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This paper proposes an index to evaluate the influence of
channel disposalof sediments removed from a reservoir on the
downstream channel environment. This index is based on four
factors : the deposition/scour depth and the sediment
concentration with channel disposal of sediments, the ratio of
the deposition/scour depth and the ratio of the sediment
concentration betweenwith and without channel disposal of
sediments. The influence of channel disposal of sediments on
the channel is classified into five levels based on the values
of the index. They are little influence, minor influence,
mediuminfluence, severe influence, and very severe influence.
A case study on the channel disposal of the Bai-Ho reservoir
sediment during flood discharge was conducted. The HSPF model
was used to analyze the channel flow, sediment transport,
channel bed deposition/scour, and the sediment
concentration in the flow with or without channel disposal
of sediments. The proposed assessment index was then used to
evaluate the impact on the channel environment, and the
impacts were compared for different amounts of disposal of
sediments and different disposal methods. The results show
that the sediment transport efficiency decreases as the
amount of disposal sediment increases, and the more disposed
sediment the more influenceon channel environment. Two disposal
methods were used and analyzed. One is that sediment was
disposed into the channel from the initiation to the end of the
flood discharge, and another from the initiation to the peak of
the flood discharge only. Under the same disposal concentration
of sediments and same flood discharge, the former could
dispose more sediment but result in more severe impact on
channel environment, compared with the latter. It is found
that the proposed assessment index could efficiently evaluate
the impact of the channel disposal of sediment on the
downstream channel through the case study.
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