PART III: WAVE RUNUP AND OVERTOPPING OF SEAWALLS, SEA DIKES, 

 AND BULKHEADS CAUSING FLOODING AND/OR EROSION 



15. The approach to be used in this section will be to build on the 

 findings made during the recent model study of wave overtopping of the 

 Roughans Point seawall and subsequent model tests of the Cape Hatteras and 

 Virginia Beach seawalls, (Ahrens , Heimbaugh, and Davidson 1986). Other 

 sources of information such as that by Douglass (1986), the extensive study of 

 seawalls and sea dikes conducted at the Hydraulic Research Station, 

 Wallingford, England, and research at the Port and Harbor Research Institute, 

 Yokosuka, Japan, will be investigated. Important recent foreign references 

 are Owen (1982a, 1982b) and Goda (1985). 



16. Findings from the Roughans Point and Cape Hatteras seawall tests 

 will be summarized here because they are a starting point for study of this 

 general problem area, and they provide a conceptual framework for further 

 progress in developing strategies for reducing wave overtopping of seawalls 

 and related coastal structures. The primary purpose of the Roughans Point 

 study was to conduct laboratory tests to determine the overtopping rates for 

 various seawall/revetment configurations. This information will be used to 

 develop a cost-effective plan to reduce flooding due to wave overtopping in 

 the community of Roughans Point, Massachusetts (Hardy and Crawford 1986). 

 Additional Cape Hatteras seawall tests were conducted to extend the findings 

 made during the Roughans Point study to somewhat different seawall profiles, 

 including severely recurved and vertical walls. One of the most important 

 findings from the Roughans Point study was that all of the overtopping data 

 for a revetment/seawall configuration could be consolidated into a single, 

 well defined trend through the use of a new dimensionless freeboard parameter. 

 This parameter seems to be effective even for test series that included 

 several or more water levels and a wide range of irregular wave conditions. 

 The new freeboard parameter F' is defined as follows: 



F ' - : \i/3 (1) 



H L 

 mo p 



where 



16 



