In 1769, the Cornish Copper Company made a canal of about half a mile in length from Hayle to Copper-house, to bring small vessels to the copper works; and erected small flood gates near the upper end, to keep the canal clear of sand. The harbour of Hayle before 1788, was seldom accessible to vessels of more than 70 tons burthen through the accumulation of sand on the bar, which crosses its entrance; and from the sudden shifting of the sand banks, vessels were frequently exposed to danger both in entering and in leaving the harbour. In 1788 the company carried a wear across the entrance of Phillack creek, and erected flood gates on the southern side of it. These were opened to admit the coming tide, and at high water were closed.

In this way all the water which had flowed into the creek was confined until the tide below the gates had left the harbour. Two hatches in the gates about four feet square were then drawn up by means of cog wheels, and the water rushed through the openings with a force sufficient to carry off all the loose sand and mud which had collected in the channel. The harbour as well as the entrance to it was hereby considerably deepened. To increase the force of the water from the gates, another wear was erected across the bar at the mouth of the harbour, by means of which the stream was always kept in one channel. In 1808 two more flood gates were erected on the north side of the creek; which by doubling the quantity of water discharged at once, deepened the harbour still more. There is now at ordinary spring tides twenty feet of water on the bar, and at high springs twenty-four feet. Vessels of 250 tons burthen may come up to the coal quays; and (the canal having been deepened) vessels of 120 tons to the copper works. The tide flows without the harbour, nearly three hours before it enters it; and in consequence it has left it three hours before low water 

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The History of Cornwall: From the Earliest Records and Traditions, to the Present Time, Volume 2

Penaluna, 1824

[https://books.google.co.uk/books?id=HtxSAAAAcAAJ&dq=francis+gregor+trewarthenick+dorothy&q=mellanoweth#v=onepage&q=phillack&f=false