Geoarchaeological Assessment for the Tres Rios Project, Maricopa County, Arizona

Statistical Research, Inc. (SRI), under subcontract to ASM Affiliates, conducted geoarchaeological investigations in the U.S. Army Corps of Engineers (COE) Tres Rios project area. The Tres Rios project involves flood control, wetland restoration, water reclamation and reuse (creation of wetland, marsh, and open water areas), and construction of a pipeline and levees. The project area is located in central Arizona in the area surrounding the confluence of the Salt, Gila, and Agua Fria Rivers. The study area contains two distinct reaches of the Gila River. The eastern half of the project area contains the terminal reach of the lower Salt River and its confluence with the Gila River. This 3-km- (2-mile-) long reach is characterized by a wide, unstable channel with multiple low-flow channels and many mid-channel bars and islands, traits resulting from a large sediment load, erodible banks, and highly variable discharges (Graf et al. 1994). The western half of the project area contains the uppermost reach of the lower Gila River, beginning at the Gila-Salt confluence and extending 6.5 km (4 miles) west to the vicinity of the Agua Fria River’s confluence with the Gila. The channel of this reach is also braided; the gradient is significantly lower, however, resulting in denser vegetation and more channel deposition than in upstream reaches (Graf et al. 1994).