Seite - 376 - in Book of Full Papers - Symposium Hydro Engineering

2. DESIGN OF THE WATER RELEASES The objective of these experimental releases was to determine the most effective flow rate to remove fine sediments and sand from the river bed. Several flows are tested in order to determine the most efficient flow to entrain sand particles while avoiding the movement of coarser sediments essential to the functioning of the aquatic fauna. These tests will allow us to determine the flow magnitude and duration required for the overall rehabilitation of the bed, and then the frequency, magnitude and duration of the releases to be carried out routinely. Three water releases of 10, 15 and 20 m3/s were tested, each lasting 4 hours. To meet environmental and safety constraints, the hydrographs were characterized by a progressive ascent to 10 m3/s to limit effects on fish, then a plateau of 1h at the same flow corresponding to an alert wave necessary for the safety of third parties. The target flow rates were then maintained for 4 hours. The transit time of these releases was estimated to be about 2.5 hours. However, we retained a duration of 4 hours to ensure the success of the operation. The releases were conducted on September 6, 13 and 20, 2016. Fig. 2 Hydrographs of the clear-water releases conducted in 2016. 3. MONITORING PROGRAMME To evaluate the effectiveness of the water releases, an ambitious monitoring programme has been implemented, targeting every major component of the aquatic ecosystem. Two monitoring objectives are targeted : (1) to directly evaluate the effectiveness of the releases (with respect to reduced channel bed clogging) and (2) to evaluate the overall effectiveness of flow restoration measures on biota over a period of at least 3-6 years. This article corresponds to the first phase of the study. 0 15 30 45 60 75 90 105120135150165180195210225240255270285300315330345360375390405 Water release 1 0,2 2,5 5 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 5 0,2 0,2 0,2 0,2 Water release 2 0,2 2,5 5 10 10 10 10 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 10 5 0,2 0,2 0,2 Water release 3 0,2 2,5 5 10 10 10 10 15 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 15 10 5 0,2 0 5 10 15 20 25 Fish discharge Security discharge Fish min flow = 0,24 m3/s 4 hours 4 hours 4 hours 376