• Water Supply
  • Water Supply
  • Water Supply
  • Water Supply
  • Water Supply
  • Water Supply
  • Water Supply
  • Water Supply
  • Water Supply
  • Water Supply

Water Supply

Sonoma County Water Agency provides high quality drinking water to over 600,000 people
in Sonoma and northern Marin Counties.Watershed

Long-term Water Supply Strategies

At the direction of its Board of Directors, the Sonoma County Water Agency is soliciting public input on proposed strategies for addressing long-term water supply problems presented by regulatory requirements, endangered species and changing weather conditions. Possible strategies to address the challenges facing the water agency include updating a state regulatory decision on water flows in the Russian River, known as Decision 1610; evaluating the impacts of climate change on water supply; exploring opportunities for storing winter water underground to be used in the summer (known as “groundwater banking”; and working with the county and cities to implement low impact development standards.

For more information, view our Water Supply Strategy Action Plan page


Russian River System

The Russian River originates in central Mendocino County, approximately 15 miles north of Ukiah. It drains 1,485 square miles including much of Sonoma and Mendocino counties, and reaches the Pacific Ocean at Jenner, 20 miles west of Santa Rosa. Its main channel is 110 miles long and flows generally southward from its headwaters near Redwood and Potter Valleys, to Mirabel Park, where the direction of flow changes to generally westward as it crosses part of the Coast Range. There are five principal tributaries: the East Fork of the Russian River, Big Sulphur Creek, Mark West Creek, Maacama Creek, and Dry Creek.

Three major reservoir projects provide water supply for the Russian River watershed: Lake Pillsbury on the Eel River, Lake Mendocino on the East Fork of the Russian River, and Lake Sonoma on Dry Creek. Lake Mendocino and Lake Sonoma provide water for agriculture, municipal and industrial uses, in addition to maintaining the minimum stream flows required by Agency water rights permits. These minimum stream flows provide recreation and fish passage for salmon and steelhead. Most of the streamflow in the Russian River during the summer is provided by water imported from the Eel River. Streamflows are augmented by releases from Lake Mendocino and Lake Sonoma.

Scott Dam and Lake Pillsbury: 

Scott Dam is a concrete gravity dam on the Eel River captures a drainage area of 298 square miles and forms Lake Pillsbury. Lake Pillsbury has a storage capacity of 86,388 acre-feet. Since 1923, the lake stored water for diversion to PG&E's Potter Valley Hydroelectric powerhouse through a tunnel constructed through a mountain ridge. Outflow from the powerhouse flows into the East Fork of the Russian River

Coyote Valley Dam and Lake Mendocino:

Located on the East Fork of the Russian River, Coyote Dam is a rolled earth embankment dam that forms Lake Mendocino.  Lake Mendocino is a U.S. Army Corps of Engineers project that began storing water in 1959. It captures a drainage area of about 105 square miles, and provides a total storage capacity of 118,000 acre-feet with a water supply pool of 70,000 acre-feet. 

Warm Springs Dam and Lake Sonoma:

Located about 14 miles northwest of Healdsburg, Warm Springs Dam is a rolled earth embankment dam that forms Lake Sonoma. The Sonoma County Water Agency generates electricity at Warm Springs Dam through a hydroelectric turbine.  Located at the confluence of Warm Springs Creek and Dry Creek, this lake began storing water in 1984 and has a total storage capacity of 381,000 acre-feet with a water supply pool of 212,000 acre-feet. 

Warm Springs Dam is a multi-purpose reservoir that serves as a flood control, water supply and recreational facility. The Water Agency is the local cost-sharing partner for Warm Springs Dam, and determines the amount of water to be released when the lake level is in the water supply pool, and the US Army Corps of Engineers manages flood control releases.


River Management System

Mirabel & Wohler Collectors:

The Water Agency has constructed six collector wells adjacent to the Russian River. Collectors 1 and 2 were constructed in the late 1950’s and are located near the Wohler Bridge. Collectors 3, 4 and 5 were constructed between 1975 and 1985 and are located near Mirabel Park. Construction of the Water Agency's newest collector well, Collector 6, was completed in the spring of 2006. Groundwater is extracted by each collector well from the alluvial aquifer adjacent to and beneath the Russian River.
A typical collector well has a 13-foot to 18-foot diameter concrete caisson (pipe) extending approximately 80 feet below the surface of the natural streambed. Six to twelve horizontal intake laterals (perforated pipes) ranging from 8-inch to 18-inch in diameter extend radially from the bottom of each caisson into the aquifer. Each collector well houses two large vertical turbine pumps equipped with electric motors that range from 1,000 horsepower to 2,000 horsepower.

Inflatable rubber dam:

The Water Agency operates an inflatable dam on the Russian River in the Mirabel area to increase production capacity during peak demand months. Operation of the inflatable dam increases production capacity in two important ways. First, surface water immediately behind the dam can be diverted to a series of infiltration ponds that are constructed adjacent to the three Mirabel collector wells. Fish screening facilities ensure the safety of the fish in the river. Second, infiltration to the underlying aquifer behind the dam is significantly improved by increasing the recharge area from the river. Permanent fish ladders provide fish passage when the dam is raised.

Well Field:

As a stand-by water source, seven vertical wells were constructed in the late 1990’s near the Mirabel collectors, providing 7 to 10 million gallons per day (mgd) of back up capacity.

Chlorination facilities:

The naturally filtered water entering the collector wells is extremely clean and requires no additional treatment+; however, chlorine is added as a precaution against possible contamination in the distribution system.

pH Adjustment/Corrosion Control System:

The Russian River water has a natural pH of about 7.1 - 7.6. To reduce corrosion of lead and copper present in indoor plumbing fixtures, it is desirable to raise the pH of the river water to 8.3 - 8.5. The Water Agency operates pH Adjustment/Corrosion Control facilities, located at the Wohler pumping plant and at the chlorination facility, where sodium hydroxide is added to the water supply. This treatment helps reduce dissolved metal content entering the wastewater treatment plants in areas served by the Water Agency.

Water Supply Wells

Santa Rosa Plain Wells: the Water Agency operates three groundwater wells in the Santa Rosa Plain. These wells pump groundwater from several hundred feet below the ground surface and are capable of providing up to 7 million gallons per day. The wells were originally constructed in 1977 in response to drought conditions. Two of the wells were replaced in the late 1990’s.

Aqueduct Transmission System

The aqueduct system consists of storage tanks, pipelines and booster (pump) stations and is designed to carry the anticipated (average) daily demand during peak demand. Maximum demand usually occurs during July or August.

Tanks: Eighteen steel water storage tanks placed throughout the transmission system store about 129 million gallons.

Pipelines: The Water Agency has about 79 miles of underground pipeline extending from the Russian River to Santa Rosa, Cotati, Petaluma and Sonoma. The pipes range in size from 16 inches to 54 inches in diameter.

Santa Rosa Plain wells: Three wells are capable of providing about 4-6 million gallons per day, and were constructed in 1977 in response to drought conditions.

Booster stations:
Seven booster stations are located in the water transmission system with pumps to maintain water flow and adequate pressure within the aqueducts.


Water Testing

Water Rights

As early as 1954, the Water Agency applied to the State Water Resources Control Board, which has the authority over water rights, for rights to appropriate Russian River water. Riparian water rights entitle the owner of land containing or abutting a natural stream the right to use natural flows by direct diversions for beneficial purposes without a permit. If water is to be stored for use in another season, owners must obtain an appropriative water rights permit. As the local project sponsor for the construction of the Coyote Valley and Warm Springs dams, the Water Agency retains rights to some of the water stored in these reservoirs and controls the releases from the reservoirs' water supply pools. The Water Agency also has rights for direct diversion and rediversion of water at the Wohler and Mirabel collectors. The Water Agency is required to maintain minimum streamflows, according to Decision 1610, at various points on the Russian River and Dry Creek in accordance with its water rights permits.