The Failure of the Baldwin Hills Reservoir Dam
On December 14, 1963, the dam built to contain the Baldwin Hill Reservoir located in southwest Los Angeles failed, releasing 250 million gallons of water into the housing subdivisions below the dam. Approximately 277 homes were damaged or destroyed and five people were killed by the disaster (Hamilton and Meehan, 1971). Although there is speculation that waterflooding operations in the Inglewood Oil Field (located to the west and south of the reservoir) were partially to blame for the failure of the reservoir dam, the dam itself did not fail due to an induced earthquake. Records from the Seismographic Laboratory of the California Institute of Technology located 15 miles northeast of the reservoir showed no earthquakes large enough to cause internal damage to the reservoir during the period 1950-1963 (Jansen, 1988). Instead, the sealing layers in the floor of the reservoir failed due to the “creep” of several geologic fractures below the reservoir, which caused the release of water through the floor of the reservoir that resulted in the structural failure of the dam itself.
The Baldwin Hills Reservoir was constructed between 1947 and 1951 by the Los Angeles Department of Water and Power. The reservoir was constructed on a hilltop and was formed by a dam on the north side and earthen dikes on the other three sides, which were constructed of materials excavated from the reservoir bowl. The soil under the reservoir was composed of porous material and was bisected by three known geologic faults (Jansen, 1988). The floor of the reservoir was made watertight by the use of two layers of asphalt with compacted earth between them. Below the upper layer of asphalt and earth, a level of pea gravel with tile drains was installed to allow the monitoring of leakage from the bottom of the reservoir. Extensive discharge from the drainage system was recorded during the initial filling of the reservoir, and filling was discontinued until repairs to the reservoir could be made (Jansen, 1988). Cracking in concrete portions of the reservoir was noted as early as 1951.
The Inglewood Oil Field was discovered in 1924 and covered approximately 1,200 acres when fully developed. At the time of the failure of Baldwin Hills Dam in 1963, the field had more than 600 producing wells, and the closest wells were located within 700 feet of the reservoir structure. The oil reservoir is divided into multiple compartments due to a series of geologic faults. Several of these faults not only divide the Inglewood Oil Field but also continue to the surface and are present on the site of the Baldwin Hills Reservoir. The depth of the wells in the Inglewood Field is between 2,000 and 4,000 feet. Due to subsurface fluid withdrawal, the ground level above the field exhibited a surface subsidence of approximately
10 feet by 1964. In order to increase production, waterflooding operations were commenced in 1954 and expanded in 1955 and 1961. These injection operations increased pore pressure in portions of the oil field from 50 psi to over 850 psi by 1963 (Hamilton and Meehan, 1971). Injection depths were as shallow as 1,200 feet.
The dam structure failed due to subsurface leakage of reservoir water beneath the floor of the impoundment and under the foundation of the dam itself. The subsurface leakage was caused by a cracked seal extending across the floor of the reservoir in line with the breach in the dam (Jansen, 1988). Movement of the geologic faults crossing the floor of the reservoir with downward displacement of 2 to 7 inches on the western side of several faults caused cracking in the asphalt membrane seal and allowed water to enter the porous soil beneath the dam. Later excavations of the bottom of the reservoir indicated that leakage had occurred for an appreciable amount of time before the dam failure. The slow movement of the faults beneath the reservoir has been attributed to (1) natural causes inherent in the geologic setting, (2) subsidence of the ground surface caused by oil and gas operations or by the filling of the reservoir with water, or (3) pressure injection of water in the Inglewood Field at shallow depths for oil and gas operations and in the presence of a fault system.
Hamilton, D.H., and R.L. Meehan. 1971. Ground rupture in the Baldwin Hills. Science 172(3981):326-406.
Jansen, R.B. 1988. Advanced Dam Engineering for Design, Construction, and Rehabilitation. New York: Springer.