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produced by a wave generator, which can be reoriented to obtain directionality 

 of the waves. Monochromatic waves have been used in previous studies of 

 Curren and Chatham (1977, 1980), Bottin (1982), and Seabergh (1983), but 

 capabilities currently exist for generating irregular waves for future studies. 

 Results of fixed-bed modeling can assist in the determination of breakwater 

 location to minimize rip current occurrence, scour around structures, offshore 

 sediment transport, and hazards to swimmers. These results are also used to 

 evaluate wave attenuation characteristics for various wave conditions, water 

 levels, and breakwater lengths. 



Tracer studies. Sediment tracer studies are conducted by placing 

 lightweight sediment as a thin veneer over the fixed-bed bottom contours and 

 observing the location of sediment accumulation and direction of transport. 

 This technique was successfully used by Bottin and Chatham (1975). 

 Selection of the tracer material is based on criteria of Noda (1971), which 

 relates model to prototype ratios of sediment size, specific gravity, and 

 horizontal and vertical model scales. Noda's method assumes a distorted scale 

 exists in a movable-bed model. Because an undistorted model is used for 

 fixed-bed modeling to accurately model wave refraction and diffraction, a 

 range of tracer sediment sizes is determined by using the vertical scale ratio 

 first and then the horizontal scale ratio to evaluate sediment size scale ratios 

 for the same specific gravity. In the Presque Isle, Pennsylvania, study 

 (Seabergh 1983), the prototype sediments varied from natural sands with 

 median diameters ranging from 0.11 to 0.25 mm to coarser sands used for 

 beach fill with a median diameter of 1.8 mm. Using the Noda method for 

 crushed coal specific gravity of 1.35, the model sediments were required to be 

 2.05 to 2.69 times the prototype size. Therefore, the crushed coal particle 

 diameter ranged from 0.22 mm (2.05 x 0.11) to 4.84 mm (2.69 x 1.8), and 

 0.5-mm crushed coal was used in the tracer study. Results may be used to 

 evaluate the effects of breakwater distance offshore on longshore sediment 

 transport and to duplicate qualitative tombolo development. 



Movable-bed modeling. A movable-bed model section is constructed and 

 inset in an area of the fixed-bed model. Wave conditions, water levels, and 

 sediment size are adjusted to produce the documented prototype phenomena 

 (base case) and then the same hydrodynamic conditions are used with the 

 different improvement plans installed in the model, one at a time, to 

 demonstrate effects on the shoreline. The sediment size for the model is 

 determined by the same technique as described for the tracer tests, only 

 different scaling criteria may be selected. In the Presque Isle study, a 0.9-mm 

 crushed coal was used to model the beach fill sediment. The model sediment 

 is continually fed along the shoreline interface where sediment is removed as a 

 result of wave effects. These tests take considerable time to allow the 

 sediment to redistribute itself and to show effects of the in-place detached 

 breakwater structures on improving the stability of the shore material. The 

 model results give only qualitative information on the sediment transport. 

 Results may be used to evaluate bathymetry response to a detached breakwater 

 and beach fill readjustment due to the breakwater. 



Chapter 3 Tools for Prediction of Morphologic Response 



