Modeling Soil Erosion and Sediment Load for Red River Basin (Vietnam): Impact of Land Use Change and Reservoirs Operation

Erosion and sediment transport have critical implications for aquatic ecology, agriculture, water supply and river navigation. In recent years, with the construction and operation of several reservoirs in Red river basin (China-Vietnam), such as Hoa Binh, Lai Chau, Son La, Thac Ba, Tuyen Quang etc., this issue has raised high interest and concern. Reservoirs have been built to meet several important needs including: increasing energy, irrigation, and drinking water demand. However, there are some important issues related to the construction and operation of reservoirs, which the decision maker should pay attention on: they trap sediments and reduce sediment concentration in rivers downstream reservoir, then increasing riverbank erosion and localized erosion around hydraulic structures. In addition, land use change is also to be considered as causing effect on sediment erosion and transport. The aim of this work is to evaluate the effects of separate factors (reservoirs, land use change) and also the combination of such factors on sediment load in the Red River basin. To make this evaluation, an updated and enhanced version of the soil erosion and transport model at the catchment scale, namely DIMOSHONG_RUSLE is applied to the Red river basin. More than 50 years of monthly precipitation, runoff and suspended sediment load data at the monthly scale are processed. Two different historical landuse maps 1983 and 2000 of Da river (right bank of Red River) and a random land use change of Lo river (left bank of the Red River) were also generated base on statistic data of the government. The effect of land use change, reservoirs is assessed on the basis of trends observed in the last decades. Results are in good agreement with observed data. The trap efficiency of the model for Thac Ba reservoir (1971) and Hoa Binh reservoir (1985) are 90% and 94%, respectively, causing the sediment load at Son Tay stations decrease of 55%. Following the construction of two additional reservoirs, Tuyen Quang reservoir (in Lo river) in 2005, and Son La reservoir (in Da river) with the deposition coefficient of 92 % and 67%, the result was caused the coefficient sediment of the Da river cascade system decreases 98% (at Hoa Binh station), and also makes the sediment load to lower reach of the Red River 92 % (at Son Tay station).