Riprap Sizing for Modified ARS‐Type Basin

A riprap sizing criterion for the original Agricultural Research Service (ARS)\‐type low‐drop structure was previously developed. The structure was required to reduce the required rock size. A 1:12 Froude‐scale model of the modified ARS‐type low‐drop structure with a baffle plate was constructed and tested to derive a riprap sizing procedure for stabilizing the stilling basin. Thirty‐four tests with the baffle plate and 12 tests without the baffle plate with varying discharges, submergences and riprap sizes. The drop height and channel geometry remained constant for all tests. The ratio of the approach unit discharge and median stone size was related to the submergence for determining the stable riprap size. The riprap size needed to stabilize the modified stilling basin is approximately 40% smaller than the riprap needed to stabilize the original stilling basin.