and sand was accumulated at the Cave Rock Bight. Where previously a 

 depth of 40 feet L.W.O.S.T. existed in the Bight, there occurred a shoal- 

 ing of 11 feet on the completion of the Breakwater. Although there must 

 have followed a period of temporary 'starvation* of the area north of the 

 Breakwater, while this new beach was building up, there was no record of 

 final erosion on the Ocean beaches - on the contrary, the reverse is the 

 case. It appears that the movement of the littoral current was diverted 

 from its normal path merely to take a longer course than formerly before 

 striking the beaches again. In fact, it could be said that the construction 

 of the Breakwater actually had a beneficial effect upon the beaches, since 

 there followed an appreciable accretion of sand on both sides of the piers. 

 Turing this period, the depth of water at the entrance to the harbour re- 

 mained in the vicinity of 6 to 8 feet. These facts indicate that there was 

 a constant movement of sand in the general northerly direction. 



DRfiTGING OPERATIONS 



With the advent of ocean-going vessels of deeper draught, it became 

 obvious that dredging of the harbour entrance would have to be undertaken 

 to maintain an adequate depth of channel. On account of the steady supply 

 of sand passing the entrance, a bar was always forming there and dredging 

 operations commenced in 1895 with the object of deepening the harbour 

 entrance channel. From that date the entrance level of approximately 18 

 feet was established and maintained for the ensuing six years, during which 

 period an average of 200,000 cubic yards per annum of sand was removed. 



There is no doubt that it is from this period that erosion began to 

 take place on the beaches, increasing in intensity with the dredging 

 operations, as will be shown later in discussing the sand movements on the 

 beaches to the north of the entrance. Gradually the depth of water at the 

 entrance of the harbour was increased and the initial depth of 18 feet in 

 1895, when a small 500-ton dredger was employed, gradually became 42 feet 

 today, when dredgers of the 3,500-ton class are in operation. 



It is of interest to note the various stages of deepening the harbour 

 entrance channel; for example, in the period from 1906 to 1911 when the 

 minimum depth of water available at the bar averaged 3l| feet, the annual 

 removal of sand by dredger amounted to 400,000 cubic yards. This figure 

 was slightly increased during the ensuing decade when the depth was in- 

 creased to 35 feet, but during the period 1923 to 1931, when the depth at 

 the entrance remained steady at 37 feet, the annual removal of sand averaged 

 625,000 cubic yards increasing to 650,000 cubic yards in the ensuing six 

 years when the depth was increased by a further foot. From 1939 onwards, 

 the clearance was increased to the present depth of approximately 42 feet; 

 and it is remarkable that over the ensuing 20 years, the quantity of sand 

 which has had to be removed from the Cave Rock Bight sand trap and the 

 harbour entrance has remained at a fairly even average of 800,000 cubic 

 yards per annum. 



