b. As in steady unidirectional flow, this free-surface flow 

 effect depends on the Froude number based on peak fluid velocity and 

 the thin dimension of the obstacle. Smooth, breaking, or jetting 

 runup can occur, depending on the Froude number and the geometry of 

 the obstacle's front face (Sec. 11,4). 



c. At a circular pile, wave scattering is overwhelmed by flow 

 stagnation effects when the Froude number, F^ = (U^/2ga) - (H^/La) , 

 becomes significant compared to unity (Hallermeier, 1976). 



d. The patterns of measured crest height versus pile orientation 

 with respect to wave direction are largely independent of pile shape. 

 Basically similar patterns are obtained with smooth and channeled 

 piles; all the patterns have a front maximum region, a lesser maximum 

 at the rear, and intervening symmetrically located minimums (Figs. 20 

 and 26). 



e. With increasing peak fluid velocity, in patterns normalized 



by incident crest height, the front maximum becomes higher in a manner 

 consistent with crest stagnation, the rear maximum generally becomes 

 lower, and the minimums become deeper (Figs. 21, 22, 23, 27, and 28). 



f. Measured runup of a single crest at the front of a thin circular 

 pile agrees well with calculated velocity head, U^/2g (Fig. 4 in 

 Hallermeier, 1976), while mean measured runup in steady wave action 



is larger than the calculated velocity head (Table 5) . However, 

 velocity calculations are problematic for the test waves. 



g. The patterns show several definite effects of pile shape. 

 The angular width of the front maximum region is linearly related to 



an angle measuring the shallowness of the pile channels (Fig. 30, eq. 4), 

 The pattern minimums are farthest toward the rear for the smooth piles 

 (flat plate and circular piles), and the minimums are farthest toward 

 the front for deeper pile channels (Figs. 20, 27, 28, and 31; eq. 5). 



h. Similar .stagnation effects are measured in test situations 

 that are geometrically similar (identical Froude number but different 

 scale), although the Reynolds number affects the pattern away from the 

 front maximum region (Figs. 24 and 34). With minor caution, the test 

 results can be extrapolated to prototype situations of interest in 

 coastal engineering (Sec. IV, 3). 



i. A small number of water level gages on the circumference of 

 a circular pile might be used for high-resolution direction measurements 

 of individual nearshore crests (James and Hallermeier, 1976). Available 

 laboratory data permit making major design choices for a field installa- 

 tion (Hallermeier and James, 1974), although several uncertainties 



67 



