Backwater Rise due to Large Wood Accumulations

During flood events, transported large wood (LW) may accumulate at river infrastructures or is retained intentionally at retention structures. In both cases, the accumulation results in backwater rise upstream of the clogged cross section. Previous studies determined various governing parameters for the estimation of backwater rise, but the findings are still contradictory. In addition, the effect of organic fine material (e.g., branches or leaves) was so far neglected. Therefore, a series of flume experiments was conducted to clarify the influence of the governing parameters on backwater rise due to predefined LW accumulations. The hydraulic conditions, LW accumulation characteristics (compactness, accumulation length, LW diameter), and the organic fine material were varied systematically. Based on the results, backwater rise mainly depends on the approach flow Froude number, compactness of LW accumulations, and percentage of organic fine material. The findings of this study resulted in a design equation to calculate backwater rise due to LW accumulations, contributing to the estimation of the hazard potential assessment of river infrastructures for flood events. Furthermore, the present study contributes to an enhanced process understanding of LW accumulations in rivers.