Flooding Report in Shanard, Shanliss and Shanowen
13th March 2008
Dublin City Council have produced a report into the flooding in Dublin last August. I’m publishing the section of the report dealing with Shanard, Shanliss and Shanowen:
Shanard Road Flooding
Approximately 8 houses on Shanard Road were directly affected by the flooding on August 9th 2008, from no.12-26. These houses are at a low level, relative to the road, and once the road flooded, the houses were quickly inundated. Residents also reported that rainwater flowed overland from Shanliss Road, which is at a higher level than Shanard Road, and gathered at the local low point in front of these houses.
Following the flooding, approximately 1,130m of the drainage network in the area was camera surveyed. Drainage Division are currently pressure cleaning the drainage network in the area.
The camera survey and subsequent pressure cleaning revealed that there is a significant problem with scale in the pipelines in this area. Scale occurs when minerals, which are naturally occurring in the soil, are dissolved, seep through joints in the pipes, and solidify within the pipe. It forms a hard, concrete-like deposit, which can then act as an obstruction, reducing the flow capacity of the pipeline.
Scale is not easily removed by pressure cleaning, and more aggressive methods are just as likely to damage the pipeline as clear the scale. The cleaning programme is ongoing at present, and will continue until the pipelines are completely clear.
The pipeline on Shanard Road has been completely cleared, along with a section on Shanowen Avenue. This should afford a considerable level of protection in any extreme rainfall event in the immediate future, carrying storm water away from the vulnerable low lying area to overland flow on Shanowen Avenue. For information, gullies on the affected roads were cleaned in March 2008, and again in August & September 2008 as a precaution.
Improvement Measures
At present Drainage Division are studying possible measures to improve the capacity of the drainage network in the area. Increasing the capacity would allow the drainage network to accommodate more extreme storms than at present, reducing the likelihood of future property flooding.
- In addition to works on Shanard Road/Shanowen Avenue, a significant pressure cleaning programme will also take place on Shanliss Road, Shanowen Grove and Shanowen Road. This should increase the capacity of the drainage network on Shanliss Road, and reduce the amount of overland flow reaching Shanard Road in an extreme rainfall event.
- An abandoned overflow sewer on Shanard Road is being investigated. It may be possible to carry out works to restore this line to service, depending on the condition of the pipeline, its capacity, whether it has been cut-off/excavated, and whether it discharges at a suitable point.
- Should the overflow be returned to service, the extra capacity provided can be exploited by installing additional gullies.
- Drainage Division are examining the possibility of installing a ramp at the junction of Shanliss Road / Shanard Road to divert flow overland, away from Shanard Road, and will liaise with the Roads and Traffic Dept.
Drainage Division will continue to monitor the operation of the drainage network during extreme weather events in the area.
