A Stable Channel Design Approach for the Rio Salado, Salt River, Arizona

Planned environmental restoration of the Rio Salado (also known as the Salt River) involves the design and construction of a stable soft-bottom low flow channel through a 8-kilometer (5-mile) project reach in Phoenix, Arizona. The low flow channel will have a minimal footprint, thereby maximizing the area available for restoration in the overbank areas, yet convey the low-flow design discharge of 340 cubic meters per second (cms), or 12,200 cubic feet per second (cfs) (a 4-year peak discharge), without significant scour and/or deposition. This paper presents the low flow channel design approach. The channel was initially designed using channel stability methods and then refined using a sediment transport model. The initial channel slope, channel geometry and grade control locations were determined during the stable channel analysis. The stable channel slope was estimated using several analysis methods: evaluation of existing stable channel conditions; erodible channel design guidelines from the U.S. Army Corps of Engineers (Corps); stable channel slope estimate equations from the Albuquerque Metropolitan Arroyo and Flood Control Authority (AMAFCA); and the Corps' Hydraulic Design Package for Channels (SAM). The channel cross section geometry was determined using velocity constraints and normal depth methods. Sediment transport modeling was then used to refine the channel geometry until scour and deposition were minimized, determine the optimum grade control elevation and placement, and find the overexcavation depth in depositional zones that resulted in minimal maintenance. Guide dike structures were designed and strategically located to maintain the alignment of the low flow channel, protect the main channel bank, and minimize formation of secondary channels in the overbank areas.