Morena Dam
| Morena Dam | |
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View of Morena Reservoir from near the dam, looking upstream, c. 1918
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 Location of Morena Dam in California
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| Country | United States |
| Location | San Diego County, California |
| Coordinates | 32°41′07″N 116°32′51″W / 32.68528°N 116.54750°WCoordinates: 32°41′07″N 116°32′51″W / 32.68528°N 116.54750°W |
| Purpose | Water supply |
| Construction began | 1896 |
| Opening date | 1912 |
| Owner(s) | City of San Diego |
| Dam and spillways | |
| Type of dam | Rockfill |
| Impounds | Cottonwood Creek |
| Height | 177 ft (54 m) |
| Length | 550 ft (170 m) |
| Reservoir | |
| Creates | Morena Reservoir |
| Total capacity | 50,694 acre·ft (62,530,000 m3) |
| Catchment area | 114 sq mi (300 km2) |
| Surface area | 1,475 acres (597 ha) |
| Normal elevation | 3,039 ft (926 m) (spillway) |
Morena Dam is a rockfill dam across Cottonwood Creek, a tributary of the Tijuana River, in southern San Diego County, California in the United States. Originally completed in 1912 and raised several times afterward, the dam is one of the oldest components of the city of San Diego's municipal water system, providing between 1,600 to 15,000 acre feet (2,000,000 to 18,500,000 m3) of water per year. It is one of the few facilities in the San Diego water supply system that relies entirely on local runoff.
Morena Dam is located in the Cleveland National Forest at the headwaters of Cottonwood Creek, about 40 miles (64 km) east of downtown San Diego. The dam is 167 feet (51 m) high from the riverbed and 550 feet (170 m) long, with a height of 177 feet (54 m) from the foundations. Altogether the dam contains 335,300 cubic yards (256,400 m3) of earth and rock fill. At its full height, the reservoir can hold 50,694 acre feet (62,530,000 m3) of water, covering 1,475 acres (597 ha). The drainage area above the dam is 114 square miles (300 km2) and includes the tributary Morena Creek, for which the dam and reservoir are named.
Water is released via a 387-foot (118 m) long tunnel, fed by an intake tower that can draw up to 595 cubic feet per second (16.8 m3/s) water from different elevations of the reservoir. The spillway is located on the north side of the dam and has a crest 310 feet (94 m) long, topping out at 3,039 feet (926 m) above sea level. Flood flows through the spillway are controlled by steel flash gates 7.5 feet (2.3 m) high. The spillway has a capacity of approximately 25,000 cubic feet per second (710 m3/s).
The Morena reservoir serves primarily for long-term storage of winter flood flows in Cottonwood Creek, and is the uppermost of a chain of three reservoirs – Lower Otay, Barrett and Morena – that provide water to the city of San Diego. Water released from Morena Dam travels several miles down Cottonwood Creek to Barrett Lake, where it is diverted to Lower Otay via the 14-mile (23 km) long Dulzura Conduit. From Lower Otay Reservoir the water enters the Otay Water Treatment Plant, before flowing into the municipal water network. The entire project is known as the Cottonwood-Otay Water System.
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