The wind stress coefficient is based on one given by Van Dom (1953) and 

 others which is assiomed to be a function of wind speed; thus, 



k = X , for W < W^ (3-58) 



(3-59) 



where the constants Kj^ and K2 are usually taken to be 1.1 x 10"^ and 

 2.5 X 10"^, respectively. W^ is a critical wind speed taken as 14 knots 

 (16 miles per hour) . 



Introducing the bottom and free-surface stress relations into 

 Equations 3-53 and 3-54 gives 



(3-60) 



(3-61) 



an estimate of the amount of setup that can be attributed to the onshore 

 effects. The setup attributed to longshore effects can be obtained by 

 rewriting Equation 3-60 in the following two-component form: 



^ _ kW^ cos 6 (3-62) 



ax " gD 



^ = iY^ (3-63) 



ax gD 



The total setup along the x-axis is the sum of the two components or, 



^ = !!^ + !!z (3-64) 



ax ax ax 



In the finite-difference niomerical solution of the reduced equations, 

 values of S^ and Sj. are evaluated at points spaced Ax apart along a 

 single Cartesian axis (the traverse line). The values of S, the total 

 setup for the increment, can be regarded as being the water level midway 

 between two points along the traverse line, midway between x and x + Ax 

 at a time t. The longshore volume transport of water V is also evaluatei 

 between points. Wind stress data and the Coriolis parameter are supplied 

 at the points x and x + Ax. The subscripts and superscripts i and n 



3-104 



