Suction Removal of Sediment from between Armor Blocks

This paper presents the results of an experimental investigation on suction removal of sediment from between armor blocks/stones placed on a loose bed. The process of suction has been investigated. It was found that the vortices that form in the holes between the armor blocks are key to the process. The sediment swept into these vortices is entrained into the main body of the flow by these same vortices (the suction removal of sediment from between the armor blocks). The critical condition for the onset of suction was determined. It was found that the onset of suction is governed by two parameters: (1) the Shields parameter (based on the sediment size); and (2) the ratio of sediment size to stone size, d/D. The variation of the critical Shields parameter for suction as a function of d/D was determined for a broad range of the parameter d/D, namely, 0.001 <~d/D <=1. The timescale of the suction process and the downward displacement of stones (the general lowering of the armor layer) have also been investigated.