(Figs. 24 and 34). These results verify that the peak water patterns 

 are primarily caused by crest stagnation at the obstacle, with signifi- 

 cant secondary effects of obstacle geometry. 



IV. EXTRAPOLATION OF THE LABORATORY RESULTS 



The laboratory tests were designed to be approximate models of wave 

 transformation near an isolated, rigid vertical pile in common nearshore 

 situations (Table 3). The conclusions based on the data can be extra- 

 polated to prototype situations if the modeling is essentially valid. 

 The following discussions assess the importance of the pile confinement 

 within a narrow wave tank, and of inaccuracy in modeling the prototype. 



1. Effects of Pile Confinement. 



In a narrow wave tank, measurements can include effects of the tank 

 walls. Constriction of the flow through the reduced tank cross section 

 causes increased velocity past the pile, so the incident wave does not 

 fully define the flow at the pile. In addition, the bow wave occurring 

 upstream of the pile may be compressed by the confining tank walls. 

 Either effect might influence the peak water measured at the pile. 



Taking b to be tank half-width, these effects are partially dis- 

 cribed by a blockage parameter Z equal to a/b or X/2b. If Z is 

 very small, as in the 14-foot-wide tank (85-foot tank) used in this 

 study, effects of pile confinement are negligible. However, the other 

 wave tank (96-foot tank) used was only 1.5 feet wide; Z was usually 

 on the order of 0.1, so flow constriction effects may be significant 

 in the 96-foot tank tests. 



Saunders (1957) described a correction procedure for the flow con- 

 striction effect, using a calculated Bernoulli contour system for the 

 flow in the reduced section. This procedure is standard for correcting 

 data from tests in unidirectional flows, and may be used to calculate 

 peak water level adjustments caused by flow constriction in the present 

 tests, if maximum crest flow is assumed to be steady unidirectional 

 flow. Using equation 4-4 in Petryk (1969) for open-channel flow, the 

 situation defined by a/b = 0.167, d = 1.00 foot, and F^ = 1.2 results 

 in about a 2-percent reduction of water depth at the pile. This is a 

 relatively minor correction for this example of extreme flow constriction 

 from the present test series. Furthermore, in reporting wind-tunnel 

 tests on the effects of wake splitter plates, Apelt and West (1975) 

 expressed doubt about the applicability of a Bernoulli contour calcula- 

 tion- to the case of a bluff body with a trailing plate, and did not 

 attempt to correct their data for flow constriction effects. Similar 

 doubts arise concerning correction calculations for the present tests 

 of piles with leading and trailing sharp edges. For these reasons, the 

 measurements have been reported as recorded, without correcting water 

 level for the flow constriction by the pile. 



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