inlets toward amplifying tsunami runup (eg. Figures 

 72, 133). 



(h) The historical evidence for tectonic earth 

 movement, whether horizontal, vertical, or "both. 



(i) The geological nature and stahility of the 

 coastal area, particularly the susceptibility to 

 submarine landsliding, earth avalanches, and to 

 consolidation under vibration. 



(j) The history of tsunami inundation for the region. 



All these considerations amount to a risk analysis for defin- 

 ing a design earthquake or a design tsunami. In this, sta- 

 tistical guidelines such as Figures 17, 23, 28, ^1, and 71 or 

 Equations (2), (3), (6), and (l9) may be useful. Distribution 

 functions of frequency of occurrence of tsunami runup height 

 (cf. Wiegel, I965 ) are also helpful. The economic aspects of 

 the problem should determine whether tsunami barriers are 

 both feasible and justifiable. 



(2) Estimates of water velocity likely to be encountered at 

 different places from the design tsunami should properly take 

 account of the wave propagation in the area. If bore forma- 

 tion is expected, velocities at the front are calculable from 

 Equation (D-17) (Appendix D) with K = 2.0, say. If bore 

 formation or breaking does not occur, velocities may be 

 calculated from Equation (D-2) or (D-20). 



(3) Water forces on objects, which are not unreasonably large, 

 may be calculated by use of Equation (D-I6), Appendix D. The 

 Reynolds number appropriate to the flow and the shape of the 

 object should be determined in order to arrive at a suitable 

 value of drag coefficient Cp. More careful analysis may be 

 needed to allow also for lift-forces developing from the flow 

 between the object and its support. 



(h) Water forces on objects which present large continuous 

 surfaces such as breakwaters , seawalls , large buildings , 

 highway embankments, etc., may be calculated by use of 

 Equation (D-2U), Appendix D, or its simplification Equation 

 (5iii). If the latter, an appropriate value of the pressure 

 coefficient C needs to be chosen between the range 1 to iH. 



Harbor Structures 



(1) Breakwaters should have stone or blocks of sufficient 

 weight to resist the flow of water at expected scour- 

 velocities from overtopping. 



378 



