Murphy is currently undertaking a Design, Build and Operate scheme at Stillorgan Reservoir on behalf of Irish Water. The existing facility provides drinking water to over 200,000 customers in the Dun Laoghaire-Rathdown and Dublin City region.
The existing site is a modular storage facility for treated drinking water, built in two stages between 1862 and 1885. Covering an area of 16 hectares, it comprises three open reservoir cells: the Gray, Upper and Lower Reservoirs. These represent the penultimate open storage system in Europe. The facility is fed from water treatment plants at Vartry, County Wicklow and Ballymore Eustace, County Kildare, via Saggart Reservoir. Constructed over 150 years ago, there are various issues with the structure and operating system, in addition to the challenges posed by open storage.
The aim of the current project to remove the open storage that is currently in operation and replace it with a covered reservoir of 160ML storage capacity. This will ensure a long-term, secure and sustainable water supply to the region, meeting current and future regulatory requirements.
Sensitive receptors are a key challenge on the Stillorgan Reservoir project. The majority of local residents are located close to construction works on the northern embankment of the Gray Reservoir in Stillorgan Heath. To address this, normal working hours have been reduced and the monitoring of noise, dust, vibration and odour has been increased.
As the Gray Reservoir has not been fully drained since its creation in 1885, there are a number of challenges involved in the drawdown operation. Six piezometers are being utilised in the upper embankment to monitor any movement and ensure stability. Siphoning will remove the need to use the existing valves and operating system, which have been defunct for over 30 years.
The current project aims to deliver the 160ML reservoir, using the most sustainable and innovative construction techniques possible, while remaining at all times economical.
A significant innovation will be the removal of concrete baffle walls within the cells of the newly constructed storage units and replacing them with geotextile curtains. These will provide the same operational value but at lower cost and with less construction time.
Pipework design for the works has been optimised in order to ensure there will be no wastage or needless runs of pipe. Pre-cast concrete has also been explored for different aspects of the construction process and this too will have a large saving on time.