Previous Efforts 



176. Only recently have researchers begun using laboratory facilities to examine differences between 

 regular and irregular waves on beach profile development. Consequently, studies documenting the 

 differences are limited. 



177. Mimura, Otsuka, and Watanabe (1986) conducted a series of small-scale, movable-bed model tests 

 using irregular waves. The test flume was partitioned down the center line, and a fine-grained sand 



(0.18 mm) Wcis used on one side while a coarse-grained sand (0.75 mm) was used on the other side. Initial 

 beach slopes of 1:10 and 1:20 were tested, and irregular wave tests were conducted to cover the range of 

 previous tests performed using regular waves. 



178. Mimura, Otsuka, and Watanabe examined several different aspects of sediment transport to 

 determine the most appropriate irregular wave parameter for each case. As a result of their tests, they 

 concluded that the mean wave height of irregular waves gave best correspondence to regular waves when 

 used to predict whether the profiles were either eroding or accreting. The prediction technique they used 

 was formulated with a coefficient based on regular wave tests. They further concluded that use of i/1/3 in 

 the formula required modification of the coefficient. 



179. Threshold of sediment movement under irregular waves was found by Mimura, Otsuka, and 

 Watanabe to be better represented in existing prediction expressions by i/1/3 than by the mean wave 

 height. They based their conclusion on experimental determination of critical depth for motion under 

 irregular waves compared with a formulation previously determined for regular wave tests. They stated 

 that this finding is logical because the sand grains are more responsive to the larger waves in the wave field. 



180. Profile evolution in the Mimura, Otsuka, and Watanabe tests was observed to be much slower for 

 the irregular wave case, and this was thought to be the result of both erosive and accretive wave conditions 

 being present in the irregular wave train. A representative wave parameter could not be specified for 

 sediment transport rate because both the mean wave and the significant wave height (i/1/3) produced 

 similar results. 



181. Recently, success hcis been reported in efforts to numerically simulate profile response due to 

 cross-shore sediment transport (Larson 1988, Larson and Kraus 1989). The numerical model of Larson and 

 Kraus (1989) incorporates several empirical formulations obtained from analysis of prototype-scale wave 

 tank experiments conducted with regular waves. Application of the model to field situations requires 

 specification of representative statistical wave heights. In simulations of documented field erosional events, 

 they found that the numerical model produced better results when the energy-based Hmo was used as the 

 equivalent wave height. Use of the average wave height as the irregular wave parameter did not perform as 

 well because an insufficient quantity of sediment was moved during the simulation. Their simulations of 

 field events provide a link between the proper representative irregular wave statistic and the equivalent 



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