The state of groundwater resources in France

Transcription

1 et travaux n 43 Etudes The state of groundwater resources Quantitative and Qualitative Aspects (Extracts from the French version - written by Ariane Blum, Ifen) i n s t i t u t f r a n ç a i s d e l e n v i r o n n e m e n t

2 THE STATE OF GROUNDWATER RESOURCES IN FRANCE QUANTITATIVE AND QUALITATIVE ASPECTS (extracts from the French version - written by Ariane Blum, Ifen) institut français de l environnement 1

3 CONTENTS THE STATE OF GROUNDWATER RESOURCES IN FRANCE: QUANTITATIVE ASPECTS General introduction Water abstraction Distribution of groundwater abstraction according to different uses Geographical distribution of groundwater abstraction Groundwater table in THE QUALITY OF GROUNDWATER RESOURCES IN FRANCE Nitrates Contamination of groundwater by nitrates Trends in nitrate concentrations in groundwater Pesticides Contamination of groundwater by pesticides Main pesticide substances found in groundwater Other organic micropollutants General introduction Results Mineral micropollutants General introduction Results CONCLUSION List of acronyms and abbreviations Bibliography institut français de l environnement 2

4 THE STATE OF GROUNDWATER RESOURCES IN FRANCE: QUANTITATIVE ASPECTS GENERAL INTRODUCTION Precipitation (excluding overseas territories) averages 475 billion m 3 from year to year. Of these 475 billion m 3, 297 return to the atmosphere by evapotranspiration. Effective rainfall thus amounts each year to 182 billion m 3 of water (Source: IFEN, from MEDD). Any estimation of the volume of water that is available each year to feed into water reserves has to take into account exports and imports of water to and from neighbouring countries, in other words, the amount of water entering or leaving France in its rivers. Exports are thus estimated at 18 billion m 3 and imports at 11 billion m 3 (excluding the Rhine). Figure 1 - Map of effective rainfall for the hydrological year and ratio to the average for France's domestic water resources therefore amount to 175 billion m 3. The proportion that infiltrates into groundwater reserves is estimated at 100 billion m 3, with the remainder (75 billion m 3 ) feeding into surface waters (rivers, lakes and reservoirs). Nationally, the volume abstracted from groundwater reserves each year to meet the needs of human activities (6 billion m 3 ) is much smaller than the volume feeding into them (100 billion m 3 ). In terms of quantity, the risk of water shortages is therefore relatively non existent at national scale. However, needs vary considerably between regions and abstraction from some water tables exceeds their rate of replenishment. Source: MEDD (Department of Water). institut français de l environnement 3

5 WATER ABSTRACTION The following information is from a report on water abstraction in 2001 (entitled Les prélèvements d'eau en France en 2001 ) produced by IFEN for the French Water Data Network (RNDE). The report is available on the RNDE web site. Each year, some 34 billion m 3 of fresh water are abstracted (excluding overseas territories) to meet the needs of human activities (production of drinking water, industry, irrigation and energy). Of the total volume, 19% (6.3 billion m 3 ) is taken from groundwater reserves. Excluding the energy sector, which accounts for 19 billion m 3 alone, mainly from rivers, the proportion of abstraction from groundwater tables rises to 44%. This overall figure seems very low in comparison with the 100 billion m 3 feeding into aquifers each year, but its distribution varies not only between sectors but also between regions, and for some aquifers, the rate of abstraction is so high that their level is dropping steadily. Finally, abstraction from groundwater does not have the same repercussions as abstraction from a river, since groundwater, once used, is released into rivers. The water tables are therefore not replenished directly and the water volumes abstracted are generally lost. Distribution of groundwater abstraction according to different uses The volumes of water taken from groundwater reserves vary considerably according to different uses (Figure 2). Of the 6 billion m 3 of groundwater abstracted each year, over half is used to produce drinking water (59%), mainly because these resources are generally of better quality. Most of the remainder is used by industry (23% of the annual volume) and crop irrigation (18% of the annual volume). Cooling water for conventional and nuclear power stations is only taken occasionally from groundwater reserves (0.3% of the annual volume). Figure 2 - Abstraction of groundwater according to use in 2001 in billion m Drinking water supply Industrial uses Irrigation Source: Water Agencies - RNDE. Data processing: IFEN, Energy Geographical distribution of groundwater abstraction Water abstraction rates vary widely between uses and regions (Figure 3). For example, regardless of the end use, more groundwater is taken in the North, East and Centre regions, in parts of the South-West and in the Rhone Valley. This is mainly due to the geological context in these areas. Sedimentary regions like the Paris Basin, the Aquitaine Basin and the Rhone Valley have very extensive groundwater reserves, unlike basement regions (Massif Central, Corsica and Brittany, for example) where water is mainly abstracted from small rivers. Abstracted volumes are shown here by département. Administrative divisions are obviously not the ideal way of representing hydrological units. However, we do not have sufficient data on abstraction locations or, more specifically, on the aquifers being used, so that it is not possible at present to draw up an exact map of the volumes abstracted from each aquifer. Nevertheless, in response to the requirements of the Water Framework Directive (WFD), there has been substantial progress in 2004 in the identification of these aquifers and a map of abstractions per groundwater body should become available in the near future. institut français de l environnement 4

6 The state of groundwater resources Figure 3 - Water volumes abstracted per département in 2001 for drinking water supplies (excluding overseas territories) Source: Water Agencies. Data processing: IFEN, institut français de l environnement 5

7 GROUNDWATER TABLE IN 2003 For more detailed information on the water table level, please refer to the monthly bulletins published on the RNDE web site ( heading: Synthesis ). The following indicators have been developed to assess the level of the main water tables. France has some 3,500 aquifer systems, of which the majority are small and highly localised, so that it is clearly impossible to provide an indicator for each one. On the maps in figure 4, the symbols supply information on overall trends in water levels (or piezometric levels). The background represents a simpli- fied view of aquifer types: the main and alluvial aquifer systems are in grey; areas with no major individualised aquifer system are in white. The maps show seasonal and regional variations in water table levels. Groundwater played an important role during the drought in Thanks to the high levels of precipitation in previous years, replenishment in early summer was generally satisfactory, so that there were sufficient groundwater reserves to limit the impact of the drought on the downstream areas of the main rivers. Figure 4 - Trends in the main aquifers, 2003 Water table levels markedly above the norm above the norm normal below the norm markedly below the norm Recent trends rising stable dropping major systems and alluvial aquifers systems with no major individualised aquifer early march early may early july early september Source: BRGM. early november institut français de l environnement 6

8 THE QUALITY OF GROUNDWATER RESOURCES IN FRANCE NITRATES Contamination of groundwater by nitrates Figure 5 - Contamination of groundwater by nitrates in 2002, in comparison to the natural status Figure 5 shows the degree of groundwater contamination by nitrates in comparison to their natural state. Only the blue category denotes water of natural or subnatural quality. Natural water generally contains no more than 10 mg/l of nitrates and any higher concentration is a sign of human influence. The map, which is based on data produced by the Water Agencies, shows that the highest nitrate concentrations are in the northeastern segment of France and in the East (Rhine Valley aquifer). Concentrations above natural levels are also frequently observed in the Rhone Valley. Altogether, in 2002, 62% of the 1,048 sites sampled had nitrate concentrations above 10 mg/l, reflecting human influence on groundwater. However, it is not always easy, at national scale, to pinpoint the source of these anomalies. In urban and industrial environments, nitrate pollution tends to occur at specific points, so that it is virtually impossible, on such a large scale, to match the results observed in water tables with potential nitrate sources. In agricultural zones, on the other hand, nitrate pollution is diffuse, which means that it extends over a wide area. Results from the National Groundwater Monitoring Network (RNES) can therefore be cross-referenced with an indicator reflecting the extent of agricultural activities, as shown in Figure 5. This shows that nitrate concentra- Source: ADES - Water Agencies (National Groundwater Monitoring Network- RNES) and CORINE Land Cover Data processing: IFEN, institut français de l environnement 7