Figure 1-6.—Various types of seawalls.boxes called caissons, each of which is floated over itsplace of location, and then sunk into position. Amonolithic (single-piece) concrete cap is then cast alongthe tops of the caissons. Sometimes, breakwaters andjetties are built entirely of caissons, as shown in figure1-15.A groin is a structure similar to a breakwater or jetty,but it has a third purpose. A groin is used in a situationwhere a shoreline is subject to alongshore erosion,caused by wave or current action parallel or oblique tothe shoreline. The groin is run out from the shoreline(usually there is a succession of groins at intervals) tocheck the alongshore wave action or deflect it awayfrom the shore.A mole is a breakwater that is paved on the top foruse as a wharfage structure. To serve this purpose, itmust have a vertical face on the inner side, or harborside.A jetty may be similarly constructed and used, but it isstill called a jetty.STABLE-SHORELINE STRUCTURESThese structures are constructed parallel with theshoreline to protect it from erosion or other wavedamage.A seawall is a vertical or sloping wall that offersprotection to a section of the shoreline against erosionand slippage caused by tide and wave action. A seawallis usually a self-sufficient type of structure, such as agravity-type retaining wall. Seawalls are classifiedaccording to the types of construction. A seawall maybe made of riprap or solid concrete. Several types ofseawall structures are shown in figure 1-16.A bulkhead has the same general purpose as aseawall; namely, to establish and maintain a stableshoreline. However, while a seawall is self-contained,relatively thick, and is supported by its own weight, thebulkhead is a relatively thin wall. Bulkheads areclassified according to types of construction, such as thefollowing:1-9
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