Water & flood risk

A flood risk assessment either supports a planning application or explains why one should not be made, and we will write the second if that is what the modelling says. Two of the eleven sites we assessed in Flood Zone 3 last year we advised our clients not to pursue. Both accepted it; one had already spent £180,000 on an option agreement, which is precisely why the assessment should come before the option and not after.

We build hydraulic models in HEC-RAS and Flood Modeller depending on the reach, and we use the Environment Agency’s own model where a suitable one exists rather than rebuilding it — which is cheaper for you and, more usefully, means the Agency is reviewing a model it already accepts. Climate change allowances are applied to the current guidance and stated explicitly on the plan.

On drainage we design to the non-statutory technical standards with SuDS as the default. Infiltration is tested rather than assumed — a BRE 365 test costs a few hundred pounds and a soakaway designed on an assumed infiltration rate that turns out to be wrong costs a great deal more. Where the ground will not infiltrate we say so early, because it changes the whole drainage strategy and sometimes the layout.