CONCLUSIONS
Since
the operation of the XLD reservoir began in 2000, the objective of
mitigating riverbed elevation increases in the LYR has been achieved.
With the proposal of the new goals
for environmental protection and high-quality development of the Yellow
River Basin, the environmental management and rehabilitation of
floodplains have received increasing attention from people in all walks
of life. Our
research
investigated the changes in the sediment budget and morphology of the
braided reach between HYK and GC in the LYR, and the main findings are
as follows:
During the operation of the XLD reservoir from 2000 to 2017, the total
eroded volume of the braided reach (between HYK and GC) was
approximately 11.47×108 m3, of which
approximately 8.38×108 m3 occurred
along the main channel and 3.09×108m3 in the floodplains. The main channel was fully
scoured, with an average erosion rate of 14.16 cm/yr, leading to
increases in channel depth and bank-full discharge. The floodplains
gradually changed from a sedimentation pattern to an erosion pattern,
with an average erosion rate of 1.30 cm/yr, due to the implementation of
the WSRS, continual construction and reinforcement of control works
along the channel and other human activities.
Sediment is the primary source of a sustainable agro-ecosystem in the
lower Yellow River, which influences morphological development and may
counteract floodplain subsidence and soil erosion. The shortage of
sediment resources is unfavourable to the environmental management of
floodplains.
We
propose a new management mode for the floodplains in the LYR. Some
floodplains in local reaches are rebuilt into high floodplain, second
floodplain and new floodplain areas, with some mechanical measures such
as pipeline sediment transport and floodplain filling.
This
mode could eliminate the unfavourable form of a secondary suspended
river and optimize the allocation of sediment resources downstream,
which lays a good foundation for the environmental management of the
lower Yellow River and the economic development of the floodplain
region.