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Drainage Assessments in Northern Ireland (NI)

Drainage Assessment in Northern Ireland (NI) and further afield are undertaken to ensure proposed new developments, and their surrounding areas, are not damaged or flooded in the event of heavy rainfall. A successfully executed Drainage Assessment will ensure storm water generated as a result of heavy rainfall is managed safely. Extreme rainfall events are becoming increasingly common and more extensive (as seen worldwide and in increasing flood risk in Northern Ireland). A Drainage Assessment in Northern Ireland is required under government guidance PPS15 (FLD3) for all new developments 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 across Northern Ireland for a range of clients, including private individuals, developers, planning consultants, contractors, housing associations and architects.

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

Drainage Assessment in Northern Ireland includes services:

  • A site visit / walkover by a qualified OSM Environmental Consultant
    • 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 in Northern Ireland or further afield is undertaken by OSM Environmental Consultants and 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 in Northern Ireland?

The need for a Northern Ireland Drainage Assessment 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, OSM Environmental Consulting 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.