As the water rises in the tube, the cork floats on the surface 

 until the maximum stage is reached. As the water level starts 

 to fall in the tube, a quantity of the burnt cork adheres to 

 the measuring stick to leave a fairly permanent ring showing the 

 maximum stage. The maximum stage may then be determined at any 

 later date by removing the measuring rod and reading the level 

 of the cork ring. 



In the Board* s tests the tube was mounted over a small wave 

 flume, the bottom end of the tube extending 0.7 foot below the 

 water surface; the water was 1.25 feet deep. Waves were then 

 mechanically generated in the flume, and measurements of the amount 

 of rise and fall of the water level within the measuring tube were 

 made visually against a scale marked on the tube. Wave charac- 

 teristics (height and period) were measured simultaneously using 

 a standard two-probe resistance gage. A 1 on 6- slope, wave-absorbing, 

 gravel beach was placed in the far end of the tank to prevent wave 

 reflection. Wave periods tested in this tank ranged from 0.72 

 to 4.70 seconds, and wave heights from 0.03 to 0.70 foot. The 

 measured values are shown in Figure 1 as a dimensionless plot of 

 R/H vs H/T where R is the water level rise inside the tube above 

 the still water level, H is the measured wave height, and T is 

 the wave period. The parameter H/T is essentially the deep water 

 wave steepness (HA) being related by the equation HA = (g/2TT) 

 (H/L ); it is used rather thjin the actual steepness values because 

 of its greater simplicity in computation. Actual measured values 

 of water level rise ranged as high as 0.24 foot. 



The plotted points show that the rise inside the tube varied 

 from as little as one-tenth of the wave height for very steep 

 short period waves to as much as 8 or 9-tenths of the height for 

 lower steepness, longer period waves. The points were segregated 

 as to wave period to see if this had an additional effect. As 

 may be seen from Figure 1, actual period value appeared to have 

 very little effect as long as it was above a value of slightly 

 over 1 second; but for periods lower than this value an effect 

 was observed. 



To further test the possible effect of wave period, and to 

 ascertain the validity of the model tested, certain tests were 

 also made in the large prototype tank of the Board in conjunction 

 with other tests being performed there. A 9-foot long tube was 

 obtained and mounted near the wall of this tank, and measurements 

 were obtained for essentially prototype waves of 5.6, 7.9 and 

 11.3-second periods ranging in height from 1 to 6 feet, in a water 

 depth of 15 feet. Measurements were again obtained visually by 

 reading against a scale mounted on the tubing. Measured rises 

 inside the tube junounted to as much as 2.5 feet for a 6-foot wave. 

 These prototype measurements are also shown in Figure 1. They 

 may be seen to fall in with the much smaller scale data obtained 

 in the small wave flume; they consequently show very little wave 

 period effect to exist, other than that taken into account by 

 variation in wave steepness. 



29 



