H13G-0996
Linking Climate and Anthropogenic Signals with Groundwater Levels in a Southern California Watershed
The importance of groundwater in regional hydrologic budgets and the world's water supply is unquestionable. Increasing climate variability as well as increasing demand on limited water resources highlights the need for improved understanding of linkages between regional climate, surface water fluxes and groundwater recharge. This study focuses on the potential impacts of climate variability and anthropogenic pumping on groundwater levels in Las Posas Basin located in southern California. Precipitation time series and groundwater levels were analyzed throughout the Las Posas basin for the period 1975-2004. Water level variability was analyzed for over 300 individual wells and a correlation matrix was computed to establish well locations (or groups) with similar hydrologic behavior. A representative well from each established "group" was chosen for subsequent analysis. Both climate and selected well data were subjected to frequency analysis using Fast Fourier Transform (FFT). The time series of precipitation, the El Nino–Southern Oscillation (ENSO) index, well levels, and pumping rates were analyzed. The results suggest the existence of significant periodicities between 2.0 and 6.0 years in both the precipitation and the well level data that are partially coincident with ENSO cycles. Assessment of the complex interactions between climate variability and groundwater levels will facilitate improved water resources planning and management in water- stressed regions where marginal changes in hydrologic budgets have large implications.
H13G-0997
A Basin-Averaged Water Balance Approach to Estimate Catchment-Scale Groundwater Flow in a Semi-arid Mountainous Catchment
Quantification of the contribution of groundwater flow from highland areas of mountainous watersheds to semi-arid and arid valley bottom unconsolidated aquifers is increasingly needed for the assessment of water resources in many populated areas. In mountainous environments, however, data for Darcy equation parameters are limited, leading to uncertainty in estimates of groundwater flow of up to two or more orders of magnitude. An alternative method for estimating regional groundwater flow from highland to valley bottom areas was developed for the semi-arid Okanagan Basin, British Columbia, Canada. The method involved a basin-averaged water balance approach, using mean annual surface water run-off (RO) data for 9 gauged tributaries with spatially distributed estimates of mean annual precipitation (P) and actual evapotranspiration (AET), to develop basin-averaged relationships for prediction of recharge-driven groundwater flow through the bedrock highland areas. Groundwater flow from highland bedrock areas to unconsolidated valley bottom aquifers was subsequently accounted for through a calibration exercise using a spreadsheet tool developed for the project. Average annual AET was the most difficult parameter to quantify at the tributary catchment scale. Spatially distributed AET estimates were developed using temperature and precipitation data, with consideration of expected AET ranges established based on available data for the region. Results for the bedrock areas in the Okanagan Basin indicated basin-averaged partitioning of mean annual precipitation as 68% AET, 19% to surface water run-off (in streams), and 13% to net recharge (groundwater flow). The influence of AET and surface water run-off parameter uncertainty on regional bedrock groundwater flow calculations was a factor of 2 (AET range of 60-70% catchment precipitation) and 1.2 (RO range of 14 to 26%), respectively. This approach allows for preliminary estimates of water budget constrained recharge- driven groundwater flow at the catchment or basin scale.
H13G-0998
Seasonal interactions between deep aquifers and sea water in the Pingtung coastal zone of southern Taiwan
Stable isotopes, tritium and radiocarbon were analyzed in several waters from Pingtung coastal zone, southern Taiwan, including coastal groundwater and offshore seawater samples were determined to show the freshwater- saltwater interaction. Previous submarine groundwater discharge (SGD) studies in coastal aquifers often focus mainly on shallow (<10 m) and narrow (<5 km) zone within the coastline. This study has been done for the fluid discharge at the deep seafloor in the study site. The δ18O depleted layers are found along the deep sites of Kaoping Canyon outcropped from deep aquifers and extend for considerable distances away from shore. Waters from the SGD tongue along the Kaoping Canyon are distinct in terms of salinity, δ18O, δ13CDIC and radiocarbon. The isotopic compositions of submarine seawaters are characterized by significant variability and heavy isotope enrichment. The groundwater end-member can be represented by data of groundwater wells monitored in the Pingtung Plain. The stable isotopes data showed good separation of freshwater with seawater groups. Important reactions have occurred in these mixing zones which would affect the local distribution of chemicals. However, the geochemical characteristics and relevant reactions in the upper and lower mixing zones are found to be distinctively different. At the first order, the SGD processes and seawater intrusion may seem to be exactly opposite. However, detailed results show that SGD in the Pingtung coastal zone is mainly fed by coastal contaminated groundwater and re-circulated seawater (with a few groundwater percentage), which raises a potential environmental concern with implication for the management of groundwater resource in the region.
H13G-0999
Autonomic and Climatic Impacts on the Dutch Coastal Groundwater System
Half of the Netherlands is located below sea level and still land subsidence is taking place. As saline groundwater is found within a couple of meters below ground surface, salinization of the freshwater resources is taking place. Above mentioned process together with anthropogenic activities like groundwater exploitation and differentiated water level management is called the autonomic process. As a consequence, salt seepage affects the quality of surface water and reduces the freshwater volume necessary for drinking, environmental, industrial and agricultural purposes. Apart from this autonomic process, the Dutch delta will be jeopardized by climate change due to two effects: sea level rise and a combination of changing precipitation and evapotranspiration. Calculations with a regional density dependent 3D model for the coastal province of Zuid-Holland show increasing piezometric heads for all implemented climate scenarios due to sea level rise. This will, however, only happen at areas less than 10-20 km from the coastline or large rivers. Up to 5 km from the coast, the piezometric heads will increase with more than 50% of the sea level rise. In the inland areas, land subsidence causes decreasing piezometric heads. Salinization of the groundwater system will take place in most parts of the Dutch delta. Around the islands of Zuid-Holland, the main cause for salinization is sea level rise. The autonomic process on the other hand dominates the salinization of the polders. Due to increasing piezometric heads and salinization, the salt seepage will increase up to 20% for inland polders and up to 75% for coastal polders. The effects of the changes in recharge and evapotranspiration are small in general and depend on the climate scenario and area. Adaptive and mitigative activities like land reclamation offshore and desalinization of saline groundwater show some positive effects on the chloride concentrations of the groundwater. Nevertheless, this cannot reverse the ongoing salinization of the Dutch delta.
H13G-1000
Comparison of Numerical and Steady-state Models to Predict Vertical Water Flux With Application to Water Delivery Canals
In the U.S. alone, as much as 50 percent of irrigation water carried within unlined water delivery canals may be lost during transport, resulting in wasted resources and degradation of cropland due to salinization and low water tables in some locations. To minimize this loss, it is important to quantify where and when the seepage occurs. The use of heat flux as a tracer has become an accepted technique for detecting interactions between surface and groundwater sources. Most commonly, flow is assumed to be only in the vertical direction, through an isotropic, homogeneous porous medium, allowing the use of the one- dimensional advection-conduction equation for heat transport. Both analytical and numerical approaches to the transient and steady-state forms of the equation have been employed; however, few studies have considered the variability between these approaches. This study uses synthetic data to explore systematic differences between numerical and analytical transient models and a steady-state model. The models were then applied to one year of temperature data collected between July 2006 and 2007 at several large water delivery canals in eastern Colorado. Preliminary results show that the numerical transient model best fits the observed data, and variability in error during the modeled period suggest that seepage rates vary throughout the year.
H13G-1001
Assessing Ecological Flow Needs and Risks for Springs and Baseflow Streams With Growth and Climate Change
Ecological flow needs assessments are beginning to become an important part of regulated river management, but are more challenging for unregulated rivers. Water needs for ecosystems are greater than just consumptive use by riparian and aquatic vegetation and include the magnitude, frequency, duration and timing of flows and the depth and annual fluctuations of groundwater levels of baseflow supported streams. An ecological flow needs assessment was adapted and applied to an unregulated, baseflow dependent river in the arid to semi-arid Southwestern U.S. A separate process was developed to determine groundwater sources potentially at risk from climate, land management, or groundwater use changes in a large regional groundwater basin in the same semi-arid region. In 2007 and 2008, workshops with ecological, cultural, and physical experts from agencies, universities, tribes, and other organizations were convened. Flow-ecology response functions were developed with either conceptual or actual information for a baseflow dependent river, and scoring systems were developed to assign values to categories of risks to groundwater sources in a large groundwater basin. A reduction of baseflow to the river was predicted to lead to a decline in cottonwood and willow tree abundance, decreases in riparian forest diversity, and increases in non-native tree species, such as tamarisk. These types of forest vegetation changes would likely cause reductions or loss of some bird species. Loss of riffle habitat through declines in groundwater discharge and the associated river levels would likely lead to declines in native fish and amphibian species. A research agenda was developed to develop techniques to monitor, assess and hopefully better manage the aquifers supporting the baseflow dependent river to prevent potential threshold responses of the ecosystems. The scoring system for categories of risk was applied to four systems (aquifers, springs, standing water bodies, and streams) in the groundwater basin. The process was developed to allow water managers to assess and prioritize potential impacts to the biological, historical, or cultural aspects of the four types of systems from groundwater abstraction. These approaches can be adapted to other baseflow dependent, unregulated rivers or to assess risks to natural features associated with water sources in other regions.
H13G-1002
Groundwater and Land Subsidence Monitoring in 3 Mega-Cities, Indonesia, by Means of Integrated Geodetic Methods
In urbanized cities, one of the urgent problems is the monitoring groundwater variations especially connected with the land subsidence. In Jakarta, Indonesia, there are more than several tens of observation wells and the monitoring of the groundwater levels have been conducted so far. However for monitoring the variations of groundwater storages, we need additional information about groundwater mass variations as well as land movements which can be obtained by modern geodetic techniques. Therefore we intend to employ a new technique of precise gravity measurements combined with GPS, and InSAR techniques. The gravity changes due to groundwater mass movements are measured as gravity changes by means of precise gravimeters. An infinite water table of one meter thickness causes about a 40-micro gal gravity change. Thus, an accuracy of 10 micro gals or better is required for the hydrologic problems. It is not easy to achieve an accuracy of 10 micro gals by means of a spring-type relative gravimeter, for instance Schintrex gravimeter. We therefore propose a new method to combine absolute gravity measurements and relative gravity measurements. For this purpose, we employ a portable absolute gravimeter A-10, for the measurements at some control points, and employ relative gravimeters of superior portability for the measurements at most points around the control points. Because groundwater variations cause vertical land movements in many cases, it is also important to monitor the height changes at the gravity points. Moreover the rate of gravity changes versus height changes depends on the density of the material which causes the gravity changes, thus it gives important information about the mechanism of the deformation. Therefore we employ GPS measurements for monitoring height changes. We also employ In-SAR images to identify the areas of the subsidence occurs. The first experimental measurements in Jakarta have been conducted in August 2008. The same measurements have been conducted in Bandung and Semarang subsequently. In these cities large land subsidence has been expected as well. We employed A10 (number 17) for the absolute measurements and a Schintrex meter for the relative ones. We plan to conduct the gravity measurements repeatedly for next 2 years with an interval of one, and expect to reveal secular groundwater changes and associated land subsidence in these cities.
H13G-1003 INVITED
Study of Sub-basin Scale Groundwater Variations in Asia Using GRACE, Satellite Altimetry and in-situ Data
A project to assess the effects of human activities on the subsurface environment in Asian developing cities is now in progress (Research Institute for Humanity and Nature., 2008). In the project, precise in situ gravity and landwater observations combined with GRACE (Gravity Recovery and Climate Experiment) satellite gravity data is proposed to evaluate local groundwater level changes of the developing urban areas in Asia. It is necessary for precise and accurate estimation of the local groundwater variations to separate local groundwater level changes from regional or global scale landwater variations. GRACE data is useful to estimate large scale landwater variations. Using GRACE Level 2 monthly gravity field solutions, we previously recovered landwater mass variation around Bangkok, in Thailand, which is one of the test areas of the project and located on the downstream of Chao Phraya river basin in the Indochina Peninsula. However, it is difficult to distinguish landwater signal of Chao Phraya river basin itself with the neighboring 3 large river basins because of the limitation of the spatial resolution of the GRACE monthly solutions. In this study, we recovered mass variation of Chao Phraya river basin using GRACEfs along track range rate data instead of the monthly solutions. We used the method developed by Chen et al (2007), which uses GRACEfs line-of-sight range acceleration measurements. We also tested the recoveries of landwater mass variations in other small scale river basins including Jakarta, Seoul and Taipei, which are also study areas of the project. Using the sub-basin scale landwater mass variation recovered by GRACE, we estimated groundwater level change in the project study areas by combing with in situ landwater and gravity observations. Satellite altimetry data is also used to separate groundwater variation from other landwater components as a constraint of river water storage variations.
H13G-1004
Modeling Multiple Stresses Placed Upon A Groundwater System In A Semi-Arid Brackish Environment
In semi-arid areas groundwater systems are frequently not sufficiently characterized hydrogeologically and long term data records are generally not available. Long-term time series are necessary, however to design future groundwater abstraction scenarios or to predict the influence of future climate change effects on groundwater resources. To overcome these problems an integrated approach for the provision of a reliable database based on sparse and fuzzy data is proposed. This integrated approach is demonstrated in the lowermost area of the Jordan Valley. The Jordan Valley is part of the Jordan Dead Sea Wadi Araba Rift Valley, which extends from the Red Sea to lake Tiberias and beyond with a major 107 km sinistral strike-slip fault between the Arabian plate to the east and the northeastern part of the African plate to the west. Due to extensional forces a topographic depression was formed. As a result of an arid environment it is filled with evaporites, lacustrine sediments, and clastic fluvial components. A subtropical climate with hot, dry summers and mild humid winters with low amounts of rainfall provide excellent farming conditions. Therefore the Jordan Valley is considered as the food basket of Jordan and is used intensively for agriculture. As a result hundreds of shallow wells were drilled and large amounts of groundwater were abstracted since groundwater is the major source for irrigation. Consequently groundwater quality decreased rapidly since the sixties and signs of overpumping and an increase in soil salinity could clearly be seen. In order to achieve a sustainable state of water resources and to quantify the impact of climate change on water resources a proper assessment of the groundwater resources as well as their quality is a prerequisite. In order to sufficiently describe the complex hydrogeologic flow system an integrated approach, combining geological, geophysical, hydrogeological, historical, and chemical methods was chosen. The aquifer geometry and composition is described with the help of geological, hydochemical, and geophysical methods. As far as the water budget is concerned, the recharge to the considered aquifer is estimated with geological methods and available data sets, while the abstraction from the aquifer is estimated with the help of remote sensing techniques. A historical approach is used to detect the general conditions under which the groundwater system has been in the past. Afterwards this information is implemented into a flow model. On the basis of the findings a numerical 3-D transient model integrating all important features of the hydrogeological system was developed.3 In order to be able to give reliable predictions about the impacts of climate change scenarios on the groundwater system the flow model was tested against stress periods depicted during the historical review of the test area (model period: 1955 – 2008). These stress periods include periods of intense rainfall, of drought, and of anthropogenic impacts, like building of storage dams and of violent conflicts. Recommendations for future sustainable groundwater abstractions are given.
H13G-1005
Groundwater flow system determined by multiple age tracers and stable isotopes in Jakarta area, Indonesia
The Jakarta groundwater basin is one of the most developed basins in Indonesia. Jakarta city lies in the coastal plain of the Java Sea (to the north) with an elevation ranging between 0 and 200 meters above sea level. The area belongs to a humid tropical climate; the annual rainfall is between 1,500 and 2,500 mm due to the influence of tropical monsoon. Low permeability Miocene sediments that crop out at the southern boundary of the basin form the basement of the regional aquifer system. The geology of the basin aquifer consist of marine Pliocene and Quaternary sand, and delta sediments having thickness up to 300 m (Fachri et al. 2003). Groundwater samples collected from springs, hot springs and wells during September 2006 and March 2008 are analyzed for Tritium, CFCs, and 14C. As the result of 14C analysis has not yet reported, these age tracers can determine not only natural groundwater flow system of the studied area but also the human induced groundwater perturbation caused by the local groundwater consumption. Tritium concentration ranges 0.5 to 1.4 T.U. (N=23), which shows less significant difference in sampling point and sampling depth. CFCs age shows around 20 to 25 years age in mountainous area. While in urban discharge area, CFCs ages are around 10 to 15 years in shallow wells (up to 60m depth) and over 40 years in deep wells (bellow 60m). This CFCs age result indicates that the groundwater age becomes older with increasing depth. Similar tendency was also observed by Geyh et al.(1989) using 14C age. During presentation, we intend to analyze the groundwater flow system including 14C age in Jakarta area with the help of the potentiometric change of the local groundwater aquifer caused by the recent over pumping and its regulation.
H13G-1006
Flood water storage as a resource for agriculture and groundwater recharge: the empting of artificial leaking ponds
The large industrialization, intensive agriculture and the increasing population is giving rise to a lack of water resources. There is the need of capturing runoff for storing the water and using it during dry periods, but people now opposes to the realization of new dams. In Italy Public Authorities are showing a great interest in using ponds or small lakes located in the fluvial surroundings for storing water. The reservoirs can be filled up during flood events and can become, maintaining the water for a certain period, a resource for agriculture and a source of artificial recharge of groundwater. The hydraulic risks in the management of such small structures and the economic budget are lower than those involved in traditional reservoirs. In this work we propose a set of relationships with the aim of describing the interactions between the pond lakes and the beneath groundwater. This methodology allows to estimate the emptying time of the lake and its relative flow rate in a very fast way. It requires only a few parameters: the geometry of the problem, the initial lake and groundwater level and the hydraulic parameters of the aquifer and of the bottom of the lake. The solution of the problem was split in two cases: groundwater level always below the lakebed and groundwater level interacting with the lake level. It is possible to identify the two cases comparing the maximum flow rate drained from the aquifer (QS) to the one provided by the lake (QL). If QS is greater than QL the groundwater level maintains below the lakebed and vice versa. The two cases are well represented by simple relationships developed by the authors. These relationships were obtained using the results provided by a numerical model developed using MODFLOW 2000 with the LAKE3 package. Considering the first case, the relationship between the lake, groundwater level, the time and the leakance is represented by a straight line in a semi-logarithmic plane. In the case of the lake interconnected with the aquifer, the history of the lake level in the time has to be described by a set of dimensionless plots with the governing characteristics numbers that were identified by the writers.
H13G-1007
Efficiency Evaluation of Open-Loop GHPS Operation Under Various Hydrogeological Conditions
Geothermal heat pump system (GHPS) can be cost-effective renewable energy sources. In order to develop the GHPS which has certain hydrogeological characteristics, understanding the thermohydraulic process of an aquifer is necessary for effective usage of open-loop GHPS. Experimental and numerical tests are performed for two concepts of open-loop GHPS: simple open-loop and energy storage concept. In simple open-loop sets, tests were performed fixing the locations of pumping and injection wells. In contrast, tests in energy storage sets were conducted by changing the locations of wells in a seasonal cycle. Experimental test using sand tank was performed only for the simple open-loop concept, while numerical tests were performed for the both concepts. Numerical modeling results using FEFLOW were compatible with the experimental results. In the simple open-loop sets, the temporal temperature change in a pumping well was measured. Effective operation conditions are obtained with high hydraulic conductivity (3X10-3 m/s) and long distance (60 cm) between wells on hydraulic gradient 0.025 because the effect of injected water temperature must be minimized. In the energy storage sets, thermal recovery factors (R) under various conditions were calculated to evaluate the efficiency. Low hydraulic conductivity (3X10-5 m/s), hydraulic gradient 0.0 and long well distance (more than 20 m) are the best conditions for operation efficiency (R=37.92) because faster groundwater flow lead to advection or down-gradient ¡®drift' of stored energy beyond potential recovery regions. In the case of two-layered aquifer, the porosity and groundwater flow characteristics of each layer sensitively affected the migration of thermal plume. Two-layered aquifer with the top-layer of low hydraulic conductivity (3X10-5 m/s) and porosity (0.2) is profitable for the effective open-loop GHPS operation under hydraulic gradient 0.0 and well distance (20 m). The results from experimental and numerical tests can provide a helpful guideline for effective usage and design of open-loop GHPS under various hydrogeological conditions.
H13G-1008
Assessment of Change Drivers Affecting the Sustainability of Gravity Fed Water Supply in the Alto Beni Watershed of Bolivia
In the Alto Beni region of Bolivia, most communities rely on gravity fed systems for their drinking water. Gravity fed drinking water systems are often viewed as a feasible and sustainable method of delivering safe natural spring water to developing communities, because minimal treatment is required and pumping is unnecessary. However, communities in the Alto Beni watershed are finding the need to extend their systems to more distant springs to provide sufficient water. Drivers of change within the watershed that have the potential to affect the sustainability of gravity fed water systems include a 3% population growth rate, an expected 200% increase in agricultural use of land, expansion of water and sanitation coverage (83% and 72% increases in coverage respectively), and a changing climate with a roughly 1.5% projected increase in the mean annual temperature from the 1990s and a 2 to 4% decrease in dry season precipitation by the 2030s. These changes affect both demand and supply from springs. Indicators for these change drivers are evaluated in seventeen watersheds within the Alto Beni. The research presented is the beginning of a monitoring program using low cost methods and local participants to study the impacts of changes on the sustainability of water systems in the region.
H13G-1009
Anthropogenic Influence On Groundwater Quality In Jericho and And Adjoining Wadis (Lower Jordan Valley, Palestine)
The Lower Jordan Valley is part of the Jordan-Dead Sea Rift. The graben is filled by sedmiments of limnological and marine origin. Towards the Dead Sea, the occurance of gipseous and salty sediments on the valley floor increase. The southern part of the Lower Jordan Valley, where the city of Jericho is situated, is an arid area (<150 mm precipitation/year), with less amount of exploitable fresh groundwater or surface water. Jericho was founded on an alluvial fan, closely to the western mountain range in front of mouth of Wadi Qilt. The fan serves as reservoir for infiltrating water from wadi runoff and groundwater from the crataceous aquifers of the western shoulder. The fan is surrounded by unsuitable aquifers of the graben, which are filled with saline water. The aim of this study, which takes place inside the multilateral SMART-project, is to understand the vulnerability of the Jericho groundwater aquifers in connection with lowering the groundwater table by overexploitation and the intensively use of pesticides Jericho and its vicinity are of most importance for the Palestinians. However, beside the about 25,000 residents, the tourism industry and the vital agriculture depend on sufficient and expoitable fresh water resources. Because the demand of water is increasing, overexpoitaion takes place. Due to over extraction of groundwater a huge depression cone is evolving during the dry season which is filled up again according to the groundwater recharge in the rainy season. Concomitantly, depression cone in the fresh water aquifers leads to an infiltration of the surrounding saltwater. The amount of saltwater which infiltrates into the freshwater resource was calculated by different stable isotope methods (d2H, d18O) and hydrochemical analyses of wellwater. The agriculture is main consumer of groundwater - over 60% of the pumped water is used for inefficient irrigation. Additionally, an intensive use of pesticides in concentrated liquid and gaseous forms for vegetable gardening hold the danger to pollute the groundwater via irrigation return flow. This return flow most probably endangers the quality of the water resource, because shallow wells nearby extract it directly from the underground. However, one result of the first screening campaign concerning pesticide remnants in the groundwater wells of Jericho, just traces have been detected. Thus, the higher amount of chemicals is retained by the soil during infiltration of irrigated water. The detected low concentrations in groundwater of the fan may be the result of outleaching from agricultural areas from the mountain range. The flood water of Wadi Qilt infiltrates partly in the fluviatil sediments. The ongoing investigations in the Wadi Qilt-Jericho area include an approach of combined hydrochemical and hydraulic studies to simulate the complex groundwater system at the edge of the graben and to prepare a sustainable groundwater management strategy for the area of Jericho.
H13G-1010
Numerical simulation of groundwater flooding: An example from the UK.
The numerical simulation of groundwater flooding is increasingly necessary as the problem is gaining
recognition from government bodies and climate change may bring more extreme events. However
producing a suitable simulation of groundwater flooding involves many technical challenges. The timescale
of the development of the flood can be short, recharge must be calculated correctly, the unsaturated zone
must be considered as well as the "usual" suitable simulation of the saturated zone. The latter requires good
simulation of absolute as well as relative values, since the timing and extent of the water table reaching the
ground surface must be simulated well. All these factors combined with data scarcity makes simulation of
groundwater flooding difficult.
The Natural Environmental Research Council, in the UK, is funding a consortium to examine the problem of
groundwater flooding in the Chalk, a micro-porous fractured limestone, which is an important aquifer for water
supply in South-East England. This consortium, consisting of the British Geological Survey, Imperial College
and the Centre for Ecology and Hydrology are studying groundwater flooding in the Pang and Lambourn
catchments, located 50 kilometres to the west of London. A modelling system is currently under development
of simulate the groundwater flooding which occurred in winter 2000/1, winter 2002/3 and summer 2007.
The project has taken an existing groundwater flow model to simulate the groundwater flooding that occurred
in winter 2000/1. The groundwater flow model, originally developed for another part of the catchment, has
been run with daily stress periods as opposed to monthly in the original model. This reduction in the length
of the stress period has resulted in a much improved simulation of the groundwater and river baseflow
hydrographs during the flooding. Analysis of the time lag between recharge and groundwater rise using the
model shows that there is a spatial and a temporal distribution in time delay between recharge leaving the
soil zone and arriving at the water table. The time delay, normally of the order of 20-25 days, reduces to less
than 10 days under flooding events. Unsaturated zone processes, therefore, need to be examined to
explain this change in delay.
http://www.groundwaterflooding.org.uk
H13G-1011
Quantifying Spatial and Temporal Variability of Mountain System Recharge in Semi-Arid Catchments
Groundwater recharge is likely to be altered as a result of climate change and variability impacting groundwater resources. In semi-arid Basin and Range systems where Mountain System Recharge (MSR) represents a significant component of recharge, this impact is likely to be more pronounced. Despite the importance of MSR in such basins' water budget, physical processes that control MSR have not been fully investigated due to complexity of recharge processes in mountainous catchments and limited soil moisture and water level elevation data. In most groundwater models, MSR is either derived from empirical relationships or estimated during the model calibration and water balance analysis. Therefore, these models are not capable of assessing the impact of climate variability and change on groundwater resources. The objective of this research is to enhance our conceptual understanding of MSR, and quantify temporal and spatial variability of MSR in selected semi-arid catchments in the Basin and Range province of Arizona. Water budget analysis was performed on a seasonal time scale using the Soil and Water Assessment Tool (SWAT2005). Isotopic and soil moisture data were used to provide a constraint on recharge seasonality and water balance partitioning. Preliminary results show annual variability of MSR with pronounced differences in winter and summer seasons. The ratio of MSR to precipitation varied between (0-20%) in summer with a median of 8% compared to (0-50%) in winter with a median of 18%. Moreover, a threshold response of MSR to winter and summer precipitation and soil moisture was shown over the simulation period in different catchments. These results demonstrate the advantage of using modeling approaches that can evaluate these seasonal recharge thresholds. The results further highlight the need for further understanding of the physical factors in semi-arid catchments that control precipitation partitioning into MSR such as vegetation, soil type and slope.
H13G-1012
An Isotopic Investigation of Groundwater Recharge in the East Mesa Area of the Salton Sea Basin
The Salton Sea Basin, a closed topographic basin located in arid southeastern California and a portion of Baja California, Mexico, is home to some of the most productive agricultural lands in the United States. In the Imperial Valley, in the southern portion of the basin, groundwater use is limited owing to the wide availability of imported water, low urban demand, and water production and quality limitations. Intense interest in developing new water supplies and, separately, restoring the Salton Sea has led to renewed interest in the availability of groundwater in the Imperial Valley, especially the East Mesa area, where decades of leakage from unlined canals has likely impacted groundwater. This study uses isotopic tracers of the water molecule to examine the source of water and groundwater residence time in the East Mesa area between the All American and Coachella canals and the Salton Sea. Groundwater samples were collected from 12 wells and from the All American Canal at Drop 1 for stable isotopes of the water molecule and for tritium-helium groundwater age. Remote well locations, unfavorable well construction, and a dearth of monitoring wells with small open intervals, however, placed limitations on both sample integrity and on spatial coverage of the sampling area. The aridity of the Salton Sea area, and the long history of irrigation with Colorado River water, has marked the groundwater with an evaporated Colorado River water stable isotope signature. High tritium waters (captured in the extensive surface storage system of the Colorado River during peak fallout) that have infiltrated in the Salton Sea area make another good tracer of groundwater transport. Recently recharged groundwater, with tritium-helium apparent ages of less than 2 years, has a chemical and isotopic signature that closely matches water from the canal, and is found in wells directly adjacent to the All American canal. Mean apparent ages of 10 to 40 years were observed in wells at distances of 1 km to more than 7 km from the canal. These wells have isotopic signatures of less evaporated Colorado River water, indicating recharge took place after emplacement of at least some of the dams but during a time of high tritium fallout from atmospheric weapons testing. Overall, the results suggest that there has been significant leakage from the unlined canals, and that water penetrates to much greater depth in the East Mesa study area when compared to the Central Imperial Valley where irrigated agriculture dominates the landscape. These are consistent with other interpretations based upon purely geologic and water budget considerations.
H13G-1013
Oasis Recharge Detected by Satellite Radar Interferometry
We report an anomalous surface uplift in the desert of Oman during 2006-2007. The uplift is collocated temporally and spatially with anomalously high rainfall, seismic tremors, and water discharge from wells. We use remote sensing InSAR data from the satellite Envisat and GPS data to study the uplift. The transient uplift evolves spatially with time, and consists of two narrow bands, approximately 700 m long by 100 m wide, forming a 'V' shape, and leading to two elliptical features, approximately 600 m by 2.5 km. We interpret the bands as feeders to two oases and study the temporal evolution of the recharge. We form month-to-month interferograms to study the transient uplift. The feeders uplift at a rate of 1-2 cm/month, and then slow down at different times. One oasis uplifts during 3 months with an average rate of 5 cm/months in the satellite line of site (LOS) direction. The second oasis uplifts with an accelerating rate during at least 6 months, reaching a rate of 16 cm/months in the LOS direction. Both uplifting regions expand spatially during this activity.
H13G-1014
Lineament Mapping for Groundwater Exploration Using Remotely Sensed Imagery in Different Terrains
Developing methods for analyzing remote sensing data to delineate fractures and discontinuities in hard-rock terrains could be used to improve well-siting strategies in regions where the primary sources of groundwater are bedrock wells. Groundwater recharge/discharge zones might also be detectable using remote sensing techniques that are sensitive to temperature, vegetation, and water content differences. Fracture networks and discontinuities are difficult to characterize because of inadequate information available from drilling records and conventional mapping. Most features, such as bedding planes, foliations, and faults, occur as linear features called lineaments and these are sometimes visible in aerial photos and remotely sensed imagery. Bruning (2008) demonstrated how lineaments could be mapped using remotely sensed imagery by identifying patterns based on color, tone, and texture, and demonstrated a suite of digital image processing techniques, such as principal component analysis and various indexing methods, to enhance the visibility of features from different data sources. This approach was developed for a relatively small volcanic area (4 km by 16 km) in Nicaragua. We are adapting this approach to study a regional system of multiple aquifers and created a lineament map of the Quito aquifer system in Ecuador using ASTER, RADARSAT, and Landsat images together with a Digital Elevation Model. The normalized difference vegetation index was used to detect fractures and faults that affect the occurrence of vegetation associated with proximity of groundwater. The normalized difference water index is sensitive to water content in vegetated areas. In addition to applying the approach to a new and larger volcanic region, this method was used in an attempt to identify the cavity network in a karst terrain in a Northern area of Puerto Rico where groundwater is the main supply of drinking water for inhabitants and also contributes to base flow for surface water bodies. A comparison was made between mapping lineaments in volcanic and karst terrains. Drainage patterns in karst are not as linear as in volcanic terrain and connections are not as apparent in comparison to lineaments in volcanic terrains. Nevertheless, the analysis of the imagery provides additional insights into the subsurface structure that complements topographic information.
H13G-1015
Approaches for Assessing Groundwater Availability Under Competing Demands and Climate Change
The Yakima River Basin in eastern Washington, like many areas of the arid American West, struggles with issues of water allocation. The 1 billion dollar agricultural economy in the basin lowlands is one of the largest in the United States and is principally based on the diversion of about 6,000 ft3/s of surface water. The mountainous uplands generate the snowmelt runoff for irrigation and fish habitat, making riverine transport of surface water of paramount importance. Surface water in the basin is fully appropriated in average years and over-appropriated in dry years, but there are increasing demands for water for municipal, fisheries, agricultural, industrial, and recreational uses. These demands must be met through the use of groundwater, increased storage, greater conservation, and or purchasing water rights. In some areas, groundwater pumping has caused water level declines of more than 300 ft, potentially reducing streamflow in reaches with senior surface-water rights or instream flow requirements for endangered species. A variety of analytic tools have been developed to address the issues of water management under existing conditions, future growth scenarios, and potential regional climate change, including a comprehensive assessment of groundwater. The hydrologic and hydrogeologic framework that has been developed is integrated into an overlapping series of groundwater models. The models have been designed to evaluate 1) surface water impacts from existing pumpage and potential new pumpage, 2) effects of projected changes in climate on groundwater use, 3) potential improvements in irrigation efficiencies on water availability, 4) artificial recharge and aquifer storage systems, and 5) the relative utility of various aquifer management strategies. In combination, these approaches may lead to a way to accommodate municipal, agricultural and ecological needs of the basin within the physical limitations of the hydrologic system.