Cumulative sediment trapping by reservoirs in large river basins: A case study of the Yellow River basin

Reservoir sedimentation has been a serious problem for reservoir operation and watershed management worldwide, which highlights the importance of accurate estimate of the deposited sediment amount. With reservoir information derived from remote sensing dataset and observed hydrological records of water and sediment, this paper is concerned with the cumulative reservoir sediment trapping in the Yellow River basin. The river basin was divided into 12 sub-basins, upon which the reservoirsʹ sediment trapping efficiency (TE) and their interception effects on inflowing sediment were estimated with sediment records extracted from 179 field sampling stations. The results show that, with the sediment TE greater than 80% for all the sub-basins, theoretically the basin-wide reservoirs are able to trap most sediment. For the whole river basin, the sediment TE averages 95.2%, which indicates that the reservoirs can collectively make a significant anthropogenic signature on basin-wide sediment delivery. A basin-wide sediment yield map was generated to estimate the reservoir sedimentation amount. During 1950–1970, annually about 2.483 Gt of sediment was transported into channels from sloping lands. Taking into account the actual water storage changes and the reservoir construction history, the actual reservoir sedimentation rate was estimated at 0.59 Gt/yr after corrections, which represents 47.6% of the river basinʹs total sediment load reduction. Globally, reservoir sedimentation in the Yellow River basin represents about 12–15% of the global mean rate. Up to 2010, approximately 19.32 Gt of sediment has been trapped by Yellow River reservoirs, and totally about 40.32 Gt of sediment has been artificially fixed if silt check dams are also considered. With huge amounts of sediment deposited, these reservoirs have been losing their storage capacity to sedimentation at a rate of 0.6% per year. The magnitude is expected to enhance in future following new reservoir completions. Thus, more efforts are strongly needed to explore the associated responses.