H , =1 meter (3.28 feet) 



sb 



V = 0.20 meter per second (0.66 feet/second) 



LcjU 



W =50 meters (164 feet) 

 X =18 meters (59.1 feet) 



FIND ; Longshore energy flux factor P 

 SOLUTION: 



(a) Using equation (4-52), calculate V/Voru . 



(i) .« = O-Kf ) - O.n* (i) in (i) = 0.33 



(b) Now, using equation (4-51), calculate P 



(9.8) 1025 (1) (50) (0.20) (0.01) .n, , ^ 

 P. = 7~s~"\ •" 387.6 newtons per second 



(■T— )(0.33) (87.13 pounds per second) 



(c) The value of P. corresponds to a sediment transport rate of 499,000 

 cubic meters per year (653,000 cubic yards per year) using equation (4-50) . 



(d) Annual average sediment transport rates for any field site would be 

 estimated from LEO with a P. value obtained by averaging the P 

 values computed for each observation by the above method. 



*************************************** 



d. Energy Flux Example. Assume that an estimate of the longshore 

 transport rate is required for a locality on the north-south coastline along 

 the west side of an inland sea. The locality is in an area where stronger 

 winds blow out of the northwest and north, resulting in a deepwater distribu- 

 tion of height and direction as listed in Table 4-12. Assume the statistics 

 were obtained from visual observations collected over a 2-year interval at a 

 point 3 kilometers offshore by seamen aboard vessels entering and leaving a 

 port in the vicinity. This type of problem, based on Summary of Synoptic 

 Meteological Observations (SSMO) wave statistics, is discussed in detail by 

 Walton (1972) and Walton and Dean (1973). Shipboard data are subject to 

 uncertainty in their applicability to littoral transport, but often they are 

 the only data available. It is assumed that shipboard visual observations are 

 equivalent to significant heights (Cartwright, 1972; Walton, 1972). 



This problem could be solved using Figure 4-39, but for illustration, and 

 because of a slightly higher degree of accuracy possible from the direction 

 data given, the problem is illustrated here in detail. 



In this example, the available data are the joint frequency distribution 



of H and a . For each combination of a and H , the corresponding 



Q , „ is calculated for Table 4-13 in the following manner. The basic 

 ao H 



equation is a form of equation (4-50) written 



O O ^ '00 



4-101 



