A modelling-based assessment of suspended sediment transport related to new damming in the Red River basin from 2000 to 2013

Abstract The Red River is an Asian river system strongly affected by global changes. This paper aims to characterize and quantify the suspended sediment flux (SF) over the basin under the influences of short-term climate variability and dam constructions. SF was evaluated at the outlets of main tributaries and along the main course of the Red River from 2000 to 2013 based on daily simulations from a modelling study. A reference scenario (without dams) was carried out to disentangle the impacts of short-term climate variability and damming by comparing to actual conditions. Without dams (reference scenario), the basin would generate 106.9 Mt yr−1 of SF to the downstream delta from 2000 to 2013, with a specific sediment yield (SSY) of 778.8 t km−2 yr−1. However, under the impacts of short-term climate variability and dams, the mean annual SSY decreased to 84.5 t km−2 yr−1. At the outlet of the basin, the annual mean SF of 2008–2013 (after new dam constructions) got reduced by 90% (10% related to short-term climate or atmospheric variability and 80% to dam constructions) compared to the reference scenario (without dams) during 2000–2007. The Thao tributary is the most sensitive to short-term climate variability while the Da tributary is mostly affected by the huge-capacity dams. Mean annual retentions of sediment by dams ranged from 7.1 to 111.0 Mt yr−1. Simple rating curves between monthly mean discharge (Q) and SF were established for estimating SF at the outlet of the tributaries and the Red River. High soil erosion (above 2000 t km−2 yr−1) occurred in the middle Thao and the lower Da tributaries. Precipitation, slope and agriculture practices are the key influence factors for soil erosion in the basin.