The hydraulic design of adoptable piped highway drains must meet the requirements of the current edition of ‘“Design & Construction Guidance (DCG)”’ published by Water UK in accordance with section 104 of the Water Industry Act 1991.
Input data and hydraulic modelling results should be submitted to the council.
Hydraulic design – protection against flooding
The system must be designed to meet the requirements of the current edition of Water UK’s “Design & Construction Guidance (DCG)”.
The system should be designed not to flood any part of the highway or site in a 1% (1 in 100-year return period) design storm or any other design storm event that is set out in the latest version of ‘Sewers for Adoption’ including an allowance for climate change set in line with current Environment Agency development recommendations plus 10% for urban creep.
Designs should also show the line and extent of flow paths and the potential effects of flooding for storms greater than those allowed for by the design. Water from the highway should not at any time leave the highway. If this is not possible then additional information on where this water goes must be provided along with confirmation/evidence that no property will be subject to flooding from the highway.
Minimum pipe size
The minimum pipe diameter for adoptable highway drains, other than gully connections, is 225mm. The minimum size for a road gully connection is 150mm.
Culverted watercourses will be minimum 450mm. Please refer to the Flood Risk Management Strategy for further information.
These are absolute minimums, please note all pipe systems should be accompanied by calculations and or modelling providing suitability for ability for use.