The Button Dock in Crescent City survived mainly because of the 

 steel straps and the "bolted connections between the decking and pile caps 

 and the abundant cross-bracing. The absence of moored ships at the dock 

 also helped. 



These findings show the importance of adequate connections between 

 pilings and decking on a timber dock in tsunami-endangered regions. It 

 is equally important that the piles be capable of resisting vertical 

 uplift forces without being drawn out of the ground. 



All the boatfloats in Kodiak Harbor were completely demolished when 

 the piles to which they were attached broke as result of the heavy lateral 

 forces caused by the tsunami. 



The breakwaters at Kodiak City were badly damaged, by settlement 

 during the earth tremors, and by erosion from the tsunami. These break- 

 waters were built mainly to protect the harbor from local wind waves , 

 and the annor stones were not large enough to resist scour from high- 

 velocity water. At Seldovia, Kenai Peninsula, the breakwaters, which 

 were built to protect the harbor against local wind waves, suffered 

 damage from both the earth tremors and the tsunami overtopping. The 

 breakwater at Cordova, Prince William Sound, was apparently undamaged. 

 At Crescent City, California, the breakwaters, built partly with 25-ton 

 tetrapods in the cover layer for protection against large storm waves , 

 also sustained no noticeable damage during the tsunami attack. 



The pattern of structure damage resulting from tsunamis has almost 

 always been the same. Land structures, weakly secured to their founda- 

 tions, have been swept away either by sheer force of moving water or by 

 battery from accumulated debris cascaded in front of an advancing wave. 

 In some cases displacement has occurred merely by lifting of a structure 

 through floatation. In harbor areas, breakwaters have been denuded by 

 weir-action flow across their tops. In dock areas, pile structures have 

 been eroded by scour at the base, battered by ships, or stripped of their 

 decks by buoyant forces. Solid dock walls have been overturned by suction 

 action during wave withdrawals; dock slabs, collapsed by erosion of sup- 

 porting sand fill; retaining walls, undermined and destroyed. 



If the economics justify it, special seawalls, dikes, breakwaters, 

 or barriers may be designed to shield low- lying areas. Such protection 

 may be built on land (in the dry) or in water at advantageous points. 

 Examples are the proposed Hilo Harbor tsunami barrier, the Narragansett 

 Bay storm-surge barriers, and the tsunami-barrier walls built in Japan 

 at Yoshihama and Yamada (cf. Horikawa, I961). Design criteria demand 

 deep and firm foundations, interlocked construction for mass walling, 

 non-erodable revetments and breakwater capping in front and rear, even 

 possible closure gates of unique and dependable design. 



The problem of immunizing dock and harbor facilities is much more 

 difficult. Again economy is a factor which will predicate just how 

 substantial a breakwater or harbor enclosure should be built, or how 



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