TR(BR)-116 : Determination of specific yield in the zone of water table fluctuation

Abstract

Regional dynamic ground water potential is evaluated from observed water table fluctuation and specific yield. There are different methods by which the specific yield in the zone of water table fluctuation can be determined. The simplest method is soil moisture measurement in the zone of fluctuation. Long duration pumping tests in unconfined aquifer are conducted to find the delayed yield and this value can be taken as the specific yield.

In the present study a mathematical groundwater flow model has been developed for determining the specific yield in the zone of water table fluctuation. A discrete kernel approach has been used to solve the water released owing to specific yield from the dewatered zone. A family of type curves for different ratios of specific yield to elastic storage coefficient have been obtained using which the specific yield and the elastic storage can be obtained from aquifer test data. The variation of well function with nondimensional time parameter exhibits three distinct parts. The early part like Theis curve has steep slope. The middle portion is flat due to the recharge from the dewatered zone. The latter part is again similar to Theis curve. As time increases the Theis well function and well function of the present analysis converge.