Application of DWAT for inflow estimation in a data-scarce agricultural reservoir

Climate change has intensified drought conditions, and various approaches have been developed to ensure stable water supply using reservoirs. In South Korea, many agricultural reservoirs are monitored only in terms of storage (water level), while inflow data are not available. This limitation poses a challenge for developing drought response strategies, highlighting the need for methods to estimate reservoir inflow under data-scarce conditions.

In this study, we propose a methodology for estimating inflow scenarios for agricultural reservoirs using a physically based hydrological model constrained by observed storage (water level) data. As a case study, the Donghwa Reservoir, an agricultural reservoir located in the Seomjin River basin, was selected, and the Dynamic Water Resources Assessment Tool (DWAT) was applied. DWAT is a physically based hydrological model that represents surface water and groundwater processes and is widely used for water resources planning and management.

In the model setup, a prescribed time series of agricultural water withdrawals from May to September was applied, and catchment parameters were adjusted using observed reservoir storage data. The comparison between observed and simulated storage indicates that the model reasonably reproduces the overall variability and statistical characteristics of reservoir storage. However, there are limitations in directly representing artificial operational elements considered in actual reservoir management, such as flood control storage and water intake restrictions. Consequently, larger deviations between observed and simulated storage occurred during periods of extreme drought and flood between 2017 and 2020.

The proposed approach demonstrates the feasibility of estimating inflow scenarios for reservoirs without inflow measurements using a physically based hydrological model and provides a methodological basis for future drought analysis and the development of operational strategies for agricultural reservoirs.

Keyword: DWAT(Dynamic Water resources Assessment Tool), drought, agricultural reservoir, inflow estimation, storage-based calibration

Acknowledgement: This work was supported by Korea Environment Industry & Technology Institute(KEITI) through Aquatic Ecosystem Conservation Research Program, funded by Korea Ministry of Climate, Energy and Environment(MCEE) (RS-2025-02304832).