Peter's Waterways Blog The Foss Barrier Pumping Station: Computational Fluid Dynamic and Physical Modelling of the Foss Barrier This was first published in IWA West Riding's Milepost in February 2017 as a report on a presentation to the the Chartered Institution of Water and Environmental Management.

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Despite the academic sounding title this was a rewarding evening meeting of the Tyne and Humber Branch of CIWEM, (the Chartered Institution of Water and Environmental Management). The problem that occurred to cause the barrier at the mouth of the Foss to be raised was explained and then the modelling to find a solution was discussed. This was followed by a visit to a physical model used to verify the proposed solution.

Foss model: the chap in jacket and tie shows the scale

Model's flow contol valves

In December 2015 York faced unprecedented flooding when water from the River Ouse and River Foss combined to form devastating floods. The Environment Agency made the decision to raise the flood barrier on the River Foss as the pumping station capacity was lower than the flow arriving at the pumps from the River Foss. Had this decision not been taken water levels in the River Foss would have increased. Held behind the Foss Barrier the water level would have exceeded the observed flood level. Around 3,500 properties in the city were at risk and approximately 627 homes flooded on Boxing Day 2015, with between 300 and 400 people being evacuated. In light of the December 2015 event, funding was made available and the decision taken to maximize the pump capacity of the existing eight pumps. The Computational Fluid Dynamic (CFD) and Physical Modelling informs the design to achieve this objective.

About the Foss Barrier The Foss Barrier was constructed in 1989.  It consists of a moveable barrier system (a large ‘turn and lift gate’) which when in place, effectively isolates the Foss from the Ouse, stopping water from flowing back upstream.  A system of eight high volume pumps (existing pumping capacity of 30.4 cubic metres per second) maintains water discharging from the Foss into the Ouse.  In short, when the barrier is lowered, the optimum level of water in the Foss is maintained by pumping water around the barrier, directly into the Ouse, thus maintaining a steady water level in the River Foss. The modelled solution was to raise the pump capacity to the maximum using the existing pumping station buildings. This turned out to be about double the existing capacity. The modelling was required to show how (if) the new system would work with the increased flow both into and out of the pumps. The pumps were first modelled on the computer, which enabled many scenarios to be tried, then the preferred solution was modelled in the physical laboratory in Yeadon to prove the principle.

Foss barrier looking upstream

Peter Scott @peterjohnscott