height), and one is at the crest of the tsunami while the other is at 

 the leading edge, the storm wave at the tsunami crest will have a higher 

 celerity (U.S. Army Engineer District, Honolulu, 1960). Therefore, the 

 tsunami can cause one storm wave to overtake and superimpose itself on 

 another storm wave, producing higher waves at the shoreline. 



Storm waves alone may be more severe than a tsunami at some exposed 

 coastal points. Shepard, MacDonald, and Cox (1950) refer to the 

 Kalaupapa Peninsula, on the Island of Molokai, Hawaii, where the 1946 

 tsunami left driftwood at elevations slightly more than 2 meters (7 or 8 

 feet) above normal sea level, but winter storms had left driftwood 6 

 meters above the same datum plane. A combination of a winter storm and 

 a large tsunami could be very destructive. 



Houston and Garcia (1974) assume that tsunami runup on a shoreline 

 will have a runup height (vertical rise) equal to the wave height at the 

 shoreline. This assumption is based on the idea that a tsunami will act 

 like a rapidly rising tide. The assumption was compared with a few cases 

 where both height and runup data were available. For those cases, which 

 included the 1960 tsunami at Hilo, Hawaii, that produced a bore-fronted 

 wave, the predicted value of runup equal to wave height at the shoreline 

 compared well with the maximum runup measured in the area. Nasu's (1934) 

 data for a tsunami occurring in Japan also indicate that the total runup 

 was about equal to the wave height at the shoreline at many locations. 

 Wiegel (1965) reports that maximum runup elevations above MLLW at Crescent 

 City, California, were equal to or greater than the maximum wave height 

 (crest-to-trough) at the Crescent City tide gage for the 1952, 1960, and 

 1964 tsunamis. Magoon (1965) indicates that the 1964 tsunami at Crescent 

 City had an elevation of about 6 meters above MLLW along a substantial 

 length of shoreline, and that the line of maximum tsunami inundation 

 generally followed a contour at that elevation. While the assumption 

 that maximum runup heights will equal the tsunami height at the shoreline 

 provides an initial estimate, this assumption cannot always be used with 

 accuracy. The effects of ground slope, wave period, and the possible 

 convergence or divergence of the runup must be considered. 



The results of Nasu (1934) indicate that the tsunami height at the 

 shoreline and the runup height are dependent on the configuration of the 

 coastline. At Kamaisi, Japan (Fig. 50), on the north side of a bay, the 

 runup height was actually somewhat less than the wave height at the shore- 

 line, equal to slightly more than 3 meters. At Hongo (Fig. 51), at the 

 head of a bay, the tsunami flowed directly up a canyon along a streambed, 

 and the maximum runup height was about 11 meters (36 feet) . At Ryoisi 

 (Fig. 52), the tsunami intruded into a small inlet opening onto the main 

 bay, flowed up a canyon along a streambed and highway, and reached a 

 maximum runup height equal to about 10.5 meters (34 feet). The wave at 

 Kamaisi was probably traveling parallel to the shoreline as it flooded 

 into the bay. The wave at Hongo and Ryoisi was probably traveling in a 

 direction oriented directly along the axis of the canyons as the surge 

 came onshore . 



149 



