Sly Park Dam is located near Pollock Pines, California in the United States. The dam impounds Sly Park Creek and Hazel Creek, natural tributaries of the North Fork Cosumnes River, to form a , reservoir called Jenkinson Lake. It was constructed as part of the American River Division of the Central Valley Project to provide irrigation water to a portion of El Dorado County, California. The dam was begun in May 1953, with clearing operations, and was completed in mid 1955.
The earthfill Sly Park Dam is high, with a hydraulic height of , and long. Its auxiliary dam is high and long. The spillway of Sly Park Dam is actually in the auxiliary dam: it is a concrete chute long and can carry per second, while the outlet works at the foot of the dam can carry per second. The drainage area of Sly Park Creek behind the dam is . The Camino Conduit diverts water roughly west from the Jenkinson Reservoir for irrigation purposes. Water is also diverted from Camp Creek into Jenkinson Lake to increase the total water yield.
Jenkinson Lake watershed
The Jenkinson Lake watershed consists of the approximately 16.5 square mile area between Sly Park Dam and the Cold Canyon Tributary of Sly Park Creek. This area includes both forks of Sly Park Creek, Hazel Creek, and the Cold Canyon Tributary of Sly Park Creek. Jenkinson Lake receives insufficient inflow from this area and additional water is diverted from outside the watershed through the Camp Creek Diversion Tunnel to meet demand. The area played a significant role in the gold rush era of California's history.
Climate
Like most of California, the Jenkinson Lake watershed has a Mediterranean climate, with hot dry summers and cool wet winters. Located on the windward side of the Sierra Nevada, the watershed receives a large amount of precipitation relative to other reservoirs in the Central Valley, such as Folsom Lake. The area receives an annual average precipitation of 51.6 inches. Precipitation typically occurs October through May as rain and snow, though the reservoir's watershed is low enough in elevation that continued runoff from snow pack is not significant. The reservoir is necessary to store water for use during the dry summer months.
Environment
Elevation in the watershed ranges from 3400 to 5600 feet. The area is mountainous and consists of steep slopes and rocky outcrops. Soils in the area are deep with high water holding capacity. There is a high potential for landslides and the subsequent siltation of streams. The major mineral deposit in the area is gold. This was an important factor in the development of the area. Gold and other mineral deposits in the area may also be rich in iron and sulfides, which may impact water quality.
Vegetation in the area consists of oak woodland and mixed conifer forest. Common softwood tree species include ponderosa pine and douglas fir. Hardwood tree species include blue oak and black oak. Manzanita, western mountain mahogany, and poison oak are common understory plants, in addition to annual grasses. Vegetation plays an important role in stabilizing slopes in the area. Removal of vegetation by logging, development, and fire may increase erosion and the risk of landslides. Vegetation also provides important habitat for wildlife.
The Jenkinson Lake watershed supports a wide variety of animal species. Mammals include California mule deer, American black bear, and mountain lion. Common birds include the mountain chickadee and stellar's jay. Raptors include golden eagle, red-tailed hawk, and great horned owls. Reptiles include rattlesnake, gopher snake, and rubber boa. Wildlife makes the area an attractive recreation destination. Some mammals may also carry giardia, which may impact water quality.
Land use
Historical land use in the area included mining, ranching and timber harvesting and milling. Following the discovery of gold in California, miners quickly populated the area. The development of agriculture and commerce followed the miners. Large amounts of water were required for hydraulic mining, and the miners built many water conveyance structures, some of which are still used today. The gold rush was the first significant human impact on the watershed.
Before Sly Park Dam was built, the area where the reservoir now exists was known as Sly Park Ranch. Grazing and agriculture took place at Sly Park Ranch. There was also a timber mill, Sly Park Mill, located near the second dam on Sly Park Creek.
