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Last update:16th May 2007 Quick links:
European and worldwide groundwater trends |
GroundwaterWhat's new on this page...What is groundwater?Groundwater refers to the saturated zone of rock that lies below the water table. The amount of water that the rock can hold and the ease with which it can move will vary enormously with the type of rock. A geological formation that can hold water, but will also allow it to move freely enough to be abstracted is called an aquifer. Major aquifers can supply large volumes, whilst minor aquifers supply small (but still usable) volumes. Non aquifers either hold negligible amounts of water, or prevent it being taken out. A map showing major aquifers in the UK is available from the Environment Agency Profile of subsurface water
Source: UK Groundwater Forum Why is groundwater important?Groundwater is the largest available reservoir of fresh water. It forms an important source for abstractions in the South West, and thus quality and availability are of utmost importance. In some areas almost all of the water used for public supply is derived from groundwater sources. Where the water table meets the land surface it may emerge as springs, form wetlands or the source of a river. Groundwater can contribute significantly to the base flow of a river and acts to maintain flow during dry periods.
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Nitrate levels
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Chloride levels
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Sulphate levels
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Sodium levels
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Magnesium levels
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Calcium levels
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Groundwater levels taken from a borehole at Woodyates Farm provide an indication of the long term behaviour of water levels in the main chalk aquifer in the South West (see graph below). Typically water lost from abstraction is replenished in the winter months by high rainfall and low rates of evaporation. The flow regimes of many chalk streams in Dorset and Hampshire are controlled by groundwater inflows, and over-abstraction can lead to low flows and their associated impacts on the local environment. Recent studies have focused on river water levels in Hampshire.
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Source: Environment Agency (2004)
Due to the high demand for water in the relatively densely populated Thames Region, the groundwater quality of the major aquifers has been studied in detail. Thames Groundwater Quality Reports have been produced, and these are now available to download.
In the Midlands, approximately 40% of the public water supply is provided by groundwater. Some areas are totally reliant on groundwater and thus susceptible to elevated nitrate levels. Several large cities are located on important aquifers, and their impermeable covers act to lower the volume of direct recharge. The nitrate concentrations in the Midlands are also increasing. The Environment Agency report Midlands Regional Geology, Hydrology and Groundwater Issues provides more detail for this area.
Groundwater quality in the South West is generally of good quality when compared to the rest of England and Wales. Nationally, nitrate levels have been rising for the past 20 years (Groundwater Quality in England and Wales, 1980 to 2001) and in some cases exceed safety limits. It costs around £16 million a year to remove nitrates from the public water supply. As a result, Nitrate Vulnerable Zones (NVZs) now cover 55% of England and 3% of Wales. These attempt to lower nitrate levels in groundwater by limiting the amount of nitrogen fertiliser applied to farmland. Details of local groundwater protection zones can be found on the Environment Agency’s What’s in your backyard?
It is an offence to pollute groundwaters under the Water Resources Act 1991. The natural movement of groundwater in an aquifer from an area of recharge to an area of discharge results in natural purification through filtering. However, due to the slow nature of this geological remediation, once polluted groundwaters are extremely difficult (and costly) to clean. The costs of deteriorating groundwater quality on a national scale can be found at the UK Groundwater Forum.
Groundwater Levels in England and Wales show both intra-annual and inter annual variation between 1992 and 2003. These fluctuations around the mean levels are predominantly a result of weather conditions (and thus recharge/replenishment rates).
Most European countries use more surface water than groundwater.
However, in some countries (such as Denmark and Iceland) the high quality
and accessibility of groundwater makes it more cost effective to abstract
from these sources than surface reservoirs. In some countries over-abstraction
has resulted in potential water deficits, and it is estimated that around
50% of wetlands in Europe have ‘endangered status’ due to groundwater
overexploitation.
Groundwater quality varies from country to country. In some parts of Europe hydrocarbons and heavy metals are serious problems according to the European Environment Agency’s Sustainable Use of Europe’s Water?. However, excess nitrates in groundwater form a significant widespread problem in some parts of Europe (see map below).
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Source: European Environment Agency (1998)
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Source: European Environment Agency (1999)
Globally regions with sustainable groundwater balance are declining, a result of depletion due to enhanced abstraction, waterlogging and salinisation caused by poor drainage, and pollution created by agricultural and industrial activities. See The Global Groundwater Situation for more information.
The International Groundwater Resources Assessment Centre has developed a Global Groundwater Iinformation System (GGIS) map that provides a user friendly interactive method to promote the sharing of knowledge on a global scale.
Monthly Groundwater Levels Update – recent groundwater statistics of key indicator sites in England and Wales.
The UK Groundwater Forum - provides information on groundwater aimed at a varied audience, ranging from school children to policy makers. This site also provides a summary of the groundwater aspects of the Water Framework Directive.
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