(e) Problem . Marina del Rey, a small-craft harbor designed 

 to provide mooring for about 6,500 vessels, is located in Santa Monica 

 Bay about 15 miles southwest of downtown Los Angeles (Fig. 4-12). The 

 harbor is exposed to wind waves generated from all deepwater directions 

 between west-northwest and south-southwest. After construction of the 

 harbor, waves entering the 1,000 -foot -wide entrance channel were observed 

 to reflect off the vertical, concrete perimeter walls of the harbor, re- 

 sulting in intolerable wave conditions in several of the harbor basins. 



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

 to investigate the existing wave conditions within the marina, and to 

 determine the optimum plan for reducing the wave heights in the harbor 

 basins to an acceptable level (less than 2 feet). 



(g) The Model . The tests were conducted in a three- 

 dimensional, undistorted-scale, geometrically similar replica of the 

 existing harbor basins and jetties with enough area seaward and on either 

 side of the navigation opening to allow proper reproduction of the inci- 

 dent waves (Fig. 4-13). The area of the model was approximately 15,000 

 square feet, equivalent to about 3 square miles in the prototype. The 

 model was constructed of cement mortar to a linear scale of 1:75 (Fig. 

 4-14). Scale selection was based on the depths of water required in the 

 model to prevent excessive bottom friction effects, the absolute size of 

 the model waves, the capability of the existing wave generators as com- 

 pared with those required as a function of model scale, the cost of model 

 construction, efficiency of model operation, and the dimensions of the 

 available shelters. After selection of the linear scale, the model was 

 designed and operated in accordance with Froude's law. Model waves were 

 generated by a 40-foot-long wave generator with a trapezoidal-shaped, 

 vertical-motion plunger. Regular, monochromatic waves were used in the 

 tests. Wave heights at selected locations in the model, measured by 

 electrical wave height gages, were recorded on chart paper by a six- 

 channel oscillograph. 



(h) Test Procedures . From tide level data for the Los 

 Angeles area, the average of the highest tides during each month of a 

 4-year period (1958-1961) was +6.5 feet mean lower low water (MLLW) 

 (U.S. Coast and Geodetic Survey, 1958-61). This value was used in the 

 model tests to minimize the effects of bottom friction. Available deep- 

 water wave data (National Marine Consultants, 1960; Marine Advisers, 

 1961) prepared from hindcasting techniques were used, in conjunction 

 with information from the preparation of refraction diagrams, to obtain 

 the characteristics of shallow-water waves for use at the position of 

 the wave generator in the model. Because of the urgency of the project 

 (wave action in the harbor was preventing use of large areas of the wave 

 basins and was causing damage to some of the perimeter walls), preliminary 

 refraction diagrams were used to position the wave machines during initial 

 stages of model operation. After completion of the refraction study, the 

 previously selected wave directions were found to correspond closely to 

 those calculated; therefore, they were used throughout the remainder of 

 the testing program to avoid repetition of that part of the testing 



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