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Modelling geomorphic responses to human impacts and extreme floods: Application to the Kander river, Switzerland
Source: https://en.wikipedia.org
Jorge Alberto Ramirez, Andreas Paul Zischg, Stefan Schürmann, Markus Zimmermann, Rolf Weingartner, Margreth Keiler
Historical background• In 1714 Kander river flowed into the Aare river:
• Causing massive flooding in the region of Thun
Source: Google maps, Wirth et al. (2011)
Historical background• In 1714 Kander river flowed into the Aare river:
• Causing massive flooding in the region of Thun • Kander river was deviated to lake Thun by engineering works
Source: Google maps, Wirth et al. (2011)
Kander correction
Historical background• In 1714 Kander river flowed into the Aare river:
• Causing massive flooding in the region of Thun • Kander river was deviated to lake Thun by engineering works• Four years after Kander correction eroded ~30 m
Source: Google maps, Wirth et al. (2011)
30 m
1714
1718
River bed Kander correction
Aims• Can we model geomorphic effects of human intervention in fluvial systems?:
• River restoration• River engineering
• Test landscape evolution model (LEM) on Kander correction• Determine sensitivity of LEM to extreme flood events (climate change)
Source: https://mostlyaboutmayflies.wordpress.com, http://www.theadvocateproject.eu, www.gettyimages.ch
Restoration Engineering Extreme floods
CAESAR-Lisflood
• Landscape evolution model simulating erosion and deposition within river reaches (CAESAR)
• A hydrodynamic 2D flow model (based Lisflood FP model) that conserves mass and partial momentum
Source: https://sourceforge.net/projects/caesar-lisflood/
Model test using Kander Correction• Erosion: incision of channel
30 m
5 m
1714(year 0)
1718(year 4)
2016(present day)
River bed
• In ~4 years the Kander correction eroded ~30 m• Afterwards the river eroded less and ‘stabilized’• Channel erosion propagated upstream
Source: http://media.web.britannica.com
• Deposition: development of delta in lake Thun
Model test using Kander Correction
Lake Thun
Kander Correction
• Present day topography was used to represent the river banks
• Historical data was used to develop river channel and Kander correction
Topography
elevationhigh
low
Lake Thun
Kander Correction
Discharge
12 year simulationHourly Discharge 1986-1998
time (hr)
Disc
harg
e (m
3s-1
)
Simme
Kander
Sediment inputs
• 20,000 m3 yr-1 were added to both the Simme and Kander
• High flows were ≥ 30 m3 s-1 and we assumed upstream sediment transport occurred above this threshold
• Amounts of sediment were proportionally added over time based on the discharge that was above the threshold
time (hr)
Sedi
men
t (m
3 )
Source: Geschiebehaushalt Kander, 2014
Simme
Kander
Grainsize distribution
Source: Geschiebehaushalt Kander, 2014
• 6 grain size classes (silt to boulder) were estimated from Kander and Simme• Each gird cell in the model initially contains the same grainsize percentages
Initial Conditions• Kander without correction
• 1986 discharge and sediment inputs for Kander andSimme were repeated
• Grainsize mixing occurred, channel erosion anddeposition
• Model ran for a total of 8 years until the reach wasin equilibrium: 3% difference between sedimentcoming in and out of the reach Erosion (m)
Deposition (m)1.5-2.61-1.50.5-10.05-0.5
Lake Thun
1-1.70.5-10.05-0.5
Kander correction: 1714
Source: Geschiebehaushalt Kander, 2004
Elev
atio
n (m
)
Lake Thun
• The correction Length: 340 m, Width: 32 m, Slope: 0.8%.• A ramp connected the correction to the lake• Lake Thun was added to the DEM at the location of the shoreline.
The lake was set as a non-erodible plane.
Correction
Distance (m)
Lake
Correction
Ramp
Lake
A
BA
B
Kander correction: 1714
Source: Geschiebehaushalt Kander, 2004
Elev
atio
n (m
)
Lake Thun
Correction
Distance (m)
Lake
Correction
Ramp
Lake
Lake Thun
elevation (m)668
556
Wall A
BA
B
Kander correction model
water depthhigh
low
Lake Thun
Kander Correction
• Simulated 12 years of movement of water and sediment• Every year topography was recorded (1714-1726)
water & sediment inputs
Model test: Kander erosion
Distance (m)
Elev
atio
n (m
)
Kander correctionyear 0
Lake
Correction
Lake
Flow
Elevation Profile
Model test: Kander erosion
Distance (m)
Elev
atio
n (m
)
Kander correctionyear 0
year 1
year 2
Lake
year 4
• 29 m of erosion within 4 years
Correction
Lake
Elevation Profile
Model test: Kander erosion
Distance (m)
Elev
atio
n (m
)
Kander correctionyear 0
year 1
year 2
present day
Lake
year 4year 12
Correction
Lake
Elevation Profile• 29 m of erosion within 4 years• 2 m difference with todays river
Model test: Kander erosion
Lake Thun
Year 1 (1715)
Erosion (m)0-22-55-1010-1515-2020-2525-35
900 m of upstream incision within 12 yrs
Model test: Kander erosion
Lake Thun
Year 1 (1715) Year 12 (1726)
Erosion (m)0-22-55-1010-1515-2020-2525-35
900 m of upstream incision within 12 yrs
Model test: Delta formation
Year 0 (1714)
outlet
Lake Thun
Elevation (m)558-559559-560560-561561-562562-563
563-564564-565565-566566-567567-614
Delta 1860
Lake Thun
Model test: Delta formation
Year 0 (1714) Year 6 (1720)
outlet
Lake Thun
Elevation (m)558-559559-560560-561561-562562-563
563-564564-565565-566566-567567-614
Delta 1860
Lake Thun
Model test: Delta formation
Year 0 (1714) Year 6 (1720) Year 12 (1726)
outlet
Lake Thun
Elevation (m)558-559559-560560-561561-562562-563
563-564564-565565-566566-567567-614
Delta 1860
Lake Thun
…more time needed
Response to extreme floodsDetermine sensitivity of LEM applied to steep rivers and extreme flood events
Kander riverDi
scha
rge
(m3
s-1)
DateSource: http://www.bafu.admin.ch
Extreme hydrographs
Peak discharge (m3 s-1)
50 100 200 300 400 500
Floo
ddu
ratio
n (h
r) 6
12
24
48
72 X
144
Time (hr)
Disc
harg
e (m
3s-1
)
Duration (hr)612244872144
2005 flood
36 scenariosSediment added proportional to discharge
Hydrographs 600
500
400
300
200
100
• Determine how much incision occurs with flood events of different magnitude and duration
Response to extreme floods Lake Thun
water depthhigh
low
water & sedinputs
? m
1714(year 0) River bed
incision
Geomorphic change
Peak discharge (m3 s-1)
50 100 200 300 400 500
Floo
ddu
ratio
n (h
r) 6
12
24
48
72
144
Absolute change in elevation (m)0-0.50.5-1.01.0-1.51.5-2.02.0-2.5
Distance (m)de
posit
ion
eros
ion
Chan
ge in
ele
vatio
n (m
)
Distance (m)
Elev
atio
n (m
)
A
A
B
B
Correction
discharge 500, duration 144
discharge 50, duration 6
Model produces plausible erosion and deposition under extreme flood conditionsFlood duration has greater effect on change in elevation than peak dischargeSingle extreme flood events can produce up to 6 m of erosion, 4m of deposition
X
X
Geomorphic change
Peak discharge (m3 s-1)
50 100 200 300 400 500
Floo
ddu
ratio
n (h
r) 6
12
24
48 X
72
144 X
Absolute change in elevation (m)0-0.50.5-1.01.0-1.51.5-2.02.0-2.5
Distance (m)de
posit
ion
eros
ion
Chan
ge in
ele
vatio
n (m
)
Distance (m)
Elev
atio
n (m
)
A
A
B
B
Correction
discharge 50, duration 144
discharge 500, duration 48
Flood that is 3 times longer, and 10 times lower in peak discharge produces similar change in elevationLong duration floods (6 day) with relatively low discharge are geomorphically important
ConclusionsCAESAR lisflood can replicate geomorphic effects of human intervention in fluvial systems, this includes:
River bed incisionUpstream incisionDelta formation
Model produces plausible erosion and deposition under extreme flood conditions
Long duration floods with relatively low discharge are geomorphically important
Modelling geomorphic responses to human impacts and extreme floods: Application to the Kander river, SwitzerlandHistorical backgroundHistorical backgroundHistorical backgroundAimsCAESAR-LisfloodModel test using Kander CorrectionModel test using Kander CorrectionTopographyDischargeSediment inputsGrainsize distributionInitial ConditionsKander correction: 1714Kander correction: 1714Kander correction modelModel test: Kander erosionModel test: Kander erosionModel test: Kander erosionModel test: Kander erosionModel test: Kander erosionModel test: Delta formationModel test: Delta formationModel test: Delta formationResponse to extreme floodsExtreme hydrographsResponse to extreme floodsGeomorphic changeGeomorphic changeConclusions