in which wave energy is added due to wind stress and subtracted due to 

 bottom friction and percolation. This method uses deepwater forecasting 

 relationships originally developed by Sverdrup and Munk (1947) and revised 

 by Bretschneider (1951) to determine the energy added due to wind stress. 

 Wave energy lost due to bottom friction and percolation is determined from 

 the relationships developed by Bretschneider and Reid (1953). Resultant 

 wave heights and periods are obtained by combining the above relationships 

 by numerical methods. The basic assumptions applicable to development of 

 deepwater wave-generation relationships (Bretschneider, 1952b) as well as 

 development of relationships for bottom friction loss (Putnam and Johnson, 

 1949) and percolation loss (Putnam, 1949) apply. 



The choice of an appropriate bottom friction factor f^ for use in 

 the forecasting technique is a matter of judgement; a value of f^ = 0.01 

 has been used for the preparation of Figures 3-21 through 3-30 which are 

 forecasting curves for shallow-water areas of constant depth. These curves, 

 which may be used like Figures 3-15 and 3-16, are given by the equations: 



and 



^ 

 U^ 



= 0.283 tanh 



0.530 1^^ 



2-nU 



= 1.20 tanh 



0.833 



,0.75 



,U^ 



tanh 



gd \ 0.375 



tanh 



(3-25) 



■ ,(3-26) 



which in deep water reduce to Equations 3-21 and 3-22 respectively. 



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



EXAMPLE PROBLEM ************** 



GIVEN : Fetch, F = 80,000 feet, wind speed, U = 50 mph . , water depth, 

 d = 35 feet (average constant depth), bottom friction factor f^ = 0.01 

 (assumed) . 



FIND : Wave height H and wave period T. 



3-46 



