Response of channel scouring and deposition to the regulation of large reservoirs: A case study of the lower reaches of the Yellow River (Huanghe)

The lower reaches of the Yellow River (Huanghe), a typical "raised bed river," have experienced many huge flood events in Chinese history. As the main factor controlling the topographic evolution of the channel, the water and sediment-supply conditions of the Yellow River have undergone significant changes since the implementation of the water and sediment regulation scheme (WSRS) in 2002 by the joint operation of large reservoirs. Hence, it is necessary to conduct systematic research and evaluation on how the regulation scheme influences the scouring and deposition of the downstream channel. This study used the elevation data of 79 fixed profiles collected between 1992 and 2012 from the channel downstream from Gaocun in the Yellow River to establish a digital elevation model. The elevation model was used to investigate the spatio-temporal characteristics of channel scouring and deposition in the study area and to determine the main controlling factors. The results show that on an inter-annual scale, the channel scouring and deposition pattern began to change from substantial deposition to rapid erosion after 2002. On a seasonal scale, the overall characteristic was erosion in the flood season and deposition in the dry season; however, the erosion rate in the flood season increased and the deposition rate in the dry season decreased after 2002. From the spatial perspective, the downstream riverbed experienced net deposition before 2002 and net scouring after 2002. The WSRS altered the regimes of water and sediment of the river and therefore dominated scouring and deposition in the downstream channel. Since the implementation of the WSRS, continuous channel scouring in the study area provided about 41% of coarse-grained sediments for the Yellow River, and formed an important source of sediments entering the sea. However, because of the formation of an armor layer of coarse-grained sediments on the downstream riverbed surface due to continuous scouring after the implementation of the WSRS, the erosion flux of the river channel in the lower reaches of the Yellow River has shown a significant decrease since 2005. This study provides a typical case study for the response of the topographic evolution of rivers to water and sediment changes under the influence of intense human activities.