from the WIS hindcast (1956-1987). Each wave condition from the percent 

 occurrence tables was run four times with the COSMOS model to represent 

 four different lake levels (with the duration for each wave condition factored 

 by the fraction of time associated with each of the four representative lake 

 level conditions). Each input wave and water level file consisted of approxi- 

 mately 1,000 conditions. 



For calculations of average annual alongshore sediment transport, the 

 C0SM0S-2D numerical model assumes that the profile shape remains fixed 

 (i.e., profile changes due to cross-shore or alongshore sediment transport are 

 not computed). The selection of input profiles is discussed in Parson, Morang, 

 and Nairn (1996). 



Output from these runs consists of a description of the northerly and south- 

 erly sediment transport components across each profile. Net alongshore 

 transport across the profile is calculated from the two components and total 

 transport for the entire profile is also calculated. Net alongshore sediment 

 transport values are given for each run in Table 3. Positive sediment transport 

 values represent transport to the south. All of the predicted average annual net 

 sediment transport values are directed to the south. Distributions of the aver- 

 age annual net alongshore transport across each profile for the three grain sizes 

 are given in Figures 5, 6, and 7. While the net transport values for the 0- to 

 2-mm runs fall in the range of approximately 70,000 to 80,000 m^/year 

 directed toward the south, a review of the southward and northward compo- 

 nents reveals that the transport is much reduced for the profiles with a revet- 

 ment (i.e., R14 to R23, excluding R22). The southward directed transport 

 component ranges from 375,328 m^ at Line R8 to 170,794 n?/yea.T at R14. 

 These differences in predicted transport rates are related directly to the profile 

 shape since the same profile azimuth was assumed for each line (and since the 

 same wave input was used for each line). Therefore, the low predicted values 

 at Lines R14 and R23 (and to a lesser extent, R17) are a direct result of the 

 deeper profiles at these locations (i.e., due to the absence of a beach at the toe 

 of revetment structures). For Line R12, the peak transport occurs along the 

 inner beach with a secondary peak over the first large bar. Line R14 results 

 show that the peak transport occurs over the first bar offshore of the toe of the 

 revetment. 



Parson, Morang, and Nairn (1996) noted that the prefill beach sediment had 

 a composite djQ of about 0.3 mm and that the natural sediment (i.e., unaltered 

 by beach nourishment) may be best represented by a d^Q of 0.4 mm. There- 

 fore, a second set of alongshore transport calculations were performed with a 

 djQ of 0.4 mm. The results are summarized in Table 3 and presented in Fig- 

 ure 6. For the important southward directed transport component, the pre- 

 dicted values range from 159,500 m^/year at Line R9 to 79,900 m^/year at 

 Line R14. This range of values corresponds more closely to the 

 84,000 m^/year which was estimated by USAGE (1973) to be trapped on the 

 north side of the harbor. One would expect similar values for profiles located 

 north of the harbor. Sediment trapped on the north side of the harbor is 

 derived entirely from the southward-directed transport component (i.e., waves 



Chapter 4 Analyses of Coastal Processes and Geomorphology 



17 



