Flow Resistance of Rock Chutes with Protruding Boulders

Steep and short rough channels, such as rock chutes, are used in river restoration as grade stabilization structures. The stability of these channels can be increased using boulders placed over the base material. The boulders can be placed with different configurations such as randomly or in rows. In each case, their presence affects the geometry of the channel and modifies the hydraulic resistance. This paper shows the results of tests conducted on rough channels with or without the insertion of protruding boulders. The parameters that influence the flow resistance, such as slope, relative submergence, and blocks disposition, were systematically investigated to describe the hydraulic behavior of the structure. The aim is to define a relationship, useful for practical design, which relates the flow resistance in terms of both Darcy-Weisbach friction factor and Manning coefficient. The results were combined with available data for loose rock riprap, to determine new experimental relationships.