H53E-01
Probe Length Effects on Thermally-Biased TDR Measurements
Time-Domain Reflectometry (TDR) is a well-established technique for continuous, in-situ measurement of volumetric water content in field soils. Recent studies have shown that errors in the measurement of the soil dielectric constant may occur due to thermal variations present in the soil medium. These temperature effects in turn influence the determination of volumetric water content and must first be corrected for. The effect of TDR probe length, at ambient temperature conditions only, has also been investigated with results indicating a pronounced shift in measured waveform activity. This work presents a laboratory investigation of the extent of TDR probe length influence within volumetric water content measurements using probes subjected to a wide range of moisture content and thermal-variation scenarios.
H53E-02
Ground Water Recharge Estimation Using Water Table Fluctuation Method And By GIS Applications
Quite often it has become a debating point that how much recharge is occurring to the groundwater table through rainfall on one hand and through recharge structures such as percolation ponds and checkdams on the other. In the present investigations Musi basin of Andhra Pradesh, India is selected for study during the period 2005-06. Pre-monsoon and Post-monsoon groundwater levels are collected through out the Musi basin at 89 locations covering an area11, 291.69 km2. Geology of the study area and rainfall data during the study period has been collected. The contour maps of rainfall and the change in groundwater level between Pre-monsoon and Post- monsoon have been prepared. First the change in groundwater storage is estimated for each successive strips of areas enclosed between two contours of groundwater level fluctuations. In this calculation Specific yield (Sy) values are adopted based on the local Geology. Areas between the contours are estimated through Arc GIS software package. All such storages are added to compute the total storage for the entire basin. In order to find out the percent of rainfall converted into groundwater storage as well as to find out the ground water recharge due to storageponds, a contour map of rainfall for the study area is prepared and areas between successive contours have been calculated. Based on the Geology map, Infiltration values are adopted for each successive strip of the contour area. Then the amount of water infiltrated into the ground is calculated by adjusting the infiltration values for each strip, so that the total infiltrated water for the entire basin is matched with change in Ground water storage, which is 1314.37 MCM for the upper Musi basin while it is 2827.29 MCM for entire Musi basin. With this procedure on an average 29.68 and 30.66 percent of Rainfall is converted into Groundwater recharge for Upper Musi and for entire Musi basin respectively. In the total recharge, the contribution of rainfall directly to Groundwater recharge is 8.53 and 8.81 percent and the remaining 21.15 and 21.85 percent is due to groundwater recharge from water conservation structures such as check dams, contour bunds, tanks, etc. for Upper Musi and for entire Musi basin respectively. The difference is attributable to the canal recharge in the case of Lower Musi. Therefore the Upper Musi values may be taken as a percent of Rainfall that is converted into Groundwater recharge.
H53E-03
A nested modeling scheme to integrate regional groundwater flow and local groundwater flow/land subsidence processes; an application to the Tokyo metropolitan area, Japan
Many mega cities have experienced huge land subsidence due to significant groundwater extraction, and hence, enacted strict regulation of groundwater use. In Tokyo metropolitan area, the groundwater potential has recovered relatively rapidly after the cessation of groundwater extraction, however, it has caused damages to the underground infrastructures. Now, some researchers state that it is better to re-start using appropriate amount of groundwater to reduce the costs necessary for maintain underground infrastructures. To incarnate this, it is desirable to quantitatively estimate what amount of ground re-subsidence might occur by groundwater extraction. In the fields where both significant drawdown/land subsidence and the recovery of groundwater potential have been experienced, past maximum effective stress inside clayey layers is critical for estimating subsidence behavior. To trace the effective stress profiles in the clayey layers by numerical simulation, spatially high- resolution modeling is necessary. On the other hand, groundwater flow regime is rather large in space, and hence, it is difficult to set the boundary condition for the area of interest. Thus, combining both regional flow model with high resolution groundwater flow/land deformation model is desirable. We developed a new scheme to integrate regional groundwater flow and local groundwater flow/land subsidence coupled models to reduce computer load without large errors and applied it to the Tokyo metropolitan area, Japan. This modeling scheme could represent temporal changes of the stress profile in clayey layers, land subsidence in the drawdown period and land expansion in the groundwater recovery period in the Tokyo lowland quite well, and we believe that this scheme works out for predicting future groundwater potentials and land deformation in urban areas.
H53E-04
Extension of Leakage Theory to Unconfined Aquifer Flow
Semi-analytical solutions for the problem of leakage in an unconfined aquifer bounded below by an aquitard of finite or semi-infinite extent are presented. The homogeneous anisotropic unconfined aquifer of infinite radial extent is pumped continuously at a constant rate from a well of infinitesimal radius. The aquitard is also homogeneous, anisotropic and of infinite radial extent. Flow in both the aquifer and the aquitard is allowed to occur both vertically and horizontally. Exact solutions in the double Laplace-Hankel transform space for drawdown response in the unconfined aquifer using assumptions for leakage from classical and general leakage theory are developed. The latter also yields a solution for drawdown response in the underlying aquitard. The inverse transforms of the solutions are obtained numerically. Theoretical results are presented. They show that leakage can cause significant departure, at both early- and late-times, from the solution with no leakage. In the classical leakage theory case, the aquifer drawdown response reaches steady-state at late-time, whereas such a state is not attained in the general leakage theory case. These results conform to published results for leakage in confined aquifers.
H53E-05
Geophysical and Hydrological Characterization of Alluvial Fans in the Valle El Sauz Encinillas, Chihuahua, México.
The Valle El Sauz Encinillas (VESE) is located 92 km north of Chihuahua City, México. Despite being the principal aquifer feeding Chihuahua City, and being flanked by two well studied geological features (Bloque Calera-Del Nido to the West, and the Sierra Peña Blanca to the East), a lack of available hydrogeological data prevails in the valley. The goals of this study are two: 1) geomorphometrical analysis of the sub-basins and alluvial fans, and 2) determination of the alluvial fan geoelectrical units via electrical-resistivity soundings. The Basin and Range system forms a closed sub-basin with a lacustrine basin system in extinction process. The aquifer is located in alluvial Quaternary sediments, with varying granulometry, reaching a thickness of 600 meters at the center of the valley. The biggest alluvial fan in the VESE is located at the Cañón de Santa Clara, and intersects the playa-lake deposits of the Laguna de Encinillas. This fan has a surface of 73.2 km2 and an average slope of 0.437°. The geomorphometrical analysis included the sub-basins, currents, and the fans in the area. These analyses allow a comparison between alluvial fans in the VESE and those in Death Valley, California, USA. The alluvial fans in both areas show a similar behavior in all plots. Twenty electrical resistivity soundings (Schlumberger array, AB/2 distance of 400 m) were performed in the alluvial fan. The basement and four other geoelectrical units were identified in the fan. The geophysical data, granulometric determinations, plus geochemical information of twelve wells in the area were analyzed. These data show how the decrease in granulometry, both frontally and laterally in the fan, results in a rise of the hydraulic conductivity and transmisivity values (water wells in Los Sauces and El Faro). However, both the permeability and the water quality in its distal portion, are affected by the playa lake deposits, the raising ratio of clay-size sediments (and evaporites) in the center of the valley, near to Laguna de Encinillas.
H53E-06
Operator Splitting Method Applied to a System of Advection-Diffusion Equations with Nonlinear Reactions
In this work a second order operator splitting method is applied to solve a system of advection-diffusion equations with non linear reaction terms. This kind of systems represents, for example, the transport of species in porous media undergoing biodegradation. Besides the numerical difficulties associated with advection- dominated flows, stiffness may be introduced into the system since the range of characteristic reaction time is huge. This is avoided with the use of the algorithm proposed here. Approximation of time derivative is obtained using standard procedures. The spatial advection-diffusion part is solved by means of the standard Galerkin finite element method. Numerical results are presented and analyzed for different test cases in one spatial dimension. The extension of the algorithm to multridimensional multispecies transport is discussed.