Waves may transport large volumes of sediment. In some 

 circumstances, especially for longshore transport, the direction of 

 sediment transport can be predicted, but estimates of the transport rate 

 can be an order of magnitude wrong. For transport perpendicular to the 

 coast, it is often difficult to predict even the direction of net 

 sediment transport. Given the uncertainty about sediment transport by 

 currents alone or by waves alone, it is very difficult to predict the 

 effects of waves and currents together on sediment transport. 



A difficulty inherent in any sediment transport problem is the 

 appropriate description of the sediment. Even though sediment size and 

 density can be surprisingly uniform, the variation encountered adds 

 complexity to any computation. (On the other hand, the remarkable 

 ability of oscillating flows to sort materials by size and occasionally 

 by density suggests that the techniques of minerals processing should be 

 examined for improving fundamental understanding of sediment transport.) 



Next, consider the difficult distinction between bedload and 

 suspended load in wave-induced sediment transport. First, it is 

 difficult to define bedload in a way that has practical meaning in 

 interpreting measurements, even when only currents are considered. 

 Second, the addition of waves to even small currents is likely to 

 increase both bedload and suspended -load transport. Bedload transport 

 due to waves and currents has been reported from laboratory experiments 

 by Inman and Bowen (1962), Abou-Seida (1964), and Tanaka, Ozasa, and 

 Ogasawara (1973). The difficulty of interpreting these experiments is 

 seen from results for coal by Tanaka, Ozasa, and Ogasawara (1973). 

 Seven out of eight of their measurements show the net bedload transport 

 to be opposite to the direction of the current. Bijker, van Hijum, and 

 Vellinga (1976) include a few measurements of wave and current sand 

 transport, and they note that in the absence of current the direction of 

 sand transport depends upon wave shape. See also van de Graaf and 

 Tilmans (1980). 



Another difficulty in predicting sediment transport is the 

 influence of bed form. First, it is difficult to predict the bed form 

 that will result, and second, it is more difficult to predict the effect 

 of bed forms on sediment transport rates. For currents without waves, 

 the shape of the bed form depends on depth, velocity, and sand size, but 

 available information on the relations among these variables has, to 

 date, come largely from laboratory facilities (Southard, 1971; Southard 

 and Boguchwal, 1973). Extension of these relations to prototype scale 

 is uncertain for the current only case; considerably less is known for 

 the wave and current case, particularly for storm conditions on a 

 prototype scale when most of the transport occurs. 



For sediment in suspension, the turbulence and the current are two 

 important factors. Measurements of turbulence with good spatial 

 distribution under a combination of waves and currents are reported by 

 Iwagakl and Asano (1980) and Kemp and Simons (1982). Kemp and Simons 



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