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 HAMBURG, 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, Harburg-Wilhelmsburg and Wandsbek (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 Elbe. 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 "Billbrook" 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.