subjected to large waves only when winds blow directly onshore. Conversely, 

 sites located on headlands are exposed to waves from many directions. Figure 

 14 illustrates the relationship observed between shore configuration and 

 successful erosion control (Knutson, et al., 1981). Eighty-five percent of 

 plantings in coves were either successful or partially successful. 



c. Sediment Grain Size. In general, low-energy beaches tend to have 

 finer grained sediments and a more steeply sloping foreshore. High-energy 

 beaches tend to have coarser sediments and more gradual sloping foreshores 

 (Wiegel, 1965). Slope and grain size are, therefore, potential indicators of 

 wave climate. Knutson, et al. (1981) found the grain size of the swash zone 

 (the zone of wave uprush) sediments to be an indicator of site planting 

 potential (Fig. 15). Eighty-four percent of the planted sites with mean 

 grain-size values of less than 0.4 millimeter were successful or partially 

 successful. Conversely, 82 percent of sites above 0.8 millimeter were 

 failures. Measurements of shore slope have not been found to be reliable 

 indicators of planting success. 



d. Winds . Winds moving over water transfer energy to the water surface 

 in the direction of the wind. Each geographical region has a characteristic 

 wind climate. Local wind roses are useful in determining the direction from 

 which predominant winds and the most severe storm winds occur. Although wind 

 roses in close proximity to a project area are not always possible to obtain, 

 knowledge of the direction of predominant winds and storm winds can be help- 

 ful. No general methods of interpreting these data to forecast planting 

 success have yet been developed. 



e. Ship-Generated Waves . Shore areas in close proximity to ship traffic 

 will be subject to ship-generated waves. The height of waves produced by a 

 given vessel depends primarily on the speed of the ship and, to a lesser 

 extent, on the hull form, draft, and water depth below the keel (Sorensen, 

 1973) . The wave climate produced by vessels at a particular shore site will 

 depend on the magnitude of the ship-generated waves, traffic frequency, and 

 the distance between the shore and the vessels (Table 1) . 



Of particular importance in Table 1 is the fact that relatively small 

 vessels, such as the cabin cruiser, can produce waves comparable to those of 

 larger craft, such as the fire boat, if the two are proceeding at similar 

 speeds. Table 1 also illustrates that maximum wave height is significantly 

 less at a 150-meter distance from the sailing line than it is at a 30-meter 

 distance. Overall, wave height was reduced from 25 to 50 percent at the 150- 

 meter distance. Though local boating patterns should be considered in deter- 

 mining site suitability, there are no guidelines for using this information to 

 forecast planting success. 



f. Offshore Depth . Offshore depths have a substantial effect on the 

 height of waves that a particular storm will generate. Theoretically, a 

 constant 13.9-meter-per-second wind blowing over water with a constant depth 

 of 1 .5 meters for a distance of 16 kilometers will generate waves less than 

 0.5 meter in height (U.S. Army, Corps of Engineers, Coastal Engineering 

 Research Center, in preparation, 1983). The same conditions for a constant 

 depth of 12 meters will produce waves 0.8 meter high. Therefore, shore areas 

 with shallow offshore depths will be more easily stabilized. 



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