Experimental Study of Sediment Flow Discharge in New System of Bottom Intakes with Porous Media

Bottom rack intake is one of the most popular structures for diverting water in steep rivers. The problems of corrosion, deformity, and clogging of the bottom racks in long term inspire a new system of bottom intake in which a filled trench of porous media replaces the bottom racks. Diversion of a specified amount of water through the porous media, when the void space in the granular material is filled with fine sediments in comparison to the bottom racks, requires much larger structure. For the proposed water intake, lower cost of construction and maintenance and higher compatibility with the river morphology are considered as major advantages. This research deals with an experimental model with two-story channel, the lower one is used to convey diverted water through the porous media and the upper one is used to carry the remained flow to downstream. Measurements of the diverted discharge were performed for different rates of flow, grain, and sediment size distributions as well as surface slopes of intake. Results show that despite clogging of the suspended sediments in porous media, using appropriate grain size with a surface slope of the porous media increases the discharge coefficient of system. In comparison to the clear water flow, the diverted discharge reduction induced by clogging is not significant and the efficiency of system in long term with no operation effort is confirmed. An empirical formulation has been proposed based on the concept of Darcy's law for surface infiltration. The equation is found to be dependent on size ratio, Reynolds number, and hydraulic gradient. The theoretical predictions in comparison with the experimental results have shown a good consistency.