Estimating over thousands of reservoirs sedimentation and effects on sediment flux through a newly proposed sediment transport model

Dam largely traps sediments, leading to serious channel starvation and coastal erosion. Trapped sediments cause reservoir sedimentation, reducing dam capacity and its lifespan. Estimating dam trapping effects on sediment reduction and reservoir sedimentation is therefore important in sediment management and dam operation. Such effects may be more serious in small reservoirs (storage capacity < 108 m3) than large ones considering their huge amount and long-term operation with seldom desilting. However, small reservoirs’ effects on sediment flux as well as their sedimentation are hardly calculated because of data limitations. In this study, we established the DAM SEdiment trapping (DAMSE) model to simulate sediment trapping by dams in the river network. In particular, the model considers the process of bedload replenishment after sediment trapping. We take the Jinsha River as an example and calculate over 2400 reservoirs sedimentation. Our model confirms the bedload as an important source of sediment after trapping by dams. Sediment flux of the Jinsha River is primarily affected by large dams, especially by mega-dams, which caused two drops of 62% and 99% in 1998 and 2013, respectively. Small dams trap an average of 6.5% sediment of annual flux but only cause a 2% reduction because of bedload replenishment. Despite of limited effects of small dams on sediment flux, a total of 6.7 × 108 t sediment was trapped by small reservoirs, accounting for 24% of total sedimentation. Sedimentation occupies over 20% capacity of small dams but less than 5% of large dams. High siltation in small dams increases dam breaking and sediment hazard risk at watershed. We therefore suggest desilting small dams and exploring the sedimentation as a potential sand and stone resource.Highlights A model is established to simulate sediment trapping by dams in the river networkBedload is an essential source to replenish sediment after trappingOver 2400 reservoirs sedimentation and effects on sediment flux are estimatedMega dam is primarily responsible for sediment flux declineSmall dam has non-negligible sedimentation, putting the watershed in potential danger