Recent flash flooding across Birmingham has again highlighted the challenges UK urban drainage systems face in coping with extreme weather events. In response, ACO Water Management is urging local authorities and developers to prioritise rainfall interception at the surface, before it reaches sewers that were not designed for modern volumes.
Recent heatwaves have delivered long dry spells, baking the ground unusually hard, so that when intense rain arrives it runs off rather than naturally soaking away. This is especially a problem in urban areas where paving and hard surfaces have spread steadily through urban creep, causing water to reach combined sewers within minutes, overwhelming them and pushing untreated flows into homes, roads and watercourses.
The instinct is often to make pipes bigger, but that means digging up roads and does nothing to counter the water arriving in the first place.
Rain gardens, permeable surfaces and attenuation systems store water and release it slowly. Retrofitted into streets and car parks, these measures can significantly cut runoff and dozens of small interventions across a catchment add up to a serious reduction in flash flood risk.
Sam Hawkins, Head of Specification & Design at ACO Water Management, said: “We keep trying to solve the urban flooding issue by upsizing pipes, but the real answer revolves around using a range of hard and soft sustainable drainage systems (SuDS) to reduce the volume of water that makes it to the sewer system. The challenge here is that SuDS uptake remains inconsistent.”
Schedule 3 of the Flood and Water Management Act has not been enacted in England, meaning sustainable drainage remains a matter of policy rather than law, and adoption and interpretation vary widely between authorities and developers.