Under the Federal navigation project for Mission Bay, dredging of the 

 entrance channel and deposition of spoil on Ocean Beach at no cost to 

 any project for shore protection has recently been completed. In order 

 to obtain the maximum benefits from this beach fill, it was essential 

 that the groin considered in this report be built prior to northward 

 shifting of the fill by summer waves. Accordingly local interests pro- 

 ceeded with construction of the groin at Cape May Avenue and the shore 

 protection project for Ocean Beach, as recommended by the reporting 

 officers, is now substantially complete. 



Imperial Beach is a small residential community with a population 

 of 285. It lies on the ocean shore about 3.5 miles north of the Mexican 

 border. The improved frontage where protection is required has a narrow 

 sandy recreational beach about 6,300 feet long. The southerly section, 

 5,700 feet long, is owned by San Diego County and the northerly section, 

 600 feet long, is Federally owned and occupied by the U. S. Naval Radio 

 Station. The ocean waters in the Imperial Beach area are contaminated 

 by sewage discharged by the international sewer 0.7 mile north of the 

 international boundary. Efforts are being made to correct this condition. 

 At Imperial Beach the problem is one of gradual erosion which has re- 

 duced the beach width. The erosion has been caused by inadequate natural 

 supply of beach material. Control structures which have reduced flood 

 flows in the lower Tia Juana River, coupled with lack of floods since 

 1928, have greatly reduced the volume of detritus brought to the shore. 

 The lack of protective beach has exposed upland public and private 

 property to damage. Restoration of the former width of protective and 

 recreational beach and prevention of further erosion are desired. 



Coronado is a residential city on the peninsula separating San 

 Diego Bay from the ocean. The present problem area is at Bay View Estates, 

 a development on the bay side of the city between the U. S. Naval Air 

 Station on the west and the ferry landing on the east. The shore is 

 privately owned. The bay shore at Coronado consists of eroding low clay 

 bluffs. No material moves into the area to supply the beach, and the 

 eroding bluffs contribute little material of adequate size to form a pro- 

 tective beach. Property owners desire determination of the most economical 

 means of stabilizing the shore. 



The tides on the ocean shore of the study area have a diurnal 

 inequality, the mean and diurnal ranges being respectively about 3.7 and 

 5.3 feet. In the northern part of San Diego Bay the ranges are 4.2 and 

 5.8 feet. The maximum tide each year is about 7 feet above mean lower 

 low water. Characteristic waves are swells generated in distant ocean 

 areas. They have heights up to 10 feet and periods up to 20 seconds 

 with the greater heights and shorter periods occurring in the winter. 

 Winter waves generally approach the shore from upcoast of normal, summer 

 waves frequently approach from downcoast of normal. In San Diego Bay 

 waves are those generated by local winds and ship traffic. They have a 

 maximum height of about 2 feet and periods of about 3 seconds and approach 

 the shore from west of normal. 



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