Tide and Storm Surge Modelling at Bidston Observatory

Philip L. Woodworth, 4 August 2016.

One of the main objectives of the research at Bidston Observatory was to understand more about the dynamics of the ocean tides, that is to say, the physical reasons for why the tide propagates through the ocean as it is observed to do. Before the advent of digital computers, the only way to approach these questions was from basic mathematical perspectives, in which eminent scientists such as Pierre-Simon Laplace in France excelled in the 19th century, and in which Joseph Proudman at Bidston was an acknowledged expert in the 20th century.

Similarly, there has always been considerable interest in the reasons for large non-tidal changes in sea level, including in particular those which occur due to the ‘storm surges’ generated by strong winds and low air pressures in winter. For example, following the Thames floods of January 1928, Arthur Doodson at Bidston chaired a committee for London County Council that undertook a detailed study of the reasons for the storm surge that caused the flooding, and made recommendations for protecting the city in the future.

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Tide Gauges and Bidston Observatory

Philip L. Woodworth, 4 August 2016.

Everyone knows that the level of the sea goes up and down. Most of these changes in level are due to the ocean tide (at Liverpool the level changes due to the tide by more than 8 metres at ‘spring tides’), but changes of several metres can also occur due to ‘storm surges’ that occur during bad weather, while slow changes in level can take place due to climate change and because of the geology of the adjacent land.

Changes in sea level are measured by devices called ‘tide gauges’: the more suitable name of ‘sea level recorders’ has never been widely adopted in the UK although Americans often call them ‘water level recorders’. There are as many types of tide gauge such as:

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Hartnup moves in

This article appeared in the Liverpool Mercury on 20th December 1866, two days before Liverpool’s astronomer, John Hartnup, took possession of Liverpool’s shiny new observatory on Bidston Hill. It makes fascinating reading 150 years later.

The New Liverpool Observatory

Bidston-hill has hitherto been chiefly noted for its picnic parties, and for entertainments in which ham and eggs were the principal ingredients. It will now acquire a wider celebrity as the site of one of the most complete observatories at present in existence – one which is certain to make the Dock Board spoken of with respect by men of science, and to render Mr. Hartnup’s position, as astronomer of Liverpool, an object of something like envy to his professional brethren. For the interests both of the port and of science, it was certainly a good thing that the space which the old observatory has occupied during the last 22 years, on the Prince’s Pierhead, was required for docks. Close to the river on one side, and the murkiest part of the town on the other, Mr. Hartnup was often in a fog, not by any means intellectually, but materially, and still more frequently had his nicest observations interfered with by the smoky canopy which overhung his post of observation. Obliged to cast about for a new site, the dock board selected Bidston-hill as the most eligible situation to be found in the neighbourhood for an observatory. The design and erection of the building were left to Mr. Lyster, the dock engineer, and he and his staff have produced a work of which they have no reason to be ashamed. Commenced in 1864, it has been gradually growing up by the side of the old lighthouse, which formerly was the sole occupant of the height, and now with its two domes and picturesque outline, stands out as a prominent feature in the landscape. The transfer of instruments from the old observatory has been for some time in progress, and at the beginning of next year Mr. Hartnup will probably be able to resume his labours – made still more important by this change – under conditions more favourable than he has yet enjoyed.

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Bidston Observatory and Its Tide Prediction Machines

This article originally appeared in the newsletter of the Friends of Bidston Hill in February 2016. It is reproduced here with the permission of the author, Philip Woodworth.

The role of Bidston Observatory has changed several times through the years. In its early decades, following the decision in the 1860s by the Mersey Docks and Harbour Board to move the Liverpool Observatory from Waterloo Dock to Bidston Hill, the focus was on astronomical measurements. These were required in order, amongst other things, to determine accurately the latitude and longitude of the site. Famous names involved included John Hartnup and his son (also John) and W.E. Plummer. Other areas of science undertaken by the Observatory included meteorology and seismology. In addition, it provided several local services, such as the calibration of accurate chronometers for port users and precise timing via the “One O’Clock Gun”.

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