Checking flood risk properly for a specific address
Flood risk is the one constraint in this corpus that cannot be answered by locality, and treating it as an area-wide fact is the mistake to avoid in both directions — neither assuming a whole neighbourhood is affected nor assuming it is not. The starting point is the Environment Agency’s flood map for planning, which is published for exactly this purpose and returns a result for an individual address or site. It distinguishes risk from rivers and the sea into zones, and it is the source a planning authority will refer to. Two refinements matter. First, fluvial flood risk is only one source: surface water flooding, where drainage capacity is exceeded during intense rainfall, is mapped separately and is a genuine and growing risk in London on ground that the river map shows as low risk. Haringey’s Strategic Flood Risk Assessment, produced by Jeremy Benn Associates and released in February 2015, considers risk from all sources across the borough and is the more complete local picture; the council also publishes flood investigation reports. Second, the maps describe the situation without defences or with them depending on the layer, and a site behind a defence is not the same as a site at no risk. For a householder project the practical consequences scale with what is proposed. A single-storey rear extension at existing floor level in a lower risk zone usually raises nothing beyond sensible detailing. A larger proposal, a change in the number of dwellings, or anything creating habitable accommodation below ground can require a site-specific flood risk assessment submitted with the application, and can attract the sequential approach to siting vulnerable uses. Establishing which of those you are in takes one search and costs nothing, and it belongs at the very start — not because it is likely to stop the project, but because it changes the specification of the ground floor and the answer on basements, and both are expensive to revisit.
