LOCAL authorities and developers across the UK are being urged to prioritise rainfall interception at the surface, following the recent flash flooding in Birmingham.
ACO Water Management said this again highlighted the challenges urban drainage systems face in coping with extreme weather events, stressing the importance of intercepting rainfall 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, ACO explained. 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.
ACO said the instinct is often to make pipes bigger, but that means digging up roads at enormous cost and disruption, 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, the firm added that 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 that is the most expensive and least effective solution. The real answer revolves around using a range of hard and soft sustainable drainage systems (SuDS), such as rain gardens and attenuation systems, to reduce the volume of water that makes it to the sewer system. The challenge here is that SuDS uptake remains inconsistent.”
