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AbstractFine sediment coming to the channels from the catchment during period of heavy rainfall flows in suspension and interacts with the channels’ bed material and gets deposited into the pores of the bed. Experiments have been carried out to study this process by using a 30 m long, 0.20 m wide and 0.5m deep tilting laboratory flume. Two uniform and one non-uniform sediments were used as bed material. The deposition of fine suspended sediment of size 0.064 mm within the pore space of the surface layer of coarse sediment of the channel bed was studied under different equilibrium concentrations of suspended load in the flow. The bed material was moving as bed load only under the hydraulic conditions of the experiments. The porosity of surface layer of stream bed material got reduced due to deposition and subsequent sheltering of fine sediment within the pores of the coarse bed material. A basic mathematical model to quantify the reduction in porosity of bed material due to the process of deposition is developed and applied to compute the porosity of the bed material for different equilibrium concentration of fine sediment in the flow.