Development of self-dynamic desanding measures through physical model experiments

Sediment surplus in rivers of the Bohemian Massif is a problem for habitats of freshwater pearl mussels (Margaritifera margaritifera). These relatively fine sediments get remobilized already at mean discharge conditions, leading to mechanical stress on the mussels. Further, this increases flood risk in certain river stretches. Thus, removal of the sediment is a necessity. Due to economic and ecological reasons, riverbed dredging should be avoided. In present work, a nature-based solution for self-dynamic desanding (SDD) was investigated with physical model experiments. Through SDD, sediment shall be deposited on the floodplain during high-flow conditions, where it can be removed cheaply without in-stream work.

The physical experiments were based on a stretch of the Malše River at the Austrian/Czech border in 1:20 scale and conducted in three stages. At first, in-stream measures were investigated to optimize the transport of sediment from the main channel onto a lowered floodplain. Secondly, measures on the lowered floodplain were developed to optimize deposition. Finally, these measures were tested in a quasi-unsteady flow scenario based on a one-year flood wave. Through these experiments, SDD was improved and the descending branch of the flood wave was established to be a decisive factor on the efficiency of the proposed measures, as deposited material was washed back into the main channel. Modifications of the developed measures mitigated this issue, leading to a slightly lower deposition than in the steady case. In the end, the model showed a capacity (in nature scale) of up to 14.6 m³ of deposited sand on an area of about 120 m² .