Introduction
The goals of our project are to evaluate the coastal area attributes that contribute to high reflection coefficients and large waves. We chose this project for its relevance to the Coastal Engineering class and the opportunity for hands on experience in conducting experiments as well as wave transformation analysis. Our project also applies to practical applications in engineering coastal structures and evaluating beach characteristics in a way that mitigates damage from large waves.
Wave reflection is a process that can return (rebound) incident waves when the
waves impinge on a structure or sloping bed. Reflection occurs when an
incoming wave hits the shore and is rebounded back to the open water. The
magnitude of reflection is determined by the reflection coefficient, Kr:
Hr = Kref*Hi
Hmax = Hi + Hr
Hmin = Hi – Hr
(picture courtesy of Chin Wu)
Kr = Hr/Hi = (Hmax – Hmin)/(Hmax + Hmin)
Many factors affect the reflection coefficient. Of the beach characteristics, there are surface roughness, porosity and slope. Other factors include the frequency and steepness of the oncoming wave. Bellow is a table of the various factors and their relationship to Kr:
Beach factors Reflection Coefficient
| surface roughness | larger for smooth surfaces, smaller for rough surfaces |
| porosity | larger for impervious surfaces, smaller for porous surfaces |
| slope | larger for steep slopes, smaller for gentle slopes |
Other factors Reflection Coefficient
| wave steepness | larger for steep waves, smaller for flat waves |
| wave frequency | larger for low frequency, smaller for high frequency |