Drainage design in a climate emergency

16 March 2020

In the past few months many areas of Britain have seen very high rainfall.

Looking out of the window from my desk I can see the Avon river level is recurrently high. A walk at lunch following storm Dennis showed the weir in Bath city centre was barely visible under the vast quantities of water pouring downstream. This is likely to be a more and more regular occurrence as the effects of climate change become more severe and widespread. So what can we as building designers do?

Our objective as drainage engineers is to reduce as far as reasonably possible the risk of flooding to buildings, and therefore provide safe spaces for people to live and work. We follow the Sustainable Drainage System (SuDS) hierarchy of infiltration as our first option, before considering attenuation and discharge to local watercourses and public sewer systems. This reduces the intensity and volume of water hitting watercourses like rivers in storms. Infiltrating rainwater into the ground through soakaways allows for the gradual release of water into the underground natural water system. Design of soakaways requires specific site testing and analysis to ensure that the natural water table is sufficiently below the soakaway base and that enough storage volume is provided for intense storms with consideration for additional rainwater intensities due to climate change. Our designs are done in consultation with the Lead Local Flood Authority and Environment Agency wherever relevant to ensure a collaborative approach is delivered for our clients.

Maria Schaerer
Senior Engineer