Arup is delivering upgrade works to the water supply schemes on two of the Aran Islands, Inis Óirr and Inis Meáin. The islands are located approximately 10km off the western coast of Galway and are accessible by ferry or by air.
This project represents an unusual challenge as there are no surface water features on either island in the form of streams, rivers or lakes. Groundwater tends to be high in salinity and some boreholes, which have been previously used as water sources, have been abandoned in recent years. The islands are currently entirely dependent on rainfall as their drinking water source.
Increasingly, the islands are becoming dependent on tourism as the main source of income. While permanent residents may number 200 to 400, daily visitor numbers can reach up to 2,000 during the height of the tourist season. This has put enormous strain on the existing water supply schemes. A hydrogeological study carried out in 2015 identified that an excess of rainfall in the winter period could potentially be captured to alleviate the summer deficit.
The current works that our process team are undertaking include the preparation of detailed designs for raw water storage tanks and seeking planning permission to construct the storage tanks in highly scenic areas. The design challenges have mainly resulted from the lack of suitable locations to construct new tanks. Land ownership issues on the islands tend to be complex with many land packets owned by co-operatives which can have as many as 70 members. This has driven the need for innovative design solutions and, currently, the proposed design for the largest tank comprises an elevated structure with a capacity of 4,500m3. The elevation was necessary to construct the tank over a 2m deep natural well on the site of the existing water treatment plant. Once delivered, the scheme will provide Irish Water with a resilient water storage system for future water demand on the islands.