EVALUATION OF HEC-HMS AND SWAT HYDROLOGICAL MODELS FOR RUNOFF SIMULATION IN DATA SCARCE REGION OF OSUN RIVER BASIN

Abstract

The quantitative prediction of hydrological components using hydrological models could be used to develop better land and water management policies. In this study, a comparative analysis has been carried out to evaluate the performance of two distributed hydrological models (Soil and Water Assessment Tool (SWAT) and Hydrologic Modeling Systems (HEC-HMS)) as a rainfallrunoff predicting tool in the Osun River Basin of Southwestern part of Nigeria. The Arc hydro extension of ArcGIS 10.5 software package was used in spatial data preparation. The models' input parameters were obtained using the Digital Elevation Model (DEM) in conjunction with the LULC map, soil map, and climate data. HEC-GeoHMS was used to create background map file, lumped basin model, a grid-cell parameter file, and a distributed basin model for the HEC-HMS model. HEC-HMS 4.8 was used in the simulation of runoff in Osun River Basin and the model components includes losses (SCS curve number), runoff transform (SCS unit hydrograph), analysis of meteorological data, open channel routing, rainfall-runoff simulation, and parameter estimation. The SWAT model set up of land use, soil and slope, and minimum area threshold values set, respectively, yielded 179 Hydrological Response Units (HRU), which are unique combinations of land use, soil type and slope. The Osun River Basin was categorized using a flow accumulation threshold of 250 km2, which divided the basin into 15 sub-basins. The models were run for period of 2010 to mid-2021 for surface runoff prediction in the Osun River Basin. The models' performance was evaluated using coefficient of determination and relative error goodness of fit statistics. The two models were compared in terms of runoff simulations at the basin outlet. The findings revealed that observed and simulated hydrographs were fairly correlated. The R2 and predicted R2 values are 0.81 and 0.68 for the HEC- HMS model while for the SWAT model, the R2 and predicted R2 values are 0.70 and 0.49, respectively. The models reproduced the observed stream flow patterns at the Sepeteri station fairly well. The seasonal dynamics of the simulated runoff in the hydrographs are consistent with the observed runoff, with the exception of inadequate findings at the peak value. The results indicate that the more complex HEC-HMS model outperforms the SWAT model in terms of runoff prediction capability. The results indicated that the model is suitable for hydrological simulations in the Osun River basin