scope:

PURPOSE AND SCOPE

The purpose of this document is to detail National Grid's technical and procedural requirements for flood resilience of new and existing operational electricity substations. Operational compounds outside substations, such as cable sealing ends, are currently excluded from the scope of this document.

This specification expands upon the requirements outlined in National Grid Policy Statement PS(T)095 - 'Flood Mitigation Policy' and should also be read in conjunction with Engineering Technical Report ETR138 - 'Resilience to Flooding of Grid and Primary Substations', published by the Energy Networks Association.

It should be noted that this document includes sections on the design of site drainage to protect against local flooding due to extreme rainfall events, and as such will apply at all new substation builds, not just those deemed to be at risk of flooding from the Environment Agencies flood zone maps. It shall not generally be necessary to retrospectively apply rules on site drainage to existing sites, unless that is a particular requirement of the project.

Section 1 of this document details National Grid's requirement for flood modelling and risk assessment. This will be used to assess the need for flood mitigation measures at particular sites. For detailed guidance on Flood Risk Assessment methodology, run-off calculation, detailed drainage design etc. designers shall refer to recognised industry practice and the Environment Agency website.Sections 2 to 4 of this document detail requirements for particular types of flood defence and associated infrastructure. These sections are primarily intended for retrospective use on existing substation sites, but could in some instances be used for new build substation sites.

Definitions are detailed in Part 2 and are italicised throughout this specification.

All Hold Points in this specification shall be agreed with the National Grid Civil AssuranceEngineer.