42 EFFECTS OF WINDS AND OF 



Under the conditions stated, 



V- _ _ - (54) 



area of cross-section of the stream D 



By substitution from (53) and (54) in (52) there is obtained 



From the foregoing equation by solution for S there is obtained 



(55) 



C 2 \D 



Q' 2 

 in which is a constant, during the steady regime under consideration, 



o 



which will be called C\. 



Q2 



This constant, C\ = , depends on the influences which fix C, the Chezy 







coefficient, and upon the action of the wind upon the water, which fixes Q. 

 Equation (55) may for the present purpose be conveniently written thus : 



(56) 



Let the difference of elevation of the surface of the water at any two points 

 along the axis of the strip under consideration be called Hd and let the dis- 

 tance between the two points be called L. 



Then 



Hd = SL (57) 



From (56) and (57), for any short portion of the strip on which D is con- 

 stant, 



(58) 



In general, under the influence of a steady wind, the surface of the water 

 along any strip during the steady regime will have some such shape as that 

 shown in the curve labeled "disturbed water surface" in figure 1, plate 4. 

 On that curve, which is drawn for a strip on Lake Erie along the line BB 

 and for a west wind, the surface of the western part of the strip is shown 

 depressed below, and along the eastern part elevated above, the normal 

 elevation which it would have if no wind were blowing. One point on the 

 curve, there shown at 1,027 thousands of feet west of the Buffalo gage, is 

 shown as unchanged in elevation by the wind. Call such a point the nodal 

 point of the strip. 



Let H be the total disturbance of elevation of any point on the strip under 

 consideration. 



