ATLAS Guide
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T12.5: The Role of the Sequential and Exception Tests

The sequential approach to considering development sites is designed to promote sites where the risk and hazard from flooding events is negligible or non-existent over those where higher flood risk is a factor. Should there be no lower-risk options available and/or there are other material factors in favour of developing higher-risk sites then these options need to go through a robust process to demonstrate that they are acceptable in terms of the sequential approach.

Adopting the sequential approach to fluvial and coastal flooding is relatively straightforward using information on risk is available from the area office of the Environment Agency or, where available, from the Strategic Flood Risk Assessment. The Flood Zone mapping on the EA’s website is not sufficiently detailed for planning purposes. Information has historically been less readily available when appraising the risk from other types of flooding such as surface water flooding, however as SFRA’s are charged with considering all sources of flooding then increasingly this information should be available via SFRA’s. Where information exists on the probability of flooding from other sources then it should be treated in a similar fashion to river flooding in terms of mapping probability and assessing viability when applying the sequential and exception tests. Maps with sufficient detail to enable broad areas that may be susceptible to surface water flooding are becoming available from the EA, and on a local level, see T12.4.

The mechanism is for sites to first be considered under a Sequential Test which is applied at either the regional, sub-regional, local, or site-specific level, as appropriate. In the case of an allocated strategic site, the approach should be straightforward if the policy base has been sequentially tested via a SFRA. However a site-specific FRA would still be required to demonstrate how a proposal complies.

If however a potential site is yet to be sequentially tested in a Local Plan or its proposed use is not in accordance with this then the sequential test needs to be applied. This is in order to demonstrate that there are no other appropriate and reasonably available alternative sites where the flood risk is lower. In order for a site to be considered against the sequential test, the developer’s case is thus assessed by the LPA, and should include evidence on:

  • vulnerability classification(s) for the uses within the proposed development (see table below, taken from Technical Guidance to the NPPF);
  • flood risk to the specific site in question; and
  • availability of suitable and potentially deliverable alternative sites which have a lower flood risk.

The table below (3) is reproduced from Technical Guidance to the NPPF: 
table flood risk

In some cases, development in flood risk areas has to be considered if there are no reasonably alternative and available sites to accommodate a similar development within a planning authority’s administrative area, and/or there is a regeneration imperative. Under such circumstances the Exception Test should be applied. This, as specified in the NPPF requires the following to be satisfied:

  • that the flood risk is outweighed by the wider sustainability benefits to be provided by the development;
  • it must be demonstrated  that development will be safe fro it's lifetime and will not increase flood risk elsewhere, and ideally reduce flood risk overall.

Bothe elements of the exception test would need to be passed for development to be allocated or permitted.

In addition, it must also be demonstrated that uses with the highest vulnerability have been appropriately sited, that flood resilience and resistance measures have been incorporated and that priority has been given to including sustainable urban drainage measures. 

Last Updated on Thursday 29/03/2012 - 12:05PM

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Advisory Team for Large Applications (ATLAS), 2014