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<br />water flows. The maximum normal depth Yn is 5 feet and the maximum <br />normal velocity Vn is 7 feet/sec. for erosion resistant soils and 5 <br />feet/sec. for easily eroded soils. <br />2. The trickle channel shown in this case is a rectangular <br />concrete channel. The concrete channel ends at the upstream end of the <br />upstream riprap apron. A combination cut-off wall and foundation wall, <br />to give the end of the trickle channel additional- support, is provided. <br />The water is allowed to "trickle" through the upstream apron and through <br />the vertical wall. Riprap trickle channels would simple feather into <br />the upstream apron. <br />3. A lO-foot long apron is provided upstream of the cutoff wall <br />to protect against the increasing velocities and turbulence which result <br />as the water approaches the vertical drop. Type M riprap can be used <br />for this apron. <br />4. The vertical wall should have the same trapazoidal shape as <br />the approach channel. The wall distributes the flow evenly over the <br />entire width of the drop structure. This is important to prevent flow <br />concentrations which would adversely affect the riprap basin. <br />The trickle channel is ended at the upstream end of the upstream <br />apron to prevent the trickle channel from concentrating additional wate.r <br />." ~ <br />. ~~ <br /> <br />at a point during high flows, thus exceeding the design assumptions. <br />The apron and the vertical wall combine to disperse the flow <br />concentrated in the trickle channel. The trickle flows are allowed <br />through the wall through a series of notches in order to prevent <br />ponding. The voids in the riprap below the notch inverts are expected <br />to silt in rapidly, or they can be filled at the time of construction. <br />The wall must be designed as a structural retaining wall. It will <br /> <br />to <br />