Flood Consequence Assessment, Caerphilly


We were appointed to undertake detailed flood modelling and Flood Consequence Assessment (FCA) over a number of years, which formed part of a wider detailed planning application. Our assessments demonstrated that the proposed phased development could proceed, with all concerns regarding flooding addressed to the satisfaction of Caerphilly County Borough Council and Natural Resources Wales.


Flood Consequence Assessment – Llanbradach, Caerphilly

We have been involved in the Flood Consequence Assessment at this particular site from early 2017. Through two phases of development, have undertaken iterative assessment to address the flood risk posed to the development.

We were instructed to commence an assessment of the general site with regard to the likely impact of flooding from the Rhymney River which is present to the south. Once it was understood what ground levels could be utilised to reduce the risk posed by flooding, the development was then progressed in two phases, with each phased assessment being undertaken to determine satisfaction of all local and national guidance, e.g. Technical advice note (TAN) 15: development and flood risk.

The aspects that the detailed FCA works were required to address included:

  • Ground levels via land raising to achieve safe development.
  • Was this in keeping with the local area and accessible infrastructure?
  • Would new properties remain dry and/or tolerable during a flood event?
  • Due to the additional flood plain taken up by the development, could it be demonstrated that flooding to neighbouring properties would not increase?
  • Once Phase 1 was constructed, could it be demonstrated that it would not have a detrimental affect on Phase 2 proposals and neighbouring properties/areas?



The works required some iteration with regard to the scheme layout, the number of residential units and a number of detailed flood modelling assessments to help bring this scheme to a satisfactory conclusion and gain planning permission.

Welsh Government are expected to release updated TAN15 guidance and associated supporting flood mapping in 2021.

The update to the 2004 guidance has been anticipated for approximately two years and it is expected that there will be significant changes to law and how flood risk is assessed for planning. Any planning applications made after December 1st 2021, will need to fully comply with the new guidance. More information about the process can be found on the Natural Resources Wales website.


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