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



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



GIVEN: Lake Erie has a mean depth of d = 61 feet and its length % is 

 220" miles or 116,160 feet. 



FIND : The fundamental period of oscillation T-, if j = 1. 

 SOLUT ION : From Equation 2-83 for an enclosed basin, 



4 1 



211, 

 T 



1 



T. = 



2(116,160) 



» 1 [32.2(61)]^^ 



Tj = 52,420 sec. or 14.56 hrs. 



Considering the variability of the actual lake cross-section, this 

 result is surprisingly close to the actual observed period of 14.38 

 hours (Platzman and Rao, 1963). Such close agreement may not always 

 result. 



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

 Note: Additional discussion of seiching is presented in Section 3.84. 



2.54 WAVE REFLECTION FROM BEACHES 



The amount of wave energy reflected from a beach depends upon the 

 roughness, permeability and slope of the beach in addition to the steep- 

 ness and angle of approach of incident waves. Miche (1951) assumed that 

 the reflection coefficient for a beach x> could be described as the 

 product of two factors by the expression, 



X = X,X2 , (2-85) 



where x-, depends on the roughness and permeability of the beach and is 

 independent of the slope, while Xz depends on the beach slope and the 

 wave steepness. 



Based on measurements made by Schoemaker and Thijsse (1949), Miche 

 found that x, *» 0-8 for smooth impervious beaches. A value of x * 0.3 



2-117 



