Groundwater Runoff in Small Mountainous Basin
(Lange Bramke, Germany) – Testing a Separation Method
Based on Groundwater Table and Discharge Data
L. Holko (1), A.Herrmann (2), M. Schöniger (2) & S. Schumann (2)
(1) Institute of Hydrology, Slovak Academy of Sciences, Ondrasovecka 16, 031 05 Liptovsky Mikulas,
Slovakia, holko@svslm.sk
(2) Institute of Geography and Geoecology, Langer Kamp 19c, D-38106 Braunschweig, Germany,
a.herrmann@tu-bs.de
Introduction
Experimental catchments all around the world provided a lot of evidence on the importance of
groundwater runoff in the course of single flood events. Such results were mainly obtained through the
use of environmental tracer techniques, which generally contributed invaluably to the change in ideas
on runoff generation. Though isotopic separation is a routine technique nowadays, its application
needs careful sampling and analysis in well-equipped laboratories hence in most cases it cannot be
run on the long-term basis. The separation method introduced by KLINER & KNEZEK (1974) is based on
groundwater table-discharge relationship and provides information on groundwater runoff during
events. It can be used also for the long-term evaluation of groundwater runoff. HOLKO (1995) indicated
that the results may be comparable with those found from isotopic separation. In the present study
long–term data from a small mountainous basin of Lange Bramke, Harz Mountains, Germany (543700 m a.m.s.l.; 90% forested by Norway spruce; fractured and faulted paleozoic sandstones,
quartzites and slates) are used to separate the groundwater runoff proportion. Results are being
verified by independent methods.
Groundwater runoff separation
Considering hydraulic connection between aquifer and stream water a relationship between the
groundwater table and stream water level exists. When the slope of groundwater table is directed
towards the stream, changes in the difference between groundwater and stream water tables
represent the groundwater runoff. In practice, the groundwater runoff can therefore be determined by
plotting discharge versus groundwater table. In this plot, usually, the top boundary concentration of
dots form an envelope line which represents that portion of discharge which is actually formed by
groundwater runoff (Fig. 1). This line can be used to calculate groundwater runoff for distinctive
groundwater tables.
Separation results
The separation method was used to compute daily groundwater runoff from semi-confined fractured
rock aquifer in the Lange Bramke catchment basin for the period 1987-1998. The results show that the
major portion of basin runoff is actually groundwater. If the available data span over the period of
several years, the envelope lines (and consequently the separated groundwater runoff) determined for
single years differ from the envelope line determined for the whole period. Usually, the envelope line
determined for longer period gives lower groundwater runoff in single year than the envelope line
determined for that particular year. An example for hydrological year 1995 is given in Fig. 1.
569.0
Groundw ater table
[m a.s.l.]
Groundw ater table
[m a.s.l.]
569.0
568.5
568.0
1987-1998
568.5
568.0
1995
567.5
567.5
0
20
40
60
Discharge [l/s]
80
0
100
20
40
60
Discharge [l/s]
80
100
200
200
1995
1995
Total catchment runoff [l/s]
Total catchment runoff [l/s]
150
150
Groundwater runoff [l/s]
Fig. 1: Groundwater runoff in hydrological year 1995; left - computed from the envelope line derived
for the whole period 1987-1998, right – computed from the envelope line determined on the basis of
data from hydrological year 1995
Discussion
The separation results have been compared with those from the synthetic DIFGA separation approach
which is based on the linear storage concept and long-term averages (SCHWARZE et al. 1991), and
furthermore with results from the analytical isotope approach (HERRMANN et al. 1989). Taking different
study periods within the more than 50 years long observation series of discharge in Lange Bramke
into account, the magnitude for groundwater discharge found here is confirmed in about the same
order by the oxygen-18 results. The mean transit time of this component is around 2.5 years.
Additionally, other hydraulic storage parameters like volume of mobile water and effective porosity are
generated from the complete isotope hydrological approach. DIFGA generally allows to separate the
subsurface components into three components being the flow through macro-pores (and fracture
runoff), as well as the slowest initial and the delayed baseflow component. All three show results
comparable with those of the isotopic and the envelope line separation. DIFGA also enables to
discriminate each subsurface reservoir hydraulically by the same parameters as the isotope technique
allows.
Conclusion
The groundwater separation technique proposed by KLINER & KNEZEK (1974) is a simple way to
compute daily groundwater discharge provided that daily groundwater and discharge data are
available. Separation results seem to be rather realistic as can be concluded from the comparison of
results with those generated by the environmental tracer approach. Latter additionally informs about
10/1/95
9/1/95
8/1/95
7/1/95
6/1/95
5/1/95
4/1/95
3/1/95
2/1/95
1/1/95
12/1/94
10/1/95
9/1/95
8/1/95
7/1/95
6/1/95
5/1/95
4/1/95
0
3/1/95
0
2/1/95
50
1/1/95
50
12/1/94
100
11/1/94
100
11/1/94
Groundwater runoff [l/s]
the age of this component. Further consideration of the DIFGA technique proves that the groundwater
reserve of the basin consists of at least two components which originate from different hydraulic
systems, and supports the high value of the multilateral integrated scientific basin approach. As a
result, the expensive isotope technique may be restricted to calibration purposes for the more
practicable but, according to the study, reliable empirical approaches for basin groundwater systems.
References
HERRMANN, A., KOLL, J., LEIBUNDGUT, CH., MALOSZEWSKI, P., RAU, R., RAUERT, W., SCHÖNIGER, M. &
STICHLER, W. (1989) Wasserumsatz in einem kleinen Einzugsgebiet im paläozoischen Mittelgebirge
(Lange Bramke/Oberharz). Eine hydrologische Systemanalyse mittels Umweltisotopen als Tracer
(Turnover of water in a small basin in the paleozoic highlands. A hydrological system analysis using
environmental isotopes as tracers). Landschaftsökologie und Umweltforschung 17, Braunschweig,
305pp
HOLKO, L., 1995: Application of stable environmental isotopes in hydrological research of a mountain
catchment. (in Slovak), PhD thesis, Inst. of Hydrology SAS, Bratislava, 100pp
KLINER, K. & KNEZEK, M. (1974) The underground runoff separation method making use of the
observation of groundwater table. (in Czech with English abstract), Journal for Hydrology and
Hydromechanics, vol. XXII, no. 5, 457-466
SCHWARZE, R., HERRMANN, A., MÜNCH, A., GRÜNEWALD, U. & SCHÖNIGER, M. (1991) Rechnergestützte
Analyse von Abflußkomponenten und Verweilzeiten in kleinen Einzugsgebieten (Computer-aided
analysis of runoff components and transit times in small basins). Acta Hydrophysica 35 (2), 143-184