TIME IN YEARS

(PARTIAL SERIES DATA IN ORDER OF O C C U R R E N C E )

6

0 0

Z'

TIME IN YEARS

'

D A T A IN ORDER OF MAGNITUDE

I T

10 20 R A N K O F V A L U E

io

Fig. 5.17

-

^Flood peaks in the Danube, Vienna-Nussdorf, 1961-1970.

54

2oc n

=, 2 2

a 0

U W CK a

J 100

a

3 z e z u

Q k

E 3

2

100 c

200

300

't I

^Iu

^e

^{nl b 0}

^e

Fig. 5.18

-

Deviation of annual precipitation from the mean at Hannover from 1951 to 1970.

I I

1970 1080

'

¹⁹⁹⁰

Fig. 5.19a

-

Band diagram of water demand.

Emmcrrdorf

4

^{Gail -River}

,

3( ~ i ~ l a c h ~

I \ Gaillitz

Fig. 5.19b

-

Band diagram of sediment size distribution of river Gail.

total

Scale tar drinking water demand

I

106mJ1 in o mop legend

Triangle diagram showing reservoir capacity in a mop

Isometric diagram of regional oquifcr capacity ond exploited component Square diogram S h i n 9 wotcr demand

of different users in o region

Fig. 5.20

-

Use of plabe and isometric figures to represent magnitudes.

5.2 Hydrological Maps

The following section is not intended to constitute a treatise on hydrological mapping in view of the availability of the Unesco/WMO publication "Hydrological Maps" (Unesco/WMO, 1977). For questions on cartography and mapping techniques, the reader is referred to this publication.

Hydrological maps are treated here with regard to their value as a teaching aid.

5.2.1 Introduction

Whilst maps have always shown some hydrological information, such as river courses, swamps, lakes etc., they are not proper hydrologicalmaps.

generally in use is still rather unsophisticated but the field of hydrological mapping is now in a phase of rapid development.

required to compile hydrological maps but demonstrates very much that hydrologists in many cases have only just discovered the use of hydrological maps as a tool for their daily work and as a teaching aid.

and civil engineers often have not been trained in the art of mapping.

why hydrologists often prefer descriptions, tables and graphs although a map is much more suitable for demonstrating phenomena and their quantitative aspects over an area. In contrast, hydrogeologists, again as a consequence of their education, are much more used to preparing and utilizing maps; geological mapping has a long tradition. Thus, it is not surprising that the first hydrogeological maps were clearly derived from geological maps;

maps showing the dynamics of groundwater are, however, rather new. Sophisticated types of maps have been developed allowing the presentation of even three-dimensional phenomena such as generally occur in groundwater; even the existence of several aquifers does not create serious difficulties.

known tools of geographers. Permanent features are amenable to mapping, but hydrology, as a science of the hydrological cycle, deals with changing phenomena. A hydrological map, there- fore, is not necessarily permanently valid and needs an explanation as to its origin, its way

The type of hydrological map at present This fact not only reflects the large amounts of data

Hydrological mapping is rarely found in the curricula and syllabi of hydrology courses, This perhaps explains

real hydrogeological

A physical map shows permanent features (rivers, mountains, etc.) and is one of the best-

56

of compilation and in some cases, even as to its purpose. Such an explanation would either be in the form of a printed note beneath the map or an accompanying booklet, and might concern the contents of the map, the reliability of data, the preparation of the map, its cartography, the interpretation of the method of presentation and its legend.

5.2.2 Technical Points, Cartography Scales

The following classification has been introduced and is widely used:

large scales : up to 100,000;

medium scales : 1 : 100,000 to 1 : 500,000;

small scales : 1 : 500,000 and smaller.

Large-scale maps are generally prepared for or used in connection with special projects or programmes, whereas very small-scale maps are normally used for teaching, scientific and demons- tration purposes. For detailed studies or projects, large-scale maps (generally 1 : 25,000) are used; for a general overview, maps of 1 : 1,000,000 or much smaller are useful.

Cartography

In some cases hydrological maps call for specific requirements related to the character of the phenomena presented. Discharge and quality of water in rivers need special forms of present- ation since the phenomenon is not observed within an area but along the line of the river.

Hydrological maps, therefore, usually have an outstandingly rich choice of cartographic tools such as:

symbols (points, triangles, etc.)

lines (different thicknesses, dashed, coloured);

curves (with symbols or other signs);

Dands (different thicknesses, structures, coloured);

diagrams (simple, compound, geometric figures);

isolines or area markings (colours, bands, shading, screens, overlays, superimposed markings, area signs).

Base Maps

In general, hydrological maps are made using existing base maps on a given projection or scale.

Depending on the purpose of the maps, outline maps (showing only main items such as rivers, towns, etc.) or normal topographical maps are used. Outline maps are preferred for small scales; the larger the scale the more valuable is a basic map showing more detail. In

addition, in order to avoid confusion between the topographical detail of the base map and the superimposed hydrological detail, map-makers prefer the base map to be printed in light grey or brown rather than the customary black. Such maps are generally available at scales larger than 1 : 200,000 and in particular at 1 : 50,000, 1 : 25,000 and larger. Since these maps are very commonly used, they are normally inexpensive and have the advantage of being comparable with other maps.

Course organisers are advised to have a stock of base maps of the region in which the students are conducting their field work so that the students may map their results. Immediate mapping in the field facilitates the visualisation of the project and helps to identify

mistakes on-the-spot; mapping irregularities are much more easily identified than errors in tables.

The International Hydrogeological Map of Europe (1 : 1,500,000) is being published on the same scale and with the same projection, background, sections etc., as the geological map, the tectonic map and the deposits map, etc. The same principle is generally applied to atlases

-

not only for economic reasons but also to facilitate comparison.

Legends

The choice of the scale may be regarded as the most important decision of the map-maker. The scale influences the quality of presentation and also determines the detail included in the legend.

ly in the field of climatic and geological maps. No recommendations exist for surface water.

In many countries standardised legends have been developed for specific reasons, particular-

For hydrogeological maps, an international legend for hydrogeological maps (Unesco/IAHS, 1970) has been developed with a view to facilitating the preparation of maps.

certain symbols and modes of presentation for several phenomena of groundwater hydrology.

5.2.3

It recommends

General Classification of Hydrological Maps Network Maps

Network maps permit interpretation of the quality of the network,

observations and the representativeness of data. They contain all gauges and observation stations for measurement of the chemical composition of water, temperature, discharge and biological parameters. An indication of the meteorological network is frequently omitted though this would be a very valuable addition for the hydrologist. Groundwater observation stations should also be shown in a network map, although very often they are to be found in maps compiled by different agencies.

of water agencies or authorities and borders of administrative districts.

Maps Showing Hydrological Phenomena

the universality of

Network maps may also indicate the areal responsibilities

Due to the changing character of hydrological phenomena, many maps describe momentary conditions, averages, durations, variabilities, frequencies, intensities, etc. The first type of map deals with observed data. These data may concern properties and conditions existing at the moment of observation (examples: discharge 1.1.1970 7 am, borders of inundated area of the flood of

...,

temperatures of water in a lake, etc.). These maps generally emerge from observations taken at various places at the same moment or for the same event. This type of map is a typical product of the field work of students. Maps such as these show data without any interpretation or evaluation. The same generally applies to any map of totals and absolute values, including the results of physical and chemical analyses.

A very common group of maps deals with evaluated data such as averages, maxima or minima.

Most of the maps of water quality, discharges and temperatures have been drawn on the basis of a long series of data developed with rather simple mathematical processes (calculation of averages).

years of data.

these data, a third group interprets the data. In this group all maps of duration, variability, frequencies, intensities, beginning or ending dates of a phenomenon, of tendencies and

developments, are included. These maps require the existence of reliable and sufficient data and need careful treatment. Maps of this kind are absolutely indispensable for the work of hydrologists since they are most suitable for describing particular aspects of the hydrological cycle, especially changes in hydrological and hydraulic conditions.

For mean levels and discharges, averages are obtained from twenty or even thirty Whereas the first group deals with the actual dataland the second group with averages of

Reliability

The considerations above are based on the assumption that sufficient and reliable data are available.

In

many cases the available data do not justify the preparation of a detailed map or they demand qualification on their representativeness and reliability. Lack of quantity or quality of data may only lead to schematic maps or to maps on such a small scale that the mapping requirements can be met by the amount of available data.

5.2.4 Classification of Fields of Interest

A very important aspect of classification is the place of the phenomenon within the hydrological cycle.

5.2.4.1 Atmospheric Water

The hydrologist should be familiar with the most important climatic maps (precipitation, wind, temperature, air pressure, sunshine, etc.) and he should pay particular attention to learning to read and interpret daily weather charts and even to making an attempt at prediction. Each syllabus of a hydrology course should include the study of weather charts, explanation of their symbols, description of the element presented, and exercises on how to read charts. Consider- ation of three ar more consecutive charts will help students to understand the development of the weather. Precipitation intensity maps are of particular importance. Details may be obtained from the WMO Guide to Climatological Practices (WMO, 1960). Precipitation maps are easily obtained

-

they are in all good atlases, in publications of national weather boards, 58

and are obtainable from school equipment suppliers.

with data on a given heavy rainfall and should develop for himself a map of rain intensities as a basis for the computation of a flood.

be acquainted with maps on evaporation.

The hydrology student should be supplied Besides precipitation maps, the hydrologist should

5.2.4.2 Surface Water

The description of surface water phenomena often poses immense difficulties and leads to tables, graphs or maps being prepared.

can only be presented on maps. River problems can be presented on a map but only in relation to the river itself and not in relation to the surface they drain.

ping is often the easiest way to present data in a comprehensive and instructive way.

The most generally used surface water map is the physical map showing the boundaries of the catchment areas and their sub-catchments. The map would show rivers, canals, lakes, swamps, deserts, etc., and may be supplemented with details of the hydrological network. This type of map is more geographical than hydrological.

are concerned, the maps exist only on rather large scales, whereas large lakes may be shown on a smaller scale. Maps of deltas, valleys with remainders of unregulated river systems, inundat- ed areas and changes of river beds belong to this group. Engineers in particular use these maps, since hardly any plans for construction in rivers or lakes can be drawn without a concise geomorphological map. Hydrologists and civil engineers should be able to compile, or at least interpret, maps of this kind, detailing river beds and banks for use in streamflow studies, for studies on erosion and sedimentation and for construction purposes.

Streamflow maps deal with the distribution of streamflow in a river and flow of river water through a lake.

Chemical properties and water quality maps generally show chemical concentrations or alkalinity and acidity levels anly at the spot where the sample was taken, since it is almost impossible to extrapolate chemical properties in order to describe the situation between two distant measuring points.

chemical composition of the dissolved materials. The biological component generally is the most important factor which influences the quality of surface water and the possibilities of its use. The quality of water may be divided into five categories in decreasing order of water quality:

Lakes often have three-dimensional problems which in some cases

In

spite of all this, map-

Geomorphological maps deal with the geomorphology of rivers and lakes. As far as rivers

The quality of water is not only a question of the solid matter in the water and the

oligo-saprobe zone (1) B-meso-saprobe zone (11) a-meso-saprobe zone (111) poly-saprobe zone (IV) excessive pollution zone (v).

If sufficient data are available, sub-categories may be introduced. Maps on water quality are based on observations made over a set period. Water quality maps show pollution, the in- fluence of polluted tributaries or of tributaries with relatively pure water. It is very instructive for students to see the influence of human activities (factories, cities with or without purification plants, recovery of river water, influence of water quantity, relation between pollution and population density, influence of new or overloaded purification plants).

The ecologist and planner may see from these maps how far man has exhausted the natural water resources and, in collaboration with engineers, chemists and town and country planners, can discuss whether reserves are still available, whether these reserves can be used and whether measures are necessary to improve the situation.

Simple discharge maps. One type of such maps shows the average discharge along the river, the data being obtained over a long period. Maps are available for

mean discharge;

mean high water discharge;

mean low water discharge;

and occasionally for winter, summer, rainy or dry seasons. The thickness of the line tracing the river's path denotes the runoff. The maps show very clearly the development of a river, the influence of tributaries and of important factors such as evaporation, infiltration or retention.

The hydrologist will note the difference between rivers in flat swampy areas with little seasonal variation in the discharge and mountain

minimum and maximum discharge.

Classical examples of rivers losing water on their way are the Nile and the Niger.

rivers with a great variation between the

An important type of discharge map is ralated to the drained area. The water which has passed on observation station during a given period (e.g. one year) is converted into a theoret- ical layer of constant thickness over the whole drained area according to:

R

=

-CQ 1 at where Q

=

discharge; A

t

=

time;

A

=

drained area;

R

=

depth of the theoretical water layer;

This sort of map can be superimposed on and compared with precipitation maps.

Whereas these maps are based on the idea of the discharge over a period of time (monthly or yearly), another group of maps can show the discharge per unit of area and time. For this purpose the discharge is divided by the size of the area drained

where Q

=

discharge;

A

=

catchment area;

q

=

unit discharge, dimension generally 1s”m2

The value q is most advantageous since it permits direct comparisons with the production of other river systems.

Complex discharge maps. In principle, complex regime maps describe the situation with relation to as many hydrological phenomena as possible.

If maps of precipitation P and runoff R (related to the drained area) are available, it is easy to develop a map showing the percentage of the discharge of precipitation and to show the isolines of the value

R

c1

= -

100

P

This relation may be regarded as a runoff factor and should be studied by hydrologists in connection with a topographical map, a geological map and possibly with a map on soil and vegetation.

run dry,be covered with ice or be open for navigation. Maps of this type are generally called

‘simple regime maps’.

monthly discharge and the mean discharge. On the map the river is, therefore, accompanied by two bands. One of them represents the ratio of the lowest of the twelve mean monthly discharges and the mean annual discharge. The other band represents the corresponding ratio for the

highest of the twelve mean monthly discharges.

pluvial, pluvionival, nivo-pluvial, nival (in mountains), glacial or influenced by underground karst layers. For more detailed studies, the reader is referred to Unesco/WMO, 1977.

have been omitted, the possibilities of presenting various hydrological phenomena in one map and of demonstrating their interrelation can be seen. The value of these maps for hydrology students stems from the potential of being able to show possible interaction of parameters and to introduce the student to various hydrological regimes.

A further description of the regime deals with the length of period in which a river may

Another type of complex regime map shows the relation between the minimum and maximum mean

These ratios and their relations represent the type of river discharge regime, e.g.

Although this list of complex maps is not complete and the more sophisticated possibilities

Snow and ice. Maps of snowfall have been mentioned already under Atmospheric Water. Maps of glaciers, however, deserve special mention here. One type of such maps deals with the balance of the glacier. Besides showing the contours of the underlying ground, the thickness of the glacier is indicated in isolines. Special signs show the reduction of ice masses in periods of melting as well as the amount of new ice formation from snow or water.

Papers in Hydrology’, Paris, Unesco, 1970, numbers 1 to 5, entitled:

1. Perennial ice and snow masses.

2. Seasonal snow cover.

3. Variations of existing glaciers.

4. Antarctic glaciology in the International Hydrological Decade.

5. Combined heat, ice and water balances at selected glacial basins.

Further information on the mapping of glaciers is available in the series ‘Technical

5.2.4.3 Groundwater Maps, Hydrogeological Maps

The International Hydrogeological Map of Europe. In collaboration with the International 60

Association of Hydrogeologists, the Commission for the Geological Map of the World (Sub- commission for Hydrogeological Maps) and Unesco,a set of maps at the scale 1 : 1,500,000 is being prepared and is partly available. The legend is based on:

-

groundwater in porous rocks (colour);

-

groundwater in jointed massive rocks (colour);

-

regions generally with no or only local groundwater (colour);

-

particular notes on groundwater and springs (signs);

-

particular notes on surface water (signs);

-

particular notes on artificial works (signs);

-

particular notes on geological outarops (signs).

map restricts its practical value; it is mainly intended for use in teaching and for

demonstration purposes. The map is strongly recommended for hydrology courses since nearly all aspects of hydrogeological mapping can be demonstrated. A sample sheet (Annex 1) is to be found inside the back cover of this book. Maps for other regions of the world are in preparation.

This example has been chosen since this map is internationally available. The scale of the

Approaches for Making Hydrogeological Maps

Differences between hydrogeological maps consist of the different methods of presenting hydro- geological elements and, to a greater extent, the subject to be mapped and the scientific

Differences between hydrogeological maps consist of the different methods of presenting hydro- geological elements and, to a greater extent, the subject to be mapped and the scientific

Dans le document A contribution to the International Hydrological Programme (Page 59-72)