Sediment delivery across multiple spatio-temporal scales in an agriculture watershed of the Chinese Loess Plateau

Abstract

There is a consensus that sediment delivery ratio in the Chinese Loess Plateau is close to 1 at the inter-annual timescale. However, little information is available about the sediment delivery at finer timescales. We evaluated the sediment delivery from plots to watersheds at the event or intra-annual, annual, and inter-annual timescales within the Wudinghe river basin, a 30,261 km(2) basin in the Loess Plateau. We calculated the ratio of sediment output to sediment input and presented the temporal change of the channel morphology to determine whether sediment deposition occurs. Although a single flood event frequently has a sediment yield exceeding 10,000 t km(-2), sediment deposition rarely occurs except during some small runoff events (sediment yield < 5000 t km(-2)) or dry years (sediment yield < 10,000 t km(-2)) when moving from slopes up to the main channels of the Wudinghe River. This observation suggests a sediment delivery ratio close to 1 even at the event or intra-annual and the annual timescales, but not necessarily at the interannual timescale. Such a high sediment delivery ratio can be related to hyper-concentrated flows, which have very strong sediment transport capacity even at low flow strength. Because hyper-concentrated flows are well-developed in the whole Loess Plateau, a sediment delivery ratio close to 1 below the interannual timescale possibly remains true for other rivers in the Loess Plateau