N a = ft* (63) 



For the above, N u is the prototype -to -model fall speed ratio and N, is the 

 prototype -to -model length scale ratio. The Froude scaling guidance 

 is given by 



N c = JW~ (64) 



where N t is the prototype -to -model time scale ratio. Equations 62, 63, and 64 

 can be combined to yield a unique scaling guidance that satisfies the first 

 two scaling criteria: 



N u = y/N~ = N c (65) 



Recent Successes with Movable-Bed Model Studies 



53. During the past several years at CERC numerous studies concerning 

 various problems associated with physical movable-bed models have led to very 

 important findings. The successes of the most recent accomplishments will 

 allow engineers and scientists to use these models as a tool for planning and 

 designing various coastal projects where storm- induced erosion is a major 

 consideration. This is particularly important because the methods and 

 procedures for movable -bed models are not widely accepted and numerous (often 

 conflicting) guidances have been developed. A scaled physical model was 

 recently used to validate the above guidance by simulating prototype scale 

 wave- induced scour in front of a concrete dike sloped at 1:4. The tests were 

 conducted during fall and winter of 1988. Prototype data used were obtained 

 from the large wave tank tests done by Dette and Uliczka (1987) at the 

 University of Hannover in Germany during 1985 and 1986. Based on the very 

 successful results of this study, the modeling guidance was considered 

 validated for the stated conditions. Following the validation tests, the 

 scaling guidance was used to simulate severe beach fill erosion associated 

 with a winter storm at Ocean City, Maryland during March 1989. The tests were 

 conducted without prior knowledge of post-storm profiles and results indicated 

 that model and prototype profiles showed good agreement, giving further 

 credence to the scaling guidance and its ability to model energetic (erosive) 

 wave-action movable-bed situations. In addition to the above, the studies by 

 Fowler (1992) referenced in paragraph 40 also successfully used the fall speed 

 guidance for movable-bed studies on scour in front of vertical seawalls. 



51 



