4.1.3 LA Dam

LA dam is 47m high and is founded on Saugus Formation bedrock. The dam is zoned with shell material on the upstream and downstream slopes, contains a chimney drain made of coarse materials at the center section, and has a clay zone upstream of the chimney drain. The interior slopes and perimeter road-ways of the reservoir are lined with asphalt concrete pavement. The Los Angeles Reservoir was constructed in 1977 to store treated water of the Los Angeles Aqueduct, and to replace the Lower and Upper San Fernando Dams, which were extensively damaged by the 1971 san Fernando earthquake.

During the 1994 Northridge earthquake, the dam was shaken by strong near-source ground motions, with ground motion amplitudes among the highest ever recorded. Nearby stations recorded maximum peak acceleration of 0.9 and 1 g, whereas accelerations on the right abutment and on the dam crest reached 0.43g and 0.56g, respectively.

The settlements and transverse displacements of the LA dam were obtained from the monument survey results, 1994. After the earthquake, the 7 cm thick asphalt lining that covers all upstream slopes of the LA dam displaced a lot of cracks. But these cracks were surficial, and did not extend within the embankment body.

Three slump areas were observed just west of the outlet tower. Each slump was associated with the downstream bulging of a subsided area. Small amount of fine sand were noticeable in the largest cracks surrounding these slumps.

There was no significant failure after the earthquake.

The 1994 Northridge earthquake cracked the surface pavement on the upstream slope of the Los Angeles Dam. Overall, the dam, designed to withstand severe shaking, suffered very little damage. (Courtesy of Los Angeles Department of Water and Power.)

Topographic Map of LA Dam with Cracks and Transverse movements induced by Northridge earthquake (Davis and Bardet, 1996)

Sources:

Davis, C. A., and J. P. Bardet. Performance of Two Reservoirs During the 1994 Northridge earthquake. Journal of the Geotechnical Engineering Division, Vol. 122, No. 8, 1996, pp. 613–622.

Bardet, J. P., and C. A. Davis. Performance of San Fernando Dams During 1994 Northridge Earthquake. Journal of the Geotechnical Engineering Division, Vol. 122, No. 7, 1996, pp. 554–564.

Ronnie Kamai, LA dam performance during 1994 Northridge Earthquake, Case History report, 2008

http://quake.usgs.gov/prepare/factsheets/LADamStory/