Modelling geomorphic responses to human impacts and ......Modelling geomorphic responses to human impacts and extreme floods: Application to the Kander river, Switzerland Source: Jorge

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)


• Causing massive flooding in the region of Thun • Kander river was deviated to lake Thun by engineering works


Kander correction


• 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


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


• 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


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


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


Distance (m)

Elev

atio

n (m

)


year 1

year 2

Lake

year 4

• 29 m of erosion within 4 years

Correction

Lake

Elevation Profile


Distance (m)

Elev

atio

n (m

)


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


Lake Thun

Year 1 (1715)

Erosion (m)0-22-55-1010-1515-2020-2525-35

900 m of upstream incision within 12 yrs


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


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


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


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


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


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



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

Modelling geomorphic responses to human impacts and ......Modelling geomorphic responses to human impacts and extreme floods: Application to the Kander river, Switzerland Source: Jorge

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