Welcome to Chatsworth Reservoir

HISTORY AND STATUS OF CHATSWORTH RESERVOIR

FACT SHEET & TIMELINE

1918 – Dedicated

1919 – Placed in Service

            Chatsworth Reservoir was placed in service in 1919 at a time when the San Fernando Valley was a sparsely populated agricultural area. The reservoir has two earthfill dams which provided an initial capacity of 7,400 acre-feet and a high water elevation of 884.3 feet. The dams were built using the then-accepted hydraulic-fill method which was similar to many dams throughout the United States. Under this method, the soil material forming the dam was washed or sluiced into place, and no mechanical compaction equipment was used to densify the material. Because this material was placed with little or no compaction, it typically has a low density and, correspondingly, a low strength or ability to resist earthquake loading.

1920-1950 – Agricultural Irrigation

            For many years Chatsworth Reservoir served as the principal water storage facility in the western San Fernando Valley, serving the irrigation needs of agriculture. At various times during this period, improvements to the reservoir were constructed to increase its capability to provide the required water supply. The most significant improvement occurred during 1930 and 1931 when the dams were partially reconstructed to increase the high water level of the reservoir 5 feet to elevation 889.3 feet and the capacity to 9,840 acre-feet.

1950-1969 – Domestic Supply

            As the area served by Chatsworth Reservoir was subdivided and developed to meet the demands for increased housing, the character of the West San Fernando Valley changed from an agriculture to urban setting. This transition gradually changed the requirements for Chatsworth Reservoir and its storage was increasingly used to supply residential and domestic drinking water, emergency requirements and continued agriculture uses.

Reservoir Operation and Maintenance Problems

            The transition from strictly agriculture to both agriculture and residential/domestic drinking water service resulted in a number of problems relating to operation of the Chatsworth Reservoir. The principal problem was maintaining water quality. Chatsworth Reservoir is located in a gently sloping natural valley which formed a number of shallow bays. These shallow bays created a condition which, in warm weather, encouraged the growth of algae and aquatic plants. During winter rainy periods, storm water runoff from the reservoir watershed would flow into the reservoir. In addition, wave action caused by wind would stir up mud in the shallow bays and along the shoreline. Contaminated surface water storm flow and groundwater from surrounding aerospace facilities were showing up in reservoir wells. These problems degraded the water quality and caused the reservoir to be removed from service each summer.

1969 Reservoir Improvements

            In the spring of 1969, Chatsworth Reservoir was drained and construction began on a project to improve water quality and increase storage. The improvements included deepening and shaping the shallow areas of the reservoir, constructing a bypass system to convey storm flows around the reservoir, and construction an experimental ecology pond on the northerly side of the reservoir. The experimental ecology pond was subject to removal if water quality, nuisance, or health and sanitary problems should occur.

San Fernando Earthquake – New Earthquake Design Requirements

            On February 9, 1971, a major earthquake occurred in the Sylmar-San Fernando area. This earthquake severely damaged the dams at Upper and Lower Van Norman Reservoirs, which had also been constructed using the hydraulic-fill technique. Because of the damage to these dams, the State Department of Water Resources (DWR), Division of Safety of Dams, directed a thorough stability investigation of all hydraulic-fill dams in California. These studies were required to determine the effects on hydraulic-fill dams resulting from severe earthquakes.

            As a result of this directive from the DWR, an extensive analysis and study of the Chatsworth Dams was conducted by the Department and its consultant. The analysis, which was completed in September 1972, showed that the Chatsworth Dams would not perform in a satisfactory manner if subjected to a major earthquake, either a local or San Andreas event. As a result of this analysis and discussions with the DWR, Division of Safety of Dams, it was determined that the two dams forming Chatsworth Reservoir would have to be completely rebuilt, and that no water could be stored in Chatsworth Reservoir.

Current Status

            During the period while the reservoir is out of service, the Department of Water and Power has initiated or participated in a number of programs to enhance the environment of the area surrounding the reservoir. For example, the Board of Water and Power Commissioners has agreed to allow the use of approximately 150 acres of Department property for recreational purposes administered by the City’s Department of Recreation and Parks. This property is located to the north and northwest of the reservoir, with the Valley Circle Boulevard providing a buffer between these parcels and the reservoir property.

            Another program was initiated in response to community interest in wildlife enhancement in the Chatsworth area. A dike has been constructed which will allow storm water runoff to be collected in the bottom of the reservoir to create an additional temporary ecology pond of approximately 30 acres. This pond will be maintained during the winter months each year while the reservoir is out of service, and will provide an attractive habitat for migratory birds.

            In addition to the construction of the experimental and temporary ecology ponds, selected areas of the reservoir property have been seeded with barley to provide both cover and feed for wildfowl inhabiting the area.

Future Status of Reservoir

            At the present time, a schedule for the reconstruction of Chatsworth Reservoir has not been established. The Water System has completed construction of high priority facilities, including Los Angeles, Silver Lake, Fairmont, and Lower Franklin Reservoirs. The replacement facilities for Sawtelle Reservoir are scheduled for 1984.

            In addition to replacement of seismically unsafe dams, the Water System is also involved in other high priority capital projects including the Los Angeles Aqueduct Water Filtration Plant and the Los Angeles Water System – Data Acquisition and Control (LAWS-DAC) facilities. The filtration plant is needed to reduce turbidity in Los Angeles Aqueduct water to meet Federal and State safe drinking water standards. The LAWS-DAC system will greatly facilitate optimum operation of the water system by enabling remote operation and computer gathering of operation data.

            Construction and financing of the filtration plant, LAWS-DAC system, and other capital expenditure programs such as investigations of contaminated surface water storm flow and groundwater from surrounding aerospace facilities, affect the timing of reconstructing the dams at Chatsworth Reservoir. The decision to rebuild Chatsworth Dams will be evaluated after completing these other high priority projects.