CHL. Development of monitoring plans and the conduct of data collection and 

 analyses are dependent upon the combined resources of CHL and the District/ 

 Division. The inspection for the study reported herein was completed as part of 

 the "Periodic Inspections" work unit of the MCNP program. 



Work Unit Objective and Monitoring Approach 



The objective of the "Periodic Inspections" work unit in the MCNP Program 

 is to monitor selected coastal navigation structures periodically to gain an under- 

 standing of the long-term structural response of unique structures to their envi- 

 ronment. These periodic data sets are used to improve knowledge in design, 

 construction, and maintenance of both existing and proposed coastal navigation 

 projects. These data also will avoid repeating past design mistakes that have 

 resulted in structure failure and/or high maintenance costs. Past projects moni- 

 tored under the MCNP Program and/or structures with unique design features 

 that may have application at other sites are considered for inclusion in the peri- 

 odic inspections monitoring program. Selected sites are presented as candidates 

 for development of a periodic monitoring plan. Once the monitoring plan for a 

 site is approved and funds are provided, monitoring of the site is initiated. Nor- 

 mally, base conditions are established and documented in the initial effort. The 

 site then is reinspected periodically (frequency of surveys is based on a balance 

 of need and funding for each monitoring site) to obtain long-term structural per- 

 formance data. 



Relatively low-cost remote sensing tools and techniques, with limited ground 

 truthing surveys, are the primary inspection tools used in the monitoring efforts. 

 Most periodic inspections consist of capturing above-water conditions of the 

 structure at periodic intervals using high-resolution aerial photography. Periodic 

 aerial photographs are compared visually to gauge the degree of in-depth analy- 

 sis required to quantify structural changes (primarily armor unit movement). 

 Data analysis involves using photogrammetric techniques developed for and suc- 

 cessfully applied at other coastal sites. At sites where local wave data are being 

 gathered by other projects and/or agencies (these data can be acquired at a rela- 

 tively low cost), wave data are correlated with structural changes. In areas 

 where these data are not available, general observations and/or documentation of 

 major storms occurring in the locality are presented along with monitoring data. 

 Ground surveys are limited to the level needed to establish the accuracy of 

 photogrammetric techniques. 



When a coastal structure is photographed at low tide, an accurate permanent 

 record of all visible armor units is obtained. Through the use of stereoscopic, 

 photogrammetric instruments in conjunction with photographs, details of struc- 

 tural geometry can be defined at a point in time. By direct comparison of photo- 

 graphs taken at different times, as well as the photogrammetric data resolved 

 from each set of photographs, geometric changes (i.e., armor unit movement and/ 

 or breakage) of the structure can be defined as a function of time. Thus, periodic 

 inspections of the structures will capture permanent data that can be compared 



Chapter 1 Introduction 



