Quantifying sediment retention by high-density small water conservancy facilities under insignificant variation of water discharge in the Nanliu River Basin, Beibu Gulf

Abstract

Study region: The Nanliu River Basin in Beibu Gulf, China. Study focus: The variations in water discharge and sediment load were analysed for 1961–2015. In addition, sediment retention by high-density small water conservancy facilities in the tributaries was estimated by a hydrological model with different scenarios. At the end of the study, the variation in the relationship between water discharge and suspended sediment concentration (SSC) and the impact on riverbeds were analysed. New hydrological insights for the region: The sediment load showed a dramatically decreasing trend, and an abrupt change point in 1988 was detected by a Mann–Kendall test. Compared to the baseline period (1961–1988), the sediment load in the altered period (1989–2015) decreased by 41.7%. By employing the SWAT model with different scenarios, sediment retention by high-density small water conservancy facilities in the tributaries was estimated in the basin, with a mean value of 457.1 × 103 tons/yr during the altered period. The construction of water conservancy facilities has been the key driver of the significant reduction in sediment load observed in the Nanliu River. The rating curves of monthly SSC–discharge showed clockwise patterns, which were different from the Yangtze River’s counter-clockwise pattern. SSC reductions and excessive sand mining in the main channel have strongly affected riverbeds, leading to a year-by-year drop.

Keywords

• Water discharge
• Sediment load
• Water conservancy facilities
• Suspended sediment concentration
• The Nanliu River Basin