Investigating the Role of Fish Rocks on the Movement of Sand over Gravel Bed Rivers

Abstract

In this study detailed flume experiments were conducted to examine the effects of an array of partially submerged fish rocks on sand movement over gravel bed rivers. The experimental results revealed the formation of a newly reported in the literature bed morphological feature, namely a funnel shaped 'sand ridge' upstream of the fish rock array region, and small depositional sand patches in the stoss of the individual rocks. The formation of these bed features led to the reduction in the incoming bedload rate by a factor of 5.0 - 20. A mass balance sediment analysis revealed that 63% and 14% of the eroded material deposited upstream of the fish rock array region depending on the applied bed shear stress conditions. Flow measurements in the vicinity of the rocks re-confirmed the linkage between flow and sediment depositional patterns around the rocks. The findings of this research may have ramifications in stream restoration projects for the design of engineered riffle sections installed to improve degraded waterways and aquatic habitat.