TABLE 8 

 At West Street 



Year 



Distance of fathom lines in feet 



Two Three Four 



December, 

 End 1955 



1953 



650 

 525 



850 

 855 



1,100 

 1,100 



Loss/Gain 





- 125 



+ 5 



- 



End 1959 





515 



825 



1,060 



Loss 





- 10 



- 30 



- 40 



In considering these tables, it should be pointed out that the sec- 

 tions opposite Bell Street and Rutherford Street refer to a comparatively 

 flat profile of the seabed, and that the profile steepens sharply as the 

 sections move north. Thus, it requires only a small difference in sand 

 level on the South Beach to move a contour considerably one way or another, 

 whereas this does not apply to the Central and North Beaches. 



Further north the beaches have been steadily losing ground, even in 

 the vicinity of the groynes which have- been erected on the northern beaches. 



POSITION OF GROYNES 



In regard to these structures, several interesting facts have de- 

 veloped in connection with the movement of the sand. These groynes - built 

 more in the form of breakwaters, rather than in the usually accepted form 

 of groyne - were constructed during the period 1954 to 1956, and therefore have 

 been in existence over five years. When constructed, the depth of water 

 at the end of the breakwaters averaged about ten to twelve feet, but over 

 their period of existence, sand has been eroded from the foot of the struc- 

 tures to such a degree that at places a depth of water of over 30 feet has 

 been found. There is no doubt that eddy currents are being established in 

 this vicinity, probably due to the impermeability of the structure, and the 

 inability of the waves to pass over, and a new aspect of the erosion problem 

 has been set up. Due to this depth of water, the normal gradients of the 

 beach have, in turn, been disturbed, and the sand is taking up an unusual 

 pattern for inter-groyne build-up. Instead of accumulating on the southern 

 face of the groyne - the littoral drift being northerly - the sand is form- 

 ing a central spit, and the areas on both sides of the groynes are being 



22 



