218-Effect of Cohesion on Detachment of Clay-Sand-Gravel Mixtures.

Abstract

The knowledge of detachment and transport of sediments by the stream flow is necessary for solving various problems like soil erosion in catchments, reservoir sedimentation, stable channel design, river bed degradation etc. The condition for initiation of motion and process of detachment and transport of sediments by stream flows in the form of bed load and suspended load for cohesionless uniform and nonuniform sediments are reasonably well understood. However the catchment surface and river bed material consists of mixture of cohesive as well as cohesionless material. Present study was therefore taken up to investigate the effect of presence of cohesive material such as clay on initiation of motion and process of transport by detachment of cohesionless sediments consisting of the sand-gravel mixtures. For this purpose the experiments were conducted in a 16 m long, 0.75 m wide and 0.5 m deep tilting laboratory channel. Bed materials consisting of mixture of cohesionless material sand and gravel each mixed in equal portion by weight with varying proportions of cohesive material i.e. clay were used. Experiments were conducted under changing grain shear stresses and the erosion rate was measured in the form of bed load transport rate and suspended load transport rate. Results on bed load transport only are reported herein. Critical shear stress corresponding to the condition of initiation of erosion is identified. Preliminary results from the analysis are presented herein. The detachment characteristics of the cohesive sediment with gravel size material have not been studied as yet.