fundamental or lower harmonic periods of a basin, small, deep basins (with short 

 fundamental periods) triggered by outside waves are more susceptible to surge problems 

 than are large, shallow basins. Also, the wave input at one end may induce a lateral resonant 

 surging in the direction of the short axis of the basin. 



If the ends and sides of the basin are poor wave reflectors, resonant surging will be 

 difficult to induce. Also, if the shape of the basin is irregular or its depths vary irregularly, 

 resonant surging is less likely to occur. Unfortunately, vertical basin walls are usually more 

 desirable than poorly reflective basin perimeters, and rectangular basins are more efficient 

 than irregular basins for berthing arrangements. As a result, some kind of compromise will 

 often be the best solution. 



In large, shallow lakes surging effects may be triggered by wind stress and often produce 

 fluctuations of the water surface level similar to the lunar tides of the ocean. Surge in a 

 river-connected harbor may be the result of navigation-lock operations, and hydrogenerator 

 operations of a major cooling-water withdrawal system. The body of water served by the 

 harbor site should be examined for past records of water level fluctuations and these 

 fluctuations should be considered in the harbor design. Regardless of the cause, surging 

 oscillations are difficult to reduce once the harbor has been built. Therefore, every effort 

 should be made during harbor design to ensure that surging does not reach troublesome 

 proportions in the berthing areas. 



The best way to study harbor surge is by hydraulic-model analysis. This will determine 

 the proper entrance orientation, protective structure positioning, and inner basin 

 configurations required to minimize internal water motion. Progress is being made on new 

 techniques in mathematical analog analysis from computed programming (LeMehaute and 

 Hwang, 1970) to study harbor designs. Although the analysis is not as complete as hydraulic 

 modeling, it does provide a technique to evaluate the basic features of a design. Another 

 method that gives promise of detecting flaws in preliminary design is the acoustic-analogy 

 technique (Morrow, 1966). Acoustic analogy has been used in designing resonator basins at 

 the harbor entrance, which are tuned to specific troublesome wave periods (James, 1970). 

 Such basins resonate to waves with periods within a given bandwidth of the spectrum, 

 regardless of incident direction, and reflect them back out to sea. 



Most recreational boats in a small-craft harbor are insensitive to surge with periods in 

 excess of those normally encountered in sea and swell. Large cruising and commercial craft 

 may experience fender and mooring line difficulties under long-period surging, and any 

 harbor with these vessels should be designed to eliminate its cause. 



c. Tsunamis. These long-period waves of seismic origin are relatively infrequent and 

 normally occur only in the major oceans. The major fault zones that rim the Pacific Ocean 

 have produced most of the tsunamis of record, some of which have caused great damage in 

 the coastal harbors of the U.S. Pacific coast and Hawaii. These waves usually have periods of 

 10 to 20 minutes and travel at speeds of several hundred miles per hour. Because of a low 

 steepness factor they cannot be visually detected in deep water; when these waves arrive at a 

 distant shore they may cause fluctuations of several feet in the water surface elevation. 



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