tanks ware carried forward by the surge and impacted with other tanks. 

 Some of the larger tanks were apparently set into motion by the impact, 

 and most of the tanks were ruptured. A resulting fire destroyed the 

 tank farm. 



Wilson and T0rum also mentioned the problem of a small-craft harbor 

 located immediately in front of a developed shoreline at Kodiak City. 

 The boat harbor contained a large number of fishing boats and yachts 

 which were carried into the adjacent waterfront business area by the 

 tsunami, adding substantially to the damage. Van Dorn (1965) notes that 

 harbor regulations could be instituted requiring ships large enough to 

 damage harbor structures to stand clear of a harbor in the event of a 

 tsunami warning. In the case at Kodiak City there was only about 30 

 minutes between the tsunami warning and the arrival of the first large 

 wave crest of the tsunami (Spaeth and Berkman, 1972). However, when 

 tsunamis are generated from distant sources there may be enough time to 

 clear the harbors. 



An interesting example of impact forces is reported by Wilson and 

 T^rum (1968). During the 1964 tsunami a house was washed out to sea 

 near Point Whiteshed. The house was swept more than 12 miles along the 

 shoreline, carried into the harbor at Cordova, and rammed the dock, 

 destroying the end of the dock. 



e. Hydrostatic Forces . Hydrostatic forces are normally relatively 

 small compared to surge and drag forces. The hydrostatic force on a 

 wall, per foot width of wall, for a water depth h is 



F = | pgh 2 (349) 



As seen in example problem 4, the hydrostatic force would probably not 

 exceed 10 to 20 percent of the drag force at higher water levels, and 

 would appear to be relatively insignificant at lower water levels. 



Once the initial surge has passed a structure, assuming that water 

 levels are equal on all sides of the structure, the hydrostatic force 

 will not contribute to the motion or potential motion of the structure. 

 However, this force can cause cracking of exterior walls and interior 

 flooding of the structure. 



Magoon (1962) indicated that the flooding caused by a tsunami can 

 saturate the fill behind a retaining wall. Combined with the large 

 drawdown of the water level which may occur at the seaward toe of a wall 

 during the withdrawal of a tsunami wave, large hydrostatic forces on the 

 wall may result. It is believed that this contributed to the partial 

 failure of a retaining wall at Crescent City, California. 



There was an unusual occurrence at the abandoned Kahuku Airfield on 

 Oahu during the 1946 tsunami (Shepard, MacDonald, and Cox, 1950). Blocks 



192 



