longshore transport in the vicinity of Rincon Island. When the Santa 

 Barbara Harbor breakwater created a barrier to downcoast longshore trans- 

 port a serious accretion problem occurred on the upcoast side of the harbor 

 and an equally serious beach erosion problem developed downcoast. It has 

 been necessary to restore the longshore transport at Santa Barbara by sand 

 bypassing - dredging on the upcoast side and depositing the dredged sand 

 on the downcoast side. There are no significant gains or losses of litto- 

 ral material between Santa Barbara and the Ventura River, and throughout 

 this region the prevailing waves are westerly. The estimated average 

 annual accretion of sand at Santa Barbara (280,000 cubic yards) is there- 

 fore a fair estimate of the average annual net longshore transport in the 

 vicinity of Rincon Island. 



The downcoast, or southeast, direction of this movement is also well 

 delineated by the shorelines adjacent to Punta Gorda. Immediately upcoast 

 of Punta Gorda the shoreline is a dynamically stable beach oriented along 

 an azimuth of 148°. This stable shoreline orientation is such that the 

 downcoast longshore transport capacity must match the average supply of 

 littoral material. Immediately downcoast the shoreline has an azimuth of 

 about 82°, and the downcoast longshore transport capacity exceeds the 

 supply until the shoreline orientation again approaches an azimuth of 150°, 

 slightly over a mile downcoast from Punta Gorda. The excess longshore 

 transport capacity zone is characterized by a rocky shoreline undergoing 

 erosion and with no sandy beaches. 



The potential problem of the island's interference with littoral trans- 

 port processes was considered during its design. An offshore structure's 

 interference with longshore transport arises from a reduced longshore 

 transport capacity caused by wave attenuation in the shadow of the island. 

 Tlie affected area becomes an accretion zone, and where attenuation is great, 

 the beach will build out to the structure. Considering the island's dis- 

 tance offshore in the direction of its shadow, (±7,000 feet), and its 

 maximum width of about 500 feet, it was concluded that little interference 

 with longshore transport would result. 



The coastal region from Rincon Point to Pitas Point, the next point 

 below Punta Gorda, has not generated sufficient complaints of beach ero- 

 sion in the past to cause the Corps of Engineers nor any other agency to 

 conduct organized beach erosion studies or measurement programs. However, 

 aerial photos taken in 1947, 1959, and 1967 provide a means of examining 

 the shoreline configuration in the vicinity of the island. Such examina- 

 tions permit a qualitative evaluation and comparison of accretion and 

 erosion processes .over the timespans between these flights. Changes in 

 coastal processes would be reflected by changes in the width of upcoast 

 and downcoast beaches. 



The photographic coverage available for the 1947, 1959, and 1967 

 photography is small scale, ranging from about 1:22,000 to 1:34,000. 

 However, even at these scales, significant differences in shoreline 

 configuration are readily detectable. 



37 



