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.