3 Erosion and Sediment Transport - 3.3 Measurement and calculation of soil loss

Question 1

Measurement and Calculation of Soil Loss at glance

Answer 1

 We have insufficient field data and the required monitoring networks do not currently exist.

 The assessment of erosion at large scale is only feasible by using mathematical models.

 Models need field data for calibration/validation!

 Erosion is a process, but the eroded material is usually called “soil loss”.

Question 2

Active and Passive Variables Influencing Erosion

Answer 2

Climate (natural/active)
– precipitation, snow, temperature, wind, climate change

Soil (natural/passive)
– particle size, structure, aggregate stability, susceptibility to crusting, hydraulic conductivity, field capacity etc.

Topography (natural/passive)
– slope steepness, slope length, slope form, exposition

Vegetation (natural/passive)
– phenological phase, density, species, root depth

Land management (anthropogenic)
– land cover, tillage, crop rotation, terrace construction, irrigation, erosion protection measures

Question 3

Experimental Parcel for Erosion Measurement

Answer 3

See pict on slide 29

Question 4

Models for the Calculation of Soil Loss - Deterministic Models

Answer 4

 Single event
 Physical process model
 Loss and deposition
 Transferrable to other investigation areas

Question 5

Models for the Calculation of Soil Loss - Empirical Models

Answer 5

 Long-time mean
 Statistical analysis from plot experiments
 Only soil loss
 Not transferrable without recalibration

Question 6

Erosion Models

Answer 6

 Most models attempt to combine:
– soil erodibility & landscape
– land use
– driving forces (active variables)
– erosion protection measures

 Models:
– Universal Soil Loss Equation (USLE)
– Revised Universal Soil Loss Equation (RUSLE V1, V2)
– Water Erosion Prediction Project (WEPP)
– Erosion 2D/3D (deterministic model)
– KINEROS2
– SWAT (example for hydrological models, which often incorporate empirical soil loss models like USLE/RUSLE)

Question 7

Universal Soil Loss Equation USLE

Answer 7

A = R.K.Ls.C.P [ton/ha.yr]

A: Average annual erosion rate (sheet and rill erosion only)

R: Rainfall factor (runoff erosivity index) [MJ mm / ha h]

K: Soil erodibility factor [(t h) / (MJ mm)] -> how easily can soil aggregate be broken by rain drops

L, S: Topographic factors [-]: slope length and slope steepness
C: Crop management factor [-] -> ratio of soil loss compared to fallow (bare, exposed) soil

P: Erosion control practice factor [-]

Question 8

USLE – RUSLE

Answer 8

 USLE computes unit plot erosion by R*K
 Unit plot attributes: 9% slope, 72.6 feet long, cultivated fallow.

 The factors LSCP are normalized (value 1 for unit plot conditions) .

 LSCP adjust unit plot erosion to account for differences to field conditions of the actual site.

 USLE computes long-term mean annual values of soil loss. This does not adequately represent erosion processes, neither is this a suitable temporal resolution for todays hydrological models.

 The revised RUSLE2 works with daily resolution and combines deterministic equations with the unit plot concept of the USLE.

Question 9

Estimation of Sediment Yield

Answer 9

 The Universal Soil Loss Equation does not compute sediment intake into rivers. A large fraction of the lost material is deposited in the valleys.

 Reservoir Survey Method: determine quantity of deposited sediment per year.

Question 10

Consequences of Soil Erosion and Sediment Transport

Answer 10

 Land surface
– Removal/redistribution of soil, formation of unwanted structures
– Loss of arable land and valuable topsoil, decline in productivity
– Reduction of soil functional capacity
– Damage of infrastructure (pumps, buildings, traffic)

 Aquatic systems
– Diffuse pollution by contaminants and nutrients
– Changing river beds, silting of lakes, river courses, reservoirs, docks, …
– Destruction of habitats
– Eutrophication

Note: Soil erosion is a natural process occurring over geological timescales. Where the natural rate has been significantly increased by human activity, accelerated soil erosion becomes a process of degradation and thus a threat to soil.

Question 11

Soil Erosion Risk Assessment

Answer 11

See diagram on slide 36

Question 12

Pan-European Soil Erosion Risk Assessment (PESERA)

PD Dr.

Answer 12

Quick glance at the map on slide 37