Underpass 'could flood again'

At one point the Broadway underpass was under 20 feet of water

Belfast's multi-million pound Broadway underpass could flood again, an inquiry has found.

The underpass, part of the Westlink motorway, was at one point under 20 feet of water during flooding in August.

An independent team of experts was commissioned to investigate the incident.

They have now warned it could happen again if changes to the flood defence system are not made.

Amey Consulting said although the level of rainfall which fell on Belfast had not been experienced since 1914, the underpass should have coped.

A number of motorists had to abandon their vehicles

It highlighted that the culvert diverting the Clowney Water around the motorway was designed to withstand a one-in-100 years scale of flood - August's flooding was not as severe as this and rated at a level between a one-in-50 year and one-in-70 year flood.

It has been recommended that a model of the underpass is built and a £40,000 research project undertaken to establish what changes can be made to its drainage system.

Amey Consulting said there were a number of factors that contributed to the level of flooding, including a blockage of a trash screen at the mouth of the culvert. A valve to divert water exiting the culvert into another relief culvert was also not fully open.

It was also found that banks of the open section of the Clowney Water had not been built to the required level of 500mms above the anticipated water level of a one-in-100 year flood.

My department has begun the process of arranging a commission to build a model of the drainage system Conor Murphy

At the time of the August storm, it was 300mms above this level. Amey said while the extra 200 mms would not have prevented the flood, it would have delayed it.

As well as a modelling exercise to examine the drainage system, the consultants have recommended the raising of the banks, the introduction of a more robust early warning system with more liaison with the Met office and more regular inspections of the culverts.

The banks have already been raised to the 500mm level and a new monitoring process has been introduced.

'Complex'

Regional Development Minister Conor Murphy said the report "highlighted that further work will be necessary as there are a number of complex contributory factors identified which may have impacted on the flooding".

Regional Development Minister Conor Murphy speaking about the report

"In partnership with the DBFO (Design, Build, Finance and Operate) company (HMG) and the Rivers Agency, my department has begun the process of arranging a commission to build a model of the drainage system which will be used to determine exactly how each of these factors impact upon one another during periods of high water flows," he said.

"Depending on the findings of this further analysis additional physical measures may be necessary to mitigate against a similar occurrence."