Simulation of runoff and sediment yield from a hilly watershed in the eastern Himalaya, India using the WEPP model

Abstract

Summary A study was undertaken to develop appropriate vegetative as well as structural measures to control sediment yield from a 239.44 ha small multi-vegetated watershed in high rainfall and high land slope conditions of eastern Himalayan range in India using a physically based distributed parameters Water Erosion Prediction Project (WEPP) model. The model was calibrated and validated using field-measured data pertaining to 86 storms of monsoon season 2003 and 98 storms of 2004. The daily simulated runoff and sediment yield of the Umroi watershed for the calibration and validation periods were found to match with their measured counterparts at 95% significance level as shown by the Student’s t-tests. The model simulated daily runoff quite well as corroborated by reasonably high Nash–Sutcliffe simulation coefficients of 0.94 and 0.87, low root mean square errors of 1.42 and 1.77 mm, and low percent deviations of −1.71 and −3.01, respectively for calibration and validation periods. The performance of the model for simulating daily sediment yield was also quite good with Nash–Sutcliffe simulation coefficients of 0.95 and 0.90, root mean square errors of 0.08 and 0.09 Mg ha−1 and percent deviations of 3.05 and −5.23, respectively for calibration and validation periods. Subsequently, the calibrated and validated model was used to simulate vegetative (crop, level of fertilization and tillage) and structural (rock-fill check dam and trash barrier) measures and combinations of vegetative and structural control to evaluate their impacts on runoff and sediment yield reduction. Simulations of different vegetative management scenarios indicated that replacing traditional bun agriculture and upland paddy crop with maize, soybean, and peanut would reduce sediment yield by 18.68, 29.60 and 27.70%, respectively. Field cultivator and drill-no-tillage systems have the potential to reduce sediment yield by 13.14 and 21.88%, respectively as compared to the existing practice of spading and country plough. Installation of 8 check dams and 18 trash barriers in the drainage line was predicted to reduce sediment yield from the Umroi watershed substantially with reduction of 54.67%. Simulations of combinations of management practices indicted that soybean and peanut in upland situations with field cultivator or drill-no-tillage system, and structural control in the drainage line has potential to make agriculture sustainable in the Umroi watershed with sediment yield reduction up to 78.40%. The results of the study indicate that the WEPP model can be successfully used for developing conservation management practices in high rainfall and high slope conditions of eastern Himalaya.