Simulation of Streamflow and the Assessment of Nutrient Loadings for the Indravati River Basin of India using SWAT

Indravati River basin, a northern tributary of Godavari River, has a catchment area of 44,153 km2 and is shared by the states of Maharashtra, Chhattisgarh, Telangana, and Odisha of India. It is one of the significant river basins for human and ecological needs and helps people through agriculture. However, due to rising nutrient toxicity from excessive agricultural and industrial runoff, a hydrological and water quality model is essential to assess streamflow and nutrient loadings and provide water management scenarios to reduce nutrient toxicity. The present study is focused on the development of a hydrological and water quality model to simulate streamflow, Nitrates and Ammonium ion loadings for the Indravati watershed for the period 2000-2012 using QGIS interface for SWAT (QSWAT) and for performing the Global Sensitivity analysis using SUFI-2 algorithm on SWAT-CUP for assessing the most sensitive parameters which affect the model's efficiency. SUFI-2 within SWAT-CUP was used to calibrate and validate the model over a monthly time step, with 8 parameters corresponding to streamflow and 6 parameters corresponding to nitrates and ammonium ion loadings in streamflow chosen based on the literature available. The simulation period 2000-2012 revealed a strong correlation between observed and simulated streamflow, nitrates and ammonium ion loadings. Statistical performance criteria using R-2 and Nash-Sutcliffe Efficiency (NSE) were 0.65, 0.70 and 0.67, and 0.64, 0.67 and 0.65 for streamflow, NO3- loading and NH4+ loading, respectively. SWAT-CUP calibration and validation techniques provided the best-fitted values for all 14 parameters, 95PPU plots which show the best estimation curves for streamflow and nutrient loads considered, and global sensitivity analysis using t-Stat and P-value. This study has revealed that CN2, GW_DELAY, CH_N2, ESCO, GW_REVAP, and SOL_K are the most significant parameters affecting the streamflow and N_UPDIS, RCN, SOL_NO3, and CH_ONCO_BSN are the most significant parameters affecting the nutrient loadings of the Indravati River basin. There had not been any study of this type on this Indravati River basin. SWAT is used as it provides a flexible structure that allows finding solutions for different water resources, land management, and water pollution problems. The findings of this study would aid in managing land and water resources sustainably for future purposes.