unconfined aquifer from spring to the summer season. However, the overall effect of recharge on the water balance is small because of dominant river-aquifer interactions and river water recharge. DOI
13. Scibek, J; Allen, DM.Comparing modelled responses of two high-permeability, unconfined aquifers to predicted climate change.Glob. Planet. Change, 2006, 50: 50-62 Comparing modelled responses of two high-permeability, unconfined aquifers to predicted climate change
climate change; groundwater; aquifer; recharge; groundwater-surface water interaction; numerical modelling
The responses of two small, regional-scale aquifers to predicted climate change are compared. The aquifers are unconfined, heterogeneous, highly permeable, and representative of glaciofluvial environments in southern British Columbia, Canada and Washington State, USA. In one case, river-aquifer interactions dominate the hydraulic response. The climate change data set is that predicted by Canadian Global Climate Model 1 (CGCM1), for consecutive 30-yr intervals from present to 2069. Downscaling of GCM predictions and stochastic weather generation were done for each geographic location separately. Both studies employed identical methodologies and software for downscaling global climate model data, modelling weather for input to recharge models, determining the spatio-temporal distribution of recharge, and modelling groundwater flow using MODFLOW. Results suggest observable, but small, changes in groundwater levels, forced by changes in recharge. At the site in which river-aquifer interactions occur, water levels within the floodplain respond significantly and more directly to shifts in the river hydrograph under scenarios of climate change. (c) 2005 Elsevier B.V. All rights reserved. DOI
11.Allen, DM.Sources of ground water salinity on islands using O-18, H-2, and S-34.Ground Water, 2004, 42: 17-31 Sources of ground water salinity on islands using O-18, H-2, and S-34
Stable isotopes of O-18 and H-2 in water, and S-34 and O-18 in dissolved SO4, are used to verify the interpretation of the chemical evolution and proposed sources of salinity for two islands that have undergone postglacial rebound. Results for delta(18)O and delta(34)S in dissolved SO4 on the Gulf Islands, southwest British Columbia, Canada, suggest a three-component mixing between (1) atmospheric SO4 derived largely from recharge of meteoric origin, (2) modern marine SO4 associated with either modern-day salt water intrusion or Pleistocene age sea water, and (3) terrestrial SO4. The age of the marine SO4 is uncertain based on the geochemistry and SO4 isotopes alone. Two options for mixing of saline ground waters are proposed-either between current-day marine SO4 and atmospheric SO4, or between older (Pleistocene age) marine SO4 and atmospheric SO4. delta(18)O and delta(2)H compositions are relatively consistent between both islands, with a few samples showing evidence of mixing with water that is a hybrid mixture of Fraser River water and ocean water. The isotopic composition of this hybrid water is similar todelta(18)O = 10 parts per thousand. delta(18)O and delta(2)H values for many saline ground waters plot close to the global meteoric water line, which is distinctly different from the local meteoric water line. This suggests a meteoric origin for ground waters that is different from the current isotopic composition of meteoric waters. It is proposed these waters may be late Pleistocene in age and were recharged when the island was submerged below sea level and prior to rebound at the end of the last glaciation. DOI PubMed
10.Allen, DM; Mackie, DC; Wei, M.Groundwater and climate change: a sensitivity analysis for the Grand Forks aquifer, southern British Columbia, Canada.Hydrogeol. J., 2004, 12: 270-290 Groundwater and climate change: a sensitivity analysis for the Grand Forks aquifer, southern British Columbia, Canada
climate change; groundwater recharge; groundwater/surface water interactions; numerical modeling
The Grand Forks aquifer, located in south-central British Columbia, Canada was used as a case study area for modeling the sensitivity of an aquifer to changes in recharge and river stage consistent with projected climate-change scenarios for the region. Results suggest that variations in recharge to the aquifer under the different climate-change scenarios, modeled under steady-state conditions, have a much smaller impact on the groundwater system than changes in river-stage elevation of the Kettle and Granby Rivers, which flow through the valley. All simulations showed relatively small changes in the overall configuration of the water table and general direction of groundwater flow. High-recharge and low-recharge simulations resulted in approximately a +0.05 m increase and a -0.025 m decrease, respectively, in water-table elevations throughout the aquifer. Simulated changes in river-stage elevation, to reflect higher-than-peak-flow levels (by 20 and 50%), resulted in average changes in the water-table elevation of 2.72 and 3.45 m, respectively. Simulated changes in river-stage elevation, to reflect lower-than-baseflow levels (by 20 and 50%), resulted in average changes in the water-table elevation of -0.48 and -2.10 m, respectively. Current observed water-table elevations in the valley are consistent with an average river-stage elevation (between current baseflow and peak-flow stages). DOI
9. Lepitre, ME; Allen, DM; Mortensen, JK; Gabites, JE.Differentiating sources of dissolved lead in mine waters using lead isotope techniques, Sullivan Mine, British Columbia.Water Resour. Res., 2003, 39 Differentiating sources of dissolved lead in mine waters using lead isotope techniques, Sullivan Mine, British Columbia
dissolved lead; lead isotopes; acid mine drainage; hydrogeology
This study investigates the use of Pb isotopes in acid rock drainage studies and outlines a protocol for sampling and analysis of dissolved Pb in mine waters. Groundwaters and surface waters were sampled at the Sullivan Mine, British Columbia, to quantify Pb isotope ratios and to identify possible sources of Pb in mine effluent and back groundwaters, respectively. The Sullivan Deposit is a sediment-hosted Fe-Pb-Zn massive sulphide deposit with a well-defined homogeneous Pb isotopic composition, which provided a suitable end-member for the isotopic study. The Pb isotopic compositions of water samples define a mixing line between the homogeneous Pb isotopic signature of the Sullivan Ore and at least one other more radiogenic end-member. This end-member may correspond to Pb in the host rocks (Aldridge Formation), Pb from aerosols that have infiltrated the local surficial deposits with recharge, or Pb from the surficial deposits themselves. Further study is needed to more completely characterize the composition of potential isotopic end-members in the study area. The study demonstrates that different source regions for Pb have distinct and measurable isotopic compositions, which enable "fingerprinting'' sources of Pb contamination that result from ore deposits or from other sources. DOI
8. Michel, FA; Allen, DM; Grant, MB.Hydrogeochemistry and geothermal characteristics of the White Lake Basin, South-central British Columbia, Canada.Geothermics, 2002, 31: 169-194 Hydrogeochemistry and geothermal characteristics of the White Lake Basin, South-central British Columbia, Canada
geothermometry; hydrochemistry; isotope geochemistry; British Columbia, Canada
Hydrogeochemistry and geothermal characteristics of the Tertiary White Lake basin are described in order to provide constraints on the hydrogeology and thermal regime of the basin. The basin can be divided into three flow subsystems on the basis of chemical and isotopic variations. The groundwaters evolve chemically from young Ca-Mg-HCO3 type waters in the shallow surficial sediments to Na-dominated waters in the deeper intermediate system. Surface waters and shallow groundwaters collected from wells completed in overburden have undergone extensive evaporation as evidenced by their enriched delta(18)O and delta(2)H composition. Minor evaporation identified in the isotope composition of groundwater from domestic wells completed in bedrock, as well as from springs, suggests a local to intermediate origin for these waters, and perhaps mixing with shallow evaporative waters. In contrast, the uniform isotope signatures of deep basin waters measured both spatially and vertically suggest recharge at higher elevations, and a much deeper circulation system that is essentially isolated from the shallow subsurface. Chemical geothermometry indicates that spring waters and bedrock well waters have equilibrated at temperatures of less than 20 and 60degreesC, respectively. Groundwaters encountered by deep diamond drill holes, with equilibration temperatures of less than 80degreesC, are representative of intermediate flow systems, and may serve to modify the heat flow regime in the basin. Regional groundwater flow within the basin is complex due to numerous faults that exert a strong influence on fluid circulation patterns. Transport of heat in the subsurface, which has resulted in variations in the measured thermal gradients across the basin, occurs either at depths greater than those investigated in this study or has been significantly influenced by the circulation of cooler groundwater in the central part of the basin. (C) 2002 CNR. Published by Elsevier Science Ltd. All rights reserved. DOI
7.Allen, D; Suchy, M.Geochemical evolution of groundwater on Saturna Island, British Columbia.Can. J. Earth Sci., 2001, 38: 1059-1080 Geochemical evolution of groundwater on Saturna Island, British Columbia
A detailed geochemical study of surface waters, spring waters, and groundwaters was undertaken to examine the geochemical evolution of groundwater on Saturna Island, British Columbia. The purpose of the study was to characterize the nature and occurrence of saline waters and to provide insight on chemical processes that lead to salinization in the fractured sedimentary bedrock aquifers of this small island. Major ion chemistry shows that groundwater is recharged locally but mixes with saline waters that occur at depth or near the coast. Simple mixing is complicated by cation exchange (between calcium-rich waters and sodium-rich exchange sites offered by mudstone beds) and results in a spatially variable hydrochemical composition that is dependent on the island topography and geological framework (structural, sedimentological, and glacial), in combination with groundwater use patterns. Sodium, present at exchange sites, is speculated to be a remnant of ocean water intrusion during the Pleistocene, when the island was submerged. As a result of its high mobility and conservative nature, chloride (and sulphate) has been flushed from the shallow bedrock during a process of natural desalinization but may remain trapped in the pores and fractures at depth. Modern salt-water intrusion, brought about by increased development on the island, is now competing with natural desalinization along the coast and has left many drinking-water supplies contaminated. DOI
6. Ghomshei, MM; Allen, DM.Hydrochemical and stable isotope assessment of tailings pond leakage, Nickel Plate Mine, British Columbia.Environ. Geol., 2000, 39: 937-944 Hydrochemical and stable isotope assessment of tailings pond leakage, Nickel Plate Mine, British Columbia
stable isotopes; hydrochemistry; acid rock drainage; tailings pond leakage
An integrated hydrogeochemical and stable isotope study was undertaken to assess tailings pond leakage at the Nickel Plate Mine site in British Columbia, Canada. The approach used consisted of a hydrochemical mixing model for sulfate in conjunction with stable isotope data (18O and 2H) to estimate possible levels of contamination reaching surface waters from leakage through the dam and to determine the relative percentages of "seepage" that can be attributed to leakage through the dam and to natural groundwater flow beneath and around the dam. Results suggest that tailings pond waters are diluted by groundwaters by approximately 50% before their arrival in the collection swamps, and that the leakage from the tailings pond partially by-pass the collection (and pump-back) system at a rate of between 0.09 and 0.12 l/s. Stable isotope data indicate that tailings pond waters and swamp waters are enriched in the heavier isotopes as a result of evaporation line of slope 3.9 (D/18O). The isotope date indicate that seepage beneath the dam consists of approximately 50% real seepage and 50% meteoric waters (both surface water and groundwaters). DOI
5. Ghomshei, MM; Allen, DM.Potential application of oxygen-18 and deuterium in mining effluent and acid rock drainage studies.Environ. Geol., 2000, 39: 767-773 Potential application of oxygen-18 and deuterium in mining effluent and acid rock drainage studies
stable isotopes; acid rock drainage; mining effluent; geochemical mixing
Oxygen-18 (O-18) and deuterium (D, or H-2) are routinely used in hydrologic, climatologic and geothermal studies. In hydrology, stable isotopes provide information on the type and topology (altitude and latitude) of the recharge waters and the historical effects on water, related to such physical processes as evaporation (in ponds), melting (of snow or ice), condensation, evapotranspiration and mixing. In geothermal studies, stable isotopes provide key information related to recharge and the various temperature-dependent water/rock isotope exchange reactions. The latter is assessed through the oxygen shift in the O-18/D correlation. At acid rock drainage (ARD) sites, water/rock interactions are primarily controlled by pH and oxidation potential. Using the isotopic characteristics of the rocks and the recharge waters as a basis, the relative oxygen shift of the ARD effluent can provide information on: (1) the residence time, (2) the rate of water/rock reactions, and (3) the actual pH at the rock/water interface. This paper offers a methodology for conducting oxygen and hydrogen isotope studies related to ARD and other mineral effluent problems. The methodology is based on: (1) comprehensive sampling of regional waters, ARD effluent and major contributing minerals and rocks, (2) isotopic and elemental analysis, and (3) data interpretation on the basis of a zero-dimensional (mass balance), multi-component mixing model. DOI
4.Allen, DM; Michel, FA.Characterizing a faulted aquifer by field testing and numerical simulation.Ground Water, 1999, 37: 718-728 Characterizing a faulted aquifer by field testing and numerical simulation
Faulted aquifers constitute one of the most complex geological environments for analysis and interpretation of hydraulic test data because of the inherent ability of faults to act not only as highly transmissive zones but also as hydraulic barriers. Previous studies of the fractured carbonate aquifer at Carleton University, Ottawa, Canada, characterized the flow regime as predominantly linear, but with limited radial nature, and undertook to analyze constant discharge test data using both radial and linear pow models. When used as direct input to a numerical model, the hydraulic parameters, calculated directly from hydraulic test data, were inappropriate and resulted in a poorly calibrated model. While our interpretation of the faulted aquifer remains linear-radial in nature, parameter estimation by numerical simulation highlighted the presence of hydraulic barriers associated with the faults. These barriers are not readily apparent in the constant discharge test data and act to modify the hydraulic test curves at early to mid time, leading to incorrect estimates of the hydraulic parameters. This paper describes the conceptual model and the numerical approach, and demonstrates the importance of using transient simulations for model calibration. DOI PubMed
2.Allen, DM; Michel, FA.Evaluation of multi-well test data in a faulted aquifer using linear and radial flow models.Ground Water, 1998, 36: 938-948 Evaluation of multi-well test data in a faulted aquifer using linear and radial flow models
An extensive drilling and testing program was undertaken at Carleton University, Ottawa, Canada, to characterize the aquifer for the design of an aquifer thermal energy storage (ATES) system. The substantial data base provides an excellent record of well yields and hydraulic responses to a series of aquifer tests in a faulted carbonate aquifer. Well yield variability is reflected in the wide range in specific capacity (1.4 to 75.8 L/s/m) and is dependent upon the proximity of a well to a major fault. Constant discharge data, available for nine pumping wells and several observation wells, reflect both the excellent hydraulic connection along major faults and the limited hydraulic connection between fault blocks. Three different flow models, including vertical fracture and vertical dyke (linear), and Theis (radial), are used to interpret constant discharge test data from nine pumping wells and several observation wells. In all tests, the duration of pumping is sufficient to identify early-time linear now along faults and late-time pseudo-radial flow between fault blocks. This paper demonstrates the influence of fault-induced heterogeneity on the hydraulic response of a carbonate aquifer and demonstrates the application and limitation of simple radial continuum models to aquifers of this type. DOI
1.Allen, DM; Michel, FA.The successful use of microgravity profiling to delineate faults in buried Bedrock Valleys.Ground Water, 1996, 34: 1132-1140 The successful use of microgravity profiling to delineate faults in buried Bedrock Valleys
Site selection for ground-water production wells was made easier using a microgravity survey technique. The ground-water regime beneath the Carleton University campus is dominated by fracture flow associated with major faults. These faults are located within buried bedrock valleys where preferential erosion of the bedrock has occurred. A series of faults is inferred from bedrock topography and hydrogeological testing; however, the precise orientation of the faults is to a large extent uncertain. The bedrock surface is masked by fluvial, glacial, and glaciomarine overburden of variable thickness. High precision, small-scale microgravity profiling was carried out to identify the bedrock valleys. Gravity anomalies of up to 0.05 mgal correspond to valley depths ranging from 5 to 15 meters. The density contrast between overburden and limestone bedrock is estimated as 0.3 g/cm(3). Forward modeling using a polygon technique suggests that the observed, corrected gravity profile is a smoothed reflection of the bedrock surface at depth. Based on the locations of the bedrock valleys, several faults were identified and four test wells were drilled as part of the development of Phase 2 of the Carleton Groundwater Energy Project. Three of these wells produced high yields, exceeding 60 l/sec, when converted to 12 inch diameter production wells. The fourth well also encountered a bedrock valley but with a slightly lower yield of water. The favorable drilling results have shown that small-scale microgravity profiling, in an area thai is largely unsuitable far the detection of subsurface features using other geophysical techniques, is an effective method for imaging the bedrock surface, The positions of the faults, which are known to exist on the basis of stratigraphy, geophysical well log correlations, bedrock topography, and calcite-filled fractures exposed in outcrop or core, have been more accurately defined. DOI
