Addenbrookes Surface Water Management Plan

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Project Details - Surface Water Management Plan

Client: Cambridge University Hospitals (CUH) - NHS Foundation Trust

Categories: Outline Business Case, SuDS, Surface Water Management Plan (SWMP)

When: March-April 2043

Location: Canbridgeshire, UK

In July 2015 heavy rain fell on Cambridge city centre, causing flooding to the Cambridge University Hospitals site (Addenbrookes Hospital). The Addenbrookes Treatment Centre (ATC) building saw flooding to a depth of approximately 100mm which resulted in the cancellation of operations for approximately one week and led to the diversion of accident and emergency services as far away as Birmingham.

The Rosie Maternity Hospital low level corridor, flooded to a depth of 400mm, had it been slightly deeper, it would have led to a failure of the main and back-up electrical supply building and may have led to the failure of life support systems within the hospital. The impact of the flooding led to a major incident being declared; one that was recognised as potentially catastrophic.

Edenvale Young were commissioned to investigate the causes of flooding within the hospital, assess the vulnerability of the campus to climate change, quantify the risks, develop a business plan and identify engineering options to mitigate the risk of flooding across the campus. The study also included assessing the impact of groundwater inundation and planned peripheral development to the CUH campus within the area presently defined as the Cambridge Bio-medical Campus

Outcomes

The south-western corner of the hospital campus including the ATC building and areas in front of the Rosie Hospital are at risk of flooding from high intensity short duration storms.
The capacity of the drainage network throughout the site was exceeded for comparatively low return periods (1 in 30, 3.33% AEP).
In July 2015 the majority of the pipe network was running at full capacity for a large proportion of the event leading to surface water flooding on the roads within the CUH campus.
The impact of climate change will exacerbate problems of flooding throughout the site and in particular to the ATC building. It is anticipated that there will be more frequent flood events and therefore greater damage.
The risk of flooding to the Central Sterile Services Department in the ATC building and the consequential impact on operations across the CUH site was unacceptable.
The risk of loss of life associated with loss of electricity supply to the Rosie Hospital as a result of flooding to the switchgear room on the Level 0 basement was unacceptable.

Outcomes

In order to investigate the flooding mechanisms across the site and to assess the effectiveness of flood alleviation measures Edenvale Young developed a complex 1D-2D direct rainfall hydraulic model of the hospital site. The model included all buildings, basements, highway and drainage systems including over 1800 storm sewer pipes.

The model as tested and calibrated against the July 2014 event and rainfall climate change scenarios up to a 0.1% AEP events

A range of engineering options were identified to mitigate the risk of flooding including use of barriers, upgrading of the existing infrastructure, retrofitting of SuDS and building resilience.