inland areas, can extend the zone of wave attack inshore, and can increase 

 hazards and damage. Strong offshore winds can similarly produce decreased 

 water levels. 



Storm surges, as products of the weather, can be studied by hindcast 

 methods from historical weather charts in the same general manner as waves. 

 The magnitude of water-level change is dependent upon wind velocity and 

 direction, fetch, depdi of water, and slope of the inner shelf (Shore Protection 

 Manual 1984), as well as the orientation of the storm system in relation to the 

 coast. As with tides, the configuration of the coast may influence water 

 levels, with increased elevations being particularly common in embayments. 



In many cases more direct records of storm surge can be obtained from 

 tide gages and measurement of high-water marks following the storm. In 

 recent years, there has been an increasing volume of work in storm surge 

 modelling and prediction. The Sea, Land and Overland Surges from Hurri- 

 canes (SLOSH) model (Jelesnianski and Chen 1982) and the Special Program 

 to List the Amplitudes of Surge from Hurricanes (SPLASH) models 

 (Jelesnianski 1972) are among the most widely used. 



Tsunamis 



Tsunami is a Japanese term used widely in the scientific literature to refer 

 to a train of progressive long waves generated by an impulsive disturbance 

 either in the ocean or a small body of water. A tsunami is usually caused by 

 a severe earthquake. Tsunami waves have periods of several minutes to 

 several hours and can move at speeds of 700 to 900 km/hr in the open ocean, 

 depending upon water depth. Upon approaching shallow water, their speed 

 decreases but their wave height increases dramatically. 



While tsunamis are rare, they have the potential to cause extreme 

 geomorphic change and damage to structures. Crustal movements around the 

 Pacific basin are likely to cause tsunamis. Islands in the center of the Pacific 

 basin, such as Hawaii, can receive effects from multiple sources, and are 

 particularly vulnerable. 



20 



Relative Sea Level 



Changes in relative sea level occur when there is (a) a general eustatic 

 variation of sea level, (b) uplift or subsidence of a coastal landmass, or (c) a 

 combination of the two. The net gain or retreat of land along coasts is 

 influenced by the combination of sea level changes and changes in erosion or 

 accretion over time (Bloom 1965). Transgression, the landward migration of 

 the shoreline, usually occurs with rising relative sea level unless a high rate of 



Chapter 2 Relevant Processes and Factors 



