Changes in sediment budget and morphology in the floodplains of the braided reach of the lower Yellow River

Abstract

Floodplains provide valuable social and ecological environment functions, and understanding the rates and patterns of floodplain sedimentation/erosion is critical for floodplain management and rehabilitation. The sediment entering the lower Yellow River has been dramatically reduced, and the geomorphology has changed greatly during the operation of the Xiaolangdi (XLD) reservoir since 2000. Utilizing sediment resources is the key to managing the downstream river, and the floodplains not only play the roles of flood mitigation, detention and de-sanding but also provide land to support local residents and economic development; however, the floodplain currently faces competition between land development and protection. This research presents a detailed investigation of changes in the sediment budget and morphology of the braided reach between Huayuankou (HYK) and Gaocun (GC) during 2000-2017 using digital elevation models (DEMs) and the historical bathymetry of the braided reach. During the implementation of the water-sediment regulation scheme (WSRS), the long-term low-concentration flow released from the XLD reservoir leads to a fully scoured long channel, further improving the bank-full discharge and reducing the risk of floods on floodplains. However, the floodplains have gradually changed from sedimentation to erosion due to the continual construction of farm dykes and control works, land use changes and other forms of land disturbance, including water and soil conservation measures and climate change. The cumulative eroded volume was approximately 11.47×108 m3 along the HYK - GC reach between 2000 and 2017, of which 3.08×108 m3 originated from the floodplains, with an average annual erosion rate of 1.3 cm/yr. To develop the economy and guide floodplain construction, we propose a new method of environmental management to reconstruct the floodplain domain into different zones for immigration resettlement areas, agricultural areas and resource development and utilization areas, with the methods of river dredging and floodplain filling.

The Influence of a Finite Control Boundary on the Morphological Evolution of Wandering Channels

“…It is considered that the quantity of water is the main factor affecting the section's morphology [4], and the mechanism of evolution of the river section's morphology under different water and sediment conditions has been discussed [5,6]. Based on data on the water and sediment and the measured large section, the process of change [7] and the adjustment law [8,9] of the river's section shape in different periods and under different water and sediment conditions have been analyzed. The response relationship between variation in the water and sediment, and the parameters of the river section in the Yellow River were also analyzed [10], and the process of change in the river section's shape in the lower Yellow River and its response relationship with incoming water were discussed [11].…”