2 Monitoring Plan and Data 



The objective of the monitoring effort in the Periodic Inspections work unit was 

 to establish base level data upon which long-term stability response of the Hum- 

 boldt Bay jetties could be defined through periodic inspections. Concrete dolos 

 armor units on the seaward ends of the jetties were monitored. This included 181m 

 (593 ft) of the seaward portion of the north jetty (sta 84+00 - 89+93) and 213 m 

 (700 ft) of the seaward portion of the south jetty (sta 67+00 - 74+00). The monitor- 

 ing plan consisted of targeting and ground surveys, aerial photography, photogram- 

 metric analysis of armor units above the waterline, and a ground-based broken 

 armor unit survey. 



Targeting and Ground Surveys 



Points were required to serve as control (both horizontal and vertical reference) 

 for the ground-based survey work as well as the photogrammetric work on the jet- 

 ties. Corps of Engineers brass disk monuments, as well as stationing schemes, had 

 already been established on the Humboldt Bay jetties during previous surveys. The 

 control survey for this study, therefore, made use of the existing monuments and 

 adopted the existing stationing scheme. Ground surveys were initiated from known 

 monuments on land which included stations CA 01 07, CA 01 09, and CA 01 QB as 

 shown in Figure 8. Using global positioning system control surveying and elec- 

 tronic land surveying techniques, positions and elevations of the existing three 

 monuments on each structure (Figure 8) were checked and reestablished. Positions 

 and elevations of the control points are shown below. Horizontal positions are 

 based on the California State Plane Coordinate System and all elevations are refer- 

 enced to mllw datum. 



1 4 Chapter 2 Monitoring Plan and Data 



