Multifunctional monitoring in torrent catchments
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Multifunctional monitoring in torrent catchments
E. Lang and U. Stary
Multifunktionales Monitoring
in Wildbacheinzugsgebieten
Introduction Reasons for installing monitoring systems
in torrent catchments
Multifunctional monitoring in torrent catchments is gen-
erating a variety of useable synergy benefits and is also a re- For decades, the Department of Natural Hazards and
quirement predetermined by the diversity of nature. The Alpine Timberline of the Federal Research and Training
supplied data are used to find solutions to assignments in Centre for Forests, Natural Hazards and Landscape (BFW)
the field of torrent and avalanche control and to provide an- has been involved in the development of practice-oriented
swers to interdisciplinary and scientific issues (Hydraulic methods for the sustainable protection of human settle-
Engineering, Geomechanics, Hydrogeology, Silviculture ments and infrastructure against natural hazards in Alpine
etc.). The measurement systems, which have been in use for regions. In this regard, it is essential to have comprehensive
many years, are also an important element of interdepart- knowledge about the processes taking place in nature.
mental and transnational climate change research pro- In Austria, there are around 12,000 torrential watersheds.
grams. These are threatened by floods, debris flows, landslides and
avalanches. But there are only a few stations to measure rel-
evant parameters needed to explore the processes which lead
to these natural disasters. For example, only a few of the pre-
Zusammenfassung
Die Beurteilung von Wildbacheinzugsgebieten im alpinen Raum wird oftmals durch das Fehlen abgesicherter Mess-
daten erschwert. Das Bundesforschungs- und Ausbildungszentrum für Wald, Naturgefahren und Landschaft (BFW)
widmet sich dieser Aufgabe seit geraumer Zeit um ein verbessertes Prozessverständnis zu erlangen. Der vorliegende
Beitrag beschreibt die Anforderungen an ein multifunktionales Monitoringsystem unter extremen Bedingungen und
unterstreicht die Wichtigkeit langfristiger Studien in Wildbachgebieten. Ausgewählte Ergebnisse werden anhand eines
gut beobachteten Einzugsgebiets dargestellt. Die Daten zeigen u.a. die unterschiedlichen Einflüsse der Klimaän-
derung, die sich besonders in den Parametern Niederschlag und Temperatur zeigen.
Schlagwörter: Wildbach, Schneewasseräquivalent, Talzuschub, Klimawandel.
Summary
The assessment of torrent catchments in the Alpine area is often hindered by a lack of confirmed data. The Federal
Research and Training Centre for Forests, Natural Hazards and Landscape (BFW) has been devoted to this task for
decades to close the knowledge gaps. The following paper makes an effort to show an overview of requirements on
multifunctional monitoring under extreme conditions and reveal the importance of long-term studies in torrent areas.
Selected results of long term monitoring in one special torrent catchment will be presented. The data show among
other things the different impacts of climate change which are particularly evident in the parameters of precipitation
and temperature.
Key words: Torrent, snow water equivalent, sagging of mountain slopes, climate change.
Die Bodenkultur 71 62 (1–4) 2011
E. Lang and U. Stary
cipitation stations located at high altitudes are recording
data with high temporal resolution. For this reason, the data
base for the design of protective measures against natural
hazards must be improved. The installation of monitoring
systems in torrent catchments was and is an important con-
tribution to the study of these processes and the generation
of fundamental data.
In the past, monitoring systems were installed in torrent
watersheds following disaster events (e.g. after the severe
flooding of 1965/66 in Carinthia). Today, they have gained
in importance in connection with the possible effects of cli- Figure 1: Monitoring systems of the BFW in torrential watersheds
mate change on natural hazards. Moreover, it has become Abbildung 1: Monitoringsysteme des BFW in Wildbachgebieten
evident that even state-of-the-art, computer-assisted simu-
lation techniques need model calibration and plausibility
checks which can only be implemented by using measured The following methods are used to collect data:
data and facts of nature.
• (automated) monitoring stations to gain longterm series
of measurements
Beneficiaries of monitoring data • exploitation of additional information through field sur-
veys and experiments (heavy rainfall simulation, soil and
• The operating company (for example BFW) and other vegetation mapping, etc.)
national and international research institutes in the frame
of research cooperation (e.g. Technical University of
Vienna, Technical University Graz, University of Erlan- Experimental torrent catchment of
gen-Nuernberg). Gradenbach creek/Carinthia – an example
• The Austrian Service for Torrent and Avalanche Control, of a multifunctional monitoring system
e.g. for hazard zoning and action planning
• Other stakeholders (e.g. civil engineers and power plant The catchment basin of Gradenbach creek covers an area of
operators, for project development and verification of li- about 32 km². It is located south of the Alpine main ridge,
censing requirements). near Heiligenblut in the so called “Schobergruppe”, being
• Policy-makers, e.g. to establish priorities for funding de- part of the Hohe Tauern mountain range. The highest ele-
cisions, or ranking of hazard prevention projects. vation is the “Petzeck” with 3283 m above sea level. The
confluence to the river Möll is located at about 1045 m
above sea level. The catchment is well known to experts be-
Monitoring systems of the BFW in torrential cause of the actively slumpinging mountain slope (Berch-
watersheds in Austria toldhang) located at the mouth of the torrent and covering
an area of approximately 2 km².
Currently, the Department of Natural Hazards and Alpine Interacting with the torrent at the bottom, the slope
Timberline is operating monitoring systems in the follow- threatens a land settlement at the mouth of the torrent and
ing torrential watersheds: the villages downstream of the Möll Valley. During the se-
• Oselitzenbach/Carinthia vere flooding of 1965/66, approximately 1.3 mio. m³ of bed
• Schmittenbach/Salzburg load – from the inner part of the gully, but especially from
• Gradenbach/Carinthia the gorge at the gully exit – were deposited at the alluvial
• Ponholzbach/Lower Austria fan of the Gradenbach and in the receiving river Möll. As a
• Wattener Lizum/Tyrol result the Möll has been shifted away from its river bed and
flooded extensively the Möll Valley. After the disaster, the
The sizes of the areas range from 4 km2 to 32 km2. Federal Research and Training Centre for Forests, Natural
Hazards and Landscape (BFW) installed a comprehensive
Die Bodenkultur 72 62 (1–4) 2011Multifunctional monitoring in torrent catchments
Figure 2: Berchtoldhang at Gradenbach Figure 3: Debris cone of Gradenbach in the year 1966
Abbildung 2: Berchtoldhang am Gradenbach Abbildung 3: Schwemmkegel am Gradenbach im Jahre 1966
monitoring system in the Gradenbach catchment. At the • To increase the safety of adjacent communities/adjacent
whole catchment level, meteorological and hydrological land owners through monitoring slope movement.
data are measured, including precipitation, snow water
equivalent, runoff (at open gullies, drainage system,
springs), air humidity, airflow and temperature, radiation. Results of long-term measurements at torrent
At several points are measured mountain water-table and catchment Gradenbach creek
temperature, natural ground water discharge and slope
movement. These measurements are completed by rota- The majority of the measurements reveals the importance
tional surveys and observations on-site (e.g. surveys at snow of the data regarding the highly topical issue of potential
measuring courses at altitudes between 1400 m and climate change effects on natural hazards. Slope movement
2100 m, at open land and at forest habitats). is influenced mainly by precipitation. Changes in the
spread and intensity of precipitation, as well as temperature
Data from the experimental catchment Gradenbach are (e.g. influencing the relationship between rain and snow
used deposition) have a considerable impact on triggering or ac-
• To analyse extreme torrent flood events (objective: ad- celerating the mass movement. Vegetation, particularly
vancement of flood protection measures through avail- forests, counteract slope water logging through evapotran-
ability of fundamental data) spiration and retaining of snow in the canopy. But the
• To investigate the water budget of the area concerned (to growth and relative capacity of vegetation (especially
discuss silviculture and water management issues) forests) to mitigate these effects is also influenced by cli-
• To control the efficiency of already implemented protec- mate change. Only long-term monitoring of individual pa-
tion measures and to allocate a basis for decision-making rameters, completed by field surveys can provide an insight
for future actions (slope drainage, control measures, etc.) into the complex cause-effect relationships between influ-
• To improve the understanding of cause-effect relation- ential factors.
ships and processes of large mountain slope sagging (as a
basis for developing an early warning system)
• To improve existing measuring systems and develop new Mountain slope sagging
ones (e.g. logging of groundwater, remote sensing of slope
movement) The long-term measurements of mass movement in the
• To discuss supra-regional key issues (e.g. climate change, gorge area of the Gradenbach (Figure 4) demonstrated that
regionalisation of generated knowledge) even after indications of slope ‘stabilisation’ there is still a
Die Bodenkultur 73 62 (1–4) 2011E. Lang and U. Stary
residual risk of a new disaster associated with mass move-
150
ments on “Berchtoldhang”. Precipitation (mm)
The annual movement at the toe of the slope reached its 100
Water equivalent (mm)
Discharge (1.000m3)
maximum in 2001 (Period 1979–2009: Cable 1: 55 cm;
Cable 2: 62.5 cm). In 2009 large landslides were also 50
recorded.
0
250,0 -50
02.03.
09.03.
16.03.
23.03.
30.03.
06.04.
14.04.
20.04.
27.04.
04.05.
Cable I
Cable II
200,0
-100
Slope Movement [cm]
Calendar Date
150,0
Figure 6: Precipitation, water equivalent and discharge during the
100,0
snow melt of the year 2009 (open land area; altitude:
1600 m a.s.l.)
50,0
Abbildung 6: Niederschlag, Schneewasseräquivalent und Abfluss (Frei-
0,0
land, 1600 m Seehöhe) während der Schneeschmelze im
Jahr 2009
20.01.99
20.01.00
19.01.01
19.01.02
19.01.03
19.01.04
18.01.05
18.01.06
18.01.07
18.01.08
17.01.09
Calendar Date
The amount of snowmelt water varies subject to both
Figure 4: Slope movement in the gorge area of the Gradenbach weather conditions and snow cover, and may exceed the
measured by steel wire extensometer total amount of rainfall in the spring significantly. This
Abbildung 4: Hangbewegungen (gemessen per Drahtextensometer) in
der Schluchtstrecke des Gradenbaches
means that during snowmelt, an extremely high percentage
of the total water input is seeping away.
Triggering factors
Ground water level
Slope movement is mainly influenced by precipitation. The
average annual rainfall in the period 1969–2009 was The amount of water which penetrates into the slope was
930 mm. The maximum precipitation during the year is visible in a few of the drilled holes distributed over the hill-
reached in July. Precipitation in the form of snow is mea- side. The results of the well logging suggest that the slope
sured at snow measuring lines. These lines are both in for- water level relevant for the velocity of the mountain slope
est and open land areas to explore the effect of forests on movement is determined mainly by the quantity of melting
snow interception. It has been confirmed that snow reten- snow. In years with strong slope movements, the hydrograph
tion on the canopy is often considerably high (> 50%). of the ground water level shows strong and rapid climbs and
descents, especially at one water gauge (Figure 7, gauge 3b).
250
OL1600
F 1600
200 0
3a
Water equivalent [mm]
-5 3b
15
-10 II
150
-15
Depth [m]
-20
100
-25
-30
50
-35
-40
1.1.09
29.1.09
26.2.09
26.3.09
23.4.09
21.5.09
18.6.09
16.7.09
13.8.09
10.9.09
8.10.09
5.11.09
3.12.09
31.12.09
0
85/86
86/87
87/88
88/89
89/90
90/91
91/92
92/93
93/94
94/95
95/96
96/97
97/98
98/99
99/00
00/01
01/02
02/03
03/04
04/05
05/06
06/07
07/08
08/09
09/10
Calendar Date
Winter half year
Figure 5: Water equivalent in forest (F) and open land (OL) areas Figure 7: Ground water level at different ground water gauges
(1985–2009, altitude 1600 m a.s.l.) (Berchtoldhang in the year 2009)
Abbildung 5: Schneewasseräquivalent 1985–2009 im Wald (F) und Abbildung 7: Grundwasserstand an verschiedenen Pegelmessstationen
Freiland (OL) auf 1600 m Seehöhe (Berchtoldhang Jahr 2009)
Die Bodenkultur 74 62 (1–4) 2011Multifunctional monitoring in torrent catchments
Climate change tion. However, this picture changes in the seasonal analysis
of the measurements. While rainfall in spring and winter
Temperature has a tendency to decrease, precipitation increases clearly in
summer and autumn. In relative terms, the largest increase
The average annual values show a clear positive trend with
between first and last (fourth) decade was in autumn
high statistical significance (two-tailed test; degrees of free-
(+38.6%).
dom: 39, level of significance: 0.1%). A comparison of the
first and last (fourth) decade in the test series shows a tem-
600
perature rise of +1,5 °C compared to the last one (see Fig- Precipitation height y = -1,2338x + 158,01
ure 8). The highest seasonal change in temperature was 500 2
R = 0,0725
Precipitation (mm)
recorded in spring (also a highly significant positive trend, 400
Figure 9). A comparison of the averages of the first and last
300
decade in the test series shows a temperature increase of
+2.4 degrees! 200
100
10,0
y = 0,0438x + 5,6778
9,0 Average Temperature R2 = 0,3147 0
8,0
1969
1971
1973
1975
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
Temperature (°C)
7,0
Years
6,0
5,0
Figure 10: Winter precipitation (1969–2009, altitude: 1210 m a.s.l.)
4,0
3,0
Abbildung 10: Winter-Niederschlag (1969–2009 auf 1210 m Seehöhe)
2,0
1,0
600 y = 2,4235x + 199,47
0,0 Precipitation height R2 = 0,0771
1969
1971
1973
1975
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
500
Precipitation (mm)
Years
400
Figure 8: Average annual air temperature (1969–2009, altitude: 300
1210 m a.s.l.)
Abbildung 8: Mittlere jährliche Lufttemperatur 1969–2009 auf 1210 m 200
Seehöhe
100
10,0 y = 0,0718x + 4,424 0
1969
1971
1973
1975
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
9,0 Average Temperature R2 = 0,3888
8,0
Years
Temperature (°C)
7,0
6,0
Figure 11: Autumn precipitation (1969–2009, altitude: 1210 m
5,0
a.s.l.)
4,0
Abbildung 11: Niederschlag im Herbst (1969–2009, 1210 m Seehöhe)
3,0
2,0
1,0
0,0 Different trend curves were checked. None of them showed
1969
1971
1973
1975
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
sufficient significance. Despite these strong alterations we
Years
can assume that only the future will reveal whether these are
Figure 9: Average air temperature in spring (1969–2009, altitude: signs of a lasting climate change.
1210 m a.s.l.)
Abbildung 9: Mittlere Lufttemperatur im Frühjahr (1969–2009 auf
1210 m Seehöhe)
Conclusions
Precipitation Monitoring systems in torrent catchments are installed for
The figures of the annual totals of about 40 years show a several purposes. In order to fulfil these multiple tasks, ex-
very slight trend towards smaller or increasing precipita- pensive and time-consuming preparations are necessary.
Die Bodenkultur 75 62 (1–4) 2011E. Lang and U. Stary
The often extreme exposure in the field and the harsh cli- KRONFELLNER-KRAUS, G. (1974): Erosion by Torrents in
mate in Alpine regions require robust, precision measuring General and Mass Creep (in Rock) in Particular. In Ger-
equipment. Despite the sophisticated measuring technique, man with Summary in English. FBVA, Wien. Sonder-
it is evident that the complex monitoring systems can only druck aus “100 Jahre Forstliche Bundesversuchsanstalt”,
be operated reasonably by a sufficient number of well S. 309–342.
trained staff. Experience shows that measuring systems only LANG E., STARY U., GARTNER K. (2005): Die Auswirkun-
supply representative data when trained staff are able to rec- gen außergewöhnlicher Hitze und Trockenheit auf die
ognize and eliminate immediately any sources of error. Dis- Verfügbarkeit des Bodenwassers.
turbances such as sedimentation at runoff gauging stations http://www.waldwissen.net/themen/waldoekologie/
or changes affecting precipitation measuring points etc. can klima/bfw_trockenheit_folgen_2005_DE. 14.06.2005.
be recognized and removed in time, which facilitates check- LANG E., HAGEN K. (1999): Torrential Watershed of
ing the plausibility of doubtful data. Gradenbach – Analysis of Precepitation and Runoff
The costs associated with the installation and long-term 1968–1996. In German, with Abstract and Summary in
operation of monitoring systems should not be underesti- English. FBVA-Berichte, Wien, (108): 109 S.
mated. However the environmental and experimental ben- WEIDNER S., MOSER M., LANG E. (1998): Influence of hy-
efits of such systems are worth the expense, especially with drology on sagging of mountain slopes (‘Talzuschübe’) –
regard to climate change scenarios. New results of time series analysis; Proceedings Eight
International Congress International Association for En-
gineering Geology and the Environment, 21–25 Sep-
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