N. S. Robins

Groundwater Management in Drought-prone Areas of Africa

Abstract The issues pertaining to groundwaterdrought are reviewed with particular regard to the historical and present situations in Malawi, northern Ghana and the Northern Province of South Africa. These three quite different examples highlight some of the major difficulties facing respective governmentsand donor agencies, not least the shortcomingsof drought-reliefdrilling programmes,the general lack of routine monitoring and the need for longer term analysis and assessment of groundwatersystems than is currently possible. The distinct character of groundwater systems and their reaction to prevailing and changing environmentalconditions is discussed, and it is argued that essentially predictable variations in groundwater drought vulnerability are rarely planned for or acted upon. Managementissues arising are discussed and it is suggested that governments,and particularly donors, should place more emphasis on longer term, pre-droughtmitigation measures to reduce the need for costly and sometimes ineffect...

Ground Water Security and Drought in Africa: Linking Availability, Access, and Demand

Drought in Africa has been extensively researched, particularly from meteorological, agricultural, and food security perspectives. However, the impact of drought on water security, particularly ground water dependent rural water supplies, has received much less attention. Policy responses have concentrated on food needs, and it has often been difficult to mobilize resources for water interventions, despite evidence that access to safe water is a serious and interrelated concern. Studies carried out in Ghana, Malawi, South Africa, and Ethiopia highlight how rural livelihoods are affected by seasonal stress and longer-term drought. Declining access to food and water is a common and interrelated problem. Although ground water plays a vital role in buffering the effects of rainfall variability, water shortages and difficulties in accessing water that is available can affect domestic and productive water uses, with knock-on effects on food consumption and production. Total depletion of available ground water resources is rarely the main concern. A more common scenario is a spiral of water insecurity as shallow water sources fail, additional demands are put on remaining sources, and mechanical failures increase. These problems can be planned for within normal development programs. Water security mapping can help identify vulnerable areas, and changes to monitoring systems can ensure early detection of problems. Above all, increasing the coverage of ground water-based rural water supplies, and ensuring that the design and siting of water points is informed by an understanding of hydrogeological conditions and user demand, can significantly increase the resilience of rural communities to climate variability.

Groundwater contribution to an acid upland lake (Loch Fleet, Scotland) and the possibilities for amelioration

Abstract The Loch Fleet catchment lies in an upland region in the centre of the outcrop of the Cairnsmore of Fleet granite. It is a recently acidified lake (pH = 4.4) which has been the subject of a liming experiment to restore fisheries. In the present study, hydrogeological and geochemical techniques were used to determine the contribution of ground water to the loch and its role in buffering the lake water chemistry. Diffuse groundwater seepage was detected by infrared linescan survey, and overflowing ground water (2 m above the level of the loch) was encountered in a shallow borehole. This ground water has an alkaline geochemistry (pH = 7.2, HCO 3 − = 142 mg l −1 ) determined by secondary vein calcite and hydrolysis of silicate minerals. The net gains or losses of various constituents in the ground water and in the loch outflow have been determined relative to rainfall inputs. Na, K, Ca, Mg, HCO 3 , SO 4 , Cl, Si, Sr, Fe, Mn, Li and F all show net gain in the ground water; NO 3 , Al, Zn and B show a net loss. In the acidic loch outflow, Ca, Mg, Si, Sr, Ba, Fe, Mn, Al, Zn and Li show a net gain over rainfall inputs; most of these elements derive from ground water, enhanced by evapotranspiration by a factor of 1.8. The chemical results have been used to determine that ground water contributes around 3.5 l s −1 to the loch, compared with an estimated 3–4 l s −1 derived from hydrograph analysis. This constitutes 5% of the mean loch outflow, which was sufficient to buffer the loch at around pH = 6.0 until the late 1960s. Titrations of ground water with loch water show that as little as 0.06 l s −1 (1656 m 3 year −1 ) of additional ground water would be required to restore the loch to conditions suitable for a self-sustaining fish population. Twice this flux (3310 m 3 year −1 ) would restore the loch to the conditions pertaining in the pre-industrial era. These targets could be achieved at an economic cost, it is suggested, by induced abstraction of ground water in the upper reaches of the catchment without any harmful ecological effect.

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.

Mine water rebound in South Nottinghamshire: risk evaluation using 3-D visualization and predictive modelling

Progressive abandonment of the South Nottinghamshire Coalfield raises concerns over the security of the Permo–Triassic Sherwood Sandstone aquifer which overlies the concealed part of the coalfield. A 3-D digital visualization package has been used to assemble and display the complex and diverse data-sets of relevance. Predictive scenarios have been run from these data using the University of Newcastle program GRAM (Groundwater Rebound in Abandoned Mineworkings). The work comprised three phases: (i) confirmation of the geological framework for the so-called ‘Pond 3’ area (southernmost part of the coalfield) and establishment of a water balance along with an outline groundwater flow path system for the Coal Measures and adjacent strata; (ii) the collation of detailed geometric information on the spatial distribution of discrete geological layers that are considered to have hydrogeological significance, the distribution of mineworkings within key horizons, and the locations of boreholes, shafts and pumping stations (both in the Coal Measures and within overlying strata). Possible flooding configurations have been assessed geometrically to identify ‘hot spots’ where mine water discharge to surface may occur, and areas where the piezometric level of the rising mine water might promote upward fluxes into the Permo–Triassic Sherwood Sandstone aquifer. In addition, critical areas where coal has been worked close to the base of the Permian and where hydraulic continuity may occur between the Sherwood Sandstone and Coal Measures have been identified; (iii) the GRAM model used data held in the 3-D visualization package VULCAN to define discrete ‘ponds’ within the coalfield. Recharge to the system allows each pond to fill until overflow pathways are reached, when the adjacent pond may start to fill. A variety of such scenarios have been completed and predictive data generated, which suggest that possible discharge to surface and into the Sherwood Sandstone might occur about 20 years after the end of dewatering.

Hydrogeology and hydrogeochemistry of a small, hard-rock island — the heavily stressed aquifer of Jersey

Abstract The fractured basement aquifer of Jersey provides 30% of the total water needs of the island plus baseflow to surface catchment storage. A 3-year field study has attempted to describe the groundwater resources in terms of quantity and quality. Borehole yields are typically less than 11s −1 ; the island-wide estimate of transmissivity is 3 m 3 day −1 and effective aquifer thickness is 30–40 m although deeper circulation occurs in selected fracture systems. It is estimated that much of the renewable resource is exploited. Groundwaters are predominantly derived from recent recharge, most being oxidising with measurable tritium contents. There is widespread pollution from agricultural nutrients but natural denitrification is apparent in some areas.

The use of 3D geological models in the development of the conceptual groundwater model

The conceptual groundwater model is heavily dependent on the geological framework which is used to defi ne the aquifer being studied. In the past, two-dimensional datasets such as geological maps and cross-sections were used in coordination with site-specifi c point data to build a conceptual understanding at the site or catchment scale. This is then simplified and it is this simplifi ed version which is used to build the framework for the numerical groundwater fl ow model. Due to the way the geological framework model and the conceptual groundwater model were generated they could not be viewed together; this inevitably led to a signifi cant loss of information and understanding. With the current rapid developments in 3D modelling software and the increasing availability of digital geological data it is now possible to produce detailed 3D geological models of complex aquifer sequences. In this paper we will use two case studies (Chalk aquifer of the London Basin and the Jurassic limestone aquifer of the Cotswolds) to demonstrate that by developing a detailed 3D geological model signifi cant benefi ts are gained in the understanding and development of the conceptual groundwater model.

The saline waters of Llandrindod and Builth, Central Wales

Saline or brackish mineral waters have been recorded at several locations in mid-Wales and the Welsh borderlands. The main groups are centered on Llandrindod Wells and Builth Wells where maximum salinities of 5340 and 16 380 mg l−1 respectively are found. The total discharge from these springs is very low (combined 2 l s−1) yet their flow remains almost constant. Residence times of several thousand years are derived using 14C analysis, and δ18O and δ2H results suggest that the waters at Llandrindod (although not at Builth) contain a component of Late Pleistocene water. Evidence from the Br/Cl ratios and trace elements indicates that the origin of the salinity lies within the Lower Palaeozoic formations and has not been derived from evaporites. The mineral waters have undergone complete reduction of sulphate which has led to high concentrations of Ba (maximum 53.2 mg l−1) at Llangammarch Wells. The most likely origin of these waters is the deep circulation of meteoric water over a residence time of several thousand years which has risen slowly along minor fracture systems to the points of outlet. The interconnected fracture storage of these waters implied from the various lines of evidence must be of the order >30 Mm3.

Characteristics of the Permian and Triassic aquifers of south-west Scotland

Strata from the Permian and Triassic supergroups form a series of deep sedimentary basins and associated outliers in south-west Scotland. The strata are mostly water-bearing and form valuable local aquifers which are exploited for public and private supply. Secondary permeability provided by joint surfaces, bedding planes and other features is an important component of most of the aquifers. However the development is not universal; at some sites the intergranular permeability is dominant and at others both secondary permeability and intergranular permeability are lacking. Geophysical borehole logging is used to examine the secondary permeability.

A review of small island hydrogeology: progress (and setbacks) during the recent past

Careful resource management is needed on small inhabited islands because demand can stress finite fresh groundwater reserves. Managers need to be informed how the groundwater system functions so that they can optimize the resource use and safeguard it from abuse. Hydrogeological investigation in small islands is broadly similar to basin studies on the mainland but small island scale coupled with data scarcity (including effective rainfall, permeability and baseflow) inhibit conventional groundwater flow modelling. Coastal and offshore baseflow measurement is the greatest uncertainty and research aims to better constrain its determination in the future. Small island hydrogeological investigations are challenging and aquifers can be classified as high-elevation hard fractured rock systems and low-relief karst limestone and sand islands. Although small island hydrogeological techniques have advanced considerably in the last 20 years, they must improve again in the future to help the many communities living in small island states that receive only erratic and unreliable rainfall recharge.