Design of Rock Chutes for the Stabilisation of Channel Beds

This paper presents the theory for the proper hydraulic design of rock chutes and introduces a spreadsheet-based computer program, CHUTE, to design and analyse the performance of a chute under a range of flow conditions.

The design procedure allows the computation of the water surface profile on a proposed rock chute for a given design condition. This allows the location of the hydraulic jump to be checked. The so-called factor of safety method is used to determine the median rock size required for stability at the critical location on the chute. It is shown that the critical hydraulic conditions on a rock chute occur at a flow that may be substantially less than the maximum flow for which the channel is designed. An innovative feature of the presented design procedure is the ability to analyse the hydraulic conditions over a range of flow rates (and associated range of tail-water levels) from the lowest to the highest expected flow. The critical flow rate with respect to rock size is identified and the design carried out. The full water surface profile is computed and the location of the hydraulic jump identified. The paper presents the full design procedure and demonstrates the associated spreadsheet-based software. The correct identification of appropriate downstream water levels and elements of practical chute design are also briefly discussed.