Influence of Sediment Consolidation on Hydrosuction Performance

Abstract

To alleviate problems caused by reservoir sedimentation, the hydrosuction removal of sediment deposits is an attractive option. In this technique, pumping or siphoning is used to draw water and sediment into the inlet of a pipe and convey the slurry to settling ponds. A key performance target is then to maximize the delivered sediment concentration. For fine sediment (silt and clay), deposit behavior largely depends on its degree of consolidation. To investigate how this parameter affects hydrosuction performance, a series of laboratory experiments were conducted using a small-scale suction pipe equipped with an online densimeter to measure the time evolution of the outflow sediment concentration. To help interpret the resulting signals, the evolving shape of the deposit surface near the pipe inlet was recorded. Measurements were then compared with predictions from inviscid selective withdrawal theory. Depending on the duration of self-weight consolidation prior to hydrosuction, a transition was observed between two highly contrasted sediment responses. Up to a degree of consolidation of approximately 90%, loose deposits respond much like a dense inviscid layer. Beyond this degree, consolidated deposits resist withdrawal, causing rapid freshwater breakthrough and an abrupt drop in hydrosuction performance.