LONGSHORE SAND TRANSPORT STUDY AT CHANNEL 

 ISLANDS HARBOR, CALIFORNIA 



hy 

 R.O. Bruno J E.G. Dean, C.G. Gable, and T.L. Walton, Jr. 



I , LMTRODUCTION 



1. Purpose. 



The relationship between longshore sand transport in the surf zone and wave 

 energy is of vital interest to coastal engineers concerned with design and main- 

 tenance of navigation and beach erosion control projects. As discussed in the 

 Shore Protection Manual (SPM) (U.S. Army, Corps of Engineers, Coastal Engineering 

 Research Center, 1977), past field and laboratory studies have produced a widely 

 used empirical relationship for sand transport in a shore-parallel direction; 

 however, these studies were conducted in areas where total transport may not 

 have been measured. In this study, Channel Islands Harbor, California (Fig. 1) , 

 was selected for measuring longshore sand transport because an offshore break- 

 water and twin jetties at the site form a unique sand trap. This site is 

 considered to be nearly a total littoral barrier to longshore sand transport 

 moving in a southerly direction (Herron and Harris, 1966). A further advantage 

 to the Channel Islands site is its exposure to high wave energy climate with a 

 dominant wave direction out of the west and northwest and consequently, high 

 sand transport rates in a predominantly southerly direction along the beaches. 

 Dredging records from the harbor show annual transport in excess of 1 million 

 cubic meters (Herron and Harris, 1966). The objective of this study was to 

 obtain additional data on longshore sand transport in order to reevaluate the 

 present semiempirical relationship for longshore sand transport given in Chapter 

 4 of the SPM. 



2. Location and History . 



Channel Islands Harbor is located about 110 kilometers northwest of Los 

 Angeles and 1.6 kilometers upcoast (northwest) of Port Hueneme (Fig. 1). The 

 harbor consists of entrance jetties and an offshore breakwater which were 

 constructed to provide a solution to a downcoast beach erosion problem and to 

 provide a small-craft harbor. Before the harbor construction, a serious 

 erosion problem existed downcoast (southeast) of Port Hueneme which has been 

 attributed to diversion of littoral sands into the Hueneme Canyon by the Port 

 Hueneme north jetty. Presently, sand trapped at Channel Islands Harbor is 

 bypassed to the south of Port Hueneme by periodic dredging (U.S. Army Engineer 

 District, Los Angeles, 1948; Herron and Harris, 1966). 



The offshore breakwater is 700 meters long, is located 600 meters offshore 

 in a water depth of 9 meters, and trends roughly parallel to the shore. The 

 design of the sand trap was developed empirically by considering the configu- 

 ration of the Santa Monica, California, breakwater fillet and by developing 

 diffraction patterns for generally prevailing waves (U.S. Army Engineer 

 District, Los Angeles, 1948; Herron and Harris, 1966). 



3. Physiography and Littoral Processes . 



The shoreline at the site forms the coastal edge of the Oxnard Plain, an 

 abandoned flood plain of the Santa Clara River (Fig. 1). The low, flat flood 



