Overview

Designing for exceedance can make the most of shared spaces and create multi-functional infrastructure. We may use highways to channel water, raise or drop kerbs to redirect water, and use car parks and green open space to store it. Property level flood protection and flood walls can prevent water entering properties. These measures can be used when retrofitting to reduce the risk of flooding happening in the future. In new development and through regeneration, there are more opportunities to change the topography of the landscape. This makes it easier to design for exceedance.

Designing for exceedance requires different disciplines, people and organisations to work together in partnership, with each being aware of the role that the other plays. This applies to both new development and retrofitting. In new development, spatial planners, urban designers, landscape architects and architects are the primary influencers of the design. Considering drainage and exceedance from the start often makes it easier to accommodate minor changes to create an area with a lower surface water flood risk. When retrofitting, drainage engineers may be the first to be involved, before a wider range of disciplines help develop the solution.

Making it happen

A range of success factors leads to effective designing for exceedance. It starts with having a good awareness and knowledge within the relevant professions and building the capacity (eg through training) and confidence of practitioners. This applies to those who wish to design for exceedance as well as those scrutinising development and drainage proposals and making decisions. Influencing and updating planning policy to drive a culture of change and ensure designing for exceedance takes place will provide local direction and support to those making planning decisions.

Pilot projects and case studies help to provide this confidence to design for exceedance, show what is possible and stimulate ideas. Engagement and collaboration within and between organisations helps to facilitate trust, share knowledge and overcome real or perceived barriers. Professionals having the support of managers to adopt a design for exceedance approach empowers them to use the wide range of measures available. Engaging and collaborating with communities also helps to gain acceptance of the problem, trust of professionals and organisations, and supports the development of solutions.

Greater interest in the last decade in managing flooding of all types has created new imperatives and reaffirmed responsibilities. New and clearer duties have been set through legislation. Urban drainage flooding of the type now recognised as ‘exceedance’ flows, has to be effectively controlled, recorded and mitigated. Through stronger direction, managing exceedance could and should be a requirement across all new development. With new types of drainage models, flood maps, responsibilities for maintaining registers and making surface water management plans, interest in and the management of exceedance should increase.