Wave Runup and Overtopping: A Review and Recommendations

Abstract

ABSTRACT It is not always feasible to design a coastal structure high enough to completely prevent wave overtopping by the maximum incident wave. Structures which are designed against lesser waves, such as the significant wave, will be overtopped under the design storm condition because the incident irregular wave train contains waves which exceed the significant wave height. When the purpose of a structure is to protect sensitive facilities whose failure could result in major environmental as well as economic losses, the rate of overtopping anticipated under the design condition must be predicted with reliable accuracy. The study being reported in this paper evaluates the degree to which wave overtopping can be accurately predicted for a coastal structure in the Arctic environment. In support of this endeavor, an extensive search and review of literature was performed, including reports and papers originating in Japan where the study of wave overtopping has been pursued for a number of years. The study has led to recommended design procedures as the most practical solution available from the current state of knowledge. Discussions on research needs to improve the design procedures are also presented. OVERVIEW Goda (1970) proposed a scaling factor to describe various levels of overtopping intensity, as follows:(Mathematical equation available in full paper) which in this paper will be called the "overtopping index". "Q" is defined as the overtopping volume per wave per unit width of crest, and (HoLo) is the mass transport during the forward orbital motion of a sinusoidal wave in deep water. The overtopping index is non-dimensional. According to Goda (1970), the overtopping index remains in the range of between zero and 10–4 when the overtopping consists only of wave spray. When the overtopping involves wave splash as well as spray, the index will rise to as much as 5 × 10–3. The next higher level of overtopping intensity, consisting of the leading edge of the wave run-up going over the crest of the slope, will raise the index to 10–2 The most severe overtopping situation, in which the wave itself plunges across the crest of the slope, will bring the index to a high of 10−1 Actual overtopping rates may be readily found from the overtopping index assuming a hypothetical storm wave of, say, Ho = 12 feet and T = 10 sec. The overtopping rates {in cubic feet/sec/foot of wave crest) corresponding to the upper limit for each class of overtopping intensity are: 0.01 cfs/ft for spray overtopping, 0.5 cfs/ft for overtopping by wave splash, 1.0 cfs/ft for overtopping by the leading edge of the run-up, and 10 cfs/ft for overtopping by the wave itself. It is obvious that even wave splash could pose a threat of localized flooding, depending upon incident wave characteristics.