Summary of key learning points

A number of interesting and useful learning points, success factors emerged from CIRIA Research Project RP991 Managing urban flooding from heavy rainfall – encouraging the uptake of designing for exceedance and were based on a literature review, case studies, questionnaire analysis and workshops. This section outlines the key points with the reports providing more information.


  • Exceedance will happen. The capacity of drainage systems is limited. Exceedance is unavoidable in many places. Exceedance can be managed on the surface, or do nothing and let it find its own pathways and depressions, often causing unmanaged flooding and inconveniencing communities. Various organisations have a duty to manage or design for exceedance. Engaging and working with the public, and explaining the design approach helps to foster understanding and to gain support for the proposed solutions. Where exceedance has frequently occurred in the past, it is easier to engage the public.


  • Collaboration within and between organisations. Flood risk management authorities have a statutory duty to work together. Managing or designing for exceedance falls under this requirement. It is easier to design for exceedance when those in leadership roles support the approach (such as a local authority head of service). Early engagement with key departments and disciplines helps to overcome real and perceived concerns over the impact of solutions and the risks of litigation and liability. This leads to collaboration, joint problem solving and good design to overcome health and safety concerns.


  • Making the most of multi-functional infrastructure and shared space. Space in urban areas is often limited, so the infrequent use of public (or even private) open space and highways for exceedance can create multi-functional infrastructure (eg highways, playing fields). Highways are multi-functional by design, even if not intended, as exceedance will occur by default where the drainage system design standard is relatively low (typically rainfall with a 1 in 5 year return period or a 1 in 10 chance of happening in any given year). It is better to design for the exceedance and manage flood risk in a proactive way.


  • Engaging a range of disciplines to collaborate and share knowledge of designing for exceedance. Sharing information as to what exceedance is and when it occurs helps stakeholders understand the importance and value of considering it properly. Greater knowledge sharing is necessary to encourage understanding, build capacity and promote designing for exceedance. Where organisations and individuals understand exceedance, there are more examples of good practice, helping to avoid imposing inappropriate solutions.


  • Maximising the benefits from funding opportunities. Some case studies demonstrated that exceedance management solutions received funding from non-flooding budgets (eg highway maintenance). Others demonstrate that partnership funding creates successful schemes. ‘One off ’ funding made available following significant flooding has supported the delivery of a number of schemes (eg Defra’s Early Action Funding for surface water flooding).


  • Setting planning conditions and following frameworks and design codes. Strong leadership and direction through the local planning system enables designing for exceedance to take place in new development and regeneration. Where this happens at the start of the planning process exceedance management can become integral to the final design, reducing the risk of flooding to people and property.


  • Assessing risk to inform designs and decisions. Different risks may affect or be owned by a variety of stakeholders. Some case studies demonstrate stakeholders considering and prioritising a range of risks. Where this happened, risk mitigation took place. ISO 31000:2009 provides a framework for considering and managing a wide range of risk. However, it is relatively unknown and rarely applied. Raising awareness of such standards will help to promote a risk-based approach.


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