Cache Creek (Sacramento River) - Hydrology

Hydrology

The Cache Creek Dam on the South Fork of Cache Creek, five miles (8 km) downstream from Clear Lake, was built to increase Clear Lake's capacity and to regulate outflow for downstream users of Cache Creek water. The dam was later modified to include a 3 MW hydroelectric plant. The stream has a relatively small capacity, less than a quarter of the amount the dam is able to release. There is a rock ledge a mile and a half downstream of Clear Lake, called the Grigsby Riffle, near the bridge on State Route 53. This sill restricts the amount of water that can flow through at that point. The limited capacity of the stream means that it takes a very long time to drain excess flow from Clear Lake, increasing the chance of flooding around the lake. The bottleneck is seen as a backup to prevent flooding downstream and Yolo County is prohibited from increasing the capacity of the channel by the Bemmerly Decree. The Capay Diversion Dam, 49 miles (79 km) downstream from the Cache Creek Dam, diverts water for distribution throughout Yolo County using a 175 mile (280 km) network of canals.

Water rights and flooding protection have been in dispute between Yolo and Lake Counties since the late 19th century. The Yolo County Flood Control & Water Conservation District holds appropriative rights for up to 150,000 acre feet (190,000,000 m3) per year from Clear Lake. Current treaties attempt to ensure a balance between the needs of the two counties, although high-water conditions can cause temporary disagreements.

A large part of the creek within Lake County is designated a Wildlife Area by the state of California and the federal Bureau of Land Management, on which vehicles are prohibited but hiking, primitive camping, and hunting are allowed. The South Fork presently hosts a growing population of the rare tule elk, plus winter populations of bald eagles. The ruggedness of the area tends to ensure its isolation from human activity. In 2006 the United States Congress designated 27,245 acres (110 km²) of the area as the federally protected Cache Creek Wilderness.

The Indian Valley Dam on the North Fork of Cache Creek forms Indian Valley Reservoir. The dam's primary purpose is water storage for irrigation, but a 3.3 MW hydroelectric plant was built to take advantage of the falling water.

Whitewater boating on Cache Creek includes kayaking, rafting, canoeing and innertubing which are popular in the summertime using the water released from the dams for downstream agriculture.

Nominally a tributary of the Sacramento River, Cache Creek now only reaches it during extremely wet years due to damming and diversion of the stream's water. Degradation of the channel caused by invasive plants, such as Arundo donax and Tamarix spp., as well as gravel mining has left no suitable habitat for Chinook salmon and steelhead to spawn, even if there is enough water. Consequently, there are no longer any anadromous fish species in Cache Creek.