REVIEW AND COMPARISON OF METHODS FOR ESTIMATING 

 IRREGULAR WAVE OVERTOPPING RATES 



PART I: INTRODUCTION 



Background 



1. As waves of water hit a coastal structure, the water rushes up and 

 sometimes over the structure. These closely related phenomena, wave runup and 

 wave overtopping, strongly influence the design (and the cost) of seawalls, 

 breakwaters, revetments, etc. Accurately estimating the volume rate of over- 

 topping can be vital to design engineers. For example, overtopping of the 

 existing seawall causes flooding at Roughan's Point, Massachusetts, a coastal 

 suburb of Boston. If the seawall were high enough to completely prevent over- 

 topping, it would block the town's ocean view. An alternative which will 

 reduce the flooding is a moderately higher seawall with improved backside 

 drainage. In this situation, a reliable method for estimating overtopping 

 rates for proposed seawall designs is imperative. 



2. Several different aspects of overtopping are important to engineers 

 designing coastal structures. For structures against the shoreline (seawalls 

 or revetments), the amount of water which flows over the structure is impor- 

 tant because of backside flooding. For breakwaters, wave regeneration on the 

 leeward side is an important consideration in harbor design. For rubble-mound 

 breakwaters, the stability of the backside of the breakwater is important. 

 While the different aspects of overtopping are related, this report considers 

 only the first — the amount of water which overtops coastal structures. 



3. Wave overtopping is a complex phenomenon. It includes many of the 

 complexities of both coastal wave transformations (how the waves change as 

 they approach the shore) and wave runup on structures. Even in a generalized 

 case, many variables contribute to overtopping and the relationships between 

 the variables are not well understood. 



Purpose and Scope 



4. This report discusses available methods for estimating overtopping 



