Figure 11 Width changes in the main
channel and floodplains in the different reaches.
4.3 Mode of environmental management in
floodplain
During the operation of the XLD reservoir, the riverbed elevation in the
LYR has been effectively controlled by the implementation of the WSRS,
resulting in an increase in the bank-full discharge and sediment
transport capacity of the main channel, which has reduced the
probability of large-scale floods and ensured life and property safety
on the floodplain. However, sediment resources on the floodplain have
been decreasing since 2000, and the unfavourable phenomenon of a
secondary suspended river still exists in local reaches. Moreover,
the impact on floodplain
environmental management is negative because of the shortage of sediment
resources. Sediment is the primary
source of a sustainable agro-ecosystem in the LYR, which not only
influences riverbed morphology development but also may counteract
floodplain subsidence and soil erosion. How to optimize sediment
resource allocation in the lower reaches of the Yellow River to achieve
positive outcomes for both environmental management and
economic
development has become an urgent problem.
Under the new requirements of water control and ecological urban
construction, we propose a new design idea for floodplain environmental
management; some floodplains of the LYR can be reconstructed by measures
such as pipeline sediment transport and river dredging. From the levee
to the main channel, the floodplain can be sequentially reconstructed
into different regions (see Figure 12), including the “high
floodplain”, “secondary floodplain” and “new floodplain”; among
these regions, the new floodplain together with the main channel could
perform the tasks of flood control and sediment transport in the LYR.
Through reconstruction of the floodplain domain and in coordination with
environmental management measures, different functional zones (such as
residential areas, efficient agricultural areas and ecological wetland
areas) can be formed. This mode of floodplain reconstruction can solve
the unfavourable morphology of the secondary suspended river in local
reaches and guarantee flood control safety in the LYR, promote the
development of floodplain areas and achieve positive results both in
river management and in benefits to people.