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11 The Blvd, Leeds LS10 1PZ, UK

01733 715 960

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The Foss Barrier and Pumping Station was built in 1987 in response to the 1978 and 1982 floods which caused significant damage and disruption to the city of York. To the current day, when a flood event is predicted, a mechanical gate can be closed to prevent rising waters in the River Ouse from backing up into the River Foss, preventing flooding to a large part of the city. When the barrier is down, the facility relies on up to 8 No. pumps to transfer flow from the River Foss around the barrier into the River Ouse.    

 

 

 

 

 

 

 

In December 2015, the most severe floods in a generation hit the city of York. As water levels rose, flows in the River Foss exceeded the pump capacity of the station, which forms an important part of the city’s flood defences, rendering the facility inoperable.Several contributing factors all acting together combined to deliver the ‘perfect storm’, with devastating effects on the facility.  These factors were: 

  • Antecedent conditions – long wet period.

  • Extreme rainfall.

  • Coincident high levels on Foss and Ouse.

  • Design capacity of pump exceeded.

  • Leakage and ultimate flooding of the pumping station and controls. 

 

After significant involvement in the initial emergency flood response, JBA Bentley have been engaged by the client to deliver the high-profile upgrade to the site, with the key objective being to enhance the resilience and capacity of the site, whilst efficiently solving the problem of ensuring the pump station remains operational throughout the delivery of these key works.

 

Following the flood event, an extensive interim temporary works solution was quickly required to increase the level of flood protection and provide peace of mind to the affected York residents whilst the permanent works were being developed. The interim solution consisted of a 3 meter-high platform to raise all the temporary and permanent MEICA equipment above the highest flood level.

 

 

 

 

 

 

 

 

 

Within just over 15 weeks of the incident occurring and, having fully developed the civils design in record breaking time, construction works began within the public car park adjacent to the existing facility. To facilitate efficient and effective delivery, 596 No. precast concrete blocks were used to construct the 540 m² platform. The use of the precast concrete blocks and permanent soffit form-work enabled a safer and quicker method of working, with the platform constructed in just over eight weeks. Advantages of the temporary platform and method of construction chosen include:

  • Ensured greater resilience to the existing asset.

  • Allowed the permanent solution to be built offline.

  • Maintains a working pumping station throughout construction.

  • Enabled early procurement of permanent MEICA equipment.

  • Allowed platform to be delivered in two phases.

  • Avoided excessive temporary works.

  • Reduced flood volume loss

  • Transfer-ability and reuse of the Legato blocks on completion of the works  

 

Early installation of the new pumps: From the start, one of the key objectives for the client was to ensure we increased the pump capacity of the site ahead of the following winter period (2016) to ensure the facility could deal with the sort of flows experienced in the previous year. The swift construction of the temporary platform meant that the new long lead pumps and drives could be procured and installed early in the project without the need to modify the existing building, providing a value-engineered cost saving solution.

 

The pump drives, temporarily located within shipping containers, were installed on the platform and eight new pumps, initially capable of pumping 40 cumecs (increasing to 50 cumecs once the mains power supply was upgraded), were installed within the existing wells, increasing the pump stations overall capacity by up to 55%. To ensure proactive risk management/mitigation during this phase of the project, it was critical that we maintained the functionality of the pumping station during the construction of the permanent solution, ensuring that the city remained protected at all times. Therefore, the following control measures were put in place:

  • A 24/7 call out rota was implemented (AMCO/JBAB/EA) should a flood event be forecast.

  • Phased delivery and additional temporary pumps ensured full capacity was available at all times. 

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