Experiments on the scour resistance of cohesive sediments

Abstract

Previous studies of the scour of cohesive materials as presented in engineering literature and as obtained directly by personal contact are briefly reviewed. Exploratory tests for measuring scour resistance are described, and some correlated results are presented for a test involving scour by a vertical submerged jet impinging on the horizontal surface of a soil sample. The characteristics of the scour surface were observed for a remolded and a natural sediment, and the rates of scour were measured by the weight loss of the sample. The results are presented in terms of dimensional parameters. A new apparatus is described which is designed to permit a direct measurement of a uniform shear stress developed at the surface of a cylindrical sample of a cohesive sediment. Comments are made regarding the direction of future research in this area.

Short‐term changes in the erodibility of intertidal cohesive sediments related to the migratory behavior of epipelic diatoms

“…The first two refer to a critical point for initiating erosion in cohesive substrates, which Dunn (1959) reported to be definite and reproducible in clay samples. The present observations support Moore and Masch (1962) who unlike Dunn found that some sediments required a greater force to cause incipient scour than was needed to continue subsequent erosion. It would be interesting to have more data on the microbial status of the test sediments in each case.…”

“…The use of a submerged perpendicular jet to measure the resistance of cohesive sediment to erosion is not new (Dunn 1959;Moore and Masch 1962). The importance of the present study is its adaptation to measure short-term changes in sediment stability.…”

“…3). Discussion of the use of jet systems can be found in papers by Dunn (1959), Moore andMasch (1962), andCharters et al (1973). The first two refer to a critical point for initiating erosion in cohesive substrates, which Dunn (1959) reported to be definite and reproducible in clay samples.…”

“…At this point a sudden and substantial reduction (> 30%) in light transmission within the test chamber took place. In accordance with Moore and Masch (1962) this event was termed the point ofincipient scour, and the critical pulse velocity at which it occurred was taken to be an ordinal measure of the surface cohesive strength or erodibility of the test sediment.…”

“…Water pulses of increasing velocity are triggered to establish the point of incipient scour (Moore and Masch 1962) at which the force of the pulse overcomes the surface cohesive strength of the sediment being tested. Short-term changes in the erodibility of intertidal sediments were studied in a laboratory tidal ecosystem in relation to the migratory behavior of diatom assemblages.…”