steel section of equivalent bearing strength to avoid unwanted 

 runup (Fig. 37). If wave direction is nearly constant, as it 

 is in the nearshore zone, web- shaped members may reduce cross 

 section to incoming waves, although transverse oscillations 

 will limit such applications (Apelt and Isaacs, 1968). 



(f) Estimating wave direction in the nearshore zone. The 

 following paragraphs review the status of the potential use of 

 wave runup at a pile to estimate wave direction. 



As mentioned in Section I, this study is aimed at evaluating the use 

 of wave transformation at a pile in an instrument measuring nearshore 

 wave directions. In this application, maximizing stagnation effects 

 results in a measurable relief in peak water level on a circular pile's 

 circumference. This relief is symmetrical about the direction of surface 

 flow, and wave direction may be estimated by interpolation, using a small 

 number of water level gages on the pile's circumference. James and 

 Hallermeier (1976) reported dependencies of precision in direction esti- 

 mates on the interpolation method, the angular measurement spacing, 

 the vertical measurement resolution, and the incident wave type. The 

 simplest instrument would use four water level gages spaced 60° apart on 

 the seaward pile half, to measure wave direction within ±3° over a 120° 

 range of incidence. This high measurement precision is needed for near- 

 shore wave directions, since wave refraction limits the range of incident 

 direction. The proposed instrument could measure individual crests, 

 recording direction variations. 



The reported data show that a finned circular pile can produce a 

 smaller angular range of maximum runup than a smooth circular pile. 

 However, this increased relief in water level is associated with a more 

 ragged variation of water level with angle. Thus, it seems doubtful 

 that interpolated estimates of wave direction with a small number of 

 water level gages at a finned pile could attain the precision possible 

 using a smooth circular pile. 



Figure 38 schematically shows the operation of an automatic direction 

 gage using symmetrical crest transformation at a circular pile. 

 Hallermeier and James (1974) presented an example of the design process 

 for the pile installation, using an estimate of the local wave climate. 

 Major remaining uncertainties about the proposed instrument are a fool- 

 proof objective method for recognizing crest incidence, and whether 

 available water level gages have adequate durability and resolution. 

 Development of a prototype instrument is not presently planned. 



VI. CONCLUSIONS 



The principal conclusions from this investigation are as follows: 



a. With high waves at thin surface-piercing piles, crest stagnation 

 is similar at circular and channeled piles (Figs, 14 and 19), 



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