A spatial impact assessment of human-induced intervention on hydrological regimes: a case study in the upper Srepok River basin, Central Highlands of Vietnam

Abstract

The objective of this study is to assess the impact of human activity on hydrological regimes in the upper Srepok River basin, Central Highlands of Vietnam. For this purpose, specific flow and water demand for each sub-basin were first estimated and then input into the calibrated river basin management model (MIKE Basin) to generate flow data. Future land use/cover was predicted using a geographic information system (GIS)-based logistic regression approach and the population projected from historical data. The hydrologic impact of human intervention was evaluated using the indicators of hydrologic alterations method and the range of variability approach under various developed scenarios. The results show that the overall hydrologic alteration (HA) values are classified as being moderate at all reaches; they generally increase from the upstream to the downstream reaches. Flow regimes have been altered along the river under the accumulated impacts of the operations of cascade dams. However, the impacts of land-use/cover change and population growth have been found to be greater at most of the reaches. The combined scenario shows that the HA of the Srepok 3 dam downstream reach is highest (75.7%), followed by the downstream reaches of Srepok 4 (65.8%) and Buon Koup dams (43.7%). Low flow, extreme flow, and frequency and rate of change are found to be the most alterative indicators. When environmental flow is considered, the HA of all reaches are reduced, and low and extreme flows are the most reductive indicators. It has been suggested that the trade-off between instream and offstream objectives should be considered in water allocation. The results of this study would be greatly important for future understanding of the human impact on hydrological regimes.