McMicken Dam Alternatives Analysis

Originally termed the Trilby Wash Detention Basin Dam and constructed by the United States Army Corps of Engineers (USACE) in 1954 and 1955, construction of McMicken Dam was authorized by the U.S. Congress in 1953 to provide emergency flood protection for Luke Air Force Base, the Litchfield Park Naval Air Facility, and adjacent areas. McMicken Dam is operated and maintained by the Flood Control District of Maricopa County (District). McMicken Dam was constructed as a homogenous, compacted earth fill nearly 10 miles in length with a maximum height of 34 feet. The embankment was constructed of on-site alluvial soils borrowed from a 200 to 800 foot wide strip of ground immediately upstream from the dam, now referred to as the low-flow channel. The dam was constructed with a 2.5:1 (horizontal to vertical) upstream slope, a 2:1 downstream slope, and a 12-foot wide crest. The McMicken Dam watershed is estimated to cover an area of approximately 259 square miles and the reservoir pool was designed for a capacity of approximately 19,300 acre-feet at the emergency spillway crest elevation. The emergency spillway is a 2,000 feet long broad crested weir located at the left abutment of the dam. The emergency spillway was designed for a maximum capacity of 95,000 cubic feet per second (cfs). The principal outlet for McMicken Dam is an ungated, reinforced concrete box culvert located near the left abutment of the dam and has a design capacity of 4,450 cfs with the reservoir at the spillway crest elevation. According to current regulations published by the Arizona Department of Water Resources (ADWR), McMicken Dam is classified as an "intermediate" dam with a "high" downstream hazard potential. The hazard potential is high due to the proximity of development downstream of the dam. Due to the high hazard potential, the dam is required by ADWR to safely pass the Probable Maximum Flood (PMF). 30 pp., 22 reference, various maps and photos.