Santa Ana River - Watershed

Watershed

One of the largest river basins in Southern California and the largest on the South Coast, the Santa Ana River watershed covers 2,650 square miles (6,900 km2) in parts of four California counties. The main stem of the river flows through three of these counties, and tributaries drain parts of Los Angeles County into the Santa Ana. The watershed is characterized by the flat, arid basin of the Inland Empire and the coastal plain of north-central Orange County, and is bisected by the Santa Ana Mountains, which run nearly perpendicular to the river—northwest to southeast. There are over 50 major tributaries to the once free flowing and perennial river. The Temescal Creek valley constitutes a major portion and physiographic feature of the Santa Ana River watershed. The area drained by Temescal Creek and the San Jacinto River constitute some 45% of the watershed and extend its boundaries as far south as the Anza-Borrego State Park area.

About 4.8 million people lived in the Santa Ana River basin as of 2000. Most of the population is concentrated close to the river in urban centers such as San Bernardino, Riverside, and Santa Ana. In the Inland Empire, most people live in a thin ribbon of land along the river, while the rest of the land is used for agriculture and ranching. In Orange County, however, nearly all the land is urban. As a result, the Santa Ana River watershed can be thought of as having two distinct parts, separated by the Santa Ana Mountains. Some major bodies of water in the watershed include Lake Elsinore, Lake Irvine, Lake Mathews, Lake Perris, Diamond Valley Lake, Lake Skinner, and Big Bear Lake. Only one, Lake Elsinore, is naturally formed. The rest are all formed by dams constructed by county or state water agencies. As an example, Diamond Valley Lake is for the California State Water Project.

Several major Southern California drainage basins border on that of the Santa Ana River. In the northwest is the San Gabriel River, another major river with its mouth in Long Beach. On the southwest, the San Diego Creek watershed forms much of the boundary within Orange County. Some of the rivers and streams that drain the area between the southwestern boundary of the watershed and the Pacific Ocean are Aliso Creek, San Juan Creek, San Mateo Creek, the Santa Margarita River, and the San Luis Rey River. On the east are the drainage basins of the Whitewater River and the Coachella Valley, flowing into the Salton Sea, and on the north is the Mojave River, which flows into the endorheic basin of the Mojave Desert.

However, the area that the river drains in Orange County downstream of Santiago Creek is extremely narrow, because of the diversion of its former Orange County drainage area to the Talbert and Huntington Beach flood control channels, which empty into the Pacific very near the mouth of the Santa Ana. Most of the Santa Ana through Orange County now functions as a conduit to carry runoff from upstream areas directly to the Pacific and drains very little area downstream of the Santiago Creek confluence. About 21.4 square miles (55 km2) of land that originally drained to the Santa Ana River in Orange County now is drained by the two flood control channels, colloquially called the "Talbert watershed". The river originally had many different outlets to the Pacific, one of which even extended as far north as the San Gabriel River or as far south as Newport Harbor. In fact, the original mouth of the river which drained eventually into the Pacific Ocean, was located at what is today the entrance to Newport harbor. Based on a U.S. Coastal Survey from 1878, Newport Bay was predominantly a river estuary with few open channels. The river flowed into the bay bringing with it heavy silt and making boating difficult. To eventually create Newport Harbor, sand that was deposited by the Santa Ana River had to be kept from choking the bay. In 1920, the Bitter Point Dam was built to divert the river away from the bay and on its current course to the ocean at Huntington Beach. Stone jetties were built to form the new river mouth. All of the Islands in Newport Harbor are the product of dredging and man made forming from the sands and silt deposited over time by the Santa Ana River.