STUDIES OF VERTICAL DRAINAGE THROUGH A SOIL COLUMN BY GAMMA-RAY TRANSMISSION METHOD

Abstract

The main objective of this study is to understand the vertical drainage problem and to correlate with the different theories developed by the various investigators. A lot of experimental work had been done in this subject and numerical methods had been used to understand drainage process. All these studies are res icte=d to the cumulative drainage with time. Even in these studies, the drainage process is not well understood. The main difficulty is due to lack of accurate experimental technique to measure the moisture content at different depth and at different time. some authors had tried to correlate the tensiometer studies with moisture content and thus tried to understand this process of drainage. Newly developed gamma ray attenuation technique by the group of Physics Department of University of Roorkee has been tried for this study of the soil moisture profile during the drainage process. The method of gamma ray attenuation in saturated soil water ;Sys-tem . has been developed and understood . The details of the method are presented and calibration factor of this method is given. Various theories in this drainage process are given in detail in order to correlate with experimental results S wartzendruber `s method has been taken up for understanding the drainage process. This is the only theoretical approach which predict he variation of moisture content Contd... at different depth and at different time.- . But the approximation used in this approach is not quite= sound. The experimental findings and the theoretical approach are given in detail and discussed. The method to evaluate the specific yield and constants in the expression of soil moisture versus depth and at different time as given by , 5 wartzeeridrubc•r are _give=n. The quantity of water drained out from the system had been correlated with the change in moisture so that this method can have further applicability to the determination of evapotranspiration, ground water recharge, Optimum use of irrigation water etc.