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The Sequential Test for new housing development - Christchurch

Planning Policy Statement 25 (PPS25) requires local planning authorities to follow a risk-based approach in their consideration of applications for new development. The first stage of this approach is the Sequential Test which aims to steer new development to areas with the lowest probability of flooding. Only when there are no reasonably available alternative sites within zone 1 (low probability) can development within zone 2 (medium probability) or zone 3 (high probability) be considered.

Christchurch Borough Council has produced a Strategic Flood Risk Assessment that shows Flood Zones one, two and three in the years 2086 and 2126.  This has been done to meet the requirements of PPS25 which states that development must be safe for its full design life; 60 years in the case of commercial developments and 100 years for housing.  The Sequential Test must be based on these future Flood Zones.

This page explains the process of conducting the Sequential Test for housing required by Planning Policy Statement 25 - Development and Flood Risk (opens in a new window).  Advice for commercial developments can be found on the sequential test for commercial development in Christchurch page.

Reasonably available alternative sites

Prior to consideration of any development within a flood zone in Christchurch, a Sequential Test must be conducted to demonstrate that no reasonably available alternative sites exist within zone one which could be developed instead.  The Christchurch Strategic Housing Land Availability Assessment (SHLAA) identifies potential sites for new housing across the borough and estimates how many new dwellings could be accommodated on each, called the net potential.  Sites within the first five year supply of housing sites identified by the SHLAA must be considered suitable, available and achievable, and therefore developable in line with PPS3 and PPS25.

Applicants proposing new housing within Flood Zones two or three will need to demonstrate that none of the sites identified on the five year supply schedule below are reasonably available alternatives at lower risk of flooding:

Our advice, with support of the Environment Agency, is that reasonably available alternative sites include not only sites of a similar size and dwelling capacity to the one being tested, but also smaller sites which could cumulatively provide the same number of dwellings.  For a development of 12 houses for example, the Sequential Test should consider that the same number of houses could be accommodated on two sites of six dwellings each, or three sites of four dwellings each, or indeed any other combination of smaller sites.

Intensification of residential development on a site in Flood Zone two or three will not pass the Sequential Test.  For example, the demolition of one house and replacement with two dwellings will fail the test.

It is highly unlikely therefore that residential development proposed in Flood Zone two or three, where it results in a net increase in dwellings, will pass the Sequential Test.  Applicants are advised to speak with Christchurch planning officers prior to submitting any application for development affected by flood risk.

Which Flood Zones to use?

The Sequential Test must always be carried out using the undefended flood zones which do not factor in the protection afforded by existing defences - maps are provided on the Christchurch Strategic Flood Risk Assessment page.  These zones show the extent of flooding should a defence be overtopped or breached during a flood.  The defended zones can only be considered as part of the Exception Test, and only once the Sequential Test has been passed. For more detailed maps please contact the Christchurch Planning department using the details below.

New buildings exist for many years and must be safe throughout their design life; for housing this is taken to be 100 years.  Consequently a new house built in 2010 must be safe from flooding until 2110.  The Christchurch Strategic Flood Risk Assessment provides flood maps for the year 2126 which indicate whether a site is likely to be affected in that time.

To accurately determine the risk, a site-specific Flood Risk Assessment will be required for all applications affected by current or future flood zones.

Evidence to be provided by applicants

The PPS25 Practice Guide (2009) places the onus on developers to provide the local planning authority with evidence to inform the Sequential Test.  Applicants will need to provide the following with all applications for residential development affected by flood risk:

Environment Agency Standing Advice

Planning applicants and their agents should refer to the Environment Agency Flood Risk Standing Advice for England (opens in a new window) for guidance on what to do when submitting a planning application. 

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