Assessment of the streamflow changes in the La Nga river basin

Abstract

The paper aims to assess the changes of the streamflow under the impact of irrigation constructions in La Nga river basin using the Long and Short term runoff (LST) model. The LST model was calibrated and validated for the period of 1987–1995 and 1996–1999, respectively, to simulate the natural streamflow for the post–construction phase. Statistical metrics, including R2 coefficients, efficiency coefficients (NSE), percent error (PBIAS) and standard monitoring deviation ratio (RSR) were used to evaluate the model performance. The results showed that, LST model performed well in the flow simulation by the high values of R² and NSE index greater than 0.80, RSR smaller than 0.50 and PBIAS lower than 7.22%. The comparison between the simulated (natural) and observed flows illustrated that there were changes of the flow regime in the post–construction phase. The average seasonal flow decreases 24.59% and increased 12.06% in the wet and dry season, respectively at Phu Dien station. Meanwhile, at Ta Pao station, the streamflow decreased 8.35% and increased 21.11% in the wet and dry season, respectively. The results of this study could be used in planning, managing and regulating the irrigation works'operation, and water resources management in the La Nga river basin.