Abstract
Erosional process of cohesive bottom sediments by flow has been studied using visualization experiments and quantitative measurements of flow velocity and concentration of suspended sediments. Samples of bottom sediments were made by allowing kaolinite suspensions to settle for 3 h.
Erosions of bottom sediments by flow were reproduced in the annular flume, visualized and photographically recorded by a still camera with highly sensitive film (ISO 3200) and a 105 mm micro lens. A constant temperature anemometer was used to measure the profiles of the streamwise, the transveres and the vertical flow velocities. Concentrations of suspended sediments originating in the erosions of bottom sediments were measured by a device built as a trial using an infrared emitting diode (IRED) and a photo-transistor (PT). Using the SS meter, a non-contact measurement and high frequency sampling (i. e., 1 kHz) were carried out.
The results indicated that the critical shear stress of the bottom sediments was 0.3 N/m2, and that the vortices near the bottom were closely related to erosions of bottom sediments and the scale was from 0.16-0.60cm.
