Most traditional drainage projects derive from a specific need, sometimes referred to as the driver. For example, a driver may be the draining of a new development, or it may be an improvement to the drainage of an existing development.


Where a driver is an improvement to address an identified deficiency, for example a flooding or pollution incident, then an early part of the delivery process will involve establishing the underlying cause. This process of linking cause and effect is sometimes referred to as problem understanding, and it is a fundamental component of delivering drainage improvements.


Retrofitting SuDS is an important part of addressing drainage deficiencies or generally improving the drainage of an urban area. Retrofitting can be “needs driven”, ie it occurs in response to a particular driver and is normally delivered through a defined scheme. Retrofitting SuDS in this context may be considered to be strategic.


However, there is another important way that retrofitting can be achieved, which is when opportunities occur. Opportunistic retrofitting may have nothing to do with drainage, flooding or pollution at all. It can occur as part of regeneration or any urban improvement scheme. For example, a highway surfacing programme might allow the retrofitting of kerb drainage or rain gardens at the same time. The investment then delivers two objectives: a highway improvement and a drainage improvement.


Opportunities may help deliver the needs of a particular driver, or they may occur independently. Often their effects alone are small, but when combined with other opportunities over a period of time, their effects can be significant.


The retrofitting framework recognises these two important strands, and that these strands may occur sequentially or in parallel.


When delivering a scheme to meet a specific driver, the two aspects normally proceed in parallel. On the one hand, the need can be established by linking cause to effect, and quantifying what a retrofit scheme will need to deliver, while at the same time the opportunities for retrofit can be established.


Opportunities and needs are then matched, and an outline of potential measures drawn up. These are then worked up in more detail, with the identification of specific measures, and associated costs and benefits, before the scheme is delivered. Underpinning the framework is “urban retrofitting”, which challenges the thought process of managing surface water to ensure that it is fully integrated with urban design.


The framework is broken down into several discrete steps that follow a typical project management life cycle. The framework has been developed from lessons learnt on real projects and has been written to be helpful to different stakeholder groups and different professionals. Much of it should be readily understood by the public.


For further details download a copy of CIRIA’s retrofitting guidance or the presentation on retrofitting.


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