TR(BR)-122 : Parameter determination in semipervious stream- aquifer system

Abstract

The study of stream-aquifer interaction is a prerequisite for conjunctive use management. Many numerical and analytical models for stream aquifer interaction have been developed in the past, these include models developed by Cooper and Rorabaugh (1963), Hornberger et al.(1970), Morel- Seytoux and Daly(1975), Mishra(1987), etc.

Most of the investigators have dealt with fully penetrating streams. However, streams are generally partially penetrating with a semi-pervious bed of low hydraulic conductivity. Consequently, an extra resistance to flow is offered by a partially penetrating stream due to curved flow lines near the stream and low hydraulic conductivity of the fine sediments deposited at the bottom of the stream. Only a few researchers (Halek and Svec, 1979; Hall and Moench, 1972; etc.) have considered this aspect.

Application of models of stream-aquifer interaction requires the aquifer parameters be known a priori. These parameters are aquifer-diffusivity and stream resistance. In this report first the direct problem (direct problem is the prediction of water table induced due to stream-stage variation with known parameters) and then the inverse problem (inverse problem is the determination of parameters with known variations in stream-stage and induced water table) have been solved.

The direct problem has been solved using the concept of 'retardation coefficient' as proposed by Hantush(1965) for modelling a semi-pervious stream. Discrete pulse kernel coefficients have been employed to determine water table induced due to stream-stage variation. For the inverse problem, a non linear optimization technique (Marquardt, 1963) has Peen used and a model has been developed for the determination of parameters of a semi-pervious stream and aquifer system.

Applicability of the model has been verified with published data (Reynolds, 1987) and it has been observed that the present method predicts aquifer response more correctly as compared to that used by Reynolds. This shows that the present model is applicable to similar field problems where the stream is partially penetrating and has semi-perviousness at its bed and bank.