Utilization of Continuous Operating Reference Stations (CORS) in Southern California for Deformation Monitoring

The Metropolitan Water District (MWD) of Southern California currently has 33 facilities with structures (including concrete dams, earthen dams, reservoirs, power plants, control structures and water filtration basins) that require structural deformation monitoring of some kind. For more than 20 of these facilities, three dimensional data (X,Y and Z) is collected on a twice yearly schedule to fulfill a requirement by the State of California, Division of Safety of Dams to report on the structural health of our facilities under their jurisdiction. An economical method (a reduction in both personnel and equipment) was developed t o utilize the free, static GPS data from the network of Continuous Operating Reference Stations (CORS) that are installed over Southern California for crustal motion studies. Using two CORS stations as fixed base stations (or one CORS and one on-site receiver used as a base), two vectors are measured to each deformation monument. These two vectors are processed with the precise ephemeris and analyzed to determine the relative position of the monument. This relative position is re-measured every six months and compared to the previously established positions to study trends in the structural deformation. Utilizing two vectors from two fixed CORS stations, instead of creating a typical survey network, prevents contamination of data from possible errors at neighboring monuments. Also, these surveys incorporated the use of fixed height tripods to prevent height errors and choke ring antennas to reduce multipath. This method has resulted in excellent repeatability of the horizontal position for deformation trend analysis; however, the vertical position is still being obtained with electronic leveling methods at this time. MWD has realized a 50 % reduction in personnel and equipment needed to obtain the horizontal positions on eleven facilities, several of which are discussed. 1