A thesis submitted in partial fulfilment of the requirement for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1988

The entrainment ratio, which is a · soil erodibility parameter for estimation of cohesive sediment transport, was studied experimentally using two different cohesive soils namely reddish colour silty sand soil and greyish colour silty sand soil. These two types of cohesive soils had been collected from National Park, Khaoyai, Thailand. Each soil type was used in a laboratory flume and experiments were carried out with controlled flow and mild slope conditions. The observed parameters were discharge, flow depth, flow velocity and sediment transport. Actually twenty-two sets of experiments were carried out for each type of soil with different combinations of slope and discharge. Analysis of the obtained data showed that both slope and discharge conditions affected the entrainment ratio. It was also noticed that with increase in discharge rates, the entrainment ratio for reddish colour silty sand soil decreased for a given slope condition of the channel bed. But no such trend was found in case of the greyish colour silty sand soil. Moreover, the entrainment ratio decreased with increase in slope for any constant discharge in case of both types of soil used in the experiment. It was also evident from regression analysis that the cohesive sediment transport could be related linearly with the sediment transport capacity with high coefficient of determination for both the soil types. In addition a stepwise multiple regression analysis revealed that for both soils there was a exponential relationship between the cohesive sediment transport and the flow velocity. The flow depth and slope had only an indirect effect on the cohesive sediment transport through their effect on the flow velocity.