Sunday, 30 June 2013

Cabra East Flood Prevention

In May 2013 I again raised with Dublin City Council the issue of flood prevention for homes in Cabra east.  I asked that Dublin City Council provide a report on what measures has DCC taken to reduce the risk of flooding in Cabra East? Can the Manager outline what options can be explored to improve drainage and reduce the risk of flooding in Cabra East? Will the Manager please attend a meeting with residents whose homes have been previously flooded to discuss possible options? Following is the reply I received:
The flooding of October, 2011 has previously been reported on to the City Council, Environment & Engineering Department SPC and Area Committees and was caused by an extreme event where to the amount of rainfall exceeded the capacity of the drainage infrastructure.
In relation to the Cabra area a number of mitigation measures have been considered and examined in detail. The outcome of this assessment can be summarised as follows:

An overflow pipe, 65 metres in length from Cabra Road to Annamoe Drive was constructed in December 2011. This will provide a limited level of flood alleviation on a local level on Imaal Road, Cabra Road, Leix Road and surrounding area.

A location for a swale at Annamoe Park was examined and found not to be viable due to the conflict with a foul sewer and constructability issues for pipework to Annamoe Park.

The option of a of constructing an overflow pipe from Dowth Avenue to the disused railway line (New Luas Line BXD). After analysis the RPA confirmed the following, “there is no spare capacity in the drainage system and also, a potential increased risk to flooding in areas that have not experienced flooding in the past. This is no longer a viable option.

The option of a pumped partial solution from Leix Road to Bradogue Stream at Cabra Road was considered. This would pump water from the affected areas to lower it below flooding levels in the flooded houses (around 100-200mm) is estimated at 2,335 cubic metres. This would require construction of an underground storage tank, pump station and approx 160m of 400mm pumping main. The estimated cost of this is approx €340,000, for which a source of funding has yet to be identified. In addition, there are a number of unresolved technical challenges, such as the size of storage tank/station, space required for the pumping main and capacity of receiving sewer that may make this option unviable

· The option of constructing a gravity partial solution from Leix Road to Bradogue Stream at Cabra Road is also under consideration. This could lower the floodwater level to below flooding levels of the houses (around 100-200mm). This would require approx 160m of 600mm pipeline from the low point of Leix Road to Cabra Road, at an estimated cost of €200,000.

· Another option under consideration is a gravity partial solution from Leix Road to the surface water sewer in the laneway south of Leix Road plus upgrading of the Bradogue Stream downstream. There are two facets to this project. Firstly, construction of an additional surface water sewer from the lowest point of Leix Road to the manhole in the private lane to the rear of AIB. This new sewer would be 125m long. However, 33m goes through private gardens, and permission from property owners would be required. Secondly, an up-grade of the Bradogue Stream: This up-grade is required at the junction of Dowth Avenue and Cabra Road. The new sewer required here would be 43m long & 750mm in diameter. Traffic restrictions would occur on the Cabra Road during construction of this new sewer. Cost: €250,000.

While the last two options may be technically possible, they will be subject to detailed design, require a significant capital expenditure, a number of consents from relevant property owners, and involve significant disruption during construction.

As this is a complex issue, with a number of factors to consider, the most effective means of consultation with residents would be through the Dublin Flood Forum, which it is anticipated will be initiated later this year.   Contact: Colin Egan, Assistant Engineer.  Tel: 222 2398