ANALYSIS OF THE GROUND WATER HYDROGRAPH

Josef HOFBAUER(*)

I. SYNOPSIS

This paper docs not claim to be complete. Primarily some results of a statisticalevaluation of some 500 surveying spots of the underground storage reservoirs inBavaria covering an observation period of roughly 20-30 years are outlined andexplained by means of illustrations. In addition some preliminary results obtained bya research study carried out within the scope of the IH D and promoted by the GermanResearch Service (*•) at 5 connected and interrelated yet differently configuratedground water basins or else aquifers will be shown to be briefly interpreted by means ofsome illustrations, too. A more detailed study of this topic is to be subjected to asubsequent publication.

GRUNDWASSERSTANDE IN BAYERN

Fig. 1 — Comparative study of fluctuations.

(*) Expert adviser of the ground water division of the Bayerische Landesstelle fürGewässerkunde, München.

(*•) Deutsche Forschungsgemeinschaft.

219

GRUNDWASSERSTANDE IN BAYERN -OANOLINIEN

961 96? T9&3 — 4 9 6 4 1963/66

Fig. 2 — Ground water levels in Bavaria. Hydrographs of various typical gagingstations.

GRUNDWASSERSTÄNDE IN BAYERN / , „ m SO^EN

1961 1962 196Ï 19S4 '.96? / îrl! *"

•xtl MÜNCHNER SCMOTTEKBENE

Fig. 3 — Ground water levels in Bavaria. Duration curves of various typical gagingstations.

•nwder Sternwarte m München rur die Jjhre 1&8 frs 7906 berechneter Gang des Grundwasserspiegels in Eglfing fur dx J.ihre 1850 bis 7906

kw^^mk=m£?m

fur den Tiefenbrunnen Nr2653 m f. gif mg

Fig. 4 — Hydrographs of the gaging stations Eglfing near Munich, and of the total precipitation of 100 years.

II. SIGNIFICANCE AND INTERPRETATION OF GROUND WATER HYDROGRAPHS

The hydrograph of the ground water level is the most important and quite frequentthe only means to gather some information about the hydrological and, to a certainextent, geological conditions of the subsoil. Thus it carries by far greather weight thanthe water stage hydrograph of surface runoff and might justly be referred to as thetemperature curve of the stored aquifer. To render a detailed interpretation of thiscurve, however, would go beyond the goal of this paper. In addition to the determi-nation of the potential maximum and minimum ground water level, the sloping of thecurve may quite generally be assumed to have some significance especially as to itsdescending hand. Moreover, the dependence on the discharge of neighbouring rivers orwaters as well as on local or remote storm occurrences or on artificial interventions canas well be demonstrated by means of the hydrograph. This procedure, however, doesnot only require some experience but a certain precaution seems to be advisable, too,as can obviously be noted from the examples given in figure 1. In the centre thereof,the respective ground water hydrographs of two gaging stations for 1965 are shownwith the water stage hydrographs of the neighbouring rivers or waters at the top andat the bottom respectively; both stations being located at approximately the same dis-tance from the rivers.

Übersichtskarteder Grundwasserbejirke Bayerns

Fig. 5 — Contour map of the underground storage reservoirs in Bavaria accordingto the statistical evaluation by means of "representative" gaging stations.

All data refer to NN (*). It is, of course, evident that the water stage of the decp-seeted receiving river Wenach or else tail water of the Lech impounding reservoir andthe ground water levels do not affect each other, although casual observation may urge

(•) Sea level.

222

upon such a conclusion. This mere coincidental similarity is due to the same stormoccurrence and above all to the influence of the higher altitude of the river Flossachand the headwater of the Lech impounding reservoir respectively. The headwaterelevation represented as a straight line, however, must be assumed to have in fact acourse similar to that of the accompanying ground water hydrograph.

MONATSMITTEL DER JAHRESREIHE 1938-60 UNO DES JAHRES 1965

DER „REPRÄSENTATIVEN" MESSTEILEN (DONAU)

• I LAGER LECHFELD » I WALIERSDORF !6Sb ECIFINO

Fig. 6 — Monthly mean value of the "representative" gaging stations covering theyears 1938-1960 and 1965.

III. THE RESULTS OBTAINED TILL TODAY

1. The "typical" water levels

Owing to the observation of some few typical years or else of one single extremeyear, it might be possible to estimate the high, mean, and low water level on the basisof a long standing period of validity. Figure 2 shows the superimposed water levelhydrograph of the years 1961-1965 of some typical gaging stations in Bavaria. Figure 3gives the "water level duration curve" of the same stations covering the years 1938-1965. The extreme year 1965 comprises the extreme data of an almost loo-year recur-rence.

223

2. The water level duration

The water levels act according to the law of the stable equilibrium. Figure 4 showsthe loo-year-old hydrograph of the gaging station Eglfing. This hydrograph reveals aduration of the maximum and minimum level in periods ranging from 4 to 7 years.A phenomenon being of considerable importance as to water level forecasting.

3. The "representative" gaging stations

The statistical evaluation of the highest possible number of artificially not affectedhydrographs allows the determination of "representative" hydrographs. In this pro-cedure the use of monthly mean values seems to be advisable.

According to the Hydrographie Annuals of the "Bayerische Landesstelle fürGewässerkunde" attempts have been made for the first time in 1962 to select gagingstations statistically, which as to their monthly mean hydrograph would approximateto the mean value of a great number of similar and locally appertained gaging stations.These stations are termed the representative gaging stations. The number, name,monthly mean hydrograph covering the years 1938-1960 äs well as their individualranges are represented in figures 5 and 6. By comparing the data available it can con-sequently be determined whether the hydrograph of one gaging station of the indi-vidual range concerned approximates to the mean normal hydrograph of the represen-tative gaging station and, whether it is a question of an average or else extreme year.This may turn out to be of considerable importance for the engineering practice asfar as short-term investigations are concerned, especially in case of any probableeffects due to impoundage reservoirs or artificial extractions of water.

At the representative gaging stations (fig. 6) the monthly mean hydrograph of theyear 1965 is shown in form of a dotted line. The extremely heavy movement of theground water level in 1965 already becomes an evident fact. On the whole the courseof the curve is similar to the average (i.e. similar maximum and minimum time data),the amplitude being partially a multiple; only gaging station No. 189 Haidhäuser inthe Bavarian Forest (figure 5) does not fit into the picture and must be subjected to athorough verification.

4. Flow rate and pressure transmission

Prior to the ground water movement in a horizontal direction, i.e. the flow process,the hydrograph almost generally indicates first of all the transmission of pressure.This is the case both for the confined an unconfined aquifers. The ratio flow rate tothe velocity of the pressure wave varies from 1:30 to 1:300 according to the permeability(k = 0,01-0,02 m/2). Figures 7 and 8 show the location of the territory and the gagingstations as well as the locally and periodically co-ordinated hydrographs of the gagingstations and of the rivers or waters.

224

I [ r—_ ., - f f _ • Tr i " i "

BAYERISCHE LAMOESSTEUE H1H CiWASSENKUNOE MÜNCfCN

GRUNDWASSERKARTE PUPPLINGER AUMASSTAB 1 : S900

scr— . LlNlfNOLElCHER

Fig. 7 — Outline map of the underground storage reservoir Pupplinger Au and its gaging stations.

Fig. 8. — Periodically and locally co-ordinated hydrographs of the gaging stations and of the river (har) in the Pupplinger Au.

Gartnisch-Knorrsteo

228

Eschen lohe

O GW - MtBltttl«O AMIu

Fig. 9 — Outline map of the underground storage reservoir River Loisacb Valley andits gaging stations.

229

5. Regimen

Sloping, the amplitude as well as the alteration of the amplitude of the hydrographhave considerable influence as to the estimation of ground water occurrence withregard to the balance and storage capacity. Due to periodically and locally co-ordinatedextractions of water for water supply purposes, the total,exploitations capacity can beefficiently increased. The magnitude of the amplitude admits of some interpretationas to the geologic subsurface conditions and the water recharged to, or discharged froman aquifer; this, however, apparently requires the consideration of as many hydrographsof a total ground water basin or else aquifer as possible. \

Figures 9, 10, and 11 represent the conditions of a connected and interrelatedaquifer covering an area of roughly 30 km2 (length 20 km and width about 1,5 km)within a ground water basin of about 500 km2, its location, longitudinal section aswell as the hydrographs of periodically and locally co-ordinated gaging stations, theamount of precipitation and the rivers. '

Figures 12, 13, 14, 15 and 16 represent the conditions of a connected and inter-related aquifer covering an area of roughly 700,km2 (length 35,km and width about

230

<DNord-Süd-Profil

durch das Loisachtal

Md=1:25000MdH=1:2500

Legende:

. . . . Nagelfluh

K*s

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.steiniger Grobkies [Schv<*™n*»9eO

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Tor!

Felsoberkante, seismisch enTHtttü

.Felsoberkante, elektrisch ermittelt

. .Schnittpunkte mit Querprotilen

J P Wrobel 1957

Fig. 10— Longitudinal section of the underground storage reservoir Loisach Valley (after J. P. Wrobel)

20 km) within a ground water basin of about 800 km2, its location, longitudinal sectionas well as the hydrographs of periodically and locally co-ordinated gaging stations andthe amount of precipitation (no rivers).

IV. CONCLUSION

On the basis of different examples several feasibilities are outlined to draw highlyimportant conclusions from the hydrograph, primary for the immediate applicationin the engineering practice.

By means of the hydrographs of gaging stations individual and independent groundwater basins, some are outlined to characterize the regiment of aquifers.

The data obtained result from the evaluation of some 500 individual gaging stationscovering an observation period of 20-30 years, and from an extensive study of 5 inde-pendent underground storage reservoirs or else ground water basins in Bavaria.

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Fig. 11 — Periodically and locally co-ordinated hydrographs of the gaging stationsand of the waters in the River Loisach Valley.

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Figs. 14 — Cross section of the underground storage reservoir Schotterebene (after E. Schirm).

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Fig. 15 — Periodically and locally co-ordinated hydrographs of the gaging stations (longitudinal section) and of the precipitation amount, (Schotterebene).

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Fig. 16 — Periodically and locally co-ordinated hydrographs of the gaging stations (cross section) in the Schotterebenc.