The Newlyn tide gauge

Taken from "Ordnance Survey map makers to Britain since 1791".

General dissatisfaction with Liverpool as the national bench-mark datum led to the construction of three new tide—gauges at Felix stowe, Newlyn and Dunbar, which began recording in 1913, 1915 and 1917 respectively. It had been intended to calculate mean sea-level from the results obtained from all three, hut it was found that although there was only /2 inch difference between Newlyn and Felixstowe mean sea levels, there was nearly 10 inches between Newlyn and Dunbar.

As a result Ordnance Survey decided to continue using a single reference datum. Newlyn was preferred as it was situated in an area of stable granite rock and because the gauge, perched on the end of a stone pier at the harbour entrance, was exposed to the open Atlantic. It as not therefore liable to be influenced by silting-up or undue effects of estuary or river tide delays, as had been the ease at Liverpool.

During six years of continuous recording, abstracts were made of the hourly records, from which mean sea-level was deduced. The gauge was checked twice daily, by manually measuring the drop to the surface of the water and comparing this with the recording on the tide—gauge. Barometric readings were taken, and the temperature and density of the sea water were also recorded.

Ordnance Survey ceased to maintain its general scientific interest in sea—level changes, handing over the responsibility of Felixstowe observatory to the Harhour Board in 1930, and eventually abandoning Dunbar in 1950 when low tides failed to be registered because of silting-up.

Section through the tide-gauge at Dunbar.

Responsibility for the Newlyn tide gauge continued to rest with Ordnance Survey, who provided a full-time observer at the Station until 1983 when the station was handed over to the Institute of Oceanographic Sciences. It was one of the most unusual jobs on the Survey, demanding twice daily attendance to the exposed site, 365 days a year. The job demanded a special sort of dedication personified by Mr W Hutchens who was tidal observer at Newlyn for twenty-three years.

Roy Mitchelmore, successor to MrHutchcns, with the Newlyn tide gauge.
The gauge is now preserved at Ordnance Survey’s headquarters.

 

In 1965 he was congratulated that ‘your gauge produces the most accurate record of mean sea-level in the world, with the exception of Genoa in Italy where the tidal range is less than I ft ’. All altitudes of bench—marks, apart from those on outer islands, are now related to Newlyn, and known as Ordnance Datum Newlyn (ODN)