Modeling of streamflow and water quality using SWAT model in the Ribb reservoir, Ethiopia

Water resources, mostly surface water is facing more ecological pollution due to direct or indirect contaminants. The main causes of reservoir water pollution are many human and natural activities. This study's main objective was to evaluate water quality and to model the hydrology of Ribb reservoir, Ethiopia. The soil, land use/cover, meteorological, hydrological, and spatial data are the SWAT model's most crucial inputs. This investigation makes use of the SWAT model to evaluate the annual and monthly flow, sediments, and the most important nutrients. There are two nutrients, those are nitrogen and phosphorus, that originated from organic and inorganic fertilizer that affect the water quality of reservoir due to excessive overgrazing and farming activities. Streamflow, sediments, total Nitrogen, and total Phosphorus parameters were used for the calibration and validation of the SWAT model over the time periods of 1998–2003 and 2004–2007, respectively. Using NES and R2 in Ribb Rivers, the model performance was evaluated during the calibration and validation phases. The average monthly streamflow of the Ribb River discharge was 16.56 m3/s. The total loads of sediment, total nitrogen, and phosphorus at point sources of Ribb reservoir were 43,813.98 Mg/yr, 148,116.52 kg/yr, and 26,892.27 kg/yr, respectively. Nitrogen and phosphorus were lost in the Ribb reservoir, which is 5201 kg per ha and 4052 kg per ha, respectively. The amount of evapotranspiration from the rain was approximately 36%, which is a significant loss. Analysis of hydrology and water quality is important for effective management practices. Generally, in both agricultural and urban areas, best management practices need to be adopted to solve hydrological and water quality challenges in the Ribb watershed.