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Drainage Assessment – Northern Ireland (NI)

Drainage Assessments ensure developments and their surrounding area are not damaged or flooded in the case of heavy rainfall as a result of poor management of surface water. A Drainage Assessment is required under government legislation PPS15 (FLD3) for all new developments in Northern Ireland that meet any of the following criteria:

  • A residential development comprising of 10 or more dwelling units
  • A development site in excess of 1 hectare
  • A change of use involving new building and / or hard surfacing exceeding 1000 square meters in area
  • Historical evidence of surface water flooding
  • Where a complaint has been lodged with Rivers Agency.

Drawing on a combined experience of over 20 years from both the private sector and the Northern Ireland Environment Agency, the Drainage Assessment Team at OSM have successfully completed Drainage Assessments for a range of clients throughout Northern Ireland, including private individuals, developers, planning consultants, contractors, housing associations and architects.

To discuss your site’s Drainage Assessment needs, contact a member of our Drainage Assessment Team here.

Drainage Assessment Services in Northern Ireland include:

  • A site visit / walkover by a qualified Environmental Scientist
    • Review of the site development proposals / planning application
    • Submission of a Schedule 6 agreement under the Drainage (NI) Order 1973
    • A detailed review of the current Revised Planning Policy Statement 15 ‘Planning and Flood Risk’ (Policy FLD 3) in relation the proposed development
    • Calculation of the expected peak rainfall at the proposed site during a storm event
    • Calculation of the existing and proposed site surface water runoff
    • The production of a Drainage Assessment report and submission to planning Service
  • Provision of discharge options and application (if required)
  • SuDS Designs in line with CIRIA Guidance on the Construction of SuDS (C768)

Every Drainage Assessment undertaken by OSM is carried out in line with government guidance PPS 15 (Revised Planning Policy Statement 15). Every Drainage Assessment includes a discharge consent to Rivers Agency (Schedule 6 application) or NI Water (PDE application).

To view our latest projects, including Drainage Assessment Services, click here.

What is a Drainage Assessment?

The need for a Drainage Assessment in Northern Ireland is decided by the Planning Service via consultation with Rivers Agency. These organisations will determine whether your site requires a Drainage Assessment based on the specific drainage needs relating to the type, size and surrounding environment of your development. A Drainage Assessment will vary according to the circumstances but will often assess the nature and extent of the flood risks to your site, typically relating to ineffective drainage, and methods to manage and lessen these associated risks.

Overland Flooding in Northern Ireland

OSM Environmental Consulting is one of the few environmental consultancies in Northern Ireland able to risk assess overland flow during flood events. This allows our Environmental Consultant to complete drainage assessments for Q30 flood events, resulting in significant cost savings in comparison to typical Q100 SuDS systems.

In addition, O’Sullivan Macfarlane have obtained Rivers Agency approval for a range of wet / dry swale systems in Northern Ireland for the management of exceedance flows within sites.

If you require a Drainage Assessment, contact us today.