Restoration of morphological bed forms in an experimental flume through replenishment of sediments technique

Elena Battisacco, Mário J. Franca, Anton J. Schleiss, Adrien Maire

Wednesday 1 july 2015

8:30 - 8:45h at Oceania (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) River morphodynamics

Parallel session: 8B. Sediment - River

The natural condition of rivers is safeguarded by the continuity of the transport of sediments by water from the steep slopes, throughout the basins, until the sea level. The maintenance of natural conditions is recognizable important also for the preservation of the ecology processes. It is well know that the presence of a dam strongly modifies the river behavior in the downstream reach, in terms of morphology and hydrodynamics, with consequences on local ecology. The main observed effects, on what concerns the morphology of the rivers, are sediment deficit, bed armoring, river incision and bank instability, which in turn will affect negatively the aquatic habitats and the water quality. First applied in the 1980’s, the artificial replenishment of sediments is one of the proposed techniques to solve the problem of sediment deficit downstream dams. Already adopted in many Japanese, American and German rivers, this technique still does not provide fully satisfactory results and the involved processes are still not fully known. Many field studies resulted in incomplete erosion of the replenishment volume and in insufficient transport rates to move the sediments sufficiently far downstream. A systematic series of laboratory tests are run to understand the hydrodynamics of the river flow when the replenishment technique is applied, aiming at improving the technique to provide an engineering answer for its application. Erodible volumes, with different lengths (occupancy of the replenishment volume is 1/3 of the channel width) and submergence conditions (100% and 130% submergence of the replenished volume), reproducing sediment replenishments volumes, are placed along a channel bank. Different geometrical combinations (single volume, double volumes, double aligned half-volumes, double alternated half-volumes) of erodible sediment volumes are tested. The influence of discharge, the distance travelled by the eroded sediments and the time evolution of the erosion process will be presented and discussed. KEYWORDS: River replenishment, Sediment supply, Erosion of sediment