WaterSubject

Scottish Water (SW) is undertaking a programme to improve drinking water quality to meet increasingly stringent European standards. At the same time, the amount of water abstracted, which is not subject to the provision of a formal Water Order in all areas, will have to comply with the Water Environment and Water Services (Scotland) Act 2003. This act reflects the requirements of the Water Framework Directive (WFD) to protect the ecology of each catchment.

The Lochaber project will provide improved water quality for eight communities with populations of 10–600 people in the Scottish Highlands west of Fort William, each in a separate catchment with its own water resource and treatment works. Some of the existing water treatment plants comprised simple disinfection, whereas others had sand and carbon filtration. As the villages are so small, costs have to be kept as low as possible, but environmental issues are a high priority for the local economy, as well as protection of biodiversity.

MWH were contracted by MJ Gleeson to carry out water treatment works (WTWs) design and hydrological studies as part of SW’s Lochaber Water Quality Undertakings Programme (WQUP).

There were three issues to address:

This paper focuses on the hydrological studies that demonstrated to the Scottish Environment Protection Agency (SEPA), and other stakeholders, that the water available in the existing sources complied with SEPA’s guidance for maintaining good ecological status. The impact of treatment process selection on the raw water abstraction requirements is discussed briefly.

The WFD was issued by the European Union in 2000, and was incorporated into Scottish Law in 2003 through the Water Environment and Water Services (Scotland) Act.

SEPA’s technical guidance on applications for abstractions to comply with the WFD stated that, in order to maintain the required ecological status of the water body, the abstraction should be limited to a proportion of the flow at a low flow threshold.

For the Lochaber sources, detailed ecological information was not available; hence SEPA adopted the precautionary principle and advised that, in order to maintain good ecological status, an abstraction should be limited to 10% of the flow available at any given time. However, to meet the need for consistent public water supply, when the flow in the source fell below the Q₉₅ level, it would still be acceptable to abstract up to 10% of the Q₉₅ flow. Hence it was necessary to demonstrate that there was sufficient water yield from each source that peak demand for the WTW would be no more than 10% of the Q₉₅ flow.

Consultations were held with over 20 stakeholders to identify whether there were any concerns over the proposed abstractions, and agree on measures to mitigate them if necessary.

Predictions for the whole of Scotland suggest a declining population. However, local factors have a large influence on the water requirements of each community. For example, the construction of a new secondary school in Ardnamurchan is contributing to development in Acharacle, while events held in the EC-funded Glenuig Community Centre can result in transient increases in demand.

When the populations are so small, the addition of a few houses can have a significant impact on the water demand in relation to the source yield. Demand forecasts were therefore developed following consultations with the local communities, as well as using broader trends.