Art. XXI.—On the Wave Phenomena observed in Lyttelton Harbour, August 15, 1868.
[Read before the Philosophical Institute of Canterbury, September 9, 1868.]
The evening of the 14th August was calm and clear, the aneroid stood 29·90. An unusual stillness prevailed during the night.
At 3.30 a.m., the tide being half-ebb, the water suddenly receded from the harbour, rushing past the shipping lying in the stream, and vessels anchored near the entrance of the harbour, at a supposed velocity of twelve knots. The water continued falling until 4.30 a.m., when the end of the breakwater was dry, at which position the average depth at low-water is 15 feet. At the before mentioned hour, with a loud roar, a wave of about 8 feet in height rushed up the harbour with great velocity, and at 4.50 the water was within 3 feet of the railway level; in other words, 3 feet above the highest spring tide, having risen 25 feet perpendicular in twenty minutes.
The water at about 5 a.m. rapidly receded the second time, and at 6 the bottom was again visible beyond the end of the Government jetty; at 7.15 it again rushed up in the form of a heavy ground swell, and rose rapidly to 16 feet, and immediately commenced to fall again. At 9.30, the inner end of the screw pile jetty was dry, when the reaction again took place, the water returning with even more velocity than at 7 a.m., until it resumed the level of high-water springs. Off in the stream, the water was very thick and discoloured, boiling up as it were from the bottom.
At 10.15 the water rushed out with the same force for about half an hour, and rose again shortly after 11 a.m. to 18 feet; throughout the remainder of the day the water rose and fell without any regularity, sometimes at the rate of 3 feet per hour. Aneroid, 30·5.
During the whole of Sunday, the 16th, there was no regularity of tide, the water ebbed and flowed three times in six hours; at 2.16 p.m., the proper time of high-water, there was 17½ feet, and after ebbing an hour, it rose again to about 17 feet at 4.15.
Aneroid, 30·10, stationary; weather, calm and clear; water, very thick, and continuing boiling up in large eddies.
Monday and Tuesday, the 17th and 18th, tides still very irregular, flowing one foot higher, and ebbing 1 ½ feet lower than the usual springs.
Wednesday, 19th, nothing unusual perceptible.