Abstract
Dam removal is typically intended for river restoration or as a countermeasure for aging dams. The influence of dam removal has mainly been studied in large rivers. This study is intended to investigate the influence of the sediment supplied after opening a check dam drain in a small steep stream to contribute to the establishment of sediment release technology form check dam by accumulating the basic knowledge about the influence of sediment release. Deposited sediment in the impoundment was rapidly discharged immediately after opening the drain outlet, and a moderate sediment discharge followed. The water course of the sediments deposited by repeated channel widening and riverbed degradation tended to stop longitudinal topographic changes from downstream. In addition, the turbidity during a flood was high in the first year and tended to decrease in the second year. As for the ecosystem response, changes in the benthic macroinvertebrate community were confirmed in downstream sites, and net-spinning species especially deceased immediately after the sediment supply began. Our monitoring results suggest that the increasing turbidity was suppressed during the flood because sediment release was conducted from the small-scale facility. As a result, a negative impact on the aquatic ecosystem seemed to be reduced.
Highlights
Changes in the natural flow regime or sediment dynamics after the construction of dams and weirs tend to degrade ecological integrity, cause problems with water utilization, and maintenance of river administration facilities [1,2]
This paper describes the results of monitoring the behavior of deposited sediment in the impoundment, changes to water quality during a flood, and the biological responses after sediment release from a check dam with
This study aimed to investigate the influence of sediment supplied by opening a check dam drain outlet on the topography of deposited sediment, downstream sediment transport, and the response of aquatic ecosystems
Summary
Changes in the natural flow regime or sediment dynamics after the construction of dams and weirs tend to degrade ecological integrity, cause problems with water utilization, and maintenance of river administration facilities [1,2]. Monitoring after dam removal includes the erosion process of deposited sediments, channel processes, ecological response, and changes in water quality. The large amount of sediment coming from the impoundment following dam removal leads to aggradation of the riverbed, widening of the river channel, decrease in the grain size, filling of pools, or braiding, and flattening of the channel [10,14,15,16]. Some studies have reported increasing fish diversity, no direct connection between species diversity of fish and dam removal has been observed, suggesting the need for long-term monitoring [23,24,25]
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