H21D-0838
Efficient Algorithms for Modeling the Transport and Biodegradation of Chlorinated Ethenes in Groundwater
Predicting the fate and transport of chlorinated ethenes in groundwater requires the solution of equations that describe both the transport and the biodegradation of the contaminants. In this poster, we present a model that accounts for (1) transport of chlorinated ethenes in flowing groundwater, (2) mass transfer of contaminants between mobile groundwater and stationary biofilms, and (3) diffusion and biodegradation within the biofilms. The equations for biodegradation kinetics are based on previous work by other researchers and account for biomass growth within the biofilms, the effect of hydrogen on dechlorination, and competitive inhibition between vinyl chloride and cis-dichloroethene. Therefore, the overall model consists of coupled, non-linear, partial differential equations; solution of such a model is challenging and requires innovative numerical algorithms. We developed and tested two new numerical algorithms to solve the equations in the model; one is called system splitting with operator splitting (SSOS), and the other is called system splitting with Picard iteration (SSPI). Comparison of the two algorithms shows that the SSPI method is computationally more efficient under most conditions tested, but under some conditions the Picard iteration does not converge rapidly and the SSOS is superior. The model presented here can be used to explore phenomena that depend on the interaction between macro-scale and biofilm-scale phenomena, e.g., to identify how diffusion limitations or metabolism limitations affect macroscopic contaminant fate and transport.
H21D-0839
Model Reduction in Groundwater Modeling and Management
Groundwater management requires the development and implementation of mathematical models that, through simulation, evaluate the effects of anthropogenic impacts on an aquifer system. To obtain high levels of accuracy, one must incorporate high levels of complexity, resulting in computationally demanding models. This study provides a methodology for solving groundwater management problems with reduced computational effort by replacing the large, complex numerical model with a significantly smaller, simpler approximation. This is achieved via Proper Orthogonal Decomposition (POD), where the goal is to project the larger model solution space onto a smaller or reduced subspace in which the management problem will be solved, achieving reductions in computation time of up to three orders of magnitude. Once the solution is obtained in the reduced space with acceptable accuracy, it is then projected back to the full model space. A major challenge when using this method is the definition of the reduced solution subspace. In POD, this subspace is defined based on samples or snapshots taken at specific times from the solution of the full model. In this work we determine when snapshots should be taken on the basis of the exponential behavior of the governing partial differential equation. This selection strategy is then generalized for any groundwater model by obtaining and using the optimal snapshot selection for a simplified, dimensionless model. Protocols are developed to allow the snapshot selection results of the simplified, dimensionless model to be transferred to that of a complex, heterogeneous model with any geometry. The proposed methodology is finally applied to a basin in the Oristano Plain located in the Sardinia Island, Italy.
H21D-0840
Identifying Material Property Boundaries From LIDAR Data Using Wavelet Analysis
Wavelet analysis is a signal and image processing technique that can be used to characterize variations within the signal or image. In this work, we employ wavelet analysis on LIDAR reflectivity data of a rock face to identify boundaries between different materials types on the rock face. The LIDAR data are recorded in a topologically regular but geometrically irregular array. We extract a two-dimensional intensity image map and perform the two-dimensional continuous wavelet transform to obtain wavelet coefficients at each node in the array for a single wavelet scale. Within a zone that contains a single material type, the wavelet coefficients are relatively uniform; while between zones, the wavelet coefficients change abruptly. We identify the boundaries between zones as the locations where the the spatial rate of change of the wavelet coefficients attains its local maxima. We investigate the range of wavelet scale parameters that lead to optimal boundary identification. The boundary locations identified through the wavelet analysis technique correlate well with the observable sediment structure.
H21D-0841
Application of the Chloride Mass-balance Approach for Recharge Estimation in a Humid Environment
Recharge is a critical variable for water-balance within a hydrologic basin, and is thus an essential quantity for evaluating long-term ground-water resource sustainability and quality. Recharge studies have generally focused on arid and semi-arid regions, where water resources are most scarce and recharge is most influenced by near-surface conditions. Recharge processes have been addressed to a lesser degree in humid regions. Furthermore, recharge estimation in humid regions has focused more on regional-scale estimates, either from water-balance models or ground-water flow models. However, to address issues such as focused recharge and land-use impacts on recharge, point or local-scale values of recharge integrated over varying time intervals are necessary. Environmental tracers offer the opportunity to finely quantify recharge spatially and temporally over an area. The utility of tracers in estimating recharge has been demonstrated in arid and semi-arid environments, where the water-balance approaches are inapplicable. In this setting, recharge rates are relatively small compared to the measurements of precipitation (P) and evapotranspiration (ET). As a result, small errors associated with measurement of P and ET lead to large recharge estimation errors and limit the utility of soil- water balance methods. Applications of environmental tracers to determine recharge through the vadose zone have included chloride, 18O and 2H, and the radioactive isotopes, tritium and 36Cl, with chloride and tritium being the most common tracers used. In this study we use the chloride mass-balance approach, applied to both the vadose and saturated zones, to investigate recharge to a sand aquifer in a humid setting. The results are evaluated in light of the detailed soil and sediment stratigraphy and variations in chloride loading, and compared to recharge rates determined at differing scales using other methods.
H21D-0842
Dispersion of Dense Brine Solutions in Porous Medium Systems
The behavior of non-dilute aqueous solutions in the subsurface has been studied for decades, particularly how their behavior impacts the safe storage of wastes and remediation of dense non-aqueous phase liquids. We investigate the dispersion of calcium bromide solutions in stable displacement experiments conducted in one-dimensional columns packed with porous media with different grain size distributions. Calcium bromide solutions with mass fractions ranging from 0.01 to 0.52 were used. Previous efforts to model such systems have used nonlinear dispersion relationships, but have not incorporated chemical activity into the models despite the high salt concentration in the aqueous phase. We simulate the experimental results with a model that includes chemical activity in the dispersive flux expression. The model was derived using the thermodynamically constrained averaging theory approach.
H21D-0843
Injection the compressed air in saturated soil through a defensive well in order to separate the salt or polluted water from the fresh one. Analytical evaluation.
Stream of compressed air through a well between polluted (or sea) water and fresh water creates a "hydraulic wall" that prevents mixing of them. Steady influx of air to saturated soil produces the pressure gradient from the well and replaces the water by air, hence interface increases between air and water. After stopping the compression process, the conductivity of the soil will decline because the pores are blocked by the air, so the saturated media becomes unsaturated with the decline of the conductivity. Creating such a barrier, first by the air pressure and second by the pours blocking, is a very welcomed phenomenon in the sea-fresh water interface area. On one hand it prevents the lost of the fresh water to the sea and on the other hand decreases the sea water movement into the aquifer. Another positive effect of the air injection in the well is upper streaming of the air through unsaturated zone, located above ground water, that declines the polluted water to down-seepage from the surface and defends the fresh ground water against pollution. The regular water well or special drilled one will be used as defensive well. The radius of defensive well can be smaller than the one of the water well. The explanation of the defensive well exploitation in the field for one and multi layer aquifers is presented. Analytical evaluations of the pressure loss and shape of the air-water interfaces in saturated soil are obtained in the following cases (a) steady air stream for one layer aquifer as well as for three layer ones (leaky aquifer case), (b) transient air stream for one layer aquifer. The obtained shapes of air-water interface are usually inverted cones, when the air pressure in the aquifer decreases approximately as logarithm with the distance from the well. The necessary pressure to initial the air stream in the deep layers of the aquifer is about tens percent higher than static water pressure in the well in these layers.
H21D-0844
Addressing normal fault stratification in series solutions for multilayer groundwater flow
Previously, the authors have developed an analytic series solution method for simulating 2D steady-state groundwater flow in multi-layer aquifers with natural stratification, i.e., one that can handle layering with natural geometry [Wong S. and J.R. Craig, Computational Methods in Water Resources XVII International Conference, 2008]. The issue with the current formulation is that it restricted to relatively smooth geometry of the layer interfaces: sharp changes in interface curvature can introduce errors in the series solution. In addition, it was previously assumed that the layers were contiguous and in the same sequence across the entire modeled domain. This becomes an issue when attempting to simulate multilayer aquifers dominated by normal faults. In such aquifers, layers are not necessarily contiguous and sharp gradients in layer boundaries may occur along the fault. To address these issues, various modifications to the existing solution approach have been developed and tested by the authors. These solutions incorporate variable weighting functions in the least-squares formulation and a higher density of control points in the area where the faulting occurs. These modifications, combined with a new approach for handling non-contiguous layers in multilayer series solution methods, enable analytical simulation of groundwater flow in stratified aquifers characterized by normal faults.
H21D-0845
Tide-induced groundwater fluctuation in a leaky confined aquifer system with an overlying phreatic aquifer
A solution is developed to investigate the influences of leakage and soil parameters on tidal response in a coupled coastal aquifer system consisting of an overlying phreatic aquifer, an underlying confined aquifer, and a semi-permeable layer between them. These two aquifers interact with each other through leakage. The confined aquifer is impermeable at the bottom and connected with the sea freely while the phreatic aquifer has a free surface and is represented by the nonlinear Boussinesq equation. The effects of tidal fluctuations on both the phreatic and the confined aquifer are considered. This solution is different from the ones of Li et al. (2001, Tidal fluctuations in a leaky confined aquifer: dynamic effects of an overlying phreatic aquifer. Water Resour Res 2001; 37(4): 1095-8) and Jeng et al. (2002, Analytical solution for tidal propagation in a coupled semi-confined/phreatic coastal aquifer. Advances in Water Resources 2002; 25: 577-84) in which they used confined flow equation to approximate the Boussinesq equation. Based on the solution, the joint effects of various parameters on the behaviour of the groundwater level fluctuations in the leaky confined aquifer can be clearly and accurately explored.
H21D-0846
Experimental Determination of the Mechanisms Responsible For Acoustically Enhanced Contaminant Transport in Water-Saturated Packed Columns
Previous studies indicated that low frequency range (30 to 150 Hz) acoustic pressure forcing causes an increase in effective interstitial velocity and dispersion for conservative tracers and colloids in water- saturated packed columns. However, the exact mechanisms that lead to the observed enhanced transport are not fully understood. This study attempts to improve our knowledge in this area. Uranine (conservative tracer) as well as polystyrene microspheres (colloids of various diameters) were injected into a column packed with glass beads, saturated with water. Digital photographs were taken of the column under black light at specified time intervals. In situ concentrations were determined by measurement of the fluorescence of Uranine and microspheres in the photographs using MATLAB's® Image Processing Toolbox™. Experiments were conducted by maintaining acoustic pressure of 23.0 kPa at the influent with acoustic frequencies ranging from 30 to 100 Hz. The results suggest a pore-scale process is responsible for the enhanced transport. Additional experiments were conducted at a single acoustic frequency (70 Hz) with an increasing intensity of influent acoustic pressure from 0 kPa (base case) to 23.0 kPa. A threshold acoustic pressure was determined below which the enhancement process is not observed.
H21D-0847
Modeling of laboratory experiments determining the chemico-osmotic, hydraulic and diffusion properties of sedimentary rocks
Precise characterization and modeling of groundwater flow systems are necessary for realistic performance assessments of radioactive waste disposal. In groundwater flow modeling, the gravity potential is commonly assumed as the dominant driving force of regional groundwater flow. However, the gravity potential flow model may have a limited ability to reconstruct the excess fluid pressure distributions occasionally observed in low-permeability formations. To improve groundwater flow models, geologic processes such as compaction disequilibrium, tectonic forces and diagenetic reactions have been invoked to reconstruct excess pressures. On the other hand, chemical osmosis has recently been considered as one of the driving forces of groundwater flow and a factor causing excess pressures in clay-rich formations with vertical salinity gradients. If a formation medium acts as a semi-permeable membrane, chemical osmosis induces a fluid movement in the direction of increasing salinity. Consequently, fluid pressure could increase where salinity is high and decrease where it is low. Thus, chemical osmosis could induce a fluid flow countering the pressure-driven flow in the formation. When osmotic- and pressure-driven flows equilibrate, the net flow ceases while the fluid pressures remain in disequilibrium. This means that the direction of groundwater flow might be misinterpreted without differentiating osmotically-induced pressure from those induced by other causes. However, the formation media are not perfect membranes, as they allow solute diffusion that accord to the salinity gradients. As a result, osmotic pressure would dissipate as the solutes diffuse from high to low concentrations. That means the time period during which the osmotic pressures are held in the formation depends on hydraulic and diffusive properties other than the chemico-osmotic property of the formation media. The osmotic pressures have indeed been observed in natural formations, and the chemico-osmotic properties of clay-rich materials have been demonstrated in laboratory experiments. However, it remains inconclusive whether chemical osmosis can retain the pressure disequilibrium and so influence groundwater flow in a geologic time scale. Therefore, systematic research involving field-scale investigations of pressure and salinity distributions and experimental estimations of the chemico-osmotic, hydraulic and diffusive properties of formation media is required. This study focuses on the development of a laboratory experimental system and the analytical solutions to estimate the chemico-osmotic, hydraulic and diffusive properties of formation media. The experimental system consists of a flexible-wall permeameter cell that loads confining pressures, along with a closed fluid circuit to perform osmotic, hydraulic and diffusion experiments under background fluid pressures. This experimental design enables simulating underground conditions at the depths required for safety assessments of geological waste disposal. The effectiveness of the experimental system and the analytical solutions are demonstrated with a set of osmotic, hydraulic and diffusion experiments performed using sedimentary rocks.
H21D-0848
Evaluation of submarine groundwater discharge in coastal aquifers at Osaka Bay, Japan by numerical simulation
In recent years, the coastal marine ecosystems have been deteriorated by the human activities and fisheries. One of the causes of this deteriorating situation is due to the increase of nutrient fluxes caused by the fertilizers and wastewater through the surface water and groundwater discharges from the residential and agricultural areas into coastal areas. In recent studies, it is recognized that the groundwater which contains nutrients can have a significant influence on coastal ecosystems. Submarine groundwater discharge (SGD) consists of terrestrial fresh groundwater and recirculated seawater which circulate across the aquifer–ocean interface. Recirculating seawater, which often constitutes a large portion of the total SGD, is an important component as it transports not only salt but also other chemicals from the ocean to the aquifer. Near the shore, seawater recirculation across the interface is driven primarily by tidal oscillations, waves and density variations between fresh groundwater and seawater. Recent numerical simulations show the formation of water circulations in the aquifers near the shoreline owing to the tidal oscillations. However, these calculation results do not compare with a field observation and are not necessarily an enough verification. The objective of this study is to evaluate the SGD mechanism in the Omaehama, Osaka bay under the influence of tidal effects. The developed numerical model was verified by comparing the results with the observed SGD in the Osaka bay. The study area is located in the coast of Omaehama, Osaka, Bay, Nishinomiya citiy, Japan. The automated seeepage meters with diameter of 500mm and piezometer with diameter of 13mm were installed to evaluate water dynamics below the beach slop. Electric conductivity of the pore water were also observed to evaluate the terrestrial groundwater among SGD duaring one tidal cycle. The numerical model is based on the groundwater flow equation for saturated-unsaturated fluid flow and advection-dispersion equation for solute transport. This model have been developed to simulate groundwater flow and salt transport in an unconfined coastal aquifer subject to taidal forcing across a sloping beach boundary and inland fresh groundwater discharge. Numerical simulations with two differece changes of tidal fuluctuations have been done to evaluate the characteristic of the SGD. The results shows that seawater recirculation induced by tide was ocureed when the tidal fuluctuations was large. This result qualitatively agree with the observation results, therfore the numerical model incorporating tidal effects is uesful for evaluation of SGD including recirculated seawater.
H21D-0849
The Effect of Borehole Flow on Salinity Profiles From Deep Monitor Wells in Hawaii
Ground-water resource management in Hawaii is based partly on salinity profiles from deep wells that are used to monitor the thickness of freshwater lenses and the transition zone between freshwater and saltwater. Vertical borehole flow in these wells may confound understanding of the actual salinity-depth profiles in the basaltic aquifers and lead to misinterpretations that hamper effective water-resource management. Causes and effects of borehole flow on salinity profiles are being evaluated at 40 deep monitor wells in Hawaii. Step- like changes in fluid electrical conductivity with respect to depth are indicative of borehole flow and are evident in almost all available salinity profiles. A regional trend in borehole flow direction, expected from basin-wide ground-water flow dynamics, is evident as major downward flow components in inland recharge areas and major upward flow components in discharge areas near the coast. The midpoint of the transition zone in one deep monitor well showed inconsequential depth displacements in response to barometric pressure and tidal fluctuations and to pumping from nearby wellfields. Commonly, the 1 mS/cm conductivity value is used to indicate the top of the transition zone. Contrary to the more stable midpoint, the depth of the 1 mS/cm conductivity value may be displaced by as much as 200 m in deep monitor wells near pumping wellfields. The displacement is complemented with an increase in conductivity at a particular depth in the upper part of the profile. The observed increase in conductivity is linear with increase in nearby pumpage. The largest deviations from expected aquifer-salinity profiles occur in deep monitor wells located in the area extending from east Pearl Harbor to Kalihi on Oahu, which coincides with the most heavily pumped part of the aquifer.
H21D-0850
Diurnal Evapotranspiration Signals in Coupled Groundwater Surface-Water Systems
The surface elevation of Searsville Reservoir, CA, as well as the piezometric head of the surrounding ground water, fluctuates diurnally during the summer months due to evapotranspiration (ET). The objective of this study is to try to understand the diurnal signals in fully-coupled and interacting groundwater surface-water systems like Searsville using both data analysis and numerical modeling. Data analysis reveals intriguing characteristics of the ET signals. For example, the fluctuations of the reservoir surface elevation consistently lag behind those of the piezometric head, and the phase shift first increases during early summer (around Apr-Jun), but decreases during late summer (around Jul-Sept). Modeling using simplified domains shows that the ET signals are influenced by factors such as the water table position, the source of inflow, the spatial and temporal variations of ET, the relative timing and magnitude of ET and surface water evaporation, and the saturated hydraulic conductivity of the porous medium. Given the many factors shaping the ET signals and the complexity of coupled groundwater surface-water systems, it can sometimes be challenging to extract information about the system from the signals. However, modeling in this study confirms that reasonably reliable ET estimates can be extracted from the signals using methods that account for the daily varying recharge from or discharge to the surface water. In addition, modeling using the conditions at Searsville reproduces the characteristics of the ET signals observed at the site, and illustrates the importance of the intermittent incoming creek in maintaining a relatively high water table and reservoir water elevation and in shaping the characteristics of the ET signals observed in early summer.
H21D-0851
Surface Water and Ground Water Interactions in an Irrigated Valley in Northern New Mexico
Interactions between surface water and ground water can provide many benefits like terrestrial and aquatic
species habitat, aquifer recharge, and shallow ground water return flow. In northern New Mexico, the use of
traditional irrigation systems has effectively expanded riparian functions to encompass full irrigated valley
width. The objective of this study was to characterize the surface water and ground water interactions
occurring in an irrigated valley along the Rio Grande in northern New Mexico. We used a combination of field
measurements and modeling for determining different components of the water budget. Our results show that
on average ditch flow is 0.9 cms, ditch seepage is 10%, irrigated field deep percolation is 30%, and ground
water level rise is 0.4 m over the entire valley after the irrigation season started. We calculated that on
average, 50% of the water diverted into the main irrigation ditch returns back to the river as surface return
flow and about 10% of the total ditch inflow returns as groundwater flow. Results from this study show that a
significant amount of water being diverted into the valley returns back to the river after completing its task of
supporting important production and ecological functions in this expanded riverine valley.
http://cahe.nmsu.edu/academics/waterresearch/home.html
H21D-0852
Hydrologic Assessment of Reservoir Interacting With Groundwater System
The quantification of fluid exchange between reservoir and groundwater has become important as the understanding of the physical, chemical, and biological linkages between reservoir water and groundwater has improved. Reservoirs accumulate water from surface water inflows and from precipitation on the reservoir surface; available storage is reduced by evaporation, and release of water into networks of canals mainly for use in farmlands. In this study, we intend to characterize the interactions between groundwater and reservoir. The study was carried out at Munsan reservoir, Korea. Three monitoring wells were installed adjacent to the reservoir; each with different depths of 5, 10, and 20 m. Time domain reflectometry was used to measure soil water content in the unsaturated zone. An evaporation pan was also installed for estimating evaporation of the reservoir. In-situ hydraulic conductivity of reservoir bed was determined with the use of permeameter. In addition, classical seepagemeters were used to measure the seepage flux between the reservoir water and groundwater. However, the method is labor intensive and is not effective to monitor temporal variations of flux. To complement these limitations, we designed an automatic device that could quantify temporal variations of flux between surface reservoir and groundwater. For the investigation of the effects of configurations of reservoir, numerical simulation was applied and sensitivity analysis was carried out to understand the relative importance of the input parameters. These various studies improved our understanding the groundwater system interacting with reservoir.
H21D-0853
Paleohydrostratigraphic Model of the Thelon Basin, Nunavut, Canada
The Paleoproterozoic Thelon Basin, straddling the border between Nunavut and the Northwest Territories of Canada, formed following the amalgamation of the Archean provinces of Laurentia between 1.96 Ga and 1.81 Ga. The basin filling events spanned a period between 1753Ma and 1720Ma. The Thelon basin experienced a complicated and prolonged fluid evolution history (>600Ma) and two major uranium mineralization periods (1670-1620Ma and 1240Ma-1205Ma) have been identified. This study aims at reconstructing the paleohydrostratigraphy of the basin when the uranium mineralization occurred. Hydrostratigraphy framework plays a critical role in controlling mineralizing fluid flow. In order to understand ore-forming processes of uranium deposits in Thelon Basin, it is necessary to reconstruct the paleohydrostratigraphy. Data related to seismic reflection, geochronology, paleocurrent, diagenesis, outcrops, borehole and structure are integrated. Our conceptualized paleohydrostratigraphic model is characterized by: 1) The preserved Thelon Formation is divided into three sequences by sub-Thelon unconformity and conformable sequence boundaries. The lower parts of sequences are composed of the relative coarser deposits (diagenetic aquifers) involving clay component overlain by finer grained and well- sorted sediments (depositional aquifers) which have been transferred into aquitards by early quartz cementation before mineralizing; 2) The basement decreases to the west when the basin developed based on the paleocurrent directions indication and sediments provenance analysis; 3) Expanding the maximum burial depth of Thelon Formation to c.a. 5km although only 2km is preserved according to the extensive illitization and alteration of derital grains; and 4) Some basement faults developed and disturbed the overlying conglomerate and sandstone to some extent inferred by the existence of basement-hosted uranium deposits.
H21D-0854
Compilation and Production of a Karst map of Mexico
Twenty percent of Mexico's territory consists of karst terrain, which has been classified in two main provinces: one is the peninsula of Yucatan and the mountain systems of Chiapas and the other karst bodies are distributed in the Sierra Madre del Sur and Sierra Madre Oriental. These karst bodies developed in rocks of Triassic and Cretaceous age. Due to the importance of karst features in Mexico, the International Association of Hydrogeologists through the Karst Comition requested the collaboration of the Institute of Geology, UNAM, to compile a map of soluble surface rocks in Mexico. This work seeks to classify and georeference karst locations and generate a database to link these sites with karst geological formations and lithologies, as well as geomorphological processes that have contributed to the formation of the karst bodies. Also, we want to provide a basis for cave and karst research and for management of karst resources. In order to produce a national karst map in digital form, the tools being used are: the geographical information system Arc View and Google Earth, with the support of scientific journals, hiking and speleological documents, and 1:50000 scale geological maps of Mexico elaborated by the Institute of Geology, UNAM.
H21D-0855
Management Proposals of the Sabinas Reynosa Aquifer in Northeast Mexico, and Implications in the Development of Main Towns in Chihuahua
The Sabinas Reynosa water table aquifer is located in northeast Mexico in the state of Chihuahua, where this hydrologic unit is controlled by Laramide structures. The hydrostratigraphy consists of three units. At the base is a slightly compacted conglomerate HU1. The middle unit HU2 consists of clay materials packed with a carbonate cement. The upper unit is constituted by a sandy caliche with a calcareous matrix with secondary porosity, which allows it to store and transmit large volumes of water. The three units are of Paleogene age. Recently, the towns near the Sabinas Reynosa aquifer have presented supply problems, thus, this project will determine the hydrologic characterization using the groundwater budget method in order to establish the volume of water that the aquifer will yield per unit of time. The first phase consisted of defining the balance equation, by establishing the terms involved in the budget and calculating their respective values. Two different factors were defined: the inflows and outflows. In the first case, underground inflow with 225.68 Mm3 in the last five years, recharge by irrigation with 32.08 Mm3 and anthropogenic recharge with 270.50 Mm3 were considered. In the second case, the factors include underground outflow with 359.55 Mm3, pumping with 561.43 Mm3 and evapotranspiration from the water table with 130.61 Mm3. Although this last variable was calculated on a preliminary basis, a more accurate estimate requires additional studies (in process), with the aim of obtaining a more representative value. In this work is considered that evapotranspiration takes a decisive role in the analysis of the budget and hence, in the decisions that have to be taken for the proper management of the hydrological system.
H21D-0856
Effects of Delayed Drainage in an Updated Groundwater Flow and Subsidence Model in Las Vegas Valley, Nevada
Las Vegas Valley is one of the fastest growing metropolitan areas in the Nation. To meet the water resources demand of this area, groundwater has been intensively pumped since 1905 which has resulted in large water-level declines of more than 90 meters and land subsidence of nearly two meters. To provide a basic framework for groundwater management and to better predict future subsidence rates and locations, based on a previous model (Jeng, 1998), an integral and updated groundwater flow and subsidence model is developed for a 94-year period (1912-2005). The new model is more realistic because it incorporates delayed drainage with SUB package of MODFLOW 2000 and produces results that generally reflect the shape and magnitude of measured water-level and land subsidence changes. The analysis of the effects of delayed drainage on subsidence simulation at the Lorenzi site (extensometer installation) indicates that incorporating delayed drainage enables the new model to simulate the residual subsidence, which requires simulation of the entire groundwater extraction history of the basin and incorporation of the largest time constant of the thickest interbeds. This study contributes a more accurate simulation of groundwater flow and subsidence in Las Vegas Valley than has been previously accomplished. The updated model represents the longest simulation period (1912- 2005) of any model developed for Las Vegas Valley at a basin scale and it is the only available model capable of simulating delayed drainage. Nonetheless, it could be further improved by obtaining precise data (such as pumping and recharging rates), discretization into a smaller grid and calibrating hydraulic parameters using observed water-level and subsidence (InSAR) data.
H21D-0857
The Application of Wavelet-ICA Filter to Recognize Groundwater Anomaly Pattern Caused by Earthquake
Recognition of groundwater anomaly pattern is important to earthquake hydrology. Recently, independent components analysis (ICA) has been emerging as an efficient tool in signal analysis. The use of ICA does not need any prior knowledge about each source. It requires that the signals are independent with each other. ICA requires that the number of sensors must be no less than the number of independent sources to ensure enough information for separation of all sources. In some practical applications, this requirement of ICA is not met and we are interested in separation of only one source. Wavelet-ICA filter is proposed in this study to extract the independent feature by only using one transducer. The filter employs ICA to regularize the wavelet decompositions of a signal to find the independent feature. Morlet wavelet is employed in this application for its non-orthogonality. The feasibility of the method is explored in this study. The effectiveness of this method is demonstrated by applying it to both simulated signals and groundwater levels signals collected from groundwater wells. The results show that the Wavelet-ICA method is an efficient and functional tool to recognize the groundwater anomaly pattern caused by earthquake.
H21D-0858
Investigation of the Relationship among Rainfall, Unsaturated Water Pressure and Ground Water Level Using Grey System Theory
Rainfall is infiltrated through the surface into the vadose zone and induces the variation of the ground water level. However, the hydrological system of the rainfall infiltration is complex. How to establish the relationship between the rainfall and variation of the ground water level becomes an important topic. In this study, the grey system theory is utilized to investigate the relationship among rainfall, unsaturated water pressure and ground water level. First, the grey relational analysis among ground water level, rainfall and unsaturated water pressure are performed. Six different depths of unsaturated water pressure are used for the grey relational analysis and the depth with the optimal grey relational grade is obtained. Then the GM(1,3) model is established based on sequences of ground water level, rainfall and unsaturated water pressure in the depth with the optimal grey relational grade. Second, the GM(1,2) model is established only using the sequences of ground water level and rainfall data. The comparison of the GM(1,2) and the GM(1,3) models are performed to assess the accuracy of ground water level forecast. Finally, the concept of the time lag is used to reestablish the grey models GM(1,2) and GM(1,3) and predict the variation of ground water level. The results show that the GM(1,3) model has the higher accuracy than the GM(1,2) model for ground water level forecast. The optimal time lag is equal to 23 hours in the study site. The accuracy of the ground water level forecast is higher in the GM(1,3) model with the time lag than the one without it. Keywords:Grey system theory, Ground water level, Rainfall, Unsaturated water pressure.
H21D-0859
Gravity Variation due to Hydrology at Metsahovi, Finland
The superconducting gravimeter (SG) GWR T020 has been operating continuously at Metsahovi since August 1994. The instrument has been utilized extensively in studies of Earth tides, of the gravity effect the atmosphere, and of the nearby Baltic Sea. The remaining gravity residual is mostly due to variation in terrestrial water storage. The SG is a useful instrument for hydrological studies, due to its high sensitivity.The detection threshold of SG corresponds to the attraction a horizontal water sheet 1-2 mm thick that extends also below the instrument as well. The gravity residual strongly correlates with the level of the local groundwater. The peak-to-peak variation for 1994-2007 is 8 microgals. Assuming constant variation in storage per unit area, it can be shown that 85 percent of the Newtonian attraction of the local storage is generated within 0.1 km of the SG. However, not all observed hydrological variation in gravity is due to local storage. We estimate that roughly 1/3 of it is caused by regional and global hydrology, through elastic crustal deformation (i.e., elevation change) and far-field attraction. In this estimation we have used a.o. the Watershed Simulation and Forecasting System (WSFS) of the Finnish Environment Institute, and global models such as CPC and GLDAS. As to the remaining 2/3, the local hydrogeology combines fractured crystalline bedrock with a thin overburden (typically 0…1 m, maximally 3 m) of moraine. In addition to groundwater boreholes, we have installed soil-moisture and meteorological sensors to separate the effects. A key question is the separation of the attraction of near-field water storage from the loading effect of the regional water storage, as the two are strongly correlated and the magnitude of the former depends on very local hydrogeology around the SG. Accurate modelling of the local gravity effect would allow us to use the SG to check regional hydrology from GRACE. This ongoing work is supported by the Academy of Finland in the joint HYDROGRAV project between the participating institutes.
H21D-0860
Groundwater and Surface Water Interactions of Small Arid-Landscape Lakes in Khorezm, Uzbekistan
The Khorezm province, located in northwest Uzbekistan, is part of the Aral Sea Basin. It is a productive agricultural area under severe water stress due to anthropogenic impacts. The relatively flat landscape is dotted with numerous small lakes, most of which have been formed in natural depressions that receive irrigation runoff water. Very little is known about the hydrology of these lakes, and this study seeks to fill this knowledge gap. Groundwater and surface water interaction with the lakes was assessed during the summer of 2008. Evaporation was measured using Class A pans installed less than 500 meters from the lakes. Lake interaction with groundwater was investigated by comparing water levels in near-shore piezometers with continuous lake stage measurements. Hydraulic properties of the aquifer were determined through pump and slug tests in the piezometers. The isotopic composition (delta 2H and delta 18O) of lakes, groundwater, surface inflow, and precipitation were determined through weekly sampling during three summer months. Delta 2H and delta 18O data from preliminary samples collected in March 2008 deviated from the Global Meteoric Water Line with a slope of about 5. It was also observed that March 2008 lake waters had the highest delta 2H and delta 18O values as compared to surface inflow and groundwater. The more detailed data collected in summer 2008 will be used in a mass balance model to calculate relative inputs of surface water and groundwater to lake volume. This study provides information on the hydrology of these lakes that will be used in a larger concurrent project for modelling, examination of possible land management options, and estimation of the effects of such management on the economic, ecologic, and water quality of the lakes.
H21D-0861
Groundwater Modeling of the Texas High Plains using Modflow
The objective of this study was to develop and calibrate a groundwater model for a 4-county area in the Texas High Plains of the Ogallala Aquifer Region. This study is a major component of a comprehensive regional analysis of groundwater depletion in the Ogallala Aquifer Region with the purpose of understanding short- and long-term effects of existing and alternative land use scenarios on groundwater changes. A comprehensive geographic information system (GIS) database was developed for this purpose that included a recent land cover map. This 2008 land cover map was developed using Landsat satellite imagery with ground-truth points for Dallam, Sherman, Hartley, and Moore Counties in Texas. Other GIS layers included aquifer elevation contours, surficial geology, hydraulic conductivity contours, saturated thickness areas, well locations and piezometric heads, aquifer discharge and recharge areas, topography, hydrographic data, ecological regions, and soil type data. The hydrologic simulations were done using MODFLOW. Anticipated outcomes from this modeling effort include the effect of change in land use/land cover on sustainability of the aquifer life in the study region. Our results will be used to develop strategies to conserve groundwater in the Ogallala Aquifer beneath Central High Plains and improve regional water planning.
H21D-0862
Simulation of the Entire Distribution of Groundwater Age
The groundwater ages from environmental tracers can be used to calibrate groundwater flow and transport models and to constrain their parameters. Tracer concentration measurements yield an estimated age of water at a particular location. In reality, a water sample represents a mixture derived from multiple flowpaths carrying water of different ages and traveltimes. This is not a major problem if the traveltime distribution possesses minimal variance, but in a groundwater system with substantial heterogeneity, a single average traveltime may be inadequate for accurate modeling and may give inaccurate estimates of hydrologic properties. Even use of higher moments besides the mean groundwater age may not adequately describe the important age densities represented in a given sample because the shape of underlying distribution is generally unknown. This may lead to possible misinterpretations of natural traveltime and consequent errors in estimating the values of hydraulic parameters that are related to traveltime. This clarifies the importance of the understanding and simulation of entire distribution of groundwater age. In this study we simulate entire distribution of groundwater age instead of simulating only mean groundwater age. We use the idealized synthetic system described in Bethke and Johnson (2002) that consists of two layers of aquifers adjacent to an aquitard as our framework. The goal is to compute the entire distribution of groundwater age in both transient and steady-state contexts in this system and to compare with mean groundwater age calculations.
H21D-0863
Numerical Groundwater Model of the Inarajan and Tinaga River Basins in Support of a Potential Landfill Inarajan, Guam
Geomatrix conducted a hydrogeologic assessment of the Inarajan and Tinaga River basins in southern Guam to develop a conceptual understanding of groundwater flow and occurrence in support of design, construction, and operation of a regional municipal landfill. Few previous hydrologic studies have focused on southern Guam, and thus this study provided the first detailed comprehensive assessment of groundwater and surface water conditions in the area. Data collected from an extensive field program, along with previous investigations were used to develop a hydrogeologic conceptual model describing regional and site geology, hydrostratigraphy, and groundwater and surface water flow. A three-dimensional numerical groundwater flow model of the system was developed using MODFLOW-SURFACT. The model was used to test various alternative conceptualizations and to provide a tool to evaluate landfill design and potential impacts to water resources from construction and operation of the landfill. The nature of the local watershed systems allowed for design of a basin-scale model. Historic USGS daily discharge measurements on the Inarajan and Tinaga Rivers coupled with historic precipitation records facilitated the basin scale approach. The model was calibrated to both steady state and transient conditions allowing for simulation of groundwater flow under a variety of conditions. Following calibration, predictive simulations were conducted to assess various aspects of landfill construction. The primary finding of the predictive assessments was that elimination of areal recharge resulting from construction of the landfill will cause a dramatic lowering of the water table in the weathered and fractured pyroclastic units that underlie the site. In addition, construction of the landfill will likely result in some reduction in stream base flow. Discharge of storm water runoff from the landfill into adjacent wetlands will mitigate some of the predicted impacts to base flow and replenish storage within the wetland sediments that will slowly discharge to streams during the dry season.
H21D-0864
Tertiary Aquifer Modeling Within the Mississippi Embayment
The geologic and hydrogeologic characterization of the aquifers and their recharge area within the Central United States in west Tennessee, northern Mississippi and eastern Arkansas are poorly understood. Previous investigations have utilized overly generalized outcrop boundaries of the primary Tertiary aquifers based on sparse well log information and stream down-cutting to show formation location. Acquisition of data in the form of deep oil and gas wells along with shallow lignite borehole data from the North American Coal Company is enabling us to improve upon these prior formational boundaries and recharge area delineations. Additionally, utilization of those geophysical logs with numerous well log curves is allowing us to characterize each geologic unit as to the sand/clay composition, porosity, and depiction of facies changes within a three- dimensional context. This is made possible through the utilization of the oil industry standard mapping package, Petrel®. We use a combination of methods to illustrate the presence of clay bodies within the primary drinking water aquifer, historically modeled solely as a sand unit. Identification of these clay bodies will impact ground-water flow patterns and assist water utilities in reducing contamination threats. We will illustrate aquifer thickness variability owning to faulting and paleo-erosion that again may impact ground-water pathways.
H21D-0865
Optimizing the well pumping rate and its distance from a stream
Both ground water and surface water are very important component of the water resources. Since they are coupled systems in riparian areas, management strategies that neglect interactions between them penalize senior surface water rights to the benefit of junior ground water rights holders in the prior appropriation rights system. Water rights managers face a problem in deciding which wells need to be shut down and when, in the case of depleted stream flow. A simulation model representing a combined hypothetical aquifer and stream has been developed using MODFLOW 2000 to capture parameter sensitivity, test management strategies and guide field data collection campaigns to support modeling. An optimization approach has been applied to optimize both the well distance from the stream and the maximum pumping rate that does not affect the stream discharge downstream the pumping wells. Conjunctive management can be modeled by coupling the numerical simulation model with the optimization techniques using the response matrix technique. The response matrix can be obtained by calculating the response coefficient for each well and stream. The main assumption of the response matrix technique is that the amount of water out of the stream to the aquifer is linearly proportional to the well pumping rate (Barlow et al. 2003). The results are presented in dimensionless form, which can be used by the water managers to solve conflicts between surface water and ground water holders by making the appropriate decision to choose which well need to be shut down first.
H21D-0866
Numerical Modeling of One-Dimensional Steady-State Flow and Contaminant Transport in a Horizontally Heterogeneous Unconfined Aquifer with an Uneven Base
Algorithms and a short description of the D1_Flow program for numerical modeling of one-dimensional steady-state flow in horizontally heterogeneous aquifers with uneven sloping bases are presented. The algorithms are based on the Dupuit-Forchheimer approximation. The program permits evaluation of water table elevations, tracking streamlines, delineating bounds of contaminant plume, and estimating advective travel times. The D1_Flow program was tested against three types of analytical solutions, data from the Borden Landfill, and results obtained by the two-dimensional model used on the landfill previously. The program yielded results practically coinciding with each of these. With its flexible boundary conditions and rapid execution, the code can form a suitable basis for a plume diving calculation and be integrated into a site assessment.
H21D-0867
Analytical Modeling of Groundwater Seepages to St. Lucie Estuary
In this paper, six analytical models describing hydraulic interaction of stream-aquifer systems were applied to
St Lucie Estuary (SLE) River Estuaries. These are analytical solutions for: (1) flow from a finite aquifer to a
canal, (2) flow from an infinite aquifer to a canal, (3) the linearized Laplace system in a seepage surface, (4)
wave propagation in the aquifer, (5) potential flow through stratified unconfined aquifers, and (6) flow through
stratified confined aquifers. Input data for analytical solutions were obtained from monitoring wells and river
stages at seepage-meter sites. Four transects in the study area are available: Club Med, Harbour Ridge,
Lutz/MacMillan, and Pendarvis Cove located in the St. Lucie River. The analytical models were first
calibrated with seepage meter measurements and then used to estimate of groundwater discharges into St.
Lucie River. From this process, analytical relationships between the seepage rate and river stages and/or
groundwater tables were established to predict the seasonal and monthly variation in groundwater seepage
into SLE. It was found the seepage rate estimations by analytical models agreed well with measured data for
some cases but only fair for some other cases. This is not unexpected because analytical solutions have
some inherently simplified assumptions, which may be more valid for some cases than the others. From
analytical calculations, it is possible to predict approximate seepage rates in the study domain when the
assumptions underlying these analytical models are valid. The finite and infinite aquifer models and the
linearized Laplace method are good for sites Pendarvis Cove and Lutz/MacMillian, but fair for the other two
sites. The wave propagation model gave very good agreement in phase but only fairly agreement in
magnitude for all four sites. The stratified unconfined and confined aquifer models gave similarly good
agreements with measurements at three sites but poorly at the Club Med site. None of the analytical models
presented here can fit the data at this site. To give better estimates at all sites numerical modeling that
couple river hydraulics and groundwater flow involving less simplifications of and assumptions for the system
may have to be adapted.
http://people.cecs.ucf.edu/yeh
H21D-0868
The Use of Gravity Methods in Arizona's Rural Watershed Initiative Projects
The Rural Watershed Initiative, established by the State of Arizona, was formed to address water-supply issues in areas outside the State's more populous regions, with an emphasis on regional watershed studies. In cooperation with the Arizona Department of Water Resources, the U.S. Geological Survey is conducting a number of hydrogeologic investigations under this initiative. This work has resulted in the creation of new gravity station networks for monitoring ground-water storage changes in rural areas of Cochise and Mojave Counties. Temporal-gravity surveys are used to detect local changes in the gravitational field of the Earth. The method is readily applied to measurement of ground-water storage change in Arizona's alluvial basins where significant variations in pore-space (water mass) storage occur. This results from ground-water mining and periodic focused recharge events. Aquifer-storage change is an important, but typically poorly known component of the ground-water budget in alluvial basins. In areas where water-table elevation data are available for unconfined aquifers, estimates of specific yield may also be obtained by dividing the volume of aquifer-storage change (measured with gravity methods) by the water-table elevation change in the unconfined aquifer. Two instruments are used to monitor gravity across the networks: the relative gravity meter and the absolute gravity meter. The relative meter is the primary instrument by which differences in gravity are monitored at stable monuments. Much as control benchmarks are used in conventional land surveying, repeated relative gravity surveys for ground-water storage monitoring should include a reference station where gravity is known to vary little, or where the absolute acceleration of gravity is monitored. The recent acquisition of a Micro-g LaCoste A-10 field-portable absolute gravity meter allows monitoring of these reference stations as needed. This is particularly valuable to the project objectives, where a number of absolute stations may be located throughout a basin, thereby serving to constrain a least-squares adjustment of the network of gravity differences obtained from relative gravity surveys. In 2008, new gravity monitoring networks were established in the Willcox-Douglas and Middle San Pedro Basins in Cochise County, and in the Sacramento, Detrital, and Hualapai Basins in Mojave County. Baseline absolute gravity measurements were made at the 40 new gravity stations during March and April, 2008. In addition to annual absolute gravity measurements, the simplicity of relative gravity surveys will allow for biannual gravity-change measurements at a greater number of locations within each basin. Together these two techniques provide an efficient and valuable characterization of variations in ground-water storage in rural Arizona watersheds.
H21D-0869
An integrative approach to groundwater recharge estimation: Application to Jeju Island, Korea
Groundwater resources in Jeju Island, a volcanic island located in the most southern region of Korea, are the only resources for water use. The island mainly consists of highly permeable volcanic materials and structures such as basaltic rocks and lava conduits. Water from precipitation barely resides on the surface and mostly infiltrates into the aquifers or discharges directly to the ocean. Thus, estimating groundwater recharge is critical to the water resource management in Jeju Island. The groundwater recharge was estimated using a GIS-based water balance model, WetSpass (Water and Energy Transfer between Soil, Plants and Atmosphere under quasi Steady State), and a physically-based groundwater flow model, MODFLOW. The WetSpass model estimates spatially varying groundwater recharge based on the surface dominant geo-spatial input parameters, such as soil property, land use, topography, groundwater depth, and meteorological data. The groundwater flow model estimates recharge by using the parameter estimation technique. Both models are complementary because the water balance equation and the groundwater flow equation are linked by a cell-based data process. The results indicated that the eastern and northern part of the Island showed relatively high values of recharge as compared to the western region. The results also showed that 65% of the total recharge occurred in higher elevations over than 200 m which would be a critical groundwater recharge area. The recharge estimation using coupled model provides more reliable results than the use of a single model and useful information for groundwater resource management and associated legislation.