Flow Resistance of Vertical Rib Sidewall in Open Channel

Most of flood protection walls built on the impingement in mountain rivers have been made of concrete. It may cause flood disasters because the smooth wall surface could increase flow velocity. In this study the hydraulic experiments was carried out to evaluate the effect of one side wall with rectangular vertical ribs on flow resistance in open channel. The ratio of the pitch between vertical ribs to its depth, , was designed so that it include the so-called d type and k type roughness. The range of Froude number, , based on hydraulic radius is 0.81~1.12. Flow resistance in the open channel with a rib sidewall depends on the interval length of each ribs and the flow discharge. Maximum flow resistance occurred when is 9. In the d type roughness which is less than 3, the flow resistance decreases with increase of flow discharge. In the k type roughness which is greater than 3, the flow resistance increases with increase of flow discharge. The increments of flow resistance are especially great when are 9 and 12. The resistance due to vertical rib is mostly by the shape resistance and the vertical rib on one sidewall of open channel affects on the flow resistance so that the equivalent roughness heights of vertical rib may occur in scale of flow depth. Therefore the vertical ribs may be used to reduce the flow velocity and to move the location of maximum flow velocity from the rib sidewall to the centerward in a cross section of channels.