Erosion-resistance of the cohesive sediment beds is governed by the presence of benthic organisms and biofilms in the sediment deposits. Determining the erosion resistance using the laboratory flumes may not account for the presence of benthic organisms and biofilms as they are disrupted when sampling the bed sediment for the flume tests. Therefore, it is prudent to use the in-situ erosion flumes for the quantification of the erosion parameters for the natural sediment deposits.
During my tenure at the National Water Research Institute in Burlington, Ontario, Canada as a Research Scientist, I designed an in-situ erosion flume shown in the photograph below:
The flume consists of a rectangular duct measuring 3.5 m in length, 0.30 m in width and 0.08 m in depth. The bottom part of the flume is open over a length of 1.0 m and a width of 0.30 m (test section) and it begins at a distance of 1.75 m from the flume entrance. The entrance section of the flume consists of two segments. The first segment is a smoothly contracting section in which the flow accelerates as it enters the flume. The second section is a flow establishment section and contains a set of straight acrylic tubes over the whole cross section to damp out any secondary circulation. Downstream of the test section, the flume contracts gradually into a circular cross section and connects to a pump that draws the water through the flume and discharges to the ambient water. The flow rate of the pump is controlled electronically and a digital read out provides a measure of flow rate. The flume is fitted with an observation window made up of plexiglass on the top of the measurement section. When the flume is resting on the sediment bed properly, the surface of the bed will be in line with the bottom plate of the flume on both end sections of the flume. The plan and elevation view of the flume are shown in the diagram below:
