Expert Consultancy – What is a Section 50 Application/Approval?

The Office of Public Works (OPW) have several regulatory functions under the 1945 Arterial Drainage Act and S.I 122/2010 (Assessment and Management of Flood Risks) Regulations, including Section 50 approval. Section 50 requires that inter alia:

“No local authority, railway company, canal company or similar body and no industrial concern may construct any new bridge or alter, reconstruct or restore any existing bridge over any watercourse without the consent of the Commissioners or otherwise than in accordance with plans previously approved of by the Commissioners.”

The construction, alteration, replacement or restoration of a bridge or culvert brings the possibility of changing the hydraulic characteristics of a watercourse. These changes may result in flood levels increasing upstream and/or downstream of the bridge/culvert project, increased erosion of the watercourse/flood plain, and increased deposition in the watercourse due to a change in flow velocities & turbulence and ultimately an impact on the local flood risk management plan. It is the responsibility of the OPW to safeguard against undesirable effects on the hydraulic characteristics of a watercourse with the introduction or alteration of bridges & culverts.

It is important to note that OPW consent does not confer permission to construct and does not absolve the developer from fulfilling any other legal obligations or third-party claims arising from the project.

Evidence of adherence to hydraulic design standards and considerations for hydraulic & hydrogeological conditions must also be demonstrated in conjunction with a Section 50 application. It is generally considered inefficient or impractical to design flood protection or other structures to deal with the largest flood that could possibly occur (even if it could be estimated). In practice, the design is intended to provide a degree of protection expressed as a return period. It is important to remember that the hydraulic engineer is dealing with natural events, random in nature. It is true that if the rainfall at a place is measured daily for a period, knowledge about what is a probable daily rainfall will be built up. However, it is not possible to gain any possible limiting value of daily rainfall other than intuitively.

The only answer that can be given when asked for the maximum possible discharge of a river is as follows: from the data available and by making various assumptions, it would appear that a certain value will not be exceeded on average more than once in a specific number of years.

ORS has significant experience with Section 50 applications and can provide the following expert services;

  • Topographical Surveying
  • Hydrology and Catchment characterisation
  • Hydraulic Calculations
  • Flood Modelling
  • Civil Design
  • Section 50 Application submission

Get in touch with our Environmental Team at if you have any queries on Section 50 applications.

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