Miche (1944) defined the wave reflection at a shoreline in terms of 



hich is g 



1/2 sin 2 g 



a critical wave steepness, (H/L) e , which is given by 



(f)=a 



(179) 



where g is the angle of the beach slope in radians. Complete reflection 

 will occur if the wave steepness, H/L, in deeper water is given by 



urn 



(180) 

 a 



************** EXAMPLE PROBLEM 10 ************** 



GIVEN : A tsunami has a height of 0.5 meter and a period of 20 minutes 

 in a 1,000-meter water depth. The nearshore slope S 3 = 0.1 (8 = 0.0997 

 radians) . 



FIND : If the wave is completely reflected at the shoreline. 



SOLUTION : In the deeper water, the wave celerity, C, is 



C = /gd = /9.807 x 1,000 = 99 meters per second 

 L = CT = 99 x 20 x 60 = 118,800 meters 



0.5 



= 4.21 x 10" 6 



L 118,800 

 From equation (179) 



/H \ u /26_\ 1/2 sin 2 g _ / 2 x 0.997 \ 1/2 sin 2 (0.0997) 



(r) 



c 



= 7.94 x l0 _tf 



H /H\ 



lHl) 



o 

 thus, the wave is completely reflected at the shoreline. 



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

 Wiegel (1964) indicates that where 



(181) 



!>(!). 



89 



