Prior to the construction of the Floating Harbour (completed in 1809), the river Avon was completely tidal with water rushing up and down the river channel creating huge variations in water level right in the heart of the city. With the construction of the floating Harbour, the water level was kept constant in the commercial centre of the city. The river was diverted to the south in to the New Cut. The rise and fall of the tides can still be seen in this channel just south of M Shed. This map excerpt is from Rocque’s survey of the City of Bristol of 1750 held at Bristol Museum & Art Gallery.
The history of Bristol’s waterfront environment can be traced through maps using the interactive tool, Know Your Place
Occasionally, on extremely high tides parts of the Floating Harbour are overtopped and areas of the city become flooded. If this were to occur during Tidelight’s run, the lights at M Shed would glow a particularly intense violet in response, reflecting the extreme conditions that would be clear to see.
The colour range of the lights will be set so that they can potentially respond to sea levels beyond the highest tides ever recorded at Bristol. This gives Tidelight a latent capacity to translate in to colour, future sea level rise scenarios. Image from Chris Bodle’s Watermarks Project
For visitors to M Shed the project will also be visible during the day. The colour changing lights already installed throughout the building will be lit up and change colour in response to the tides through the day during the museum’s opening hours.
As night falls the big lights in the foyer will turn on in addition to the existing lights, making the whole building a responsive ‘lantern’ visible from across across a wide area around the Harbourside. (see map).
The colour chart shows how the level of the tide translates in to colour; both the colour of the lights at M shed and as the background of the Live Tides page. This chart shows the full tidal range. It actually goes beyond the highest ever recorded tide in the Bristol Channel. The column on the left shows the level as AOD. This shows how high the tide is in relation to the land. Zero AOD is sea level. M shed and much of the quaysides in Bristol is at around 8.5m AOD. Typically the highest tides will reach around (6.5m AOD) but they can go much higher when there is also a storm surge. Sea level rise will only make these highest tides higher.
Over time the rise and fall of the tides varies. At spring tide the the tidal range is wide; the high tides are high and the low tides are low. At neap tides the highs are less high and the lows less low. At these times Tidelight shows a more limited range of colours.
The real time tide data driving Tidelight is available here and a handy, user friendly predicted tide chart is available here which graphically shows how the tidal range varies over time.