(a) Project . Breakwaters for wave protection and preven- 

 tion of shoaling. 



(b) Reference . Giles and Chatham (1974). 



(c) Laboratory . WES. 



(d) Test Period . July 1972 to October 1973. 



(e) Problem . Severe shoaling of Port Orford Harbor began 

 shortly after construction of a 600-foot-long breakwater in 1968. This 

 breakwater (built to provide wave protection for the existing pier) inter- 

 cepts and traps the south-to-north littoral transport when waves are from 

 the south and alters current patterns when waves are from the north so 

 that the north-to-south littoral currents cannot move sediment out of the 

 harbor. Extensive maintenance dredging has been required. 



(f) Purpose of Model Study . The model study was conducted 

 to (a) compare prebreakwater and existing breakwater conditions to deter- 

 mine the causes and sources of harbor shoaling, and (b) develop cost- 

 effective remedial plans to eliminate shoaling at the pier without sig- 

 nificantly increasing wave action. 



(g) The Model . The undistorted, l:100-scale hydraulic 

 model reproduced the entire harbor area, approximately 3 miles of shore- 

 line, and underwater contours to an offshore depth of -60 feet (Fig. 5-2). 

 The total area reproduced in the model was approximately 10,300 square 

 feet, representing about 3.7 square miles in nature. 



in J lest rroceaures . lestb coiisistea or measuring wave 

 heights and wave- gene rated currents, obtaining photos of wave, current, 

 and shoaling patterns, and visual observations. Using the procedures 

 discussed previously for the scaling relations of Noda (1972), crushed 

 coal (median diameter, 0.55 millimeter; specific gravity, 1.30) and nylon 

 (median diameter, 3.0 millimeters; specific gravity, 1.14) were selected 

 as tracer materials to simulate the prototype sand (median diameter, 0.21 



illimeter; specific gravity, 2.65), 



mi 



(i) Plans Tested . Initial tests were conducted for pre- 

 breakwater and existing breakwater conditions to determine the causes 

 and sources of harbor shoaling. Improvement plans consisted of modifi- 

 cations to the existing breakwater (removing sections, lengthening, rea- 

 linement, etc.) and installation of new breakwaters near Fort Point and 

 Battle Rock. 



(j) Summary of Test Results . Test results indicated that 

 (a) the source of sediment was the area seaward and to the east of Battle 

 Rock; (b) the modification of the existing breakwater was not a viable 

 alternative; and (c) a new 1,100-foot-long breakwater extending from Fort 

 Point would be required to completely prevent harbor shoaling. Shoaling 

 patterns for existing conditions and the recommended plan are shown in 

 Figures 5-3 and 5-4. 



298 



