Many questions concerning runup scale effects are left unanswered 

 by the available data. Steep structure slopes (including vertical walls) 

 have not been tested; scale effects may be negligible when the structure 

 is fronted by a horizontal bottom but may be appreciable when fronted by 

 a sloping bottom, often resulting in high relative runup. Corrections 

 indicated by the roughened slope testing (very limited) may not be 

 applicable over a wide range of wave conditions. The correction co- 

 efficient has a value of 1.0 at cot 9 = 15. The curve would have a 

 different shape if, for example, the correction coefficient for 

 cot 9 = 10 were also 1.0, but test results are not available for addi- 

 tional slopes. No large-scale testing was conducted with a horizontal 

 or gently sloping bottom fronting the structure where different scale 

 effects might well be expected. Applicability of Figure 49 for all 

 wave conditions (all dg/H^ and H^/gT 2 ) is not clear, nor is it expected. 

 Scale effects would be expected to be closely related to the presence 

 (or absence) of a relatively thin sheet or jet of water which runs up 

 the slope. The water would be greatly affected by roughness elements 

 and its presence would be a function of incident wave conditions. 



New experimental work directed at the above problems would certainly 

 clarify some points. However, until further testing warrants changes, 

 Figure 50 is recommended for use in determining scale effects in the 

 design of smooth structure slopes. 



4. Rough-Slope Scale Effects . 



Little information is available concerning scale effects in runup 

 on rubble slopes. The study by Dai and Kamel (1969) is perhaps the 

 most applicable but it was only for a rubble-mound structure with a 

 1 on 1.5 slope. Dai and Jackson (1966) measured runup on a rubble- 

 mound breakwater at two scales, but these were rather small model-to- 

 prototype scales of 1:50 and 1:100. Runup experiments on riprapped 

 slopes have not generally been designed to determine scale effects, 

 although Hudson and Jackson (1962) included two different water depths 

 (or scales) while measuring runup on a 1 on 2 slope. Most frequently, 

 tests have been conducted at a single scale (including large scales) 

 for rather limited conditions. In such cases, comparisons between 

 scales can be made only for comparable test conditions. Such compari- 

 sons between independent experiments are "uncertain because of unknown 

 factors, such as experimental methods and structure differences. 



Dai and Kamel (1969) tested a quarrystone-armored, rubble-mound 

 structure with a cross section similar to that tested by Hudson (1958) . 

 Only one slope was used, cot 9 = 1.5. Three different water depths 

 (see Table 19) were used, and these can be given in terms of the 

 Reynolds number: Re = 4.69 x 10 5 , 1.33 x 10% and 2.72 x 10 7 . Quarry- 

 stones considered to be either smooth or rough were used in the 

 various tests. The set of runup data for smooth quarrystones, and 

 Rg = 1.33 x lo 6 , appears to have the same wave conditions and runup as 

 part of the data given by Hudson (1958). This particular data set has 

 lower runup overall than for any other set of data given by Dai and 

 Kamel when specific wave conditions are compared. 



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