Environmental Statement volume 4 - Chiltern Evergreen3

3.3 The Requirements of the Exception TestWhere Essential Infrastructure is proposed (as in this case) to be located within FloodZone 3a or 3b, the Exception Test must be passed. For this there are three criteria:1. It must be demonstrated that the development provides wider sustainabilitybenefits to the community that outweigh flood risk. This should be driven by theappropriate Core Strategies evidence base SFRA (i.e. a policy SFRA as opposed toSFRAs that present flood modelling results for an authority area or region andrefine the Flood Map), where one has been prepared;2. The development should be on developable previously-developed land or, if it isnot on previously-developed (brownfield) land, that there are no reasonablealternative sites on previously-developed land; and3. A FRA must demonstrate that the development will be safe, without increasingflood risk elsewhere, and, where possible, will reduce flood risk overall.It can be demonstrated that the Scheme as a whole meets the sustainability test andthis is addressed in the TWA application documents as a whole. With regards to LocalDevelopment Documents, the Local Development Framework is currently beingprogressed and the rail chord can be confirmed to be safeguarded under the interimLocal Plan.The remaining two criteria have been applied to all development sites lying within FloodZones 3a and 3b. In addition, and in accordance with the wider aims and objectives ofsustainable flood risk management, opportunities have been sought across the schemeto reduce the risk of flooding overall.Surface water runoff rates have been calculated based upon current design footprintsand should be re-evaluated at detailed design. These calculations are presented withinthe following section. Design commitments and subsequent Level 3 assessmentrequirements have been specified for sites where a detailed assessment of the impactsof the development site on flood plain storage and flood flow pathways across thefloodplain is required.The development sites have been classified into two groups; those that lie entirely withinFlood Zone 1 and those that lie in Flood Zones 2 or 3. The Flood Zone 1 group aresummarised within section 3.4. The sites that lie within Flood Zones 2 or 3 are discussedin more detail within section 3.5. For each of these sites the Sequential Test if applicablehas been applied, along with the Exception Test criteria where required (if land is withinFlood Zone 3). Where commitments to conduct appropriate Level 3 FRA are consideredto be required during detailed design phases, these have been made.The overall results of these aspects of the assessment are summarised by site withinsection 3.6. Preliminary surface water runoff calculations have been undertaken for allrelevant sites, irrespective of extent and location. These calculations are presentedwithin Section 4 of this report.3.4 Sites Lying in Flood Zone 1Sites lying within Zone 1 by definition pass the Sequential Test. The FRA requirementsfor such developments dictate that surface water runoff calculations are undertaken.Preliminary surface water runoff assessments are provided in Section 4, together with27