On Friday 17th May twenty members of York Rotary were privileged to have a tour around the refurbished flood barrier. This was a follow up from an earlier visit in January 2018 when the Foss Barrier rebuild was commencing.
We were taken round the barrier by Mark Fuller of the Environment Agency Strategy Team. Mark has been involved with the barrier since before the 2015 floods and he was extremely informative and answered the many questions that were put to him in a very knowledgeable way.
We started outside the barrier and heard about the original barrier and the refurbishment works that were carried out, together with details of why the barrier failed in 2015 and what has been done since then to address the issues in the original barrier.
The original design was from the 1980s and was based on flooding expectations at that time. Unfortunately, in the 2015 flood, with the barrier closed as normal, the flow in the River Foss exceeded the maximum pumping capacity of all eight pumps running, resulting in the water level upstream of the barrier rising rapidly. As the water level began to exceed that downstream, the critical point was being reached where it would have become impossible to raise the barrier due to the increasing imbalance in water levels on either side, with the consequent risk of unprecedented flood levels in the Foss. With the high river level also resulting in water starting to enter the electrical switchgear rooms, the decision was taken to lift the barrier. Although this decisive move – criticised at the time, but subsequently confirmed as having been the correct decision - still resulted in the flooding of many properties, it in fact avoided the flooding of a much greater area, had the barrier remained in place.
After a major exercise involving the military delivering equipment to the roof of the barrier building by Chinook helicopter the barrier started to become operational within three days a great result.
Mark explained the background to flooding in trends over the last 100 years and indicated the general trend of increase in flood levels. We also heard about other measures being undertaken to hold back water flows upstream to try to help addressing future problems (one example is the £18m flood alleviation scheme on the Foss near Strensall).
The refurbished barrier is designed to accommodate a 1 in a 100 year storm pus climate change provision. The new barrier is better protected and its flood defences are increased from a level of 10.40m to 10.85m.
The new installation is capable of pumping a staggering 50m3 or tonnes of water per second, a staggering quantity.
We visited the tower that houses the actual barrier and saw all the mechanism that operates the raising and lowering of the barrier gate which weighs 18 tonnes.
From the barrier we went to look at the plant and control buildings. We saw where the eight pumps were located and we saw all of the associated infrastructure. The flood barrier is served by two independent high voltage supplies into the building and there are mechanisms that allow the supplies to switch over if one of them fails so that the installation can still operate.
As a further backup to the incoming supplies there are five standby generators that automatically operate in the event of a failure of both incoming supplies. The generators can supply a total of 5Mw of power and if they were operating they would use a staggering 68,000 litres of fuel a day. The barrier stores 68,000 litres of fuel and there is a mechanism for remote refuelling from the road if the generators were needed to run for more than 24 hours. One large cost of operating the barrier is an average annual electrical cost of approximately £100,000. We were impressed to see inside on of the generators and to note the massive size of its engine.
We finished the tour by visiting the control room where we had a detailed explanation of the computerised controls and the manual overview of those controls. We were all impressed by the way in which all of the systems had varying back so as ensure the safe continued operation of the system catering for all reasonably foreseen eventualities.
After the floods in 2015 and the barrier failure the rebuilding programme took seven years. The length of the programme was cause by the need to keep the barrier installation operational throughout. The redevelopment of the barrier cost approximately £40m which is not surprising given the complexity of the work that had to be undertaken and the constraints of working on a live site.
The visit was very informative and enjoyable and we thank Mark for conducting the visit.
David Fotheringham
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