sediment cascades and sediment budgets in alpine basins · sediment cascades and sediment budgets...
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Sediment cascades and sediment budgets in Alpine basins
Lothar Schrott
Department of Geography, University of Bonn
SedAlp, Final Conference, Bozen, 9. 06. 2015
Content
Sediment cascade and sediment budget – general considerations and concepts
Temporal and spatial scales
Methods (mapping, geophysics, modelling/GIS)
Case studies: Gradental (Hohe Tauern, Austria)
Turtman-valley (Wallis, Switzerland)
Schnalstal (South Tyrol)
Pasterze (Hohe Tauern, Austria)
Lessons learned: Conclusion & Outlook
2 2
Caine (1974)
Sediment cascade
Davies & Korup (2010): 90
3 3
4
(mo
difie
d fro
m C
ho
rle
y &
Ke
nn
edy 1
97
1)
Characteristics
► flow of energy and mass
► input – storage – output
► coupling – decoupling
► regulators (e.g. slope, vegetation)
► buffering capacity
Sediment cascade spatial scale
Reintal, 2012
4
Sediment budget
5
I ± ΔS = O
Slaymaker (2003), 72 “The sediment budget is defined as the accounting of sources, sinks and redistribution pathways of sediments in a unit region over unit time”.
(Slaymaker 2003, 71)
“A sediment budget is an accounting of the sources and disposition of sediment as it travels from its point of origin to its eventual exit from a drainage basin.“ (Reid & Dunne, 1996)
Storage
ΔS = I - O
5 Hinderer (2012)
Approaches in sediment budget studies, sediment fluxes and storages
6
Hinderer (2012)
Sediment
budgets
6
I – O = ΔS
Sediment storage
Denudation
Process
coupling
Sedimentation
Landform evolution
Input
Output
DRme = SV ρb/ (ρr Ad T) [mm a-1]
SY = SV ρb/(AdT) [t km-2 a-1] Sediment yield ≠ sediment budget
7 7
What do we need to construct a sediment budget?
1. Recognition and quantification of transport processes
2. Recognition and quantification of storage elements
3. Identification of linkages amongst transport processes
From sediment yield to sediment budget
Sediment yield [t/a]
specific sediment yield [t/km²/a]
sediment delivery ratio, [SDR = Y/E]
sediment budget [I=O±∆S]
8 8
Process-oriented
studies
Coupling of
geoarchives with
sediment budget
models
Stratigraphical approaches
(geoarchives)
Time scale
Spatial scale
Re
gio
na
l a
pp
roa
ch
es
“The biggest challenge in use of sediment budgets is in making the link between intensively studied smaller scale systems to the global scale“
(Slaymaker 2009, 19)
(Dikau, Hoffmann, Houben, Schrott 2006)
9 9
Tony Parsons Professor of Sediment Systems, Department of Geography, University of Sheffield
10
Sediment cascades provide answers to
+ sedimentary systems
+ quantitative approach of sediment flux and storage
but…
- lacks a consideration of time
- some quantities remains unmeasured
11
+ flowpath (direction) of sediments + amount and type of temporary sinks, processes and regulators + subsystems + coupled and decoupled areas but… - not considering process response systems
Sediment budgets provide answers to
11
Specific sediment yields in the Alps (data from river loads and reservoirs)
12
Hinderer et al. 2013
negative trend with basin area
poor corr. with relief positive trend with
discharge positive trend with glaciated areas
12
Large scale versus small scale studies >> the missing link Large scale studies: • Jäckli (1957) • Hinderer (2001) • Hinderer (2012, 2013) • Straumann & Korup (2009)
Small-scale sediment budget studies (tributaries): • Rapp (1960) • Schrott et al. (2003) • Götz et al. (2013)(this talk) • Otto et al. (2009)(this talk)
13
Large scale studies focussing on valley & lake fills
Small scale studies focussing on sediment input, storage and output
13
Why are tributaries important?
• The are an important component in the sediment cascade
• The are an important component in the sediment budget (e.g. Illgraben supplies 5-15% of the entire sediment volume of Rhone River to Lake Geneva)
• They are subject to intense changes and probably the most dynamic area in recent times (glacier retreat, increasing proglacial area, permafrost degradation, etc.)
• Our knowledge of temporary storages, sediment input and output is poor
14 14
Methods Geomorphological
Mapping
Terrestrial Laserscanning/TLS
2D Electrical Resistivity Tomography/ERT
Refraction Seismic /RS
Ground-Penetrating Radar/GPR
Core-Drilling, Sampling, Radiocarbon Dating [AMS; a cal. B.P.]
Palynologic Analyses (cooperation R. Krisai, Univ. Salzburg)
GIS-based Bedrock Interpolation (spline) and 3D Modelling of Landform Volumes
(cut/fill)
bedrock
15 su
rface
sub
surface
lab
Case study (local scale)
Gradental (Hohe Tauern, Austrian Alps)
16 16
The Gradenmoos Basin
rockwall retreat can be reconstructed in detail, since (1) sediment output can be neglected,
I = S
- a (semi)closed
denudation- accumulation-system
- subcatchment: 4.5 km², 1920 - 3283 m)
- negligible suspended and no clastic output
- multiple processes (debris flow, rockfall, fluvial, lacustrine)
17 17
Götz et al. (2013)
The Gradenmoos Basin
rockwall retreat can be reconstructed in detail, since (1) sediment output can be neglected, (2) source areas (3D) are clearly defined,
I = S
- a (semi)closed
denudation- accumulation-system
- subcatchment: 4.5 km², 1920 - 3283 m)
- negligible suspended and no clastic output
- multiple processes (debris flow, rockfall, fluvial, lacustrine)
- favourable logistics and accessibility
18 18
Götz et al. (2013)
The Gradenmoos Basin
rockwall retreat can be reconstructed in detail, since (1) sediment output can be neglected, (2) source areas (3D) are clearly defined, (3) sediment storage volumes can be quantified (spatial scale, method. approach),
I = S
- a (semi)closed
Denudation Accumulation System
- subcatchment: 4.5 km², 1920 - 3283 m)
- negligible suspended and no clastic output
- multiple processes (debris flow, rockfall, fluvial, lacustrine)
19 19
Götz et al. (2013)
The Gradenmoos Basin
rockwall retreat can be reconstructed in detail, since (1) sediment output can be neglected, (2) source areas (3D) are clearly defined, (3) sediment storage volumes can be quantified (spatial scale, method. approach), (4) intermediate storage is small (small source-sink distance, steep gradient), and
I = S
- a (semi)closed
denudation- accumulation-system
- subcatchment: 4.5 km², 1920 - 3283 m)
- negligible suspended and no clastic output
- multiple processes (debris flow, rockfall, fluvial, lacustrine)
20 20
Götz et al. (2013)
The Gradenmoos Basin
rockwall retreat can be reconstructed in detail, since (1) sediment output can be neglected, (2) source areas (3D) are clearly defined, (3) sediment storage volumes can be quantified (spatial scale, method. approach), (4) intermediate storage is small (small source-sink distance, steep gradient), and (5) onset of sedimentation can be established.
I = S
- a (semi)closed
denudation- accumulation-system
- subcatchment: 4.5 km², 1920 - 3283 m)
- negligible suspended and no clastic output
- multiple processes (debris flow, rockfall, fluvial, lacustrine)
21 21
Götz et al. (2013)
Results - Long-term (postglacial) sediment storage volumes
6.3 | 40
0.3 | 19 3.9 | 37 3.7 | 32
0.01 | 4
0.3 | 23 0.4 | 6
0.5 | 6
1.9 | 31
1.2 | 33
0.6 | 7
0.2 | 4
0.8 | 20
Total : 19.7 Mio m³ (postglacial volume: 18.3 Mio m³)
Landform volumes (Mio m³) and sediment thickness (m)
lake level: 1915.7 m
bedrock mesh
fluvial (+lacustrine!) deposits
debris flow (+lacustrine?) deposits
rockfall talus
22 Götz et al. (2013)
Short-term sediment flux 2009-2014
Two recent debris flows (TLS, DEMs of Diff.)
23
Götz & Schrott (2015) submitted
Short term input overbalances the postglacial rate by an order of magnitude !
Götz & Schrott (2015) submitted
Case study
Turtmann valley (Valais, Switzerland)
25 25 Otto et al. (2009)
Sediment storage in the Turtmann valley
26
Ott
o e
t al
. (2
00
9),
17
31
26
Sediment cascade and quantification of sediment storage
27
Otto et al. (2009)
27
real surface ~ 140 km²
Over 60% stored in hanging valleys!
Important temporary sinks
Decoupled from the main system
Case study
Schnalstal, South Tirol & Sella, Dolomites
28 28
Source area – permafrost warming
29
Krainer et al. 2012
Sella, Dolomites / Italy Sella, Grödner Joch
Schnalstal, South Tyrol (debris flow activity 1983 – 2006)
30
H 1: Thawing of permafrost (degradation) is causing an increased debris flow
activity
H 2: The presence of permafrost favours the occurrence of debris flows
30
Debris flow activity and permafrost Increasing debris
flow activity between 1983 and 2006 (46%)
Most starting zones of debris flows are situated above 2850 m (with permafrost occurrence)
Increasing active layer depth lead to higher proportions of loose debris
Sattler et al. 2011 31
Alt
itu
de (
m a
.s.l.)
Amount of debris flows (starting zone)
Area (% of total surface area)
Permafrost probable
Permafrost sensitive
Permafrost unprobable31
1983
1997
2006
Amount of debris
flows
Increase
1983-2006
31
Case study
Pasterze (Hohe Tauern, Austrian Alps)
32 32
Sediment cascade and budget, Pasterze
33
(II)
(III)
(I)
(I)
Subsystem Area [km²] Area [%]
Slope (I) 12 30.2
Glacier (II) 20.8 52.3
Glacier forefield (III) 7 17.5
Catchment 39.8 100 33
Geilhausen et al. 2012
Pasterze – dynamic glacier forefield
34
deglaciation
1953-2009:
- increase (1.3 km² /100%) of sediment storage
- main changes in the proglacial & south-western part of the forefield
- since 1998: significant retreat in the south-eastern part
34 Geilhausen et al. 2012
Scenario: Glacier retreat will lead to~600 new lakes in Switzerland! >> This will alter sediment flux and storage in the proglacial area!
35 (Haeberli et al. 2013, Linsbauer et al. 2012)
New lakes as a consequence of glacier retreat (Research roject NFP 61, Switzerland)
Temperature increase of 4°C until 2199, time steps of 15 years
35
Conclusion & Outlook we have achieved…
• sediment cascades help to identify subsystems and the flowpath of sediment fluxes
• sediment budgets can provide a unifying framework
storage component is important for hazard assessment!
we need to…
• focus on linkages between small and large scale (> 500 km²) studies
• focus on sediment-connectivity (coupled-decoupled systems)
• address limitations/uncertainties in sediment budget studies
(only short or unsufficient measured sediment balance equation components)
36 36
Thank you very much for your attention!
"We must above all shift from a culture of reaction to a culture of prevention.
Prevention is not only more human than cure… it is also much cheaper…" (Kofi Annan 1998)
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Cited Literature Davies T.R.H. & O. Korup (2010): Sediment Cascades in active landscapes. In: Burt, T., & R. J. Allison [Eds.]: Sediment cascades: An integrated approach. John Wiley &
Sons, p. 90.
Caine, N. (1974): The geomorphic processes of the alpine environment. In: Ives, J.D., Barry, R.G. (Eds.): Arctic and Alpine Environments. Methuen, London, pp. 721–748.
Dikau, R., Houben, P., Hoffmann, T. & L. Schrott (2006): Der Sedimenthaushalt geomorphologischer Systeme seit Beginn des menschlichen Einflusses. In: Deutscher Arbeitskreis für Geomorphologie (Hrsg.): Die Erdoberfläche Lebens- und Gestaltungsraum des Menschen. Z. Geomorph., N.F., Suppl.-Bd. 148: 32-40
GEILHAUSEN, M., OTTO, J.-C. & L. SCHROTT (2012): Spatial distribution of sediment storage types in two glacier landsystems (Pasterze & Obersulzbachkees, Hohe Tauern, Austria). Journal of Maps, Vol. 8, No. 3, 242–259
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Haeberli, W., Schaub, Y., Huggel, C. and Boeckli, L. (2013, b): Vanishing glaciers, degrading permafrost, new lakes and increasing probability of extreme floods from impact waves – a need for long- term risk reduction concerning high mountain regions. Geophysical Research Abstract, Vol. 15, EGU2013-3273.
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