111-2.4.3 Soil-water-situation
Subsoil conditions within the Erft River area are substantially determined by the relative position of the Erft River level. Accordingly, there are permanently flooded and water- logged soils present in the Erft River plain attributable for the most part to the Erft River flood waters. The predominant type of soil is gley with transitional formations of brown earth gley (Eskuche, 1962).
The predominant type of soil on the plains in the Erft River basin on both sides of the Erft River is loess which overlies the terrace sands and gravels and extends from south to north in increasing thickness to reach a thickness of up to 2 0 metres in the north. A high- ly developed agriculture demonstrates that this is one of the most fertile regions of
Germany.
As a type, the loess soils of the Erft River area belong to the so-called 'parabrown earths' which are characterized by a relocation of clay substances from the top soil into the enrichment horizon of the bottom soil. This provides a barrier to infiltration of water but this is not a disadvantage from an ecological aspect. The water and the air condition is nicely balanced and any extra drying-out or wetting is not to be expected. Biological activity is good, too, as indicated by the presence of many earthworms deep in the subsoil.
adverse consequences to the agriculture of the Erft River area. In the loess areas the groundwater table was already so low before the lowering campaign that it had no impact on vegetation. Generally, there is no correlation between subsoil water conditions and agricu- ltural utilization at a ground water table from 1.50-2.00 metres below the surface since plants in such cases are supplied from the adhesion waters present. It may be said, there- fore, that the water supply of the plants will also be ensured in the absence of any sub- soil water influx as has been conventional practice hitherto namely, to grow only one field crop each vegetational season. This is the reason why groundwater lowering is either of no importance to the growth of crops or even advantageous where damage due to excessive wet- ness, causing wet rot is thereby avoided.
Only in the valley plain of the Erft River where the plant roots reached the ground- water before the lowering campaign started could changes in vegetation be observed. Unti- lowering took effect, the Erft River plain used to be almost exclusively covered by wet, swampy meadows and pastures which produced unsatisfactory crops; afterwards, they were changed into profitable fertile meadows and pastures. However some damage could be attri- buted to groundwater lowering in valley plain areas with swampy soils where soil settling was observed and detrimental effects on poplar cultures were encountered due to water extrac tion.
The extensive lowering of the groundwater table has not resulted in any substantial
III-2.4.4 Influences on surface waters
Apart from the problem of large-scale groundwater lowering, the Erft River area also involves further water management problems including a number of measures to preserve existing drain- age conditions, to provide flood protection and to eliminate wastewaters.
m3/sec and often resulted in inundations and heavy damage, it was not capable of draining the substantial quantities of water originating from the mines (Heitk'&per, 1971)
.
hensive extensions to the Erft River increased its drainage capacity for larger volumes of drain waters and at the same time provided increased safety against inundation.
Where the Erft River constituted an obstruction to lignite mining because it adjoined directly the opencast mines or even passed across exploitation fields, its bed was diverted several times. These diversions were necessary to make the opencast mining operations safe and/or to permit continuous extraction.
(70 m3/sec) and the river bed dimensions determined accordingly.
advantages that introduction of large volumes of clean groundwater improves the water quality in the Erft River which is pretty much affected by wastewaters.
lower course was allocated Class II which means 'moderate pollution' class (Table 42) so that in this mining area the Erft River is today known for good fishing.
As a river with an average flow of 5 m3/sec which during flood seasons rises to 40-50 Compre-
All diversions were based on the flood water figures Besides flood protection, these operations and subsequent precautions offer the further The river has a plentiful and well-balanced biocoenosis of native species. Even its
188
Water management in opencast Lignite mining ureas
Table 42. Chemical and physical measurements
Erft at Neussr near its mouth into the Rhine
Measurements : May 1966
-
May 1967 in intervals of 14 days Measurements : May 1967-
May 1968 in intervals of 14 days-
x- =
Average of 27 single measurementsG1 pH GU Wi Ca Mg Alk.1.W. Fe Kn UC03 C1 SO4 PO4 NO3 NH4 oz m n 0 4 PSB T
1-1s OdU OdH mg/l mval mg/l mg/l mg/l mg/l mg/l w / l mg/l mg/l mg/i mg/l mg/? oc
:qLn 463 6.7 13.9 10.8 66 17 0.6 0.22 0.01 241 32 31 0.15 6.0 0.14 7.1 6.6 0.3 12.6
66/67 Max 529 8.2 15.7 12.3 76 32 2.0 4.83 0.73 275 43 49 0.8 11.8 1.52 9.6 25.9 9.0 19.7 X 502 7.5 14.6 11.7 70 21 1.0 1.0 0.29 255 36 40 0.4 7.8 0.47 8.2 10.8 3.4 16.5 Min 487 7.3 13.6 8.8 63 17 0.8 0.38 0.13 192 39 26 0.15 3.3 0.08 7.1 5.2 1.0 11.2 67/68 Max 549 8.2 15.4 12.7 74 30 1.5 4.81 0.04 178 46 67 0.82 15.5 1.79 9.4 30.7 16.4 22.1 R 523 7.7 14.5 11.6 69 21 1.2 1.54 0.28 253 43 39 0.46 7.7 0.95 7.9 11.8 3.4 17.3
The continuous flood waters of the river narrow the area of intense plant and animal population and biomass production to a small strip of maximum 1.5 metres width along the river banks.
The Erft River has almost homothermal water due to the predominant influence of the drainage water which is subject to very slight seasonal temperature variations only. This results in very interesting consequences with regard to the plant and animal life of the river;
subtropic compsopogon hockeri from warm water aquaria.
groundwater due to the continual groundwater lowering and hence still only serve as drains for surface waters. This is the reason why the discharges in these brooks depend substan- tially on precipitation which is quite different in the various seasons (Diesel, 1963).
for instance it accounts for the presence and tremendous development of the tropic/
red algae which were presumably placed into the Erft River The small brooks within the Erft River area are not often in communication with the
IIï-2.4.5 Water supply
-
Gärtner SchemeThe lowering of the groundwater meant that a large number of water supply plants failed or, at the margins of the mining area, operated under more difficult conditions, but inadequate supplies are maintained because the mining authorities provided compensation.
This substitution of water supply is being accompanied by a considerable readjustment within the area either by a merger of several large-scale supply undertakings into a joint supply facility or by connection of small-scale and even minute supply systems to central- ized grids.
which finally took care of water supply. Thus, in an effort to safeguard public water supply, one new water supply works was constructed, 13 waterworks were extended and about 8 others were replaced by connections to other systems (Heitkhper, 1971)
To permit an adequate volume of water to be extracted as the groundwater table is low- ered, wells were sunk to levels of more than 300 metres below datum level. Simultaneously, it was necessary to construct new treatment plants because the water obtained from greater depths contains a higher percentage of iron and more carbon dioxide.
are today being supplied from substitute water supply facilities.
Moreoverr the lignite mining company provided a number of its own installations
Some 240 O00 people
Water management in opencast Zignite mining areas
A major part of the water demand is met by mining drainage waters which have been avail- The total delivery from mine draining installations is currently 155 million m3 per able at a mean rate of approximately 1.2 x lo9 m3 per annum for the last ten years.
annum which is subdivided as follows (Gärtner, 1968) 95 million m per annum 3
=
62% for power stations 40 million m3 per annum=
25% for industrial needs 20 million m3 per annum=
13% for public water supply.The present water requirements in the Erft River area are about 370 million m per 3 annum and are covered by 708 installations, of which 107 plants belong to the public water supply. The current water demand is still below the average groundwater replenishment rate which is approximately 400 million m3 per annum in this area (Gärtner, 1972).
In view of the tendency towards increased demand, however, requirements may well exceed the groundwater recharge rate in the seventies. Nevertheless, such increased demands can be satisfied without difficulty from the tremendous volume of water drained from the lignite mines for another 30 years.
a considerable supply required in this area especially as the ever increasing demands are expected to grow as high as 600-700 million m3 per annum by the year 2000 and cannot be satisfied by the available resources (Heitkämper, 1971)
requirements from other sources, the water supply could possibly be provided by utilizing the remainder of the opencast mining area for water supply purposes. Intense feasibility studies for this project called ‘Gärtner Scheme’ after its initiator, are currently being made.
Termination of lignite mining will leave depressions totalling at least 3 x 10 m
because of the removal of lignite. The space thus left over would gradually fill with water in the course of time (Gärtner, 1968).
waters from other streams into the depressions but since the introduction of Erft River water is expected to be feasible only during periods of higher river discharges and the average amount available annually only 15-30 million m3 , the filling process would take decades However, the volume of water required for a fast fill could be made available from the Rhine River which has a yearly discharge of approximately 70 x LO9 m3.
be necessary to avoid substantial water pumping works and would have to pass through the left Rhine Valley at a depth of about 400 metres, ie, within the basement rock formations.
Nevertheless, it is believed that this could still be accomplished economically if novel tunnel drilling machines were used.
While the problems of refilling the excavated pits with the necessary quantities of water might be solved, it is impossible to predict how the water quality may develop. Numerous investigations conducted during past decades show that the natural state of the gradually filling basins is very much dependent on such factors as subsurface conditions encountered, weathering influences, prior depositions (overburden, ashes, debris), and the fill-up water as such. It is initially characterized by high sulphate concentrations and chloride contents with low temporary hardness in most cases. The concentration of soluble salts reduces in the course of the years.
If Rhine River water were to be added to accelerate the fill-up process it must be ex- pected that natural eutrophication and enrichment with undesirable ingredients and/or com- ponent substances will increase. Comprehensive research and investigation is being carried out at present to determine the importance of these phenomena and possible precautions to be taken.
avoiding the difficulties most likely to be raised by increasing water requirements, not only in the Erft River area which is influenced by the mining activities, but also in the neighbouring Cologne and Neuss districts.
After exhaustion of the lignite deposits and the end of lignite mining, there will be
Apart from drawing groundwater from the deeper groundwater aquifers or by meeting the
9 3
Another possibility would be to speed up the filling process, namely, by transferring
A connecting tunnel would
The project to connect the residual lakes to the Rhine River might be the best way of
i 90