Scottish superficial deposits and the water framework directive

The Water Framework Directive, which entered into force in December 2000, stipulates that Member States must, for groundwater: Within 4 years – identify river basins and assign groundwater bodies to them. Characterise these groundwater bodies. Identify ‘Protected Areas’ including bodies of water which supply more than 10 m3 d-1 drinking water supply (>50 people), and identify those bodies which are at risk of not complying with the Environmental Objectives laid down in Article 4. Within 6 years – establish appropriate monitoring programmes Within 9 years – establish management plans and surveillance. Within 15 years – ensure ‘good status’ is achieved wherever possible. This includes good status of quality and of quantity ensuring a balance between recharge and discharge. The initial assessment requires an analysis of the main characteristics of each river basin, a review of the impact of human activity and an economic analysis of water use. These objectives implicitly require a review of groundwater abstraction to be carried out, both in terms of volume and use. The initial assessment also requires an evaluation of quantitative and qualitative status of each groundwater body, part of which is the evaluation of a water budget to establish if the resource is sustainable. Detailed understanding of the role of drift deposits in each catchment is, therefore, essential because of their role in influencing recharge to and protection of underlying groundwater. In addition, where sufficiently permeable and extensive, drift deposits will themselves constitute groundwater bodies. Quaternary deposits occur throughout much of Scotland. They may be of glacial, lacustrine, fluvial, aeolian or marine origin, but are usually only a few metres thick, rarely more than 30 m and exceptionally more than 180 m (e.g. at Bo’ness in the Forth valley). Most of the glacial deposition occurred during and after the last glaciation some 18 000 years BP. Detritus, or till was deposited beneath and marginal to the ice sheet, and is poorly sorted silt and clay with some sand grade material, cobbles and boulders. The sand grade material may be dominant, as is the case along parts of the Morayshire coast. As the ice sheets withdrew, water again flowed and fluvial deposits such as eskers were laid down within the ice, and broad outwash fans were deposited beyond the ice margin. The outwash fans tend to be coarse-grained with grain size reducing with distance from the ice sheet. Lacustrine silts and clays occur where valleys and drainage channels were blocked. The retreating ice sheets left large tracts of morainic drift in the upland valleys, and subsequent resorting and redeposition has occurred resulting in flights of terraces. Permeable (more sandy) glacial deposits are widespread with major outwash fans present in the main valleys of the Borders, in the Midland Valley notably in Strathmore, Fife and between Dunbar and Lanark. There are numerous fans along the Highland border of Strathmore, along the southern shores of the Moray Firth and the eastern valleys of the Grampian Highlands. Late-glacial marine sediments of poorly permeable silt and clay with some sand and gravel occur in the Tay, Forth and Clyde valleys above present day sea level. Raised beach deposits are also common along parts of the east coast of Scotland. Recent deposits include freshwater alluvium, peat and blown sand. Alluvial terraces are common in valleys, with silt and sand the dominant grade material. Data with which to evaluate the role of superficial deposits and soils on recharge processes and aquifer vulnerability available for Scotland are sufficient to develop GIS format compilations for which algorithms could be written to assess catchment vulnerability and areas of recharge. A first pass requires ovelaying the soil map to the drift geology map to identfy areas where gley soils and podzolic soils occur which reflect weakly permeable or free draining material below. This greatly assists in characterising the till and morainic drift which is so widely distributed in Scotland. Other data include catchment Base Flow Indices, aquifer vulnerability maps, depth to rockhead, ground slope, depth to water table, borehole data, and abstraction data. A phased approach is recommended whereby an initial regional scale evaluation of recharge and vulnerability through drift is carried out to an effort of between 6 and 8 man months. This would be followed by refinement, particularly of the algorithms, and identification of data needs for problem areas and at risk areas, again of only a few man months duration. Phase three requires detailed instrumentation and catchment level investigation by way of verifying the regional evaluation and to develop understanding of critical, at risk, catchments further