Comparative Performance of the Drainage Area Ratio method and the HEC-HMS model in modeling of ungauged catchments. A Case study of River Nyamwamba.

Abstract

Globally, surface water sources play a crucial role in providing drinking water, making it essential to understand their availability and ensure their long-term sustainability. However, studies investigating surface water resources in data-poor regions are limited, leading to challenges in their effective management and protection. This research study focuses on the comparative performance of two hydrological modeling methods, the Drainage Area Ratio (DAR) method and the Hydrologic Engineering Center's Hydrologic Modeling System (HEC-HMS), in modeling ungauged catchments. Given the scarcity of data in Kasese, this study addresses the critical need for assessing the suitability and accuracy of hydrological modeling techniques for ungauged catchments like the Nyamwamba River. Data from various sources, including the Department of Water Resources Management (DWRM) and Uganda National Meteorological Authority (UNMA) were collected to facilitate the analysis. The methodology involved applying the DAR method to estimate discharges in the Nyamwamba River by transposing available data from the gauged Mubuku River catchment. In parallel, an HEC-HMS model was developed for the Mubuku River, calibrated, and validated using the available data. The calibrated model parameters, such as curve numbers and Muskingum X and K values, were then transferred to a newly created basin model for the Nyamwamba River. Historical data for Nyamwamba spanning 20 years (2000-2020) were used to simulate peak discharges in the newly created basin. An HEC-HMS model was also constructed for the Nyamwamba River using a configuration comprising six sub-basins for comparative analysis. Calibration, validation, and simulation were performed using the available data. The performance of the DAR method and the HEC-HMS (Nyamwamba, 3 sub-basins) was evaluated using statistical metrics, including Nash-Sutcliffe Efficiency (NSE) and Root Mean Square Error (RMSE). The results showed that the DAR method yielded an NSE of -0.346 and an RMSE of 4.39, while the HEC-HMS (Nyamwamba, 3 sub-basins) achieved an NSE of 0.563 and an RMSE of 0.7. Furthermore, when compared to the HEC-HMS model with six sub-basins (NSE = 0.579, RMSE = 0.6), the HEC-HMS (Nyamwamba, 3 sub-basins) demonstrated comparable performance. This research study provides valuable insights into the application and accuracy of hydrological modeling techniques within ungauged catchments, specifically in the context of the Nyamwamba River in Kasese District, Western Uganda. The findings contribute to addressing the knowledge gap in data-poor regions, facilitating informed decision-making, and sustainable water resource management practices.