salient periodically connects to the structure, forming a torabolo. When this 

 occurs, the shoreline resembles an undular crenulate bay. However, because of 

 their relatively low crest elevation, these breakwaters are overtopped during 

 storms, often causing the tombolo to become detached from the breakwater only 

 to return with mild wave conditions. The test breakwater segments have been 

 monitored, and the observed shoreline response has been used to assist in the 

 development of a physical model study for the entire proposed project (Appen- 

 dix C) . In this way, field data are being used to improve a standard design 

 tool prior to large-scale construction. 

 Colonial Beach, Virginia 



24. Two of the most recently constructed detached segmented breakwaters 

 were completed in 1982 at Colonial Beach, Virginia, on the lower Potomac 

 River. The project consists of two sites approximately 1 . 5 km apart. The 

 Central Beach Section consists of a breakwater with four segments fronting a 

 beach fill (Figure 13a) . The segments are each 60 m long with gap widths of 

 45 m, and are located approximately 65 m from the shoreline in 1.2m (MSL) of 

 water with a crest elevation of 0.4 m above MSL and a tide range of 0.5 m. 

 The structures are shore-parallel. The Castlewood Park Beach Section (Fig- 

 ure 13b) consists of three segments and fill; two of the segments are 60 m 

 long and separated by a gap of 26 m, and the third is 90 m long and 40 m from 

 the adjoining segment. This structure is located approximately 45 m from the 

 original shore. As shown in Figure 13b, the shoreline in this area is curved 

 and the segments are slightly oblique. Crest elevation is 0.4 m above MSL and 

 the water depth is 0.9 m MSL. Available fetch is small, with the area subject 

 to significant wave attack only during local storms. The project is new and 

 is being monitored jointly by the US Army Engineer District, Baltimore, and 

 the US Army Engineer Coastal Engineering Research Center (CERC) . These break- 

 waters are relatively close to the shoreline and tombolo formation is fre- 

 quent. However, the elevations of both the structure crest and the placed 

 beach berm are low. Apparently, a high tide accompanied by a storm surge can 

 inundate the project, overtop the structures, and flood the beach. This 

 postulated high overtopping component may contribute to making the tombolos 

 unstable. More definitive information on the behavior of this project and its 

 causes will result from the monitoring program. 



26 



