Abstract
An increasing number of scientific studies are tackling the management of discharges downstream of dams for environmental objectives. Such management is generally complex, and experiments are required for proper implementation. This article present the main lessons from a silt sand removal experiment on a bypassed reach of a dam on the Selves River (164 km²), France. Three four-hour operational tests at maximum discharge (10, 15, and 20 m3/s) were carried out in September 2016 to determine the discharge required for transporting as much silt and sand as possible without remobilizing coarser sediments. In September 2017, an additional flow release was performed over 34 h at 15 m3/s. Suspended sediment concentration and water level were recorded throughout the releases. Monitoring at the reach scale was supplemented by morphological measurements. The results demonstrate that a discharge of approximately 10 m3/s enables significant transport of suspended sediments (SS), whereas a discharge of 15 m3/s enables significant sand transport. The results provide operational information on silt and sand transport applicable to other small rivers. This study represents an important contribution to the relatively sparse existing body of literature regarding the effects of water releases and sediment state. Our study also demonstrates that it is possible to successfully undertake water releases in small rivers with an adaptive management approach.
Highlights
Many rivers have been regulated to limit flooding and enable a variety of uses, including hydroelectricity, leisure, irrigation, and drinking water supply
Conducting iterative water releases on the Selves River paid off with a reduction of surficial clogging, effective sand export, and water depth increases while avoiding mobility of coarser sediments, all while requiring only limited human and financial resources
The discharges were chosen empirically, they were in the necessary range for the management objectives and allowed us to identify the optimum discharge for future operations
Summary
Many rivers have been regulated to limit flooding and enable a variety of uses, including hydroelectricity, leisure, irrigation, and drinking water supply. In the northern third of the planet, 77% of rivers have a dam or river diversion in place [1]. Environmental impacts of dams have been described by many authors [2,3,4,5]. These impacts include effects of water-storage dams on the full range of the flow regime. In absence of floods, (high) sediment supply from tributaries downstream of dams can lead to aggradation of the bypassed reach (reach immediately downstream of the dam receiving only minimum flows) [2]. Sedimentation of fine sediments may significantly disrupt biological functions by bed clogging or sand deposits [2]
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