Background

The Great Barford Bypass was constructed to relieve congestion on the A421, improving traffic flow between Bedford and the M1.

The scheme included the construction of six balancing ponds to attenuate surface water runoff from the new highway.

The challenge

The drainage strategy needed to:

  • Limit discharge rates to 4 litres/second/hectare, in line with EA requirements
  • Maximise throughput across widely varying flow conditions
  • Minimise land take and construction cost for the attenuation ponds
  • Avoid blockages from debris carried by highway runoff

The solution

Marshalls supplied precast chambers with Hydro Brake® flow control units pre fitted, working in partnership with Hydro International.
Key features included:

  • One piece chambers reducing the need for concrete surrounds
  • Pre formed benching eliminating site benching and coring
  • Vortex based Hydro Brake® design offering high blockage resistance

Each of the six balancing ponds (500–1500m³) discharged via a Hydro Brake® chamber.

The outcome

  • Reduced pond storage volumes required
  • Lower construction costs and land take
  • High quality, factory fitted drainage structures
  • Improved long term maintenance access

Consulting engineers confirmed the Hydro Brake® system enabled discharge limits to be met without oversizing attenuation.