B.E. O Dochartaigh

What impact will climate change have on rural groundwater supplies in Africa

Abstract One of the key uncertainties surrounding the impacts of climate change in Africa is the effect on the sustainability of rural water supplies. Many of these water supplies abstract from shallow groundwater (<50 m) and are the sole source of safe drinking water for rural populations. Analysis of existing rainfall and recharge studies suggests that climate change is unlikely to lead to widespread catastrophic failure of improved rural groundwater supplies. These require only 10 mm of recharge annually per year to support a hand pump, which should still be achievable for much of the continent, although up to 90 million people may be affected in marginal groundwater recharge areas (200–500 mm annual rainfall). Lessons learnt from groundwater source behaviour during recent droughts, substantiated by groundwater modelling, indicate that increased demand on dispersed water points, as shallow unimproved sources progressively fail, poses a much greater risk of individual source failure than regional resource depletion. Low yielding sources in poor aquifers are most at risk. Predicted increased rainfall intensity may also increase the risk of contamination of very shallow groundwater. Looking to the future, an increase in major groundwater-based irrigation systems, as food prices rise and surface water becomes more unreliable, may threaten long-term sustainability as competition for groundwater increases. To help prepare for increased climate variability, it is essential to understand the balance between water availability, access to water, and use/demand. In practice, this means increasing access to secure domestic water, understanding and mapping renewable and non-renewable groundwater resources, promoting small-scale irrigation and widening the scope of early warning systems and mapping to include access to water.

Manganese concentrations in Scottish groundwater.

Groundwater is increasingly being used for public and private water supplies in Scotland, but there is growing evidence that manganese (Mn) concentrations in many groundwater supplies exceed the national drinking water limit of 0.05 mg l(-1). This study examines the extent and magnitude of high Mn concentrations in groundwater in Scotland and investigates the factors controlling Mn concentrations. A dataset containing 475 high quality groundwater samples was compiled using new data from Baseline Scotland supplemented with additional high quality data where available. Concentrations ranged up to 1.9 mg l(-1); median Mn concentration was 0.013 mg l(-1) with 25th and 75th percentiles 0.0014 and 0.072 mg l(-1) respectively. The Scottish drinking water limit (0.05 mg l(-1)) was exceeded for 30% of samples and the WHO health guideline (0.4 mg l(-1)) by 9%; concentrations were highest in the Carboniferous sedimentary aquifer in central Scotland, the Devonian sedimentary aquifer of Morayshire, and superficial aquifers. Further analysis using 137 samples from the Devonian aquifers indicated strong redox and pH controls (pH, Eh and dissolved oxygen accounted for 58% of variance in Mn concentrations). In addition, an independent relationship between Fe and Mn was observed, suggesting that Fe behaviour in groundwater may affect Mn solubility. Given the redox status and pH of Scottish groundwaters the most likely explanation is sorption of Mn to Fe oxides, which are released into solution when Fe is reduced. Since the occurrence of elevated Mn concentrations is widespread in groundwaters from all aquifer types, consideration should be given to monitoring Mn more widely in both public and private groundwater supplies in Scotland and by implication elsewhere.

An overview of groundwater in Scotland

Synopsis Groundwater is an important, but undervalued, national resource in Scotland. Groundwater is present both in the bedrock, where much of the flow is through fractures, and in the superficial deposits, where intergranular flow dominates. The most productive bedrock aquifers are the Permian sandstones and breccia in SW Scotland and the Devonian sandstones in Fife, Strathmore and Morayshire. Alluvium and fluvio-glacial sands and gravels can also form important aquifers and provide some of Scotland’s most highly yielding boreholes. Groundwater is generally weakly mineralized with total dissolved solids in the range 100 to 500 mg l−1 and is dominated by Ca and HCO3 type waters. There are in excess of 4000 boreholes in Scotland, and over 20 000 springs and wells used for private water supply. There are few available reliable data on the total volumes of groundwater abstracted; however, conservative estimates suggest that the total volume is approximately 330 megalitres per day for public water supply, industry, agriculture and private water supply. The volume of groundwater used in public water supply is growing annually; it is currently 7% of the daily 2400 megalitres per day supplied by Scottish Water. Scottish groundwater is under threat from agricultural activity, the mining legacy, septic tanks, localized high abstraction, and general land development. The implementation of the Water Framework Directive, and associated legislation, is an excellent opportunity to sustainably manage and develop groundwater in Scotland.

Mapping groundwater vulnerability in Scotland: a new approach for the Water Framework Directive

Synopsis A new methodology for groundwater vulnerability assessment has been devised for Scotland to meet the requirements of the Water Framework Directive. Using the methodology, a new GIS-based map of groundwater vulnerability has been produced, at a working scale of 1:100 000. The map is being used by the Scottish Environment Protection Agency (SEPA) to help characterize and assess risk to groundwater bodies. The methodology assesses the vulnerability of groundwater in the uppermost aquifer to the vertical downward movement of a non-specific contaminant from the ground surface. It considers the intrinsic properties of the pathway between the ground surface and the water table. The key difference from previous vulnerability maps in Scotland and the rest of the UK is that the new method assesses vulnerability in all aquifers regardless of resource potential. This reflects the diverse environmental objectives for groundwater bodies under the Water Framework Directive. This approach provides the flexibility to combine the groundwater vulnerability map with maps of pressures, groundwater resources or other groundwater-related receptors, as required.

3D geological models and their hydrogeological applications : supporting urban development : a case study in Glasgow-Clyde, UK

Urban planners and developers in some parts of the United Kingdom can now access geodata in an easy-to-retrieve and understandable format. 3D attributed geological framework models and associated GIS outputs, developed by the British Geological Survey (BGS), provide a predictive tool for planning site investigations for some of the UKs largest regeneration projects in the Thames and Clyde River catchments. Using the 3D models, planners can get a 3D preview of properties of the subsurface using virtual cross-section and borehole tools in visualisation software, allowing critical decisions to be made before any expensive site investigation takes place, and potentially saving time and money. 3D models can integrate artificial and superficial deposits and bedrock geology, and can be used for recognition of major resources (such as water, thermal and sand and gravel), for example in buried valleys, groundwater modelling and assessing impacts of underground mining. A preliminary groundwater recharge and flow model for a pilot area in Glasgow has been developed using the 3D geological models as a framework. This paper focuses on the River Clyde and the Glasgow conurbation, and the BGSs Clyde Urban Super-Project (CUSP) in particular, which supports major regeneration projects in and around the City of Glasgow in the West of Scotland.

Using transmissivity, specific capacity and borehole yield data to assess the productivity of Scottish aquifers

Abstract Aquifer properties data from more than 3000 groundwater sources across Scotland have been collated to form the Scottish Aquifer Properties Database, coordinated by the Scotland and Northern Ireland Forum for Environmental Research. The aim of the project was to better understand Scotlands aquifers, through the collation of a comprehensive set of quantitative data. Analysis of 157 transmissivity values, 307 specific capacity values and 1638 borehole yield values shows that Quaternary and Permo-Triassic age aquifers are the most productive, followed by those of Devonian and Carboniferous age. There is a strong correlation between specific capacity and transmissivity (r2 = 0.8), and the former may be used as a reliable indicator of aquifer productivity where no transmissivity data are available. The correlation between transmissivity and borehole yield data is significant (r2 = 0.57), although the quality of the yield data is lower overall than that of the specific capacity or transmissivity data. These data support recent categorization of bedrock aquifer productivity in Scotland, which until now has been validated only with limited quantitative datasets.

Hydrofracturing water boreholes in hard rock aquifers in Scotland

Hydrofracturing of new public water supply boreholes in Precambrian crystalline bedrock in Scotland has increased borehole yields by at least one order of magnitude, and made the difference between borehole abandonment and success. In many upland rural areas of the UK, low-productivity aquifers are an important resource for small public water supplies. Where a borehole in low-productivity crystalline rocks proves too low yielding for its designed purpose, hydrofracturing is a cost-effective means of enhancing yield.

Numerical testing of conceptual models of groundwater flow: a case study using the Dumfries Basin aquifer

Synopsis The current understanding of the groundwater flow regime in the Dumfries Basin aquifer has been developed over a number of years and encapsulated in a conceptual model. A numerical modelling study has been undertaken to test the confidence in this understanding. This study has included three activities: recharge estimation, water balance calculations and steady-state groundwater flow modelling. It has been confirmed that the highest recharge is found in the NW of the basin and that the peat and marine clay deposits limit direct recharge in the east and south. The water balance is dominated by surface water flow, in particular the River Nith brings over 3200 Ml day−1 onto the basin. Conceptualized flow directions were confirmed by the steady-state modelling. The understanding and model validity are severely constrained by a lack of flow data in the lower River Nith and scarcity of water level and aquifer property information. These knowledge gaps could be filled by flow gauging just above the tidal limit of the river and additional drilling and testing.

Assessing the effectiveness of Scotland's groundwater nitrate monitoring network

Many countries expend considerable resources collecting and reporting data from national groundwater quality monitoring networks to assess diffuse nitrate contamination, but the reliability of these data depends on the effectiveness of the network. Without a representative monitoring network of reliable monitoring points, there is a risk that groundwater management policies could be developed and implemented based on poor evidence. To help increase confidence in nitrate data, a robust, practical and repeatable method was developed to assess the effectiveness of groundwater nitrate monitoring networks, and applied to a network in Scotland. The method combines a rapid site assessment of monitoring points and local pollution pressures in order to judge the reliability of monitoring points, with a wider characterization of the network to identify which land uses and hydrogeological environments are being monitored. The analysis indicates that, with minor exceptions, Scotlands groundwater nitrate monitoring network broadly represents the diversity of conditions expected in Scotland.

Using stable isotopes and continuous meltwater river monitoring to investigate the hydrology of a rapidly retreating Icelandic outlet glacier

ABSTRACT Virkisjökull is a rapidly retreating outlet glacier draining the western flanks of Öræfajökull in SE Iceland. Since 2011 there have been continuous measurements of flow in the proglacial meltwater channel and regular campaigns to sample stable isotopes δ2H and δ18O from the river, ice, moraine springs and groundwater. The stable isotopes provide reliable end members for glacial ice and shallow groundwater. Analysis of data from 2011 to 2014 indicates that although ice and snowmelt dominate summer riverflow (mean 5.3–7.9 m3 s−1), significant flow is also observed in winter (mean 1.6–2.4 m3 s−1) due primarily to ongoing glacier icemelt. The stable isotope data demonstrate that the influence of groundwater discharge from moraines and the sandur aquifer increases during winter and forms a small (15–20%) consistent source of baseflow to the river. The similarity of hydrological response across seasons reflects a highly efficient glacial drainage system, which makes use of a series of permanent englacial channels within active and buried ice throughout the year. The study has shown that the development of an efficient year round drainage network within the lower part of the glacier has been coincident with the stagnation and subsequent rapid retreat of the glacier.