As part of the USGS continuous GPS operations in Southern California, Pacoima Dam is being monitored through a joint 'pilot' study in collaboration with Los Angeles County and other researchers within the Southern California Integrated GPS Network (SCIGN). The project was begun in order to demonstrate the feasibility of monitoring dams and other engineered structures (such as freeway overpasses and high-rise buildings) using continuous GPS technology and infrastructure.
Photo by J. Galetzka; click on it to enlarge

For other near real-time GPS results in southern California, go to SCIGN analysis (USGS Pasadena). Please read the general disclaimer, as all of the GPS results shown are generated automatically.

This map shows the topography, mapped faults (orange lines), and the 210 freeway (blue line) near the dam. Click on the red triangles to look at plots showing the latest data from the continuous GPS monitoring system. Pacoima dam is located in the San Gabriel mountains, about 5 km northeast of Sylmar, Calif. The station called CMP9 is at Fire Camp 9, about 2.5 km from the dam. Two GPS stations are on the dam itself; DAM1 is on the south abutment, and DAM2 is near the center of the dam arch.

Pacoima Dam GPS Project
This dam is a 113 meter tall concrete arch that was constructed in the late 1920's. From above it looks like this photo (from LA County web site). Pacoima dam withstood, but was damaged by, very strong ground shaking in both the 1971 and 1994 earthquakes. Due to concern about the stability of this dam in response to potential earthquakes in the future, the County purchased GPS equipment, and with assistance from the USGS in Pasadena, they began monitoring the dam using continuous GPS on September 1, 1995.

We have written a paper about the monitoring results to-date, so if you are interested in learning more about the system, please click here. The plot shown at the left here shows that seasonal air temperature changes correlate well with deformation of the dam. The dam evidently responds to air temperature by straining or flexing. This is called thermo- elastic deformation. The 15 mm peak-to-peak deformation signal we observe with the GPS system at Pacoima Dam corresponds to the annual temperature changes of about 30 degrees Farenheit (so, approx. 2 deg. F per mm displacement of the dam). The temperature data we have are from a station at Burbank. Even so, there appears to also be correlation between the 2 to 3 week smaller amplitude signal in our GPS results and the shorter-period fluctuations in air temperature recorded at Burbank.

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