Surface-Runoff-Introduction

When rainfall occurs in excess of absorption by soil, it causes runoff which increases with time and length of slope. Runoff is influenced by multiple factors like intensity and duration of rainfall, existing land use, initial abstraction, rate of infiltration, slope gradient and length, percolation rate, presence of hard substratum, antecedent moisture and so on.

Runoff is a critical factor in deciding the type of conservation needed, number and location of water harvesting and recharge structures, formulation of appropriate cropping pattern and crop selection and the water balance and water availability at the watershed scale.

Some important runoff estimation models that are in use are SCS Curve Number method, which is empirical method of estimating excess precipitation, Constant infiltration based method in which saturated soil conductivity is used as infiltration rate; Horton equation, which is based on mathematical equation; SAC-SMA (Sacramento Soil Moisture Accounting) which attempts to mimic physical constraints of water movement in a natural system and Rational method (Ramser’s method).

Under this DSS, along with the SCS Curve Number and Rational methods, Runoff model developed based on LRI database (Infiltration) and precipitation available from KSNMDC is included to estimate the amount of runoff that can be expected to occur at different levels in a watershed area.