Following recent high profile flooding events at Letterkenny General Hospital, a number of Flood Risk Mitigation Works were implemented. The works involved the construction of a new 1350mm diameter culvert along the western perimeter of the hospital site, the provision of additional screen area upstream of the culvert, and other minor works. These works were part of a range of measures implemented under the Flood Management Strategy for the hospital.
In July 2013, following intense rainfall in the area, flooding occurred in parts of Letterkenny General Hospital. The source of the flood water was a local stream known as the Sprackburn Tributary (a tributary of the River Swilly), which runs towards the hospital and enters a 1350mm diameter circular culvert running through the hospital grounds. A second flooding incident occurred on 5th August 2014, although the source for that event was surcharging at a storm manhole. In addition, the site has experienced several other flooding incidents or ‘near misses’ in recent years.
The storm flow routing pipeline (i.e. culvert) will act as a backup in the event that the existing culvert becoming blocked. It is not intended that the pipeline will be utilized during normal conditions.
The works included the following elements:
- The construction of a 1350mm storm flow routing pipe and 10 no. manholes;
- The installation of security screens and trash screens;
- The construction of a precast interceptor channel with an open grate cover;
- The construction of a protective berm
- The construction of new headwalls at the inlet to the pipeline;
- Reprofiling of the road surface at the Kilmacrennan Road entrance
In order to provide sustainable materials for the project, the specification required that goods and materials used in the works originated in Ireland, so far as was practicable. The pre-selection of local contractors to tender for the works (under the Negotiated Procedure) ensured that the project carbon footprint was minimized.
Due to the sensitive location of the works (i.e. adjacent to a live public hospital), environmental considerations were of utmost importance. More specifically, noise, traffic and air pollution had to be kept to a minimum. Particular control measures were put in place in order to manage these elements.
It was necessary to continue pedestrian and vehicular movement close to the works site. Consequently, the development of special procedures and traffic management was required to ensure that emergency access was retained, and to minimise any impact on the operation of the hospital facilities.
Use of pile driving plant, rock breakers, tunneling equipment, compressors or drills at night were prohibited in order to control noise.
Particular care was taken with respect to infection control on the construction site due to the proximity of the hospital to the works. A risk assessment was undertaken by the Infection Control Team in consultation with HSE Estates and as a result Class III Infection Control Preventative.
Measures were implemented to prevent the spread of Aspergillus. Control measures included the erection of hoarding, provision of a dust suppression system, daily road cleaning and daily dust sampling. Liaison was required between the Contractor, the Infection Control Team and the Client’s Representative in order to monitor dust control and containment measures so as to prevent exposure to Aspergillus spores.
In order to ensure the health and happiness of hospital patients, special measures were put in place in order to ensure the security of the site, the security of construction tools and machinery, and for the protection of open excavations. The completion of the works also minimized the risk of closure of the A&E at the hospital during flooding incidents. Such a scenario occurred after the flooding in July 2013, when patients had to be transferred to Derry for a number of weeks.
With respect to geology, it was a requirement that measures be taken to prevent erosion on the stream bed. TOBIN specified the construction of precast concrete structures together with stone pitching which mitigated erosion.
The Flood Risk Mitigation Works at Letterkenny General Hospital had a particular focus on the sustainable use of water, and the primary aim of the works was to address localized flooding by retaining storm flows in their intended conduits, rather than spilling into the hospital car park and buildings. As a result, the works minimized the risk of hydrocarbons and other substances from draining back into local watercourses.
In summary, the Leterkenny General Hospital Flood Risk Mitigation Works were successfully constructed under a number of environmental constraints, in particular those related to patient health; the prevention of flooding in the area will improve the quality of local watercourses; and the prevention of future flooding that will improve the health and happiness of the users of Letterkenny General Hospital.