Disturbance Caused by Bed Sills on the Slopes of Steep Streams

Abstract

Live-bed tests on steep bed slopes are run in a laboratory flume to investigate the slope of equilibrium. The tests simulate a general degradation until a new equilibrium is reached. Subsequently, different bed sill settings are tested as a countermeasure against degradation. Evidence is presented that, in some cases, the bed slope with sills is milder than the one without sills under the same flow and sediment rates. This fact implies that the efficiency of the bed sill system to stop degradation decreases as the sills are placed closer together. Tests are on the verge of sheet flow, and friction factors are heavily dependent on sediment transport. Reaches in uniform and gradually varied flow behave very differently. Bed profiles are not straight, and grain size is linked to this fact. Other detailed information on testing equipment, experimental program, time development and local scour in a total number of 111 tests is given.