MODELING A CONCRETE BLOCK IRRIGATION DIVERSION SYSTEM

Concrete block irrigation diversion systems have been proposed as alte rnatives to permanent dame of concrete or rock or temporary gravel ber ms. Permanent dams can cause stream channel instability, bank erosion, sediment pollution, ice flow blockage, and safety problems for recrea tional floating craft. Temporary berms can require substantial streamb ed disturbance and can promote sediment pollution, stream bank instabi lity, and bank erosion. A design procedure was developed based on a mo del of the hydraulic performance of concrete block diversion systems. The procedure was used to model a site on the Gallatin River in Montan a. The method relies on HEC-RAS (Hydrologic Engineering Center River A nalysis System) software combined with analytical techniques in an ite rative scheme. The hydraulic performance of different diversion config urations (the existing heavy-rock diversion system, concrete blocks or iented parallel to flow, and concrete blocks oriented diagonally) was assessed using the model under a range of now rates. The minimum diver sion dimensions (length, number, and size of blocks) that maintained b lock stability while diverting the requisite flow were determined for each model run. At the Gallatin River site, the block system oriented parallel to flow required less diversion material than the diagonal or ientation. The recommended diversion length was 51.8 m (170 ft). Trape zoidal blocks with a top width of 20.3 cm (8 in), a height of 45.7 cm (18 in), and side slopes of 2 vertical to 1 horizontal were specified. This configuration minimizes the total block mass, diverts the requir ed flow, and has a factor of safety of 2.0 against block displacement.