on the comparison of the diverted discharges in a bottom intake with porous media in clear water and sediment flow

abstract bottom rack intake is one of the most appropriate structures for diverting water in steep rivers. the problems of corrosion, deformity and clogging of the bottom racks in long term, inspires a new system of bottom intake in which a filled trench of porous media is replaced by the bottom racks. diversion of a specified amount of discharge through the porous media when void space in the granular material are filled with fine sediment in comparison to the bottom racks, requires much larger structure. however, for the new system of water intake, lower cost of construction and maintenance and higher compatibility with the river morphology in long term are considered as major advantages. the present research deals with an experimental model with two-storey channel, the lower one is used to divert water through the porous media and the upper one is used to convey the remained flow. measurements of the diverted discharge were performed for different rates of flow, grain size distributions as well as surface slopes of intake with clear water and sediment flow. the influence of clogging phenomena on diverted discharge is also examined. the experimental results show that the effect of clogging in sediment flow in comparison to the clear water is decreased as the surface slope of the porous media is increased. it is revealed that the discharge coefficient of bottom intake when clear water is passed through the channel is varied in the range of 0.06 to 0.13. when sediment flow is passed over the bottom intake, due to clogging phenomena discharge coefficient is reduced up to 5 to 35% in comparison to the clear water. experimental equations prepared for the discharge coefficients show that the significant factors affecting the efficiency of the water intakes are grain size distribution and surface slope of the bottom intake. the results show that the discharge coefficients for the water intake with the clear water and sediment flow when the above mentioned factors are selected appropriately are close to each other.