Photographic documentation 



Photography can provide both qualitative and quantitative information on a 

 breakwater's performance. Controlled, vertical aerial photography can 

 provide quantitative data on ground elevation, shoreline and berm location, 

 offshore shoals, structure geometry, structural deterioration, and beach use 

 changes. Typical aerial photographs for coastal project monitoring are taken 

 at a scale of 1:4800 (1 in. = 400 ft), with a 60-percent overlap for 

 stereographic analysis. Larger scale photography is usually used to examine 

 changes in the elevation of structural components, such as armor units, 

 between successive flights. For structural monitoring, it is important to obtain 

 photography immediately after construction in order to provide a base 

 condition for comparison. The frequency of aerial flights depends on the 

 objectives of the monitoring program. Detailed project monitoring may 

 require quarterly flights, whereas routine inspections may only need annual 

 photography. A more inexpensive, but strictly qualitative method is to obtain 

 periodic ground-level photography to document changes over time in a 

 particular location. 



Beach profiles and bathymetric data 



Periodic beach profiles can be used to document the accretion, erosion, or 

 stability of the project's shoreline. Beach profile data can assist with both 

 routine evaluation of the project and documentation of storm damages or 

 damages prevented as a result of the project. As with photography, the 

 frequency of profiles depends on the objectives of the monitoring program. 

 Beach changes can occur rapidly after initial construction and may be required 

 more frequently. It is recommended that at least quarterly profiles be 

 conducted to document beach planform development prior to reaching 

 equilibrium. If bathymetric changes due to project construction or seasonal 

 offshore profile changes are required, profile lines will have to extend 

 offshore beyond wading depth. Subaqueous surveys can significantly increase 

 the cost of the monitoring. Additionally, it is important to ensure that for 

 each profile line, the beach and bathymetric data meet and are not vertically 

 offset; otherwise, significant error can be introduced into the analysis. 



Spacing of the beach profile lines also depends on the monitoring 

 objectives. General shoreline trends can be documented with distantly spaced 

 profiles, whereas volumetric analysis of erosion and/or accretion requires 

 more closely spaced lines. EM 1 1 10-2-1617 recommends at least three profile 

 lines in the lee of a detached breakwater depending on the structure's length, 

 distance offshore, and other parameters (Figure 62). 



110 



Chapter 5 Other Design Issues 



