Field verification of a dual-porosity flow model to estimate aquifer recharge rates through playa lakes
Huda, Akm Nazmul
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The Southern High Plains of Texas overiies an extensive aquifer known as the Ogallala formation. This aquifer is the prime source of groundwater resources for this region. This aquifer has been experiencing severe depletion of its groundwater reserve due to the intensive use of water for irrigation. The natural recharge of this aquifer primarily depends on the surface mnoff water that is collected by a large number of playa lakes present in this region. The surface mnoff water retained by the playa lakes infiltrates through the playa beds and contributes to the groundwater recharge. However, the actual amount of recharge that takes place through playa beds is difficuh to quantify. Traditionally, recharge through playa lakes was estimated based only on micropore conductivity ofthe soil. However after long dry periods, playa beds tend to develop shrinkage cracks that increases the overall conductivity of soil significantly. Unfortunately, modeling the flow through a macropore system mathematicaUy is very difficult because ofthe complexities in the geometry and the spatial distribution of macropores. In a recent study, a numerical model, FTSCracks, was developed to incorporate the influence of shrinkage cracks on the overall flow rates through unsaturated soils. In FTSCracks, the systems of macropores were defined with some empirical parameters that were difficult to determine through lab tests. In this study, a series of lab and field experiments were performed to verify the FTSCracks model with field and lab data. This study was conducted also to demonstrate the ability of this model in estimation of aquifer recharge.