United Biscuits Groundwater Flooding Assessment Carlisle

Case Study

United Biscuits, part of the pladis group, asked us to support the design of a flood defence to protect their Carlisle factory, where famous brands like McVitie’s Ginger Nuts and Carrs Table Water are made and distributed.

 

United Biscuits Flood Risk AssessmentThe site was seriously flooded during Storm Desmond in December 2015 and took four months to fully recover, following an extensive period of clean up and repair.

 

A GeoSmart FloodSmart report highlighted that groundwater may have played a key role in the flooding that disrupted operations. We were commissioned to work with the design team to investigate and assess the ground conditions with two main aims;

  • Identify the contribution of  groundwater flooding to historical and future flood events, and;
  • Investigate the geotechnical ground conditions to inform the structural design of the defences.

 

We were to provide a technical underpinning so that insurance cover could be extended, following the completion and commissioning of the defence scheme.

 

The project was undertaken on a very tight timescale, requiring completion between the re-opening of the factory in January 2016 and the start of the following winter. The site was a physical challenge for the investigation work, being a busy operational facility. Concrete coring and sub-base works were undertaken within the food manufacturing area. Dust control and odour control measures were essential to prevent any health and safety impact on the produce.

 

Monitoring boreholes had to be drilled so as to minimise disruption in a tightly packed site. So that we could maximise sample recovery, a multi-utility drilling system was successfully used. Fieldwork observations, groundwater monitoring by data-logger, in situ and laboratory permeability testing were used to develop a bespoke hydrogeological conceptual model.

 

Investigations revealed that the sub-surface hydrogeology comprised a superficial gravel aquifer in continuity with the nearby river. It was slightly confined by a low permeability cohesive layer above.  The stratum beneath the gravels was identified as combined Mercia Mudstone and cohesive glacial till.

 

Our hydrological model determined that the likely groundwater component of a given flood event would be less than 1% of the total floodwater volume. Using the results, the design team could specify the required pump design within the basements on the site.

 

The ground conditions would determine the scheme design, so our work was on the critical path through the early phase.

 

We met a series of milestones through close collaboration with the design team.  Near real-time results allowed deadlines to be met while assessments remained ongoing.  Rapid data processing by the consortia including ESI, AKS Ward and Cluttons ensured we could progress quickly to implementation.

 

Early flood defence construction ran in parallel with the design process. We helped address challenges posed by the early excavation and construction works, ensuring that project momentum was maintained. This also ensured our client could meet the sequential draw-down of funding for the scheme, and to satisfy external stakeholders.

 

The hydrogeological assessment results were put through a rigorous challenge and review by the United Biscuit’s insurer’s technical specialist.

 

A revised geological model for the site was delivered, updating previously published mapping. This, together with the bespoke hydrogeological model, gained unique insight on the character of the superficial aquifer, and its relationship with the ground surface within the factory confines.

 

Delivery of the scheme was critical to the future of the facility, which is one of Carlisle’s major employers.  The ongoing site flood risk meant that a lack of satisfactory protection in the future questioned its long term viability in its current location.

 

The core value to our client lay in delivery of the scheme to timescale which will protect the factory against future flood events to the size of 2015. Our technical underpinning satisfied their insurer’s requirements, ensuring uninterrupted insurance cover for the facility ahead of the following winter period. Biscuits, income and workforce productivity were also more assured!