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 m3originated 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.