Hydrogeology in the Service of Man, Mémoires of the 18th Congress of the International Association of Hydrogeologists, Cambridge, 1985.

THE IMPACT OF GROUNDWATER AND THE ROLE OF HYDROGEOLOGY ON A CITY's GROWTH - CASE STUDY OF , FEDERAL REPUBLIC OF GERMANY. E.P. LOEHNERT Department of Geology & Palaeontology, University of Mttnster, F.R.G.

ABSTRACT This paper illustrates both benefits and problems of intense groundwater development in a highly developed country. Over the past 150 years the City State of Hamburg has relied heavily on groundwater from the underlying confined aquifers in porous Tertiary and Quaternary deposits. Currently 210 x 10& cubic metres are abstracted annually for both public and industrial use. Recharge outside the City will ensure that supplies will continue to be replenished. However problems of natural salinisation of deep aquifers and pollution of shallow aquifers will restrict use. The structure of the Federal State system also inhibits groundwater withdrawal from less populated and industrialised surrounding areas.

INTRODUCTION The City of Hamburg came into being by law in 1937 when, among others, neighbouring Prussian towns of Altona, -Wilhelmsburg and (all of them with their own water supplies) were incorporated to form the current state. It covers an area of 755 km^ (Fig. 1). With a population (in 1983) of 1,61 million the density is about 2130 inhabitants per km.2 being the highest figure in the F.R.G. A considerable number of industries, some associated with the harbour, are located in Hamburg. The area under consideration is placed in the heart of the North German plainlands at the banks of the river . Hence at a first glance water resources from the Elbe, its tributaries and harbour basins seem to be abundant. The rivers Alster and Elbe have indeed served as the main drinking water supplies for centuries. As will be pointed out in this paper, groundwater resources were increasingly developed by industries and became the only source of public supp­ lies in 1964. Consequently, groundwater has contributed immensely to the current social and economic status of the city.

HISTORY OF GROUNDWATER SUPPLY So-called field wells have been reported to exist since the 14th century. Spring water was piped from elevated to low-lying areas. The oldest well of this kind was in use for a period of 500 years (1370-1869). The major supply was, however, from streams through private "water arts", the first of these established in 1531 at the Alster. The "rock water art" used simple filtration technique in 1833 for the first time. Four arts were in existence when the great fire of 1842 devastated the city. In 1844 the English engineer William Lindley was commissioned to

- 178 - B

CENTRES OF DEPRESSION CONE : UPPER LIGNITE SANDS LOWER LIGNITE SANDS (CONTOUR LINES IN METRES B.S.L.) MAIN FLOW DIRECTION OF FRESH DEEP GRUNDWATER

SALT DIAPIRS: PUBLIC WATER WORKS

. BENEATH - 400 m S.L. AFFECTED BY SALINISATION

, ABOVE -400 m S.L. D MAIN INDUSTRIES

Fig. 1. Location map of the study area (right hand map based on Paluska et al., 1978) set up a central water supply. The Elbe river on the upstream side of the old city border was chosen for what was called the "city water art". The plant, consisting of sedimentation basins only, was opened in 1848 without taking into consideration Lindley's strong recommendation to apply sand filtration. The latter was actually under construction when the cholera epidemic of 1892 which claimed about 7600 lives occurred. Neighbouring Altona which had a sand filtration plant was hardly affected. Drilling for groundwater can be traced back to the 1830's. It was at Altona where the deepest borehole of the time in North Germany was sunk to a depth of 86,5 m in 1832/33 (Loehnert, 1967). Confined aquifer conditions were encountered in sandy Quaternary deposits. With the advent of the industrial revolution around 1860 mud drilling techniques imported from Denmark were also improved. Groundwater abstraction by industrial and private enterprises quadrupled between 1869/70 and the turn of the century to reach 6200-7800 irP per hour; this amount exceeded publicly supplied filtrated Elbe river water (.Darapsky, 1903). Wibel and Gottsche (1876) reported on a number of successful boreholes in the Hamburg area, some of them 140-170 m deep (Fig. 2). The key to the exploitation of deep aquifers was the Schaarmarkt borehole drilled to a depth of 292^ m in 1878 (Wibel, 1879; 309 m according to Darapsky). Lignite sands of Tertiary age with artesian flow and at the same time with "totally differing water quality" at 3 test levels were discovered (Wibel, 1879). Nearly a century later, the present

179 - E o o

500- 500 m m

o

a 100- 1875 1900 1925 1950 1975

Fig. 2. Development of average and maximum depth of borehole s/wells in the City of Hamburg and adjacent areas (only depths greater than 100m taken into account).

50*103r

203 t

Q. 30*- No. of CO 103 boreholes'y s T3 E 100 o

20*- Wo r I d War 103

50 10*- 103

I875 1900 1925 1950 1975

Fig. 3. Number of deep boreholes and metres drilled in the City of Hamburg and adjacent areas (Interval 1975-80 incomplète).

- 180 - author related these hydrochemical findings to the salt dome of Altona-Langenfelde (Loehnert, 1967). The cholera epidemic led understandably to accelerated drilling activities (Fig. 3) since it was obvious that people who had drunk borehole waters were not affected at all. State authorities had roughly one hundred shallow wells drilled during the occurrence of the epidemic, and this led people to believe that deep groundwater was cleanest. This naive belief sometimes led to disappointment as some results of later drilling activities proved negative. Deseniss and Jacobi were regarded as one of the leading drilling companies of those days. Screening techniques were employed as early as 1890. The population became stabilised at the beginning of the 20th century and the central water supply grew steadily (Fig. 5.). The first public plant "" extracting groundwater from shallow wells in the Elbe valley was established in 1905 against Lindley's advice. After foundation of the Hamburg Waterworks Co. Ltd. (HWW) in 1924 a second major plant "Curslack" was set up making additional use of artificial recharge. Both plants contributed groundwater to the above mentioned city water art now using filtrated Elbe water. Groundwater constituted 89 per cent of the total supply in 1938/39. A major step forward was taken in 1964 when the public supply was cut off from any contribution from the then deteriorating surface water.

HYDR0GE0L0GICAL BACKGROUND Merit is due to E. Koch who has clarified misinterpretations of previous researchers. Our knowledge on the aquifer system was deepened by the application of geophysical borehole logging in the past 20 years. Geothermal measurements yielded valuable results on flow conditions (Ludewig, 1982). The latest approach includes the use of environmental isotopes to support hydrogeological and hydro- chemical research (Loehnert & Sonntag, 1981). Porous aquifers occur in unconsolidated Quaternary (Pleistocene) and Tertiary (Plio-Miocene) rocks. The aquifer system is underlain by a Lower Miocene clay. Fig. 4 presents a generalised cross section neglecting details of the uppermost Quaternary deposits. As can be seen, deep aquifers form wide troughs (Tertiary) or narrow channels (Quaternary) between salt diapirs ascending to different depths. Hence syn- and post-sedimentary salt movements are the determining factors behind aquifer formation, thickness and depth. It has become customary to distinguish between shallow and deep (er) aquifers, the former of younger Pleistocene and Pliocene age while the latter are of older Pleistocene and Miocene age. The local names can be derived from Fig. 4 which is also intended to demonstrate local hydraulic separation of aquifers. However, interconnection exists over the total catchment area. Differences in the hydraulic heads were noted in the early days of exploration, with highest piezometric levels in the Lower Lignite Sands resulting in spectacular artesian flows up to 20 m above surface in the Elbe valley. The piezometric surface dropped due to extraction at an average rate of 0.3 m per year (max. 0.8 m or even more in centres of depression cones) as shown in Fig. 5. Today it can be assumed that the large-scale depression cone is stable except at the margins. Piezometric differences amount to 30 m between Upper and Lower Lignite Sands (Fig. 4). - 181 - SOTTORF

ELBE/-

"%/ fr^r; 'A vd'fy^f^' :C^r^^2 J S ^^srJ^r \<$ *>&.^\^ S<£x-'& PPSI AQUIFERS 6 WE1CHSELIAN SHALLOW PLEISTOCENE F77775 TERTIARY & 5 SAALIAN . PIEZOMETRIC SURFACE OF AQUITARDS & AQUIFERS LOWER LIGNITE SANDS 2^221 QUATERNARY 4 PLIOCENE AQUICLUDES P5S^ PRE-TERTIARY 3 ELSTERIAN (PLEISTOCENE) • PIEZOMETRIC SURFACE OF DEEP UPPER LIGNITE SANDS 2 UPPER LIGNITE SANDS I j SALT DIAPIRS AQUIFERS (ZECHSTEIN/TRIASSIC) 1 LOWER LIGNITE SANDS ) '

Fig. 4. Hydrogeologic cross section (Location A-B see Fig. 1). Shallow aquifer conditions of No.S very simplified (Based on Paluska et al.> 1978).

Piezometric surface with­ out industries 20

1890 1950

Fig. 5. Drop in piezometric surface at Billbrook (X in Fig. 1) resulting from industrial and public supplies (after Drobek, 1968).

182 The identification of groundwater recharge to deep aquifers is problematic. Outcrop areas hidden beneath Pleistocene deposits are certainly located beyond the city's border in the federal states of Schleswig-Holstein and Lower Saxony. Consequently deep groundwaters extracted within the City of Hamburg are mainly imported. On the other hand local recharge to shallow aquifers including bank infiltration is to a greater or lesser extent sub­ jected to contamination from streams or waste disposals. It is this tense situation that will keep discussion on water supply problems going. Some of the groundwater resources, especially deep ones, are affected by natural salinisation. The author has elaborated on this problem several times (Loehnert, 1967, 1968, 1972 a,b). Besides groundwater salinisation along the salt dome lineation Altona- -Quickborn, a second area can be recognised in the south­ eastern quarter of Hamburg (Loehnert & Paluska, 1977). Conse­ quences on future groundwater abstraction will be dealt with in the following chapter.

CURRENT SITUATION AND FUTURE ASPECTS There were serious discussions in the I960's about piping surface waters from surplus areas over long distances, even from Sweden and the Alps to satisfy Hamburg's thirst (Drobek, 1968). Desalination of sea water and less saline groundwater was also proposed. These projects have proved to be unrealistic mainly due to a lower than expected increase in the consumption rate. While there is still an annual increment of approx. 1% in the public water supply of the F.R.G. the demand in Hamburg is assumed to have stabilised. Drobek (1968) for instance calculated the HWW demand in the year 2000 to be 182 million m3 (max. 190 mill.) or even 234-243 million m3. Contrary to estimations by Drobek, the latest report by the Water Authority (Fachplan, 1984) assumes 150 million m3. The latter figure is based on a specific household consumption rate of 172 1 per head per day (1980: 151 1). The total groundwater abstraction including industrial consumption is currently 210 million m-> p.a. and is expected to rise to 215 million m^ in the year 2000. There is principally no reason to doubt the availability of this amount of groundwater from the greater Hamburg area. Restrictions, however, originate from the viewpoint of quality requirements. Valuable information on the current and future groundwater supply and demand situation is being provided by the "Fachplan Wasserversorgung Hamburg" (1984) edited by the Hamburg Water Authority. About half of the total groundwater volume abstracted in 1980 was from deep aquifers'. This proportion will remain un­ changed in the coming decades. Of major concern is the fact that the industrial abstraction rate will amount to 35 million mJ of precious drinking water quality. Not all the industrial branches depend on high quality water and it is common Hamburg water policy to curtail groundwater abstraction from deep aquifers wherever poss­ ible and whenever necessary to the benefit of public supplies. As depicted in Fig. 1 the century-long groundwater exploitation has caused depression cones in the confined water table which differ in size, location and depth with respect to the two major deep aquifers. While industrial aggregation gave rise to the piezometric decline in the Upper Lignite Sands the one in the Lower Lignite Sands originated from both industries and public supplies. A vital role

- 183 - in the latter case is played by a Quaternary channel resulting in pressure relief and salt water ascent as first recognized by the author. Mathematical modelling has proved that there should be hardly any changes in the groundwater contours up to the year 2000 (Fachplan, 1984). In fact only slight shifts of abstraction centres have been simulated taking into account the mobility of transition zones between fresh and saline waters (Fig. 6). Five of the 20 HWW waterworks are affected by underground salinisation, three of them seriously (Schulz & Wichmann, 1984). The incorporation of quality aspects in the model seems to be one of the main future tasks. The contribution of environmental isotopes to solve this problem might be as follows. According to the stable isotopes deuterium and oxygen-18 any kind of sea water intrusion, recent or of the geological past, can be excluded. Two groups of groundwater can be distinguished, one representing paleowaters, while the majority can be attributed to waters participating in the ongoing hydrological cycle parti­ cularly when having elevated tritium contents. The former group consists exclusively of saline waters with differing salinity. These waters are hardly being exploited whereas the others, both fresh and (sulphatic-) saline, occur in a number of deep wells. Recently recharged groundwater with tritium was encountered locally as deep as 200 m beneath the surface. As far as salt water is con­ cerned, solution processes at the Aitona-Langenfelde salt diapir are continuing and are possibly accelerated by abstraction. These new results complete previous findings by Loehnert & Sonntag (1981).

meq/ 7 A

14-14,3 °C 16°C

1930 1940 1950

Fig. 6. Changes of groundwater quality with time in a deep well 2 km west of Billbrook (X in Fig. 1),

184 - CONCLUSIONS Due to uniquely favourable geohydraulic conditions, ground­ water abstraction was able to reach the present state of develop­ ment in the City of Hamburg within a period of 150 years. The confined aquifer system is at steady flow conditions in the city's centre. At the margins the depression cone which extends far beyond the political border of the city state requires almost decades to stabilise. No problems are expected as to the quantitative availability of groundwater. Quality problems, however, affect both deep and shall­ ow aquifers. The former are subjected to salinisation. The stabil­ ity of the contact against fresh water needs to be thoroughly controlled, while the Elbe river water quality has already resulted in preventing its use for artificial recharge purposes. (Wichmann, 1985, in preparation). Additionally bank filtration in the Elbe valley might lead to the abandonment of supplies from shallow aquifers. There are actually politically motivated difficulties to over­ come: the City of Hamburg is surrounded by federal states which want to develop groundwater resources for the benefit of their own economies and population, to the extent that they are not inclined to support infrastructure for improving Hamburg's water supply. It was Dr Drobek, the former HWW director, who had frequently and frankly criticized this sort of water reservation by neighbouring states (Drobek, 1969). Strangely enough, due to the described natural circumstances recharge to deep groundwater extracted within the city's boundaries inevitably takes place in the neighbouring countryside.

ACKNOWLEDGEMENTS The author gratefully acknowledges the fruitful co-operation of colleagues of the Hamburg Water Authority (Baubehorde, Hauptab- teilung Wasserwirtschaft), as well as members of the Hamburg Waterworks Co. Ltd. (HWW), industrial enterprises, drilling companies, and the Geological Survey of Schleswig-Holstein. Thanks are due to Mrs Sue Hutton, Loughborough, for editorial help.

REFERENCES Darapsky, L. 1903. Die Grundwasserfrage in Hamburg. 1-19. F. Leineweber, . Drobek, W. 1969. Sohwierigkeiten und Problème der Wasserversorgung dev Grossstadt Hamburg, ndz Neue DELIWA- Zeitschr., H.5 Hannover. Baubehb'rde Hamburg, 1984. Fachplan Was server s or gung Hamburg. Amt fuer Wasserwirtschaft und Stadtentsorgung, Hauptabteilung Wasserwirtschaft. Koch, E. 1928. Die Grundwassertraeger des Niederelbegebietes. GWF Das Gas-und Wasserfach, 71, H.37. 889-895. Munich. Koch, E. et al. 1954. Erlaeuterungen su Blatt Hamburg der Hydvogeologisohen Ubersichtskarte 1:500.000. Bundesanst. f. Landeskunde, Remagen. Loehnert, E.P. 1967. Grundwasserversalzungen im Bereiah des Salzstookes von Altona-Langenfelde. Abh. u. Verh. Ver. Hamburg, N.F. XI, 29-46.

- 185 - Loehnert, E.P. 1968. Hydroohemische Zuscamenhaenge am Kontakt zw-isohen versalzenem Tiefenwasser und Suesswasser in Norddeutsch- land. XX111. Int. Geol. Congress, 17, 127-135. . Loehnert, E.P. 1972a. Contribution to the geochemistry of ground­ water in Northern Germany. Geol. en Mijnbouw, 51 (1), 63-70. s'Gravenhage. Loehnert, E.P. 1972b. "Tiefes" Grundwasser in Norddeutschland. Zbl. Geol. Palaeont. I, 1/2, 19-25, Stuttgart. Loehnert, E.P. and Paluska, A. 1977. Groundwater Salinisation in the Elbe Valley (City of Hamburg). Proc. 5th Salt Water Intrusion Meeting, 98-107. Medmenham. Loehnert, E.P. and Sonntag, C. 1981. Grundwasserversalzungen im Raum Hamburg im Lioht neuer Isotopendaten. Zeitschr. deutsch. geol. Ges. 132, Teil 2, 559-574. Hannover. Ludewig, H. 1982. Temperaturmessungen in Tiefenpegeln im Raum Hamburg und deren hydrogeologische Interpretation. Ph.D.Thesis Univ. of Oldenburg. Paluska, A., Loehnert, E.P. and Schlichting, K. 1978. JJeberblick ueber geologische Strukturen und Grundwasser des tieferen Untergrundes. Deutscher Planungsatlas Band Hamburg. Munich/Alsfeld. Schulz, M. and Wichmann, K. 1984. Geogenia groundwater pollution in the Hamburg region. Relation of Groundwater Quantity and Quality, Proc. Hamburg Symp. Aug. 1983. IAHS Publ. No.146 (in press). Wibel, G. 1879. Die geognostisohen Ergebnisse einiger neuerer Tiefbohrungen auf Hamburgisehem Gebiet und Umgebung. Verh. Nat. Ver. Hamburg-Altona, N.F. Ill, 160-174. Wibel, F. and Gottsche, C. 1876. Skizzen und Beitraege zur Geognosie Hamburgs und seiner Umgebung. Hamburg in naturhistor. u. med. Beziehung, 109-147. Wichmann, K. 1985. Groundwater recharge in a rural area of Hamburg. Congress "Wasser Berlin" (to be published).

- 186 -