Assessing runoff processes at different spatial and temporal scales in a glacierized Alpine watershed
Authors: Doer the Tetzlaf f &
Chris Soulsby
Homepage: Environmental Hydrology Research group:
http://www.abdn.ac.uk/geography/Hydrology-Group/
webpage/hydro_home.htm
3. STUDY SITE
The Alps form Europe’s highest mountain range covering an area
of 240,000 km2; around 10% of this is covered by glaciers. Many
glaciers are retreating, reflecting a response to climate change and
increased temperatures (Uehlinger et al., 2003); in some areas these
responses are very rapid. Some of Europe’s largest river systems
have their headwaters in the Alps and are fed by meltwaters from
the mountain snowpack and valley glaciers. These melt waters have
a major influence on the physical, chemical and ecological
characteristics of the river systems they drain into.
èTo
-
characterise the hydrology and tracer chemistry of the river
– floodplain system at Lake Combal
èTo
provide a preliminary, tracer-based conceptualization of the
hydrological functioning
upscale this hydrological process understanding to Alpine
watersheds
828
5. RESULTS
1111
390
1078
2018
85
275
1953
272
2364
341
56
-
- Clear spatial organisation in hydrochemistry (Figure 4).
Spatial sampling of all major water courses in the floodplain
- Electrical conductivity (mS cm
contrasting source waters
-1)
as preliminary tool to differentiate
a)
N
828
21
56
188
1111
1078
188
1110
6.2
c)
N
259
78
145
133
- Further samples analysed for dissolved oxygen (mg l-1) using hand
held probes and pH and Gran alkalinity (µeq l-1) by acidometric
titration.
b)
N
58
0
390
562
433
275
272
Conductivity mS cm -1
85
341
1110
2018
8.9
2364
7.7
Gran alkalinity meq 1-1
9.1
76
g
e
5
8
10
11
9
gla
cier
Val Veny
4
2 3
1
N
7.85
6.2
3.2
- Mainly fed by meltwaters from the Lex Blanche and Estelletes
glaciers, snowmelt from the Lex Blanche stream and groundwater
seepage from adjacent hillslopes (Figure 3).
W
7.45
7.92
Estellete Glacier
7.93
6.1
5.6
6.5
DOmg 1-1
Figure 1: Map of the Dora di Veny
7.33
d)
5.2
1953
The study area is ca. 1 km2 floodplain of a braided river (originally
a lake created by the damning of the Dora di Veni river by the
moraines of the Miage glacier) (Figure 2)
a
562
433
21
-
259
78
145
133
4. DATA AND METHODS
b)
58
Dora di Veny – an important Alpine river system in the Aosta
Valley (Italy): 90km2 catchment, mainly comprised of the southern
slopes of Mont Blanc
- Parts of the Dora di Veny’s headwaters form a relatively pristine,
classic alpine braided river – the Lago Combal floodplain
system (Figure 1).
èTo
a)
N
i
E-mail: [email protected]
2. OBJECTIVES
M
School of Geosciences,
University of Aberdeen, Aberdeen AB24 3UF
1. INTRODUCTION
7.07
7.45
7.94
Vallon lex Blanche stream
8.09
7.84
8.04
Lex Blanche Glacier
Hillslope
springs
pH
Figure 4: Maps of selected water quality parameters at Lago Combal
Snowmelt-fed streams
6.2
7.33
c)
d)
Active braiding
7.85
0
7.45
6.2
7.92
3.2
7.93
5.2
- Distinct temporal differences in terms of water source dynamics with lower conductivity’s in the river system
in September.
6.1
8.9
7.07
8.09
5.6
7.84
7.45
7.7
6.5
8.04
Glacier melt-fed stream
Groundwater-fed stream
9.1
7.94
- Early in the glacial melt season: significant groundwater contribution to flows.
Figure 3: View of Lago Combal floodplain
SW
Slopes
Groundwater
Figure 2: View across Lago Combal floodplain to headwaters
- Groundwater appears to emerge from 3 distinct sources: very high conductivity groundwater springs emerge
from rockslopes on the northern edge of the floodplain; groundwater seepage on the southern side of the
floodplain; groundwater springs re-remerge in the floodplain itself (see sample point 6).
6. DISCUSSION & IMPLICATIONS
è Development of a conceptual model of the
hydrological functioning of the river floodplain system
– quantitative assessment of contribution of different
sources using end member mixing techniques.
- Low dissolved oxygen levels consistent with the more weatherable sedimentary geology indicating long residence
times and strongly reducing conditions (e.g.sampling point 6,7 and 8).
Glacial melt water
- At the downstream end of the floodplain: conductivities and alkalinities are closer to glacial inflow waters
than groundwater.
Conductivity-range
(µS cm -1)
Mixing
è Hydrology is dominated by the melting of the high proportion of precipitation that falls as snow during winter,
the steep terrain and geological conditions of low permeability (Figure 5).
Gran Alkalinity range (µEq1 -1)
è Spring melt season (May - June) is characterised by highflood flows
Disolved Oxygen range (mg1 -1)
è July - September: glacial melt sustains river flow.
Figure 5: Mixing of groundwater and glacial meltwater
REFERENCES SEE ALSO:
Tockner, K., Malard, F., Burgherr, P., Robinson, C.T., Uehlinger, U., Zah, R. and Ward, J.V. (1997) Physico-chmeical characterisation of channel types in a glacial floodplain ecosystem (Val Roseg, Switzerland). Archiv fuer Hydrobiologie, 140, 433-463.
Uehlinger, U., Maisch, M., Rothenbuehler, C. and Zah, R. (2003) Val Roseg: A high alpine catchment. In: Ward, J.V. and Uehlinger, U. (eds.) (2003): Ecology of a glacial floodplain. Kluwer Academic Publishers. Netherlands, pp. 1-16.
Ward, J.V. and Uehlinger, U. (eds.) (2003) Ecology of a glacial floodplain. Kluwer Academic Publishers. Netherlands.
Vezzoli, G. (2004) Erosion in the Western Alps (Dora Baltea Basin): 2. Quantifying sediment yield. Sedimentary Geology, 171, 247-259.
Streamwater
(Snow melt dominated)
Glacial melt-water
60 - 191
21 - 56
270 - 840
334 - 1290
84 - 340
450 - 2364
7.6 - 9.1
7.1 - 8.3
0.0 - 6.5
Table 1. Summarized range of selected determinands in different
runoff sources at the Lago Di Combal September 2004
Groundwater
è Response of alpine river systems to climate change
is likely to have major implications for issues as water
supply, hydropower production and flood management.
è Different source waters create diverse range of
freshwater habitats in the river – floodplain systems.
è Alpine rivers, and their associated floodplains, form
unique ecological habitats; and this major European.
biodiversity resource will also adapt to climatic change.