Nearshore Wave Direction Gage

Bow wave formation can cause large variation in peak water level around a thin circular pile in shallow-water waves. The symmetry of this variation might be used to measure wave direction on a crest-by-crest basis. This paper empirically examines the resolution possible in objectively estimating the symmetry point of data sets consisting of small numbers of peak-water-level measurements made around a pile in laboratory wave action. Data sets for several types of single incident crests, in wave action of steepness such that 0.007≤H/≤0.05, were analyzed by three different estimation methods. For example, with 10 peak water level measurements (36° spacing around the pile), one estimation method gave directions within a range of 2.8°, on the average, for all test crests. The results indicate that four water-level sensors embedded in a vertical pile at 60° spacing might be used to measure the direction of single nearshore wave trains to a point within ±3° over a 120° range, in an instrument that can be made fully automatic.