Archive 2016 10

Sewerage and Drainage Water management: The importance of SuDS Changing weather patterns and increased urbanisation are the two biggest contributors to the rise of inland flooding. Marshalls water management expert Alice Couldwell discusses why integrating permeable materials and sustainable drainage systems into commercial construction is more important than ever. IN the UK we’re experiencing increasingly prolonged periods of intense rainfall and the impact on our built-up environment is becoming more dramatic. But while residents of flood-hit areas attempt to repair the damage, it’s important to recognise that draining away the water isn’t the only concern. Large volumes of surface water run-off can also cause problems with water quality; without attention, our watercourses are at risk of becoming polluted with hydrocarbons, nitrates and phosphates. Despite the threat of surface water flooding, the Government’s recent National Flood Resilience Review concentrates primarily on flood threat from rivers and seas. But with global warming expected to trigger heavier, more frequent and longerlasting rainstorms, a resilient water strategy, which incorporates surface water flooding, is a must. Taking action will help flood-prone areas, protect other regions at risk and ensure water is treated safely and efficiently. The future is SuDS As discussed in Marshalls’ Future Spaces report which examines how the built environment will be shaped over the next 10 years, undertaking a responsible approach to sustainable drainage is crucial if we’re to protect ourselves from flooding. It’s also a technique to maintain biodiversity in a changing climate. Traditional drainage removes surface www.builderandengineer.18 water via pipe systems and conveys it as quickly as possible to a receiving watercourse or sewer. However, because the flow is not controlled, this often means that flooding occurs downstream. It also means that pollutants are not removed from the water, and natural aquifers are reduced as surface water is prevented from filtering naturally down into them . Sustainable drainage systems (SuDS) – which can take the form of wet ponds, rain gardens, green roofs and permeable paving – are designed to tackle the problems traditional systems cannot. They retain rainwater at source, reducing the volume and velocity of surface run-off. In addition to vastly reduced flood risk, these systems also provide safer, cleaner water via completely natural filtration processes that occur. Successful SuDS designs address these three areas of concern – water quantity, water quality and biodiversity, known as the SuDS Triangle. In doing so, they provide natural water quality treatment, reduce the impact of peak flows and lessen the effects on local wildlife. Use of infiltration systems such as soakaways, which can be constructed in various forms, ensure water is dispersed into the ground evenly and swiftly. If we’re going to build more and build better, bringing in these vital systems at the initial design stage will ensure that neither radical intervention nor greater expense is required in the future. Since the Flood and Water Management Act was integrated into planning regulations, SuDS strategy has now become a local concern rather than national legislation, which means that approaches vary all over the UK. It would have been good to see the Government calling for consistent enforcement of SuDs as part of its Resilience Review, however despite this it’s encouraging that a growing number of local authorities are acknowledging that SuDS is a pragmatic and essential part of their planning responsibility. Many are taking steps to improve flood risk management and the way in which they manage our water resources, using freely available guidance (such as CIRIA’s SuDS Manual). Permeable paving – how it works As more projects are developed over green land, impermeable hard landscaping (such as concrete, stone or macadam) means that surface water run-off is frequently intercepted before it’s given the chance to naturally infiltrate into the ground. Permeable paving addresses this problem by collecting rainwater at source. Water filters through specially formed gaps in the paved surface and into a specially engineered sub-base. Here, the water is stored (or attenuated) until it can infiltrate naturally into the ground beneath the pavement. Sometimes, if the ground isn’t porous enough, pipes can take the water away by Alice Couldwell

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