Shimna River, Newcastle - Flood Alleviation Scheme

The principle aim of the Shimna River project was to assess whether an economical, environmentally and socially sensitive scheme can be produced which will alleviate the flood risk to affected properties, infrastructure and businesses from the Shimna River.

Flooding at Entrance to Car Park off Bryansford Avenue

Scheme Summary

  • Estimated Cost:        £6.5m
  • Length:                     1430m
  • Type:                         Clad steel sheet piled/reinforced concrete secant, piled walls and embankments
  • Status:                       Tender Stage

Key Dates

  • September 2017 - Appointment of Design Consultant Aecom
  • December 2020 - The DfI Minister made the Appropriate Assessment, signed the Confirmation Order and determined that the scheme should proceed
  • January 2021 - Start of Tender Stage
  • February 2021 - Advanced Tree Clearance

Scheme Background

The Shimna River rises in the Mourne Mountains and flows to Newcastle through Tollymore Forest Park. Within the town of Newcastle, the Shimna River merges with the Burren River in Islands Park and the Tullybranigan River at the boating lake in Castle Park, before discharging to the Irish Sea.

Newcastle has flooded regularly over the last 40-50 years. The local media have reported on floods during 1968, 1978/79, 1987, 1988 and 1994, whilst other significant flood events are known to have occurred during 1982, 1986, 1990 and 1997.

On 16 and 17 August 2008 the Shimna River flooded onto Bryansford Avenue and Shimna Road. Due to the magnitude of flooding, flood water also crossed catchments, to pond within the Burren catchment. The flood caused damage to approximately 36 properties, Island Park and affected the local schools.

The Northern Ireland Flood Risk Management Plans (FRMPs) published on 22 December 2015 as part of the implementation of the EU Directive on “the Assessment and Management of Flood Risk” identified Newcastle as being 1 of 20 Significant Flood Risk Areas in Northern Ireland. Fluvial flood risk was identified as the main concern.

A Feasibility Study and Economic Appraisal was carried out by The Department in 2015/16. This indicated that 312 properties, including two schools, within the Shimna and Burren catchments are at risk of flooding during a 1% Annual Exceedance Probability (AEP) flood event The Shimna FAS is designed to provide protection up to the 1% Annual Exceedance Probability (AEP) flood, in line with the Departments design standard for urban areas.

Scheme Description

The proposed scheme involves the construction of flood alleviation measures to reduce the risk of flooding from the Shimna River and to protect existing properties in the town. The works will extend both upstream (into Tipperary Wood) and downstream (into Island Park) from New Bridge on the Bryansford Road. The proposed works will include:

  • 1430m of clad steel sheet piled/reinforced concrete secant piled walls and embankments,
  • Construction of a new pathway,
  • Re-alignment of an existing pathway,
  • Erection of one floodgate,
  • Relocation of a drainage ditch,
  • Demolition of a number of property walls and boundaries,
  • Felling of a number of mature trees - Some replanting will take place as part of the works.

Scheme Benefits

The estimated cost of the preferred option is £6.48m and it will provide benefit in the form of flood damage avoidance to property of £8.15m over the 100 year design life of the scheme, providing a Benefit Cost Ratio of 1.26.

Environmental Statement and Habitats Regulations Assessment

The Department is required to assess the environmental effects of any proposed drainage works such as the Shimna River Flood Alleviation Scheme and detail the measures proposed to reduce or eliminate those effects. As the Shimna River is within an Area of Special Scientific Interest (ASSI) and the Mourne Area of Outstanding Natural Beauty (AONB), there is a likelihood of significant environmental effects and an Environmental Impact Assessment (EIA) has been undertaken.

It has also been necessary to undertake an Appropriate Assessment in accordance with the Conservation (Natural Habitats, etc.) Regulations (Northern Ireland) 1995.  A ‘Statement to inform the Appropriate Assessment (Habitats Regulation Assessment (HRA))’ has been undertaken to assess any impact of the proposed scheme upon the Murlough Special Area of Conservation (SAC).

Full details of the environmental processes can be found at the following link:

Scheme Reviews

Following development of the detailed design the business case was updated and resubmitted to the Department of Finance in August 2020 and was approved in September 2020.

A further review of the scheme was undertaken following the August 2020 flooding event. The scheme was remodelled using data which was collected during the storm to ensure that the proposed defences would be effective during a similar event. One of the major factors which contributed to this flooding was the trees and debris which washed down the Shimna River from the upstream forested areas blocking the Bryansford Road Bridge. Therefore the design has been refined to include the design of a totem pole structure in the river upstream of the Bridge, to catch debris and fallen trees.

Preliminary Works

To accelerate the scheme, advanced tree clearance works began on the 1 February 2021, to avoid the bird nesting season. This will allow the construction work to begin when a contractor is appointed in summer 2021.

Scheme Documents

Scheme Photographs

News

September 2017 - Appointment of the Design Consultant Aecom.

May 2018 - Notification of the intention to carry out an Environmental Statement.

June 2018 - Public Information day in the Newcastle Centre.

August 2018 - Publication of the Environmental Statement.

June 2019 - Scheme approved by the Drainage Council.

August 2020 - Major flooding event

September 2020 - Updated scheme was approved by the Department of Finance

December 2020 - The DfI Minister made the Appropriate Assessment, signed the Confirmation Order and determined that the scheme should proceed.

January 2021 - Start of Tender Stage.

February 2021 - Advanced Tree Clearance.

 

 

 

 

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