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Urban surface water flooding mitigation using gully management, staff innovation, gully monitoring r

Case Study:

Urban surface water flooding mitigation using gully management, staff innovation, gully monitoring r

Background

Surface water flooding occurs as a result of heavy and more frequent periods of rainfall, coastal surges, extreme storms and other conditions that arise as a result of climate change. This is particularly problematic in urban areas where the density of hard surfaces contributes to a decrease in natural attenuation.  A resilient city is one in which this type of rainfall is slowed down and discharges in a controlled manner through the drainage system.  Surface water flooding effects people’s ability to move around the city and can cause damage to property and business.  

The 55,000 gullies in Dublin City ensure the free flow of surface water during and following rainfall and storm events.  When gullies are blocked, the discharge of water from urban surfaces is impeded.
 
Gully blockages occur as a result of the following -
 
  • Autumnal leaf fall particularly on tree lined  roads;
  • Sudden fall of leaves or vegetation or debris during a storm event;
  • Increased weeds or silt in gully or channels during summer months;  
  • Increased general littering;
  • Parking and covering over of gullies during parades, marathons, sporting event, concerts etc.; 
  • Covering over of gullies during building and infrastructural works;
  • Poor road resurfacing /repairs that damages the channel into the gully; and
  • Continuous street parking that prevents routine street cleaning
When a gully is flushed out by heavy rainfall after a dry spell, it can also result in the pollution of surface water bodies due to the increased concentration of discharge pollutants.
 
The Surface Water and Flood Incident Management Division (SW&FIM) manage the gully system and provide an emergency response to flooding incidences.
Because of the nature and extent of the gully system, a range of measures have been taken to ensure their effective management including:
  1. Characterisation and prioritisation of gully cleaning; and
  2. Gully Maintenance Techniques and Innovations.
 
Gully Maintenance Techniques and Innovations
A range of plant including Gully Vac’s, Gully machines, mini jets  that are equipped with high pressure jetting and push rod CCTV are utilized to clear blocked pipelines between the gullies and the main sewer line.

Every gully jetted is surveyed using the push rod CCTV and each survey is recorded digitally for use by all relevant DCC staff.  
 
CCTV surveys using a crawling camera of any suspected collapsed or damaged mains sewer associated with the surface flooding are sent to the Drainage Division to facilitate increased repair response. The team also contribute to the assessment of river screens. The surveys are available in digital format.
 
During heavy rainfall the team suspend normal works and they survey their zones for any observed flooding which they then clear. They pay particular attention to tree lined roads, areas with previous flooding history and known gully blockage areas from local and staff knowledge. 
 
High pressure jetting and gully cleaning are used to respond to pooling on roads, cycle lanes, school warden crossing points and these locations are forwarded to Drainage Engineers for further assessment if repairs are needed. 
 
Gullies on certain roads, narrower streets and main thoroughfares are cleaned and inspected on a more frequent basis.
 
Gullies are inspected and cleaned in advance of events and infrastructural projects on roads and drainage system
 
Roads with heavy parking are visited continuously and the gullies are cleaned and inspected one by one until 75% of them are accounted for.

Community groups and responsible members of the public who have frequently reported block gullies were educated by the SWMU team to distinguish a blocked gully from a working gully. They then act as a trusted reporting source of blocked gullies to which there is a timely response. They also keep the kerbs clean of litter and debris. SWMU recommend that members of the public should never open or clean gullies due to the danger associated with debris in the gully e.g. needle sticks sharps contaminants.
 
Flood2.jpg
 
Sensors developed under an innovation competition by SMART Dublin in consultation with DCC staff have been installed in gullies that are known to be vulnerable locations to surface water flooding. These sensors relay real time information through a wireless network, on the water levels in the gully. They are sent to members of the SW&FIM team so that the surface water event can be responded to in a timely manner.
 
Staff Ideas for Gully Maintenance and Monitoring
Roy O Donnell Gully Manager with Dublin City Council has filed a joint patent for a “Gully Cleaning Eye Cap Holder” which can be retrofitted to old street gullies resulting in savings for retro-fitting of these gullies.
Other innovations which the team have developed include a gully lifting key, a magnetic lifter for the eye cap holders and a wheel unit to move the crawling camera during CCTV within drains.     
 
Flood3.png
Types of Gullis in Dublin city - Roy O'Donnell


 

Project Details:

Local Authority Project Contact  

 
Surface Water and Flood Incident Management (SW&FIM) Division, Environment and Transport Department, Dublin City Council
 
Barry McCann Executive Engineer, barry.mccann@dublincity.ie
Ruth Walsh Executive Engineer, ruth.walsh@dublincity.ie  
Roy O’Donnell Gully Manager, roy.odonnell@dublincity.ie,  
 
SMART  Dublin Docklands Districts
Edward Emmanuel  edward@smartdocklands.ie smartdublin.ie