Early consideration of flood risk and drainage can provide considerable cost benefits, especially where drainage requirements affect development layout and use. 

A preliminary Drainage Strategy, undertaken prior to

fixing a developments site layout, can:

  • Identify the method of surface water discharge, and whether gravity drainage can be achieved;

  • Establish required discharge rates through calculation of greenfield runoff rates using ReFH (industry leading) software;

  • Identify the approximate amount of required attenuation storage using industry leading MicroDrainage software;

  • Inform the location of SUDS based on existing topographical information;

  • Advise on the type of SUDS required to comply with National SUDS Standards;

  • Identify any site-specific drainage requirements or constraints through consultation with the Lead Local Flood Authority and Sewerage Undertaker.


Following completion of a preliminary Drainage Strategy Assessment and production of a detailed site layout, a detailed Drainage Strategy and Detailed Drainage Design can be prepared to support the planning application.


The detailed Drainage Strategy will provide sufficient information to inform the Detailed Drainage Design.

The Detailed Drainage Strategy includes:

  • Confirmation of final discharge method, connection point(s) and discharge rates with agreements in place from the relevant authority (Lead Local Flood Authority / Natural Resources Wales / Sewerage Undertaker / Highway Department / Drainage Board);

  • Calculation of required attenuation storage based upon the detailed site layout;

  • Review of chosen SUDS methods showing compliance with the National SUDS Standards;

  • An indicative drainage layout drawing.

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