Blog: Chris Digman - Bringing sustainable drainage to the fore

March 30, 2017

Dealing with the new and the old: Bringing sustainable drainage to the fore

Earlier this month, we saw the Government launch its 'Fixing our broken housing market' white paper. With 250,000 new homes needed each year, the pressure to build, and build quickly, is on. We must ensure we leave a once-in-a-generation legacy - and the right one at that. We need to do this in the face of unprecedented threats, of a changing climate, greater extremes in the weather and the storms that can lead to fluvial and pluvial flooding.

A key part of this legacy will be how we manage water in an integrated way, and in particular the surface water which can all too easily come under pressure. This applies to both brownfield redevelopment and building on greenspace. Will large scale building of housing and commercial sites be seen as an opportunity to ensure that we reduce flood risk, improve water quality and create multiple benefits? Or will we make it even harder for future generations to cope with unprecedented threats.

The local planning authorities provide a vital control point to limit the runoff rate and can set the requirement for the use of sustainable drainage systems (SuDs). Developers require the direction and level playing field at a local level, as a minimum to include SuDS. The more the bodies like local authorities, water companies and the Environment Agency, can work together, along with developers, the greater the opportunity to manage surface water in a joined up and more strategic way. For example, knowing where a development will drain to, local authorities may invest early (with minimal risk) and build a strategic solution to manage, hold and convey the flows safely from the development.  We can already see exemplars where we model, control and use forecasting to manage drainage systems live. However, whilst we have the technical ability, it is the collective working together that will help generate the widest benefits and create water resilient towns and cities.

The pressure to build new homes is only a small part of the problem. The existing stock of residential, commercial and business properties as well as all the highway network gives us another challenge. With these surfaces covering the vast majority of land within cities, it’s crucial that we tackle older sites too. But how do you encourage land and property owners to be part of a long term solution to manage the rainfall that lands on its hard surfaces?

Water companies are increasingly finding ways to work with a range of stakeholders to retrofit sustainable drainage at a local scale by understanding what’s important to individual property owners and incentivising them to enable the retrofitting of SuDS.

Business in the Community’s Water Task Force is supporting the introduction of retrofit SuDS, and in particular, those that can bring multiple benefits to the community in urban areas.  One of the key sites where this can be done is in schools.

After a first successful phase of developing an audit pack and toolkit, providing an assessment on the financial viability to remove surface water and look at the potential for retrofitting SuDS in Manchester, a new project is aiming to take that further. Bringing together a number of supporting partners of the Water Task Force, Business in the Community is developing a pilot that will see SuDS retrofitted where there is the financial incentive to complete the work on a school. In Manchester, surface water charges for businesses relate to the amount of impermeable area on their plot. Therefore the pilot will be applied where the school could move between surface water area charging bands and so create a positive cost benefit within a short period of time. Along with this work it will further the economic modelling and development of the toolkit for small sites, such as for schools and businesses to take advantage of and consider retrofitting SuDS. The economic modelling will include assessing the wider benefits, making use of CIRIA’s BeST – Benefits of SuDS Tool, so increasing the level of justification.

This collective working across the community with responsible bodies and supporting bodies will support the overall aim of the Water Taskforce to help create more water resilient cities, reducing flood risk whilst increasing the multiple benefits.  Making a success of this pilot will provide a blue-print for working with other businesses whilst also providing important learning linked to incentivisation.

Chris Digman is a Technical Director at MWH and Visiting Professor at the University of Sheffield. He is part of the supporting team from MWH working with BITC as part of the Water Taskforce.

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