the structure was occurring. An inventory of broken/cracked armor units also was 

 to be conducted to determine armor stone quality. 



Photogrammetry 



Low-altitude, aerial photographs, at a scale of approximately 2.5 cm = 6 m (1 in. 

 = 20 ft) were to be secured for the main breakwater. The photographs were to be 

 obtained from a helicopter with at least a 60-percent overlap for stereo viewing. 

 From the stereo pairs, a rectified map would be prepared using the ground eleva- 

 tions obtained at the targeted capstones as a basis for verification. From these 

 rectified photos, x, y, and z coordinates for any point on any armor stone could be 

 provided from three-dimensional stereo plotters. These photos were to be obtained 

 both early and late during the monitoring to determine movement of units above the 

 water. Base conditions would be established from which to evaluate the structure in 

 the future to determine its long-term stability response in this extremely hostile 

 wave environment. 



Since extreme wave conditions generally occur at St. Paul Harbor on an annual 

 basis, only 1 year of wave, current, runup, and overtopping data collection was 

 proposed for these elements. These data would be collected during the winter 

 season (mid-October through March time frame). In general, most of the elements 

 of the monitoring plan were completed as proposed. However, changes in 

 procedures, techniques, etc. were made in some cases during actual monitoring. 



Equipment and Data Collection 



Monitoring of St. Paul Harbor, Alaska, was conducted during the period July 

 1993 through June 1996. Actual elements of the monitoring program included 

 prototype wave gauging, wave hindcast study, wave runup, wave overtopping, 

 bathymetric analysis, broken armor unit surveys, and photogrammetric analysis. 

 Equipment and methodology used during data collection are presented in the 

 following sub-sections. 



Prototype wave gauging 



Prototype gauges were installed at St. Paul Harbor on 27 August 1994. They 

 consisted of two directional wave gauges (DWGs) placed outside the harbor at 

 approximately the 12.2-m (40-ft) contour, one nondirectional pressure gauge placed 

 along a dock inside the harbor, and one electromagnetic current meter placed inside 

 the harbor. Locations of prototype gauges are shown in Figure 14. 



The DWGs were developed at WES and included three Paros Digiquartz 

 pressure transducers arranged in a 1.6-m (5.25-ft) equilateral triangle array. All 

 gauge electronics and batteries were contained in a single cylinder approximately 



18 



Chapter 2 Monitoring Program 



