APPENDIX C: EXAMPLES OF PHYSICAL MODEL STUDIES 

 USED IN DETACHED BREAKWATER DESIGN 



1 . This Appendix discusses four site-specific model studies performed 

 at WES which involved detached breakwaters and illustrate the types of testing 

 which may be performed to aid in their design. 



Presque Isle Model Study 



2. A model study was conducted by Seabergh (1983) on Presque Isle Pen- 

 insula, Erie, Pennsylvania, which is a recurved sandspit protecting Erie Har- 

 bor. The peninsula has a lakeward shoreline of approximately 11 km and serves 

 as a state park with 11 recreational beaches. The landward connection of the 

 spit has been severed several times during storm events, and beach erosion is 

 the status quo as the spit migrates to the east. Previously constructed groin 

 systems and beachfill projects have not halted the erosion. A l:50-scale 

 (undistorted) physical model was constructed to aid in evaluating the use of 

 segmented detached breakwaters at the site. The model reproduced 2,865 m of 

 shore, including a portion of the existing groin field, and a relatively un- 

 structured section of shore. This permitted study of the interaction of the 

 proposed breakwaters with two beach types. Of particular interest was the 

 positioning of the breakwaters with respect to the existing groins. Figure CI 

 shows the extent of the shore and offshore which was modeled. 



3. A prototype segmented breakwater with three segments was constructed 

 on Presque Isle Peninsula in 1978. Monitoring the shoreline response to this 

 field test provided enough data to verify a sediment movement model. A 

 movable-bed section was constructed in the model test basin using a fine coal 

 sediment (d sn = 0.5 mm , specific gravity = 1.35). A shoreline response simi- 

 lar to that observed in the prototype was experimentally duplicated. 



Figure C2 shows how the model and prototype compared after an accretionary 

 period (Figures C2a,b), and then after the winter season when higher water 

 levels and severe wave conditions cut back the previous tombolo development 

 (Figures C2c,d). 



4. Testing of the study area (Figure CI) followed for the existing (or 

 base) conditions and included (a) measurement of the wave-generated current 

 and water circulation patterns, (b) tracer tests (in which the coal sediment 



CI 



