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Drainage Assessment Northern Ireland (NI)

Drainage Assessments are required under PPS15 for a range of reasons. O’Sullivan Macfarlane have successfully completed Drainage Assessments and flood risk assessments for a range of clients throughout Northern Ireland. These include private individuals, developers, planning consultants, contractors, housing associations and architects. Our fully equipped, in-house team of locally based environmental specialists can provide services in all aspects of a Drainage Assessment. Every Drainage Assessment includes a discharge consent to Rivers Agency (Schedule 6 application) or NI Water (PDE application).

Every Drainage Assessment undertaken by O’Sullivan Macfarlane is carried out in line with government guidance PPS 15 (Revised Planning Policy Statement 15) ‘Planning and Flood Risk’.

Drainage Assessment Services in Northern Ireland (NI) 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).

With a combined experience of over 20 years, and drawing on experience from both the private sector and the Northern Ireland Environment Agency, we have significant expertise in the field of Drainage Assessment. All our work is provided in-house using locally based Environmental Consultants. Our staff hold membership of the Institute of Environmental Science (IES) and the Chartered Institute of Waste Management (CIWM).

Background to Drainage Assessment and Flood Risk Assessments in Northern Ireland (NI)

The requirement for a Drainage Assessment or Flood Risk Assessment in Northern Ireland is driven by the Planning Service via consultation with Rivers Agency. In these planning applications, where it appears on the basis of prevailing information, that a sites drainage infrastructure is a material consideration in the determination of the development proposal. The purpose of the consultation will vary according to the circumstances, but will often involve seeking advice on the nature and extent of the flood risks. Typically these risks relate to ineffective drainage, and the scope for management and mitigation of the associated risk where appropriate. The outcome of the consultation may require the developer / applicant to carry out a Drainage Assessment for the proposed development to facilitate further assessment of the proposed development.

Types of Drainage Assessment Required in Northern Ireland

A Drainage Assessment is required for all developments in Northern Ireland where the following thresholds are exceeded:

  • 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.

In addition to the above criteria, a Drainage Assessment can be required where there is historical evidence of surface water flooding or were a complaint has been lodged with Rivers Agency.

Drainage Assessment and Overland Flooding in Northern Ireland (NI)

Our engineers are one of the few consultants in Northern Ireland (NI) who are able to risk assess overland flow during flood events. This allows our engineers to complete drainage assessments for Q30 flood events, resulting in 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 exceedance flows within sites.