plain extends about 21 kilometers along the shoreline and 13 kilometers inland, 

 and is bounded on the north by the Sulphur Mountains and on the south by the 

 Santa Monica Mountains. These mountains terminate at the sea in hard, wave- 

 resistant formations, forming the south bank of the Ventura River and Point 

 Mugu, respectively. The principal drainage features are the Ventura and Santa 

 Clara Rivers. Offshore slopes in this area are gentle except where the steep- 

 walled Hueneme and Mugu submarine canyons cut the Continental Shelf to within 

 0.4 kilometer of the shore. 



Figure 2 is a view of the study area in relation to offshore islands and 

 shows that much of the wave action is intercepted or modified by Point 

 Conception or the offshore islands. The principal avenues of wave approach 

 are from the same direction, hence, sea and swell arrive predominantly from 

 the northwest and west. Local winter storms of short duration and a limited 

 amount of summer swell, originating from the south Pacific Ocean, reach the 

 Hueneme area from the southwest and create short periods of northward littoral 

 drift. However, wave studies and long observation of the shoreline processes 

 show conclusively that there is a great preponderance of southward littoral 

 drift (Herron and Harris, 1966). 



There is one source area of littoral material, in addition to updrift 

 beaches, for the Channel Islands study site (Fig. 1) — the Santa Clara River 

 which discharges at the upper end of the Oxnard Plain. At irregular intervals 

 of 10 to 30 years, tremendous floodflows occur that form a large delta at the 

 mouth of the river extending as much as 0.8 kilometer seaward of the normal 

 alinement of the shore (Herron and Harris, 1966). However, there is no accurate 

 measure of the rate at which littoral material is supplied by the river. 



At Port Hueneme, the Hueneme submarine canyon extends to within about 300 

 meters of the shore and is the one miajor sink for littoral materials in the 

 Channel Islands area. The profile from mean lower low water (MLLW) to the 

 -18-meter depth steepens from a normal of 1 on 100 to 1 on 4 into the canyon. 

 The steep slopes of this canyon continue to depths as great as 1.5 kilometers. 



Past estimates of littoral sand transport have shown a net southward sand 

 transport on the order of 920,000 cubic meters per year for the beach area 

 between the Hueneme and Mugu submarine canyons, based on shoreline erosion 

 surveys before the Channel Islands bypassing operation (Herron and Harris, 1966). 



The entrance to Channel Islands Harbor was dredged in 1960-61, and since 

 that time the material impounded in the sediment trap has averaged approximately 

 1 million cubic meters per year; the capacity of the trap is approximately 2 

 million cubic meters. The material is usually pumped (on a biennial basis) a 

 distance of about 2 kilometers to the downdrift side of the entrance to Port 

 Hueneme, although material is occasionally placed in the "pocket beach" formed 

 by the southeastern jetty to Channel Islands Harbor and the northwestern jetty 

 to the Port Hueneme entrance approximately 1.6 kilometers to the southeast 

 (Herron and Harris, 1966). 



The net sediment transport is from northwest to southeast, but periods of 

 reversal do occur. The average sediment size at the site is approximately 

 0.20 millimeter, the textural characteristics of the material deposited in the 

 trap were reported in Bruno, Watts, and Gable (1977). 



