and detached breakwater configurations were proposed. Only those tests 

 involving detached breakwaters will be discussed here. 



12. Model tests were conducted using a crushed-coal tracer material for 

 existing conditions and the various improvement plans under different test 

 wave characteristics. The following three types of tracer tests were used: 



a. Fixed-bed tracer. Tracer material was placed on the fixed-bed 

 model surface at selected locations and/or fed into the long- 

 shore current to determine the mechanisms of littoral move- 

 ment in the study area. 



b. Semimovable-bed . Tracer material was placed in a layer repre- 

 senting beachfill on the model surface to determine areas of 

 accretion and erosion. The extent of erosion was limited by 

 the fixed model surface. 



c. Movable-bed section. The fixed-bed contours in a certain area 

 were removed to a point well beyond the breaker zone and re- 

 molded entirely with crushed coal tracer. This type of test is 

 the most reliable for determining areas of accretion and ero- 

 sion and was used for each major beach protection plan. 



13. Tracer tests for the existing condition produced an onshore move- 

 ment of coal tracer for small waves of low steepness with longshore transport 

 at the shoreline. For high-steepness waves, the coal tracer moved seaward 

 forming a bar at the seawardmost breaker zone. This material migrated north 

 or south depending on wave direction. The high-steepness waves reformed and 

 broke a second time near the shoreline, resulting in a second nearshore zone 

 of longshore transport. Detached breakwater plans tested included a single 

 structure (1,494 m long) with varying crest elevations over 213-m sections and 

 a segmented breakwater consisting of four 203-m-long segments with 203-m gaps. 

 Each plan was tested both with and without groins at the northern and southern 

 extremes of the project. Movable-bed model tests indicated that the test 

 plans without groins would, generally, result in erosion of the shore on the 

 updrift side of the test section and loss of material from the downdrift side; 

 thus, these did not provide adequate protection to the beachfill. The instal- 

 lation of groins reduced the amount of coal leaving the study area, resulting 

 in a fairly stable shore. Views of the model with a single structure and a 

 segmented breakwater in place are shown in Figures CIO and Cll. 



C12 



