Transfer of sediments in catchment ecosystems on various...

KIT – University of the State of Baden-Wuerttemberg and

National Research Center of the Helmholtz Association

INSTITUTE FOR WATER AND RIVER BASIN MANAGEMENT

CHAIR OF HYDROLOGY

www.kit.edu

Transfer of sediments in catchment ecosystems on various scales

Ulrike Scherer

Institute for Water and River Basin Management

Chair of Hydrology

Transfer of sediments in catchments

rainfall

runoff

Erosion Deposition

detachment

and transport

deposition

sediment input

Attert, Luxembourg (Photo: CRP-GL)


Chair of Hydrology

How can we measure soil erosion?

Soil erosion rates in the field

Mapping of erosion forms in the field

Long term soil erosion plots

Field experiments under controlled

rainfall conditions

Rainfall simulator (Weiherbach catchment, Germany) Long term soil erosion plot (Niederoesterreich, Austria)

Erosion rill in corn field (Wissembourg, France)


Chair of Hydrology

How can we measure sediment delivery?

Monitoring of sediment concentrations

at the catchment outlet

Automatic water sampling

Weierbach, Luxembourg

(A. Krein, CRP-GL)

Turbidity probe in the HOAL catchment,

Petzenkirchen, Austria


Chair of Hydrology

Problematik

2 0 2 4 Kilometers

N

hillslope scale small catchment basin scale

process based approaches empirical/conceptual approaches

Modeling of sediment transfer


Chair of Hydrology

Represent the entire interaction of relevant processes

Rainfall / runoff

Detachment

Transport of sediment particles and aggregates

Deposition

Based on the sediment continuity equation

Process based modeling approaches

Scherer (2008)

)t,x(x

qs

x

(x,t)

qs,in qs,out

qs solid mass flow rate, kg/(m·s)

net in- / output of particles into /

out of flow, kg/(m²·s)


Chair of Hydrology

CATFLOW-SED: Soil detachment

r

r cos

momentum of rainfall

)BBG1(cosvrm rwr

shear stress

0w Ihg

Scherer et al. (2012)

)fmp(pe critr21pot

detachment rate

attacking forces

erosion

resistance of

the soil

epot detachment rate, kg/(m²·s)

fcrit erosion resistance, N/m²

p1,2 empirical parameters


Chair of Hydrology

sediment concentration [g/l]

erosion rate [g/(m²min)] runoff [l/s]

time [min]

0

20

40

60

80

100

10 20 30 40 50 60 70 80

0.01

0.1

1

sediment concentration

erosion rate

surface runoff

Rainfall simulation experiments

in the field to determine erosion

resistance

CATFLOW-SED: Detachment

Scherer et al. (2012)


Chair of Hydrology

Transport capacity of overland flow controls sediment transport rate

and deposition

Deposition depends on the

sinking velocity

CATFLOW-SED: Transport and Deposition

Scherer (2008)

Engelund und Hansen (1967)

2

5

5

2

transport intensity, [-]

intensity of flow, [-]

resistance coefficient, [-]

xv

vy s v flow velocity, m/s

vs sinking velocity, m/s


Chair of Hydrology

Weiherbach catchment

Located in a loess region in

Southwest Germany

3.5 km²

Intensively cultivated

0

20

40

60

80

100

18:30 19:30 20:30 21:30 22:30

inte

ns

ity

[m

m/h

]

0

2

4

6

8

10

18:30 19:30 20:30 21:30 22:30

time

run

off

[m

³/s] observed

modelled

27.06.1994

Validation at the catchment scale

Gauge station in the Weiherbach catchment

Sediment yield observed modeled bias

27.06.1994 1 815 t 1 949 t + 7.4 %

12.08.1994 35 t 37 t + 5.7 %

13.08.1995 607 t 630 t + 3.8 %

Scherer (2008)


Chair of Hydrology

Erosion and deposition rates

in the Weiherbach catchment

0 - 0.01

0.01 - 1

1 - 2

2 - 5

5 - 10

10 - 20

20 - 50

> 50

Erosion rate [kg/m²]

Land use

stream

paved areas

grassland

forest

sunflower

sugar beet

corn

crop

0

0.01 - 0.5

0.5 - 1

1 - 2

2 - 3,5

3,5 - 6

6 - 10

> 10

Deposition [kg/m²]

Elevation [m]

162 - 173

173 - 184

184 - 195

195 - 205

205 - 216

216 - 227

227 - 238

238 - 248

0 - 0.01

0.01 - 1

1 - 2

2 - 5

5 - 10

10 - 20

20 - 50

> 50

Erosion rate [kg/m²]

Land use

stream

paved areas

grassland

forest

sunflower

sugar beet

corn

crop

0

0.01 - 0.5

0.5 - 1

1 - 2

2 - 3,5

3,5 - 6

6 - 10

> 10

Deposition [kg/m²]

Elevation [m]

162 - 173

173 - 184

184 - 195

195 - 205

205 - 216

216 - 227

227 - 238

238 - 248

Validation at the catchment scale

Scherer (2008)

Gauge station


Chair of Hydrology

Most widely used empirical model:

Universal Soil Loss Equation - USLE (Wischmeier & Smith 1978)

National adaptations:

i.e. Allgemeine Bodenabtragsgleichung – ABAG (Schwertmann et al. 1987)

Modifications:

i.e. RUSLE, MUSLE

Europe:

Pan European Soil Erosion Risk

Assessment - PESERA

(Kirkby et al. 1994)

Empirical/conceptual modeling approaches


Chair of Hydrology

USLE – Universal Soil Loss Equation

BA: average long-term soil

erosion rate, t/(ha·a)

R: rainfall erosivity index,

(kJ·m)/(m²·h)

LS: topographical factor, [-]

(slope length and gradient)

C: plant cover and tillage

factor, [-]

K: soil erodibility factor,

(t·m)/(ha·a·kJ·h)

P: specific erosion control

practices, [-]

BA = R · K · L · S · C · P in t/(ha·a) long term erosion rate

Butz (2005)


Chair of Hydrology

Erosion rates quantified by USLE are combined with SDR approaches

to quantify sediment yields

USLE – Application for Germany

Fuchs et al. (2012), Wurbs and Steininger (2011)

SDR sediment delivery ratio, %

BAi long term soil erosion rate, t/(ha·a)

Ai size of the area i, ha

SL long term sediment load, t

1 100

n

i i

i

BA A

SDRSL

Soil loss Sediment delivery ratio


Chair of Hydrology Fuchs et al. (2012)

Sediment delivery to surface waters

Derivation of a lumped SDR approach for German river basins




Lumped SDR approach for German river basins: validation

0.86 0.16

5002.3 ALSDR S A SDR sediment delivery ratio, %

S slope, %

AAL500 share of arable land located

close to surface water bodies

(flow distance < 500 m), %


Chair of Hydrology

Retention in river systems

Forggensee reservoir

Forggensee

Karwendel region

Analysis of local retention rates (Danube basin)


Chair of Hydrology

Retention in river basins

Comparison of observed and modeled sediment loads (Danube basin)

Without consideration of retention rates

1km

Mouth of Inn (Google maps)

With consideration of retention rates


Chair of Hydrology

Summary and conclusions

Process based modeling approaches require a large

amount of spatially highly resolved data, which is only

available for a small number of catchments.

This is why empirical/conceptual modeling approaches are

used at larger scales. But their extrapolation capability to

different landscapes and future scenarios is limited.

For the planning and implementation of mitigation

measures, the lower mesoscale (< 200 km²) is important!

Suitable modeling approaches are missing…

We need modeling approaches that balance necessary

complexity with greatest possible simplicity.


Chair of Hydrology

Development of a hydrological modeling approach for meso-scale

catchments: Focus on organizing principles in a specific landscape

Outlook

Deposition

Detachment

• kinematic wave approach

sheet flow/rill structures

Channel

• sinking velocity of

particles/aggregates

• transport

capacity

• rainfall kinetic energy

• attacking forces of

overland flow

• resistance of soils

against detachment

Super-ordinate surface

flow network

verification

m

odel fo

rmula

tion


Chair of Hydrology

Thank you!




Lumped SDR approach for German river basins

0.86 0.16

5002.3 ALSDR S A

SDR sediment delivery ratio, %

S slope, %

AAL500 share of arable land located

close to surface water bodies

(flow distance < 500 m), %


Chair of Hydrology

Limits to sediment export:

driving gradient is geopotential Δφ,

resulting in water flow (Δv)

drag force of water flow drives

sediment export Js,out

depletes Δφ

depletes Δv

relevant budget:

mass balance of sediments ms

balancing detachment, deposition,

and sediment export

Motivation: Thermodynamic Limits

runoff

generation

runoff

Js,out

sediment

export

Δφ

Kleidon, Zehe, Ehret & Scherer (HESS-D)


Chair of Hydrology Kleidon, Zehe, Ehret & Scherer (HESS-D)

Motivation: Thermodynamic Limits

Trade-off: more work by drag to detach sediments yields lower flow

velocity v

power to detach

sediments

velocity

sediment export

strength of drag force

Transfer of sediments in catchment ecosystems on various...

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