Coupling SWAT and bathymetric data in modelling reservoir catchment hydrology

Abstract

A physically based model; Soil and Water Assessment Tool (SWAT) and bathymetric data were integrated to simulate and evaluate the water balance of the Brimsu Reservoir from 2002 to 2018. The simulated water balance describes the changes in water storage of the reservoir as a hydrological component that is dependent on inflows (precipitation, runoff) and outflows (evaporation, infiltration, discharge and water consumption). In the absence of storage capacity data, a bathymetric survey was conducted to determine the capacity of the reservoir. The result showed that there has been a reduction of about 27.6% in gross capacity of the reservoir. The SWAT model indicates a satisfactory performance for both calibration (NSE = 0.66, Bias = − 5.0% and R2 = 0.86) and validation (NSE = 0.63, Bias = − 10.4% and R2 = 0.82) periods. The monthly water budget revealed that 30.50% and 69.50% of the total inflow within the catchment constitute direct precipitation and runoff respectively while 32.50%, 12.50%, 34.40% and 20.60% of total outflow represents evaporation, seepage, spillage and water consumed. Though the average final-to initial-volume ratio of 1.15 indicates that the reservoir is not emptying, and water is withdrawn from the reservoir at a sustainable rate, yet water from the reservoir does not yield the treatment plant’s design capacity of 29,500 m/day. Overall, the model demonstrated a good performance by providing quantitative information to serve as a guide for stakeholders to make better decisions in planning and managing the Brimsu Reservoir.