Effects of dam construction on total solids in the Ca River, north-central Vietnam

The river regime laws of the hydraulic properties of the cross sections of two hydrological stations (Dua and Yen Thuong) along the Ca River in north-central Vietnam were combined into power functions with exponents of 1.46–1.85 using the Manning roughness coefficient and the settling velocity or the particle size to simulate the suspended sediment load. The Nash–Sutcliffe efficiency, percent bias, and the ratio of the root-mean-square error to the standard deviation of the measured data were used to evaluate the calibration process for the pre-dam period (1994–2004) and for validation for the post-dam period (2005–2014). Effects of dam construction include a change in the relationship between the Manning roughness coefficient and sediment particle size. The observed sediment load decreased by approximately 20–40% after dam construction at both stations. We used a power function with exponents of 0.968 and 0.992 for the dissolved solid load to calculate the long-term annual total dissolved solids at the Dua and Yen Thuong stations, respectively. After dam construction, the average value of the total suspended solids–total dissolved solids ratio decreased from 3.0 to 2.3 at the Dua station and from 4.1 to 2.2 at the Yen Thuong station.