Influence of Watershed Characteristics on Water Abstraction Parameters

The two important water abstraction parameters in a watershed are the initial abstraction (I_a) and the potential maximum retention (S). The ratio I_a/S is an input to the Curve Number method of watershed runoff estimation. The standard value of I_a/S is 0.2, which was developed in the USA through the analysis of a large volume of watershed rainfall-runoff data. The recommended value of the I_a/S in India is 0.1 for black soil regions for wet to very wet watershed soils, and 0.3 for black soil region with dry soil as well as for all other regions irrespective of degree of soil wetness. It is believed that besides the distinct behaviour of black soil and other soils, there may be many other watershed features influencing both I_a and S. In this paper, the influence of three watershed features namely, soil type, land slope and land use on the abstraction ratio has been investigated by considering the rainfall-runoff data from 32 gauged watersheds. The study revealed that while soil type had a statistically significant influence on the abstraction ratio; neither land slope nor land use had any statistically significant influence on it.