Dealing effectively with surface water is indeed a key consideration for the development of any site. Below, Mark Jones, our SuDS (Sustainable Drainage System) and Flood Risk specialist, explains how the best drainage designs should start with infiltration testing.

Part H of Building Regulations

Infiltration testing can reveal how quickly surface water from roofs and paved areas may soak away naturally into the ground. Part H of the Building Regulations sets out:

  • a Hierarchy of Drainage that has infiltration as the preferred option;
  • above discharge into a watercourse and surface water sewer;
  • so it is a sensible place to start.

It is also often a requirement by Lead Local Flooding Authorities. Namely, to prove that connections to watercourses or sewers are necessary.

Given it is a building block of the design solution, consistent and robust testing is vital. Our team works to BS5930 and BRE 365 to undertake testing, to ensure that a representative infiltration rate is calculated. Trial pits are dug and filled with a clean and consistent sized stone before being filled with water. Next, we monitor the infiltration flow rate through a fixed pipe. Up to three tests occur at each location, to ascertain a representative long-term flow rate.

Once the results are in, we can then work closely with the developer to design a scheme that not only meets all the regulatory requirements but can help with the implementation of SuDS elements such as infiltration trenches, permeable paving and basins. Indeed, these excellent technical solutions receive support from the testing data. Additionally, SuDS offers the additional benefits of increasing biodiversity, creating amenity space and reducing flows into public sewers.

So, it really is worth investing a little time up-front to get the infiltration testing just right on your next development. This will ensure the final scheme has the best possible chance of approval in planning by the Lead Local Flood Authority and minimise any delays.