Modeling daily surface runoff, sediment and nutrient loss at watershed scale employing Arc-APEX model interfaced with GIS: a case study in Lesser Himalayan landscape

Abstract

The present study was carried out to evaluate performance of Agricultural Policy Environmental eXtender (APEX) integrated with GIS as ArcAPEX model in simulating surface runoff, sediment and nutrients loss from a watershed located in lesser Himalayan region in Uttarakhand state, India. Daily surface runoff, sediment and nutrient loss data measured at watershed level for the year 2010–2011. Measurement at watershed revealed average daily sediment loss in range of 1.0–1.32 t ha−1 was measured with peak of 3.04 t ha−1 on daily time-step. The loss of total carbon (TC) and total nitrogen (TN) were estimated from 0.49 to 0.58 kg ha−1 and 0.16 to 01.7 kg ha−1, respectively from the watershed on daily basis for the rainfall considered for the modelling. A total of 40 rainy days surface runoff and sediment data were collected and of which half of the events data were used for calibration and remaining for validation. The calibration was done by changing the sensitive parameters. Analysis showed that SCS CN number was found most sensitive to runoff, followed by saturated hydraulic conductivity, available water-holding capacity, CN retention parameter and C factor whereas erosion control practice (P) factor was found to be most sensitive, followed by C factor, sediment routing coefficient, average upland slope and soil erodibility (K) factor for the sediment and nutrient loss. APEX model calibrated for the watershed and it predicted quite well for the surface runoff (r = 0.92, NSE = 0.50), sediment loss (r = 0.88, NSE = 0.61 and nutrients of total carbon (r = 0.78, NSE = 0.59) and fairly for total nitrogen (r = 0.77, NSE = 0.19). The calibration and validation results indicate that APEX model can be satisfactorily used for predicting runoff, sediment and nutrient (TC) loss at watershed scale on daily time-step. The landscape is prone landslips/ collapse of field terraces etc. occurring at high rainfall events was not accounted by the model that may be a reason for under prediction of sediment loss by the model. The study suggests to incorporate landslips/collapse of field terraces, etc., processes in future improved versions of APEX for improving sediment yield prediction in the Himalayan landscape.