Background

University Hospitals Coventry and Warwickshire NHS Trust is one of the UK’s largest teaching trusts, serving a population of over one million people across Coventry and Rugby.

As part of ongoing estate investment, the Trust progressed the development of a 1,600 space multi storey car park at University Hospital Coventry. The new facility is available to staff, patients and visitors, increasing parking capacity while improving access for emergency vehicles and public transport.

The project included a requirement for an effective below ground water management system to address increased runoff from large impermeable surfaces associated with the new car park.

The challenge

Runoff from car parks typically contains high levels of:

  • Sediments and silts
  • Floatable materials
  • Oils and petroleum hydrocarbons

The drainage solution needed to:

  • Treat surface water runoff before discharge
  • Meet planning and environmental requirements
  • Fit within a constrained footprint
  • Require minimal ongoing maintenance
  • Operate reliably within a critical healthcare environment

An efficient treatment solution was required without introducing unnecessary complexity or maintenance burden.

The solution

Marshalls supplied the Downstream Defender®, a precast surface water treatment system designed to manage polluted runoff from impermeable areas.
The Downstream Defender combines high treatment efficiency with a compact footprint, typically achieving up to 80% removal of grits, silts and oils. The system features:

  • A precast concrete chamber
  • Internal polypropylene components
  • No moving parts
  • A rotational flow pattern with low head loss
  • A long, stable flow path to maximise pollutant separation

Captured sediments are retained within an isolated sump at the base of the chamber, while a built in oil and floatables trap prevents re suspension. Maintenance is carried out using standard vacuum tanker equipment.

The system is particularly effective at removing sediments that carry adsorbed metals, hydrocarbons and other chemical pollutants, making it well suited to car park drainage applications.

The outcome

The Downstream Defender installation provides a robust and low maintenance surface water treatment solution for the new hospital car park.

  • Improved protection of downstream drainage networks
  • Effective removal of sediments, oils and hydrocarbons
  • Compact solution suited to a constrained urban hospital site
  • Minimal maintenance requirements using standard equipment

The scheme supports the Trust’s wider objectives of improving accessibility and user experience while ensuring responsible management of surface water runoff.