Pavilion Building, The Priory School, Hitchin

Drainage Planning Services and Flood Risk Assessment

Services offered

  • Drainage Planning Services
  • Flood Risk Assessment

The brief

Civilistix Consulting Engineers were appointed to prepare a combined Flood Risk Assessment and a detailed surface and foul water drainage strategy.  This was for a development consisting of a Sports Pavilion Building with a front external hardstanding area, car park area and access road to the car park.

What we did

The North Hertfordshire District Council Strategic Flood Risk Assessment (2016) and EA maps showed that there was a medium/low risk of Groundwater Flooding. To adequately control this risk we proposed using the SuDS drainage approach.

An instructive Ground Investigation Report showed that infiltration systems were not feasible. There was no existing watercourse nearby, so following Part H of the Building Regulations 2010 surface water run-off hierarchy, the next option was to discharge to a public sewer.

It was proposed that the building would drain via a piped network to a tanked geo-cellular storage tank located underneath the private road before being released via a hydro-brake flow control to the existing surface water drainage system. This would control flows to 2.0 l/s for all storm events up to and including the critical 100 year plus 40% climate change event.

Permeable construction was used for all proposed external hardstanding areas (Type 3 sub-base).

It was proposed that all foul water flows from the development would gravitate to the existing foul water drainage system onsite before being released to an existing Anglian Water foul water sewer.