Summary of physically modeled detached breakwater projects 

 conducted at the USAE Waterways Experiment Station 



Four physical model studies of detached segmented breakwater systems, 

 namely Presque Isle, Pennsylvania, Lakeview Park, Ohio, Oceanside Beach, 

 California, and Imperial Beach, California, were conducted in laboratory 

 facilities at WES from 1978 to 1983. All modeling was performed in a 

 movable-bed facility and is described in detail by Seabergh (1983), Bottin 

 (1982), and Curren and Chatham (1977, 1980). A summary is presented by 

 Dally and Pope (1986), which is the basis of the project summaries presented 

 herein. 



Presque Isle model study. Presque Isle Peninsula near Erie, 

 Pennsylvania, is a recurved sand spit protecting Erie Harbor, and is also a 

 state park with 1 1 recreational beaches along the approximately 1 1-km 

 shoreline. Historically, the landward connection of the spit has been severed 

 several times and beach erosion continued as the spit migrated to the east. 

 Groin field and beachfill projects did not halt the erosion, and consequently, 

 detached segmented breakwaters were considered as a possible stabilizing 

 solution. A prototype segmented breakwater with three segments was 

 constructed in 1978, and field monitoring of the shoreline response was 

 conducted. These data were used to verify sediment movement in subsequent 

 physical models. 



A 1:50 scale, undistorted physical model as described by Seabergh (1983) 

 was constructed to evaluate the performance of the segmented detached 

 breakwaters at Presque Isle using Froude scaling laws. The model reproduced 

 2,865 m of shoreline that included part of an existing groin field and a 

 relatively unstructured section of the shore as shown in Figure 37. This 

 permitted study of the interaction of the proposed breakwaters with two beach 

 sediment types, and of particular interest was the positioning of the 

 breakwaters with respect to the existing groins. A movable-bed section was 

 constructed in the model test basin using crushed coal based on sediment 

 scaling procedures of Noda (1971). Tests were conducted for existing 

 conditions (base plan) and three segmented breakwater plans. These tests 

 included (1) measurement of wave-generated current and water circulation 

 patterns, (2) crushed coal tracer tests, and (3) crushed coal beachfill tests. 



A shoreline response similar to that observed in the prototype was 

 experimentally duplicated. Figure 38 shows a comparison between the model 

 and prototype shorelines after an accretionary period and then after the winter 

 season when higher water levels and severe wave conditions reduced tombolo 

 development. Figure 39 shows one of the proposed breakwater plans installed 

 in the laboratory model. The results indicated that a 107-m spacing between 

 46-m-long segments produced satisfactory conditions within the reach covering 

 the groin field. The optimum placement of the breakwaters was offshore of 

 the groin ends. With the groin field removed, the segments could be placed 

 closer to shore with reduced generation of offshore currents, but the tombolos 

 took longer to form. 



Chapter 3 Tools for Prediction of Morphologic Response 



67 



