Quantifying sediment yield and discharge fluctuations using the GeoWEPP in response to soil and water conservation practices

Owing to the overuse of wild land, the mountainous watersheds in Iran have experienced severe land degradation and consequent downstream flooding. To design effective soil and water conservation strategies, it is crucial to understand how sediment yield and flow fluctuations respond to conservation practices. The purpose of this study was to evaluate the GeoWEPP model for runoff and sediment yield predictions via multiple endemic inputs, namely, climate, soil characteristics, topography, and LULC. Through the calculation of four parameters related to soil properties, namely, the effective hydraulic conductivity (ke), baseline critical shear stress (τc), baseline rill erodibility (kr), and baseline interrill erodibility (ki), the assessment of the initial run illustrates that calibration is inevitable. Given the geographical context and summer snowmelt dynamics, the model was unable to estimate summer runoff accurately. To address this problem, additional modeling for meltwater runoff was incorporated. The NSE and R2 values for discharge are 0.74 and 0.84, respectively, while those for sediment yield are 0.64 and 0.51, respectively. The results indicated that good predictions of runoff and sediment yield were obtained with the calibrated GeoWEPP model at the watershed scale. The key contribution of this research is the assessment of how eight biological conservation scenarios influence watershed behavior. Eight biological conservation scenarios were considered, representing incremental increases in canopy cover in poor, medium, and good pastures, both individually and in combination, as well as an additional scenario including expanded channel cover. The results showed that enhancing canopy cover could lower runoff and sediment yield by up to 44 % and 47 %, respectively, while the channel-cover scenario could lead to increases of up to 54 % and 67 %, respectively. These findings demonstrate the model's effectiveness in accurately replicating the hydrological and erosional responses resulting from soil and water conservation strategies.