Estimation of slope length gradient (LS) factor for the sub-watershed areas of Juri River in Tripura

Abstract

The slope length gradient (LS) factor expresses the effect of topography, i.e., combining effects of slope length (L) and slope steepness (S) on rate of soil erosion. The longer the slope length, greater is the amount of cumulative runoff and similarly steeper the slope of the land the higher is the velocities of the runoff that contributes erosion. The LS factor is the most important parameter for estimation of soil loss and soil management using Universal Soil Loss Equation (USLE) and Revised Universal Soil Loss Equation (RUSLE). A precise inventory and assessment of vulnerable areas includes the formulation of correct soil management for property development. Juri is a peri-urban watershed situated in Tripura, India, having high undulating topography, which leads to increase soil erosion and land slide problem. Therefore, it has become essential to quantify the LS factor to understand the characteristics of the topographic factor, which will help the researchers for estimation of soil erosion and preparation of management plan. The present study focused to evaluate the LS factor for the sub-watershed areas of Juri River of Tripura. Two methods namely (1) suggested by Moore and Burch (1986) and (2) proposed by Wischmeier and Smith (1978) were used to calculate the LS factor. Both the methods use Digital Elevation Model (DEM) in spatial domain to estimate the LS factor. The LS factor of the study area ranges from 0 to 982.71 by method-1 and 0.66 to 285.58 by method-2. The study indicates that, the method-2 is more apposite than method-1 because it gives LS factor value, which distributed uniformly in spatial domain; whereas method-1 resulted highest LS factor value along the flow direction and it had almost same value of LS factor in the remaining areas. This study will help for prediction of soil erosion and preparation of management plan by reducing the slope length of the study area. This findings and the methodology employed can be widely used in similar mountainous to hilly watersheds around the world for calculation of soil loss.