30.5-m-long extension of the west groin toward the western head of the west 

 breakwater segment (Figure 41). This resulted in a smaller opening between 

 the groin and breakwater; thus, less wave energy penetrated the opening and 

 resulted in only a minor retreat of the west-end shoreline. The model tests are 

 only qualitative, but showed the significance of the groin for local erosion. 



Oceanside Beach model study. Oceanside Beach is a recreational beach 

 located along the Pacific Ocean approximately 129 km southeast of Los 

 Angeles and 48 km northwest of San Diego, California. Persistent erosion of 

 Oceanside Beach and accretion of sand in the Oceanside Harbor and entrance 

 channel have occurred since construction of the Del Mar Boat Basin in 1943. 



As described by Curren and Chatham (1980), an undistorted fixed-bed 

 physical model with a geometric scale of 1:100 was constructed to investigate 

 the arrangement and design of proposed structures for preventing erosion of 

 Oceanside Beach. Froude modeling laws and a crushed coal tracer material 

 were used in modeling existing conditions and several improvement plans. 

 First, tracer material was placed on the fixed-bed model surface at selected 

 locations and fed into the longshore current to determine the mechanisms of 

 littoral movement. Second, the tracer material was placed in a layer 

 representing beach fill on the model surface to determine areas of accretion 

 and erosion. However, the extent of erosion was limited by the fixed model 

 surface. Finally, the fixed-bed contours were removed and remolded using 

 crushed coal to obtain a movable-bed model. This type of modeling is the 

 most reliable for determining areas of accretion and erosion, and it was used 

 for each beach protection plan. 



Figure 41 . Shoreline in model tests with the Lakeview Park recommended plan of a 30.5-m 

 extension of the west groin (Bottin 1 982) 



72 



Chapter 3 Tools for Prediction of Morphologic Response 



