Don't panic. Scotchie's photo shows what the beach looked like when the tide was in! This photo, taken in 1895, shows what it looked like when the tide was out.
The grey stipple on this chart of 1897 shows the area of beach between the Low Water mark of ordinary tides and the High Water mark of ordinary tides. It also depicts the groynes seen in the photos which trapped the sand and shingle and helped to prevent it moving inexorably eastward along the coast as a result of longshore drift, and serve a similar purpose today in retaining the material in the modified flows now encountered.
At this time, the beach was open to the sea and consequently constantly replenished. The encircling breakwaters of the Admiralty Harbour were built between 1898 and 1909 and the hydrodynamic regime thereupon changed forever.
The tides ebbing and flowing outside the breakwaters cause jetstreams to enter through the Eastern and Western Entrances which create powerful circulatory currents within the harbour. These, allied with the effect of wind and waves during storms, are responsible for the manner in which the beach is maintained today.
The effect of the currents is modified by the ever-changing structure within the harbour. Each new berth constructed alters the current flows, as does the dredging performed to give adequate depth of water for shipping using the harbour. The WW1 blockship by the Western Entrance has been retained as it influences the wave climate in the Eastern Docks.
Variable accretion and depletion has occurred at different times and in different sections of the beach due to these manmade structures. As for the future, DHB commissioned H.R. Wallingford to model the characteristics in their test tanks of the proposed Terminal 2 and the new marina. The principal consideration was, of course, to determine the most effective design for facilitating ferry movements but one of the parameters they were invited to evaluate was whether there would be any potential degradation of the beach.
