Dams have allowed Californians and the West to harness and control water dating back to the days of Native Americans. At that time, Native Americans erected simple dams for catching salmon.
Today, California and neighboring states are home to a vast integrated system of federal, state and locally owned dams that help with flood management, water storage and water transport.
Flood management projects, for example, have prevented billions of dollars’ worth of damage and countless lives lost.
Hydropower from dams also provides a relatively pollution-free source of electricity, and has helped lessen dependence on oil, gas and coal.
Hydropower generates 15 to 20 percent of the annual electricity in California, according to the California Energy Commission.
There are also several different types of dams. Among the more common are those filled with earth (dirt), earth and rock, and those that use gravity to generate hydroelectric power.
Much of the work of dams centers on storing water and then getting the water to the right place at the right time. In California, this system has helped spark important economic activity in arid or semi-arid areas of the state including the agricultural Central Valley and Southern California.
As part of this, nearly 75 percent of the available water originates in the northern third of the state (north of Sacramento), while 80 percent of the demand occurs in the southern two-thirds of the state. The demand for water is highest during the dry summer months when there is little natural precipitation or snowmelt. California’s capricious climate also leads to extended periods of drought and major floods.
To help meet this demand, a series of dams were built on the western slope of the Sierra Nevada for both flood control and water supply. These include Shasta Dam on the Sacramento River, Oroville Dam on the Feather River and Folsom Dam on the American River.
California’s system of dams has generated intense disputes and controversies.
The water feuds have historically divided the state, pitting north against south, east against west and three major stakeholders (agricultural, urban and environmental) against one another. Intense disagreements continue to persist over the manner in which California’s water resources are developed and managed.
For example, the non-profit American Rivers named the Merced River as one of the most endangered American rivers in 2013 due to dam proposals along the waterway.
Dams and the Future
Changing public values and a greater awareness about ecosystems and the importance of keeping them healthy have generated governmental and private efforts to lessen and mitigate some of the impacts caused by dams. Water officials say achieving a careful balance among agricultural, urban, and environmental interests is considered key.
In 1972, for instance, the state Legislature moved to preserve the North Coast’s free-flowing rivers from development by passing the California Wild and Scenic Rivers Act, preserving about a quarter of the state’s undeveloped water in its natural state. The act prohibits construction of dams or diversion facilities, except to serve local needs, on portions or entire rivers around the state.
More recently, there has been a growing trend of storing water underground and interest in off-stream dams. This has several advantages over surface water storage. Sub-surface water storage is far less damaging to the environment than the construction of reservoirs and dams and usually does not require an extensive distribution system. Water banked underground also has a much lower evaporation rate than surface reservoirs. One drawback, however, is sometimes litigious water rights issues.
In November 2014 voters passed Prop. 1, the Water Quality, Supply and Infrastructure Improvement Act, which includes $2.7 billion for the public benefit aspect of surface water reservoirs.
There are some dams in the state eyed for removal because they are obsolete – choked by accumulated sediment, seismically vulnerable and out of compliance with federal regulations that require environmental balance. Dam removal is expensive, usually exceeding $100 million, not including the cost of initial studies. But for some dam owners the cost of removal is less expensive than effecting the necessary modifications such as fish ladders or seismic safety retrofits.
The near-failure of Oroville Dam’s spillways in 2017 prompted a statewide evaluation of the integrity of 93 other dams with similar spillways. Half of the dams under the jurisdiction of the Department of Water Resources’ Division of Safety of Dams (DSOD) are at least 50 years old.
DSOD dam condition assessments are based on five condition ratings from the U.S. Army Corps of Engineers National Inventory of Dams: satisfactory, fair, poor, unsatisfactory and not rated. Dams rated as satisfactory have no identified deficiencies. Dams rated as fair, poor or unsatisfactory have at least one identified deficiency.
Currently 1,151 dams (92 percent) within DSOD’s jurisdiction are rated satisfactory, with no identified deficiencies. Ninety-seven dams have a deficiency and are rated as fair, poor or unsatisfactory. Forty-four of those dams have a seismic deficiency.
DSOD may require that reservoir storage be reduced to a specific level if unsafe conditions exist.