Bridge Scour Countermeasures for the Phoenix Rio Salado Environmental Restoration Project

The U.S. Army Corps of Engineers and City of Phoenix, Arizona are partners for an environmental restoration project along the Salt River referred to as the Phoenix Rio Salado Project. The project includes the construction of a low-flow channel along a five and one-half mile reach of the Salt River beginning at Interstate 10 and proceeding downstream to 19^th Avenue. The proposed low-flow channel is a trapezoidal channel with an average bottom width of 61 meters (200 ft). This low flow channel invert is 2.44 (8) to 3.66 meters (12 ft) lower than the existing Salt River channel invert. Located within this reach of the Salt River are five roadway bridges and two sand and gravel operation conveyor bridges. Since the channel invert is being lowered 2.44 (8) to 3.66 meters (12 ft), the project included an evaluation of all bridge crossings to determine if the structures were stable under proposed project conditions. Countermeasures were evaluated for those bridges determined to be unstable. Countermeasures evaluated included roller compacted concrete (RCC) bed armoring and grade control, and local scour bed armoring, and structural retrofit. This paper summarizes the results of the evaluation along with the recommended alternative.