Wave Impact Height (WIH)
Wave impact height (WIH) is the elevation of wave runup, based on the plane and slope of the beach, minus the elevation of the toe of the bluff. This concept is illustrated in the figure below. Imagine that the bluff was not present and a wave was allowed to runup the same plane of the beach slope. This wave would runup to a certain elevation as predicted by the wave runup formulas. However, if the bluff is inserted into the picture the wave will impact the bluff, and, again, the WIH value associated with this condition is the elevation the wave would have reached if the bluff were not present minus the elevation of the toe of the bluff.
Positive values of WIH are believed to contribute directly to the erosion of bluff material, whereas negative WIHs will not directly cause erosion of the bluff.
A WIH curve for one year of buoy data is shown below. Note the red dashed line in the figure below; this line is the still water level. Still water levels were changed each month according to historical water level records.
Definition of wave impact height. WIH = wave impact height, SWL = elevation of the still water level, WS = wind setup, R* = wave runup in absence of bluff, TOE = elevation of bluff toe
Considerations for beach orientation and wave direction have been built into the WIH analysis. Also, ice cover has been accounted for based on ice coverage maps in Driver et al. (1992).
To compare different sites to each other based on WIH, a cumulative measure of WIH is needed. The cumulative measure chosen to compare WIH at different sites and to recession rates is the area under the WIH curve above the threshold value of zero, which represents the bluff toe elevation. This method is chosen to include both magnitude and duration in the cumulative measure. This cumulative measure is simply termed cumulative WIH (CWIH).