Waves backwash

The sand on a beach displays several interesting features, as seen in the upper color insert on page C-l. Ripples are the marks made in sand by waves that rush onto the shore. Rills are small, branched depressions in the sand that drain water back toward the ocean. Diamond-shaped deposits of silt are backwash marks, places where the shells of animals interfere with the normal backwash of water. Regularly spaced, crescent-shaped depressions along the sand are called cusps. No one knows for sure how cusps form, but many believe them to be due to irregularities along the beach that are enlarged by swash, the water that runs off the beach after a wave breaks. 

When waves move parallel to the coast, they simply move sand and shingle up and down the beach. On the other hand, when they approach the coast at an angle, material is moved up the beach by the swash in the direction normal to that of wave approach, and it is then roiied down the steepest slope of the beach by the backwash. Consequently, material is moved in a zigzag path along the beach. This is known as longshore or littoral drift. Such action can... 

Erosion is a natural process, and the movement of sediment is achieved by wave uprush, which transports sand onshore, and backwash, which transports sand offshore. The natural processes of erosion in coastal areas are very complex and involve flow fields created through not only the action of breaking waves but also erratic turbulent sediment transport in the water column and a shifting shoreline. Worldwide research aims to develop predictive models of this erosion process. Over time and under normal conditions, erosion is also a relatively cyclical process. Sediment can be carried offshore during one season... 

WAVE is based on the legacy DW PS software called ROSA (which was described in the first edition of this book) but there are several key differences as described in Table 10.2. Some of the key differences reflect the multi-technology nature of WAVE. For instance, users can simulate the use of RO permeate or concentrate for backwash, front flush or CIP (Clean-In-Place) purposes using WAVE. 

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