On the Salt River 41 miles northeast of Phoenix, Stewart Mountain Dam created Saguaro Lake, a 69,765 acre-foot capacity reservoir. The dam is a concrete thin-arch structure, 207 feet high, with gravity abutments. When built by the Salt River Valley Water Users' Association from 1928-1930, the dam included an open, super-elevated channel spillway equipped with radial gates.
The spillway was modified by Reclamation in 1936. The work consisted of building a concrete-lined spillway discharge channel, 450 feet long by 265 feet wide, below the existing ogee spillway; reconditioning the hoisting equipment for the radial gates; and installing individual gate operating motors and two 10-kilovolt-ampere gasoline-engine driven generators.
From 1988 to 1992, the dam was again modified by Reclamation, to meet concerns about its stability in a probable maximum flood or maximum credible earthquake. To address PMF concerns, a new spillway was constructed on the dam`s right abutment to increase its ability to safely release flood waters. As part of earthquake protection measures, a new concrete overlay was placed over areas on the right and left abutments to improve the dam`s stability. The existing power penstock and river outlet works were also replaced, the road on the top of the dam was raised and widened, and the existing left spillway and spillway wall was modified. In addition, drainage holes were drilled at selected locations in the dam`s foundation to help relieve hydraulic uplift pressures, and some areas of the foundation were grouted to help reduce seepage. Finally, 84 steel cables were installed through the dam and into its foundation to strengthen it.