Waterway 19

Feature Article

International Hydrogeological Map of Europe

by W.H. Gilbrich

Although the International Hydrogeological Map of Europe has not yet been completed, describing its production, which has occupied both the participating countries and IHP for several decades, is virtually the task of a historian.


A picture says more than a thousand words, but a map says more than a thousand pictures. Maps were already being used by medieval scientists even though such maps today may appear very nave. A more scientific approach was only possible with the advent of land surveying and spheric trigonometry.

Early maps were picturesque with wind-blowing angels, out-of-scale buildings, particularly churches, and the author put emphasis on what he, personally, felt to be important, often omitting aspects which he considered of little importance.

Records of mapping are relatively new, and started not more than three centuries ago. Geographical or physical maps, as we know them today, originated from navigation and land maps.

Early physical maps contained far too much data and it was soon recognised that a selection process was necessary. This became even more important when local or regional maps had to be combined to form small-scale maps for larger regions, countries or even continents. (Nota Bene - cartographers do not speak the same language as model makers: a small-scale map corresponds to a large-scale model!). The development of maps on a smaller scale evolved in two ways, firstly, the sub-division of general maps into specialised or thematic maps and, secondly, the use of symbols to represent certain objects. Symbols in a legend permit the inclusion of data in a concentrated, abstract form. Highly specialised maps, containing a great deal of information and on a smaller scale, appeared relatively late.

It is evident that the introduction of symbols, the translation of natural phenomena into abstract signs and the definition of thematics, could not be done in a universal manner. On the contrary, each author, university, institute and country had its own individual approach. A cartographer can easily recognise the origin and period of an old scientific map.

Another problem had to be overcome. Classical land maps describe the surface: two-dimensional phenomena on a two-dimensional sheet of paper. The introduction of a third dimension (altitudes above sea level) posed enormous problems. To begin with picture-like presentations were used, followed by the use of different colours, and finally isolines were introduced which was considered as a scientific break-through. However, none of these techniques were appropriate when developing underground maps. Hence, the art of compiling geological and hydrogeological maps involved new techniques, new abstractions for showing a three-dimensional underground and its properties on two-dimensional paper. This is neither the time nor the place to describe the long and difficult route, past failures and unfulfilled hopes, which eventually led to modern-day sub-surface maps. Today, in spite of recent advances in mapping, we lack the self confidence of past generations, as we are well aware that as far as mapping is concerned we are a long way from perfection and that, through cyber techniques, a whole new world is at the cartographer’s disposal with hiterhto undreamed of possibilities.

Small-Scale Maps

Geologists were the first to develop techniques for underground mapping. Thanks to international scientific organisations, a high degree of standardisation with regard to presentation, inherent philosophy and legends with recommended symbols, ornaments and colours, had already been arrived at more than a century ago. Hence, French geological maps resembled German ones. On the basis of local, (large-scale) regional maps, national maps were developed and, with the appearance of atlases, the need for continental maps arose. Geological maps included in atlases are generally at an extremely small scale, often 1 : 5,000,000 or even 1 : 10,000,000. It is evident that such a small scale map can only depict very general features such as the general location and disposition of aquifers and non-aquifers, together with a broad picture of the surface drainage. For more detailed information it is obvious that a map needs a larger scale, e.g., 1 : 1,000,000.

Antecedents to the International Hydrogeological Map of Europe

In 1960, the International Association of Hydrogeologists (IAH) initiated a project for the preparation of an International Hydrogeological Map of Europe, having realised that although a large number of hydrogeological maps at various scales existed in almost all European countries, none of them were the same in their scientific approach, content, presentation, or use of cartographic symbols, making comparison practically impossible and even leading to erroneous conclusions. The fact that no obvious effort was being made to prepare maps in a uniform way lead to the suggestion that a small-scale map covering the whole of Europe should be prepared. However, even for a relatively small continent like Europe, such a map exceeds normal paper size. To remedy this situation, therefore, it was decided to divide the surface area into a composite of several maps.

It was also hoped that such a map would lead to the improvement of national mapping projects.

The general purpose of the map was to provide a simplified representation of ground water in Europe as related to the geological situation. The main objective was to show the location, geographic extent, movement and constitution of the major groundwater bodies, classified according to the main types of aquifers.

Whereas large-scale maps are used for practical purposes and therefore need to contain as many details as possible, maps on a medium or small scale only give a general picture and are used primarily for information, teaching purposes, planning and scientific work.

In order to prepare an international map, agreement must be reached by the participating countries and international organisations regarding scale, an easily applicable legend and a meaningful scientific approach. Since the suggested map was the first international venture in the field of hydrogeological mapping, it was essential, from the very beginning, to secure the collaboration of a large number of scientists and to make full use of the experience of countries with a long tradition in mapping activities and hydrogeology. It is, therefore, not surprising that it took ten years to gather and evaluate such information and to establish suitable models for discussion by the scientists involved. Although the model which was finally adopted had been discussed in great detail, serious problems emerged during the preparation of the actual map, and these had to be solved at international level. The compilation of the sheets comprising the map is far from being a routine job and shows that hydrological mapping needs to be developed further. At the start of the actual work, it was understood that both the legend applied and the scientific approach had to be flexible so that, on the one hand, individual or unique events could be shown and, on the other, the necessary uniformity and clearness of the map could be maintained. The history of this map, therefore, reflects both an attempt at perfection and an aim for uniformity, as well as the peculiarities of an international undertaking. These peculiarities stem from the different ways of identifying problems in different countries, from varying hydrogeological interpretations to different national regulations concerning the compilation and publication of data and information. These rather limiting factors and the varying amount of information available in each country would have led to an unjustified simplification of the map if the permitted or actual minimum of information available in certain countries had been taken as a standard. This difficulty was overcome by the flexible nature of the map which contains all information necessary for the understanding of the hydrogeological situation.

Choice of Scale for the International Hydrogeological Map of Europe

When choosing a scale there must always be a compromise between the size of the paper, the number of sheets forming the composite, and the amount of information to be included. The European geologists agreed to a scale of 1 : 1,500,000 which allows sufficient detail but which is still viable economically and is also easy to use. The individual map sheets are organised in a pattern with horizontal (numbers) and vertical (letters) rows. Each sheet has a key (say B5) and is named after an important city (e.g. Paris). Since a map on flat paper never fully concurs with reality (curved earth surface) a projection has been chosen which, for the European degrees of latitude, minimises the deviations from reality. This projection as well as the geographic base map were provided by the Commission for the Geological Map of the World (CGMW), affiliated to the International Council of Scientific Unions (ICSU) and the International Union of Geological Sciences (IUGS).

In view of the success of the International Geological Map of Europe the same scale and division of sheets has been applied for the metallurgenic map and the Quarterny map of Europe.

It was logical to issue a hydrogeological map at the same scale, with the same projection and topographic base. The advantages are obvious: low cost, easy comparability, similar scientific approach, similar systematic. In 1962 , the choice of scale and the sub-division of the map sheets was daring. However, acceptance by the scientific community confirmed the appropriateness of the decision and no questions were posed with regard to the Hydrological Map of Europe. Nevertheless, there was a certain amount of resistance as national maps at this scale had hitherto never existed and each country was required to re-draw its contribution at the jointly agreed upon scale of 1 : 1,500,000. The fact that all European countries agreed to this scale is proof in itself of the good will of all involved. The fact that no national maps could be used without transformation helped to overcome eventual national rivalries or ambitions. There is no doubt that there was a temptation for countries with highly developed hydrological maps to impose their approach, scale and legends, but this was overcome and all the European countries contributed and co-operated.

Legend for the International Hydrogeological Map of Europe

The IAHS began studying the idea of a universally-applicable legend in 1954 and established a Standing Committee on Hydrogeological Maps in 1960 to study methods of presenting hydrological data on both small-scale and large-scale maps, and to make recommendations on the standardisation of symbols. The IAH also undertook the preparation of a legend from 1959 onwards and formed, for this purpose, a Working Group on Hydrogeological Maps. In order to assure close co-operation, a joint meeting of the IAHS Standing Committee, the IAH working Group and specialists from UNESCO and FAO, was held at UNESCO Headquarters in 1962, during which an agreement was reached on the first draft of an international legend for hydrogeological maps. Subsequently, the legend was issued by IAHS and by UNESCO in 1963 with a view to having it tested by map-makers and hydrogeologists in different countries, under different hydrogeological conditions and at different scales. The experience gained from issuing this draft served for the establishment of a legend which was published by UNESCO and IAHS in 1970 in four of the working languages of UNESCO. Since the preparation of the final version of the legend coincided with the scientific preparation of the International Hydrogeological Map of Europe, the requirements for this map could be fully taken into account. On the other hand, the legend benefited from preparatory work for the map to a considerable extent. The legend, which was published in 1970, certainly cannot be regarded as final. UNESCO took the initiative to prepare, in collaboration with IAHS and IAH, a supplement on geohydro-chemical features. This specialised legend was published in 1974.

Although not directly linked to the Hydrogeological Map of Europe but rather as a result of other regional mapping projects, the 1970 issue of the standard legend was refined scientifically and regional supplements were also issued. The same was true for the maps of the Arab States and Africa. Stocks of the 1970 version were soon exhausted due to the great demand and in order to meet requests UNESCO published a simplified, black-and-white version in its TDH series. In 1995 the IAH produced a modernised version (see IAH publication no. 17).

Definitions for Legends of International Hydrogeological Map of Europe

Certain terms are used rather loosely in both hydrogeology and cartogaphy, and it is easy for misunderstandings to arise. A short list of definitions is included here which refer to the usage for hydrogeological maps.

Ornament: a pattern of marks, lines or other symbol denoting the occurrence of a particular factor over an area of ground as represented upon the map; e.g. a stipple to represent sandy strata
Symbol: a single graphical representation to denote the presence of a particular factor at a point location on the map; e.g. a small circle to show the location of a spring.
Line: a solid or broken line may be used either to delimit an area such as an aquifer outcrop, or to join points of equal altitude (contour), equal thickness (isopachyte), or similar parameters.
Sign: a sign may consist of a line, a symbol, or an ornament, or a combination or any or all of these. Colour: a colour refers to an even “wash” of constant tone. It may be used for lines, symbols or ornaments as well as for emphasising areas of importance.
Tone: screens may be used in order to reduce the density of a colour. The value of the tone is usually expressed as a percentage of the original or full (100%) colour.



At its first session in 1965, the Co-ordinating Council of the International Hydrological Decade (IHD), when discussing hydrogeological mapping activities in general, recommended that a small-scale hydrogeological map of Europe be prepared, showing the location and extent of the main groundwater tables. This task was entrusted to the International Association of Hydrogeologists who were requested to enlist the co-operation of other international non-governmental scientific organisations including, in particular, the International Association of Scientific Hydrology. The Council emphasised that such a map would be part of an international hydrological mapping operation linked to the preparation of a world groundwater atlas.

At its third session in 1967, the Co-ordinating Council accepted IAH model no. 4 as a suitable form of representation and scientific approach and recommended that it be adopted for all sheets. It thus confirmed the recommendations of the former IHD Working Group on Hydrological Maps which had discussed the scientific approach to the map in detail.

It should be pointed out that in 1968, in view of the enormous financial implications of this project the Intergovernmental Council for the IHD decided that it should be given the status of an individual project activity funded by the Regular Programme of UNESCO and that it should no longer be executed within IHD which, until then, had provided the necessary organisational framework. IHD, and afterwards IHP, therefore, no longer played a role in the compilation of the map although a very active interest in the project was retained and reports on progress continued to be made.

Following the Council’s acceptance of the mapping project, the General Conference of UNESCO, at its fifteenth session in 1968, decided that UNESCO should collaborate over the preparation and publication of the International Hydrogeological Map of Europe, together with the IAHS, the IAH and the Sub-Commission for the Hydrogeological Maps of the Commission for the Geological Map of the World. This decision was renewed and re-confirmed by the General Conference of UNESCO at its sixteenth session in 1970 and at its seventeenth session in 1972. Besides allocating funds for the actual printing, UNESCO hosted the annual meetings of the Sub-Commission and of its Editorial Board. Later sessions of the General Conference considered the project a routine affair and, in fact, no problems of either a scientific, organisational or political nature, have ever arisen. However, problems of a financial nature occurred during the second half of the eighties and during the nineties shortage of funds lead to a complete stand-still. The attempts made to re-vitalise the project have been successful and will be reported on at the end of this article.

Initially, the organisational arrangement for the preparation of the map foresaw the close collaboration of UNESCO and the Associations and Commissions concerned, particularly the IAH, IAHS and the Commission for the Geological Map of the World (CGMW).


a )   The Sub-Commission for Hydrogeological Maps of the Commission for the Geological Map of the World was responsible for the scientific co-ordination of the hydrologeological map of Europe. Scientific and cartographic problems were discussed at annual meetings. Although no fixed rules of procedure existed any changes to be made were usually decided upon at this time. One of the Chief Editors dealt with the uniform structure and, as far as possible, ensured a uniform interpretation of the hydrogeological features. Guidelines were issued by the Chief Editors. When this sub-commission was dissolved the IAH took over it’s functions and the Commission on Hydrogeological Maps (COHYM) was thus set up.

b )   While the Chief Editor is responsible for the overall work, an Editorial Committee checks the uniformity of the map and an individual scientific editor is appointed for each sheet, to ensure that the general details, which have been previously agreed upon, are adhered to. Since one sheet usually covers more than one country, the Chief Editor has to contact the scientists responsible in the countries concerned, which so far has resulted in excellent bilateral, multilateral and regional co-operation. The assistance of the National Committees for IHP and the IAH as well as that of the Geological Surveys and other competent authorities has always been willingly given. Liaison with the IAHS, IUGS and IGU has been maintained and intensified.

c )  As the sheets become available, they are printed by the ‘Bundesanstalt fr Geowissenschaften und Rohstoffe (BGR)”, the former Bundesanstalt fr Bodenforschung (BfB), in Hanover, Germany and published jointly by the BGR and UNESCO. A contract has been drawn up between the BGR and UNESCO containing a declaration of the mutual intention to publish the map and describing it’s general characteristics and the way in which it is to be prepared. Supplementary contracts concerning individual sheets of the map are prepared when necessary and UNESCO’s financial support is defined for each map sheet issued. The map is available from UNESCO and through a German Agent, ILH, GeoCenter, in Stuttgart. It should be noted that each sheet is accompanied by an Explanatory Note and that neither one nor the other can be obtained separately.


General Description of the Hydrogeological Map of Europe

The map has been drawn up along the same lines as the International Geological Map of Europe. While the latter consists of 49 sheets, the International Hydrogeological Map of Europe will no doubt be composed of less than 35 sheets, as certain regions outside Europe, in particular North Africa, will not be included. However, available space on the map will be used to portray Iceland, parts of Ireland and the island of Crete. Each sheet measures approximately 92 x 69 cms and contains not only a section of the map but also the legend in English, German and another language, either French, Russian or Spanish, depending on the country depicted. Cross sections, details of groundwater yield and quantity, together with a bibliography are also shown.

In order to make the map comparable with other international maps as well as to save costs, it seemed advisable to compile the map according to the scale used in other related maps. As the International Geological Map of Europe was prepared at a scale of 1 : 1,500,000, the same scale was chosen for the Hydrogeological Map of Europe in view of the close connection between the geological structure and the hydrogeological features.

From 1961 to 1967, IAH also worked on the compilation of an explanatory notice to the Hydrogeological Map of Europe using sheet C-5, Bern, as an example. Four models of this sheet - the results of four experiments - were compiled and printed by the IAH with the help of IUGS. In the first two models the hydrogeological characteristics of the formations were represented by a lithological pattern superimposed in the colour used for the geological map. Three grades of permeability were then defined. The third model included the probable productivity of the various geological formations. The colour still represented the age of the formations. Lithology was expressed by conventional signs. This map thus presented characteristics common to a general map rather than including the water-bearing systems. In the fourth model it was decided to ignore the geological map and to represent the aquifers in accordance with the principles detailed above. These maps resembled geological maps where data on underground water is portrayed. A hydrogeological map is, to a certain degree, a derivative of a geological map, whose main objective is to show hydrogeological structures and systems. An example of this type of map making is the map of the French underground water systems at the scale 1 : 1,000,000. The above four sample maps served as a model for the Hydrogeological Map of Europe.


By using six colours (blue, green, red, brown, violet and orange - sometimes in different tones) as well as black and grey for point symbols, superimposures and lines, very detailed information concerning the aquifers, ground water, springs, surface water, artificial works and geological features has been included on the map. The following is a brief summary of the actual contents:

a) Sky blue has been used for ground water in porous rocks; the depth of the blue indicates whether the aquifer is extensive and highly productive or whether it is local or incoherent. Superimposures refer to the type of rock and are applied in accordance with the stratigraphical symbols in the legend of the International Geological Map of Europe.

b) Green refers to ground water in jointed massive rocks; the depth of the colour indicates either extensive and highly productive aquifers, often found only at great depth, or local or incoherent aquifers into which streams flow.

c) Brown indicates regions generally without or only with local ground water; the depth of the colour indicates either that the aquifers are shallow or very deep but unproductive.

For a), b) and c) superimposures refer to the property and/or composition of the rock.

d) Violet lines may indicate, in special cases, the contour lines of the groundwater table, groundwater divides or boundaries of certain types of ground water.

e) Orange symbols refer to the quality of the ground water, and its temperature.

f) Royal blue symbols indicate springs giving the amount of discharge and the continuity of production.

g) Prussian blue indicates surface water.

h) Red symbols illustrate artificial works, such as wells, water-works, dams, canals and pipelines.

i) Black or green lines represent geological features, such as faults, overthrusts and border of certain formations.

k) The base map consists of grey lines.

A particular problem related to coloured maps should be raised here. Although the same printer was used for each map sheet, there are, nonetheless, slight differences in the colours between the different sheets as each series of map sheets was printed at varying intervals of time. When looking at one single sheet, the map and legend are homogenous. However, if two sheets, of a different series, are placed side by side slight differences become visible. Hence, at present, the composition of all the map sheets on a wall is not fully satisfactory. Modern technology can surely overcome this problem when and if all the map sheets are re-printed at some time in the future.


As mentioned in the introduction a large number of map sheets have already been prepared ( please see table below) but, largely due to financial constraints, the project stagnated for some years. However, all partners are willing and eager to see this venture completed.

In late 1998 a new work programme was concluded concentrating on the furtherrnost parts of the Iberian Peninsular, parts of Italy, the Danube Basin and the Greek Turkish area. When launching the new programme BGR and UNESCO decided to omit one sheet in the very North (D1) covering only permafrost regions with virtually no ground water as well as a sheet covering the Caucasus area (F5). The new programme got off to a good start with the holding of a regional meeting on the Danube Basin in Bratislava, September 1999, Further meetings for the Iberian Peninsular, the lower Danube, Turkey and Greece are planned to be held in the year 2000. It is foreseen that the whole project will be terminated by or shortly after 2003, provided the momentum of regional co-operation amongst the hydrogeologists concerned is maintained, and provided that adequate funds are made available. First attempts to use modern electronic information media - email conferences and internet - are very promising permitting personal contact among the map-makers as well as the transfer of data and even making corrections on the draft map sheets.

Sheet Year
A5 - La Corua 1983
A6 - Lisboa (*)  
B2 - Island 1980
B3 - Edinburgh 1980
B4 - London 1976
B5 - Paris-Sud 1975
B6 - Madrid 1978
C2 - Trondheim 1984
C3 - Oslo 1979
C4 – Berlin 1977
C5 - Bern 1970
C6 - Roma 1990
D2- Haparanda 1984
D3 - Stockholm 1981
D4 - Warszawa 1981
D5 - Budapest (*)  
D6 - Athenai (*)  
E2 - Archangel'sk 1987
E3 - Moskwa 1979
E4 - Kijev 1981
E5 - Bucuresti (*)  
E6 - Ankara 1978
F2 - Kirow 1992
F3 - Kazan 1990
F4 - Astrachan 1995

(*) in preparation

Digitalising of the map is not foreseen at this stage in view of the enormous costs which such an exercise would incur. However, once again the Geological Map of Europe is the forerunner: a synthesis map at the much smaller scale of 1: 5,000,000 is being prepared and such a map is also envisaged for the Hydrogeological Map. This small scale map is ideal for exhibits in view of the small amount of space it occupies. It is also envisaged to conclude the termination of the project with a synthesis report - there is sufficent work for committed and dedicated hydrogeologists until at least the year 2010!!!


CGMW Commission for the Geological Map of the World
IAH International Association of Hydrogeologists
IAHS International Association for Hydrological Sciences
ICSU International Council of Scientific Unions
IUGS International Union for Geological Sciences References

Recommedend Reading

ANON. (1970): International Legend for Hydrogeological Maps - UNESCO/IAHS/IAH/Institute of Geological Sciences, 101 pp.; London.
ANON. (1975): Legends for Geohydrochemical Maps- Technical Papers in Hydrology, No. 14, UNESCO, ISBN, 92-3-001207-6, 62 pp., Paris.
ANON. (1977): Hydrological Maps. A Contribution to the International Hydrological Decade. Studies and Reports in Hydrology, 20: 204 pp.; UNESCO/WMO, Lausanne.
ANON. (1983): International Legend for Hydrogeological Maps - Revised edition. (UNESCOTechnical Document, SC-84/WS/7, 51 pp.; Paris).
STRUCKMEIER, W., MARGAT, J. (Ed.): Hydrogeological Maps: a Guide and a Standard Legend. Int. Contibution to Hydrogeol., Vol. 17; Hannover.


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