User:Wildgooseontheloose/Water in California

Surface water[edit]
California has ten major drainage basins defined for convenience of water management. These basins are divided from one another by the crests of mountains. From north to south the basins are: North Coast, Sacramento River, North Lahontan, San Francisco Bay, San Joaquin River, Central Coast, Tulare Lake, South Lahontan, South Coast, and Colorado River regions. Each region incorporates watersheds from many rivers of similar clime. Many of the drainage basins are altered, with hydroelectric power generation happening in much of the upper portion of these watersheds.

The Central Valley watershed, which incorporates the Sacramento River, San Joaquin River and Tulare Lake regions, is the largest in California, draining over a third of the state – 60,000 square miles (160,000 km2) – and producing nearly half the total runoff. The Sierra Nevada snowpack feeds Central Valley river systems and is a critical source of water in the state's long dry season when little if any precipitation falls. Up to 30 percent of California's water supply is from snowpack, and the majority of California's hydroelectricity is also generated from the Sierra Nevada snowpack. More generally, in the US one of the largest uses of fresh water is withdrawals for the energy sector. Much of California's extensive reservoir and aqueduct system is designed to store and capture runoff from the Central Valley watershed. As this infrastructure ages, dam removal in California has become more widespread--a process that has been successful overall. The Sacramento and San Joaquin Rivers converge at the Sacramento–San Joaquin River Delta, a large fresh-water estuary where much of the state's water supply is withdrawn. The Central Valley watershed provides most of the water for Northern and Central California, as well as a significant chunk of Southern California's usage.

The North Coast watershed receives the highest annual precipitation of any California watershed. It incorporates many large river systems such as the Klamath, Smith, Trinity, and Eel, and produces over a third of the runoff in the state. With a few exceptions, the North Coast watersheds are relatively undeveloped, some have federal Wild and Scenic status; the northern coastal rivers provide water to biodiverse salmon habitat, carbon-sequestering forests, and local communities; some are within the influence of tribal water and fishing rights. Water flowing in these watersheds and into the Pacific Ocean is critical for sensitive, threatened, and endangered salmonids. There have been several proposals to divert additional water from North Coast rivers to increase water supplies in the rest of California, short of adequate water conservation strategies in the rest of the state, but these projects have been rejected due to cost and projected environmental harm.

The Colorado River originates more than 1,000 miles (1,600 km) from California in the Rocky Mountains of Colorado and Wyoming and forms the state's southeastern border in the Mojave Desert. Unlike the other California watersheds, essentially all of the water flowing in the Colorado originates outside the state. The Colorado is a critical source of irrigation and urban water for southern California, providing between 55 and 65 percent of the total supply.

The Central and South Coast watersheds include the most populous regions of California – the San Francisco Bay Area, Los Angeles and San Diego – but have relatively little natural runoff, requiring the importation of water from other parts of the state.

Rivers of the Lahontan watersheds in eastern California are part of the high desert Great Basin and do not drain to the Pacific. Most of the water is used locally in eastern California and western Nevada for irrigation. The Owens River of the South Lahontan region, however, is a principal source of water for Los Angeles.