By Mark Manning
Business Development Manager, SDS Limited
If only, with the stroke of a paintbrush, we could transform the grey infrastructure of our urban landscapes to blue and green, bringing nature to the very heart of our towns and cities.
This is the vision of Sustainable Drainage Systems (SuDS). At the heart of the transformation is a principle that changes surface water from a waste product to be hidden and spirited away into something useful; we can bring it to the surface and redeploy it to benefit the health and well-being of our communities.
It’s a vision that has engaged supporters of SuDS for decades and now the magic really is beginning to happen, at least in patches, across our land. SuDS are finally in the mainstream, backed by new regulations, guidance and a growing body of best practice.
Water Companies and SuDS
As the ultimate custodians of water infrastructure, surely Water Companies should have been in the vanguard of this movement? After all, Water Companies have a huge stake in how surface water is managed, and their sewer networks are the last line of defence against surface water flooding.
In practice, it has been difficult for Water Companies to take full advantage of the opportunities that SuDS present to protect their assets. Water Companies in their very establishment, culture, and organisation are focused on water supply and wastewater collection and treatment. Equally, regulation and resources have been insufficient to encourage them to build or adopt SuDS as surface water assets.
We’ve heard increasingly stark warnings recently about the relentless advance of climate change. Our infrastructure must become more resilient to extreme weather, and the dual effects of long droughts interspersed with intense periods of rainfall. These are the very conditions that make our towns and cities vulnerable to surface water flooding. Surface water currently threatens more people and properties than any other form of flood risk, with more than 3 million properties at risk in England alone.
There isn’t the money or the space to keep building bigger sewers to accommodate more heavy and prolonged storms. So, keeping more surface water out of the sewerage system is critical. That’s why building infrastructure resilience and protecting against sewer flooding will be key performance commitments for Water Companies in PR19.
Water Companies will inevitably need to do more to exploit the opportunities that SuDS present to control surface water. It will mean working in close partnership with architects, local authorities and developers from the earliest stages of planning, to ensure good design and construction. It will also mean that Water Companies take on the job of building, owning and maintaining more SuDS themselves.
There are already encouraging signs that more SuDS are being built across the country. In August, the Government published its review of how effective including SuDS in the National Planning Policy Framework (NPPF) has been in promoting greater uptake in England for major developments. It found that almost 87% of all approved planning applications reviewed included explicit mention of SuDS.
Revisions to the NPPF have added a requirement for SuDS to provide, where possible, ‘multifunctional’ benefits. Instead of just being a means of getting rid of excess water, drainage becomes an opportunity to reuse or recycle it, and to work with nature to create biodiversity or public amenity.
Considering the multifunctional benefits of blue/green infrastructure enables drainage designers to select from a broad SuDS toolbox of natural and engineered features. For example, at SDS, we are increasingly being requested to build underground storage that is combined with above-ground public amenities or landscaped areas. Using below-ground attenuation can actually enable a drainage design to incorporate above-ground features like a pond or swale, while still achieving the required hydraulic capacity and performance in the space available.
SDS’s below-ground modular geocellular storage, GEOlight® has, for many years, been a standard means of attenuating and infiltrating excess surface water to prevent surface flooding. We are finding increasingly that GEOlight® is used in multifunctional designs. So, for example, by including storage underneath a dry pond or detention basin, an amenity can be used for most of the time, let’s say as a playing field, and designed to flood only infrequently during severe storm events. Alternatively, the underground tank can provide an overflow ensuring that a pond or wetland continues to operate efficiently, and the resident wildlife is protected.
Sewers for Adoption 8
Earlier this year, Water UK published the eighth edition of Sewers for Adoption (SfA8), which contains revised guidance aiming to clarify the conditions under which Water Companies can own and adopt SuDS as surface water assets. The guidance is due to come into force in 2019, following ratification by Ofwat. It has raised hopes that Water Companies will be encouraged to increase their use of SuDS and be more innovative and imaginative in their application.
Best Practice Guidance
A well-designed SuDS scheme avoids surface water flooding by capturing rainwater as close as possible to the point where it first falls. SuDS use a sequence of devices and techniques to mimic natural drainage processes and can use a broad toolbox of devices, both above- and below-ground features and components, to achieve the most effective and sustainable outcomes.
The SuDS Manual (C753), published by the Construction Industry Research and Information Association (CIRIA), defines the “four pillars” of SuDS as: water quantity, water quality, amenity and biodiversity. These principles put the control and treatment of surface water on an equal footing, so, where necessary, SuDS devices remove pollutants by filtering or separating out silt and sediment, debris and hydrocarbons.
For some developments, vegetative SuDS features, such as swales or wetlands, can be used successfully to treat surface water as plants help to degrade pollutants, but care must be taken not to pollute the very features intended to protect the environment. Especially for higher risk infrastructure, manufactured devices may be the most reliable and maintainable way of separating out the sediment and filtering the water before it is discharged to the environment.
Manufactured devices may be used to protect and ensure the effective operation of vegetative features, for example a hydrodynamic separator like the SDS Aqua-SwirlTM can be deployed upstream of a pond or swale to prevent it from silting up.
SuDS are not just a drainage solution for new development. Retrofit SuDS provide small, incremental improvements that achieve blue green infrastructure in urban environments. By working with highways agencies, local authorities and other stakeholders, Water Companies have an opportunity to target surface flooding hotspots with imaginative green infrastructure, from pocket parks to tree pits and traffic islands.
Recycling and Re-use
There have been encouraging developments from several Water Companies offering financial incentives and discounts to encourage householders or commercial property owners to incorporate water efficiency measures that reduce their load on the surface water sewer.
When surface water is held back in some way, whether it be an underground storage tank measuring 1000s of cubic metres, or a household water butt, it makes sense to look for sustainable ways to recycle and reuse it. Rainwater re-use systems range from simple and attractive garden planters right through to digitally-controlled technologies that combine flood protection with rainwater collection by use of smart sensing and real time controls. As a result, flood storage systems can be used to provide capacity for excess surface water during heavy rainfall, as well as harvesting rainwater for non-potable purposes like toilet flushing or garden watering.
Water Companies understand the principles of precision engineering for water infrastructure management and it is technology that may prove to be the final piece in the jigsaw that helps them achieve a more sustainable surface water infrastructure in future. In one of the latest developments, Anglian Water is reported to be using Artificial Intelligence systems for ‘digital twin’ modelling of the impact of proposed housing developments on drainage networks, for example.
The incentives for Water Companies to use SuDS as surface water assets are clear. The capital costs of expanding sewer capacity and treatment are avoided, and customers can be offered rewards for saving water and even for diverting downpipes. It’s time for all Water Companies to examine the opportunities that SuDS present and to engage in greater dialogue across the industry to encourage and support innovation.