Building layout

The effect of building layout

The distribution and layout of buildings on a site can greatly influence the potential for creating flood pathways and considerably affect property flood risk. Little can be done to affect the building layout in existing urban areas except where significant redevelopment is anticipated. However, much can be done to manage cost effectively exceedance flows in new developments by careful layout of buildings.

In any new development it is important that the drainage of the site, including extreme events, is considered at the earliest possible date. Ideally its effects should be part of initial negotiations for land acquisition as it may significantly affect land value. Flood flow paths should be considered in the light of the natural drainage pathways on the site, and space left between buildings to accommodate them. Where roads and pathways can be arranged to act in a secondary capacity as flood pathways then the management of exceedance flows will be much easier.

In particular designers and developers should be wary of locating high value property such as housing at low spots, as floodwater will always tend to accumulate there. If unavoidable, special care should be taken to ensure that such property is protected from accumulated flood volumes by raising threshold levels, and/or providing additional drainage.

In many cases it may be more cost effective to amend site layout and the above ground flood channels (major system) rather than alter the below ground (minor) drainage system.