Therefore, 



k^ = 1 + 0.75 (0.3 + 0.1) 0.37 = 1.11 , 



and the corrected overtopping rate is, 



Q^ = 1.11 (5.1) - 5.7 ft3/(sec-ft). 



The total volume of water overtopping the structure is obtained by 

 multiplying Q^ by the length of the structure and by the duration 

 of the given wave conditions. 



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



7.23 WAVE TRANSMISSION 



When incident waves hit a breakwater, wave energy will be either 

 reflected from, dissipated on, or transmitted through the structure. 

 The way incident wave energy is partitioned between reflection, dissipa- 

 tion and transmission depends on incident wave characteristics (period, 

 height and water depth), breakwater type [rubble or smooth faced, per- 

 meable or impermeable), and the geometry of the structure (slope, crest 

 elevation relative to SWL, and crest width). Ideally, harbor breakwaters 

 should reflect or dissipate all wave energy approaching from the sea, and 

 dissipate any wave energy approaching from the harbor. (See Section 2.5, 

 WAVE REFLECTION.) Transmission of wave energy over or through a break- 

 water should be eliminated to prevent damaging waves and resonance within 

 a harbor. When a permeable or low-crested breakwater must be considered, 

 an estimate of the transmitted wave height is necessary. 



For impermeable structures, crest elevation and crest width are 

 important in determining transmitted wave heights. Jeffreys (1944) and 

 Fuchs (1951) studied the transmission of waves over impermeable, submerged 

 breakwaters (crest elevation below the SWL) using linear, small-amplitude 

 wave theory. Because of the small- amplitude assumption, their equations 

 predict no wave transmission when the structure crest elevation is at the 

 SWL. For finite-amplitude waves, energy is transmitted over breakwaters 

 by overtopping even if the crest is above the SWL but below the limit of 

 maximum runup. (See Section 7.21, WAVE RUNUP.) 



Jeffreys (1944) theoretically analyzed transmission of waves over 

 an offshore bar which is similar to transmission of wave energy over a 



7-52 



