ESTIMATION OF WAVE REFLECTION AND ENERGY DISSIPATION 
COEFFICIENTS FOR BEACHES, REVETMENTS, AND BREAKWATERS 
by 
Willtam N. Seeltg and John P. Ahrens 
I. INTRODUCTION 
When a wave encounters a coastal structure or beach, a part of the wave 
energy is dissipated. The remaining energy is reflected seaward except in the 
case of a permeable or overtopped structure (Fig. 1), which allows transmission 
of a part of the energy to the leeward side. Wave reflection may have undesir- 
able effects because the reflected waves are superimposed on the incident waves 
to increase the magnitude of water particle velocities and water level fluctu- 
ations seaward of the structure. These enhanced motions may be a hazard to 
navigation or may undesirably alter sediment transport patterns. This report 
presents methods for estimating wave reflection coefficients for beaches, 
revetments, and breakwaters of waves approaching the structure at a normal angle 
of incidence (wave crests are parallel to the structure axis). 
II. LITERATURE REVIEW 
Previous investigators have experimentally and analytically studied wave 
energy dissipation and reflection characteristics for a variety of structures. 
Various prediction techniques have been proposed to estimate reflection coef- 
ficients for specific types of energy dissipation. Miche (1951) proposed a 
wave reflection-coefficient prediction technique that is often quoted in lit- 
erature (e.g., Sec. 2.54 in U.S. Army, Corps of Engineers, Coastal Engineering 
Research Center, 1977). He assumed that there is some critical deepwater wave 
steepness below which the reflection coefficient is a constant. For conditions 
where wave steepness is greater than the critical value, the reflection coef- 
ficient is proportional to the ratio of the wave steepness to the critical 
value of wave steepness. Predictions using Miche's approach give the right 
order of magnitude estimate of the reflection coefficient, but as Ursell, Dean, 
and Yu (1960) illustrated, predictions may be conservative by a factor of 2. 
Moraes (1970) has performed some of the most extensive laboratory tests to 
date on monochromatic wave reflection from a variety of smooth and rough slopes. 
$j ____ 
Hj Incident Waves 
ee 
Hy Transmitted Waves 
Reflected Waves Hr 
Kr = Hp / Hj Kt = Ht/Hj 1 
Figure 1. Wave reflection and transmission from a coastal structure. 
