Results of rainfall experiments

(overview):

INTRODUCTION

Reclaimed lignite mine sites require long-term and safe structuring of

recultivation areas. Lignite burden dumps contain hydrophobic

substances that cover soil particles. Consequently, these soils show

strong water repellency, which influences the processes of infiltration.

Erosion by water leads to explicit soil losses, especially on heavily

endangered water repellent and non-vegetated post mining soil

surfaces. Erosion processes are involved in acidification of surface

waters by input of pyrite containing sediment.

INFILTRATION AND SOIL EROSION MODELLING ON LAUSATIAN POST MINE SITES Franziska Kunth, Jürgen Schmidt TU Bergakademie Freiberg | Soil and water conservation unit | Agricolastraße 22 | 09599 Freiberg | Phone: 03731 / 39- 2679 | franziska.kunth@student.tu-freiberg.de | EGU Vienna 2013

Study site 1

Study site 2

Study site 3

Rainfall intensity [mm/min]

0.63 0.63 0.65

Endinfiltration [mm/min]

0.03 0.13 0.22

Runoff coefficient

0.87 0.66 0.29

Mean sediment concentration [g/l]

27.1 29.4 0.74

Net Erosion [t/ha]

2.8 2.1 0.03

PRELIMINARY RESULTS

Measured infiltration rates on non-vegetated water repellent sites were

extremely low. Therefore, a newly developed water repellency-factor

(calibration factor Fphob) was applied to depict infiltration and erosion

processes on water repellent dump soils. For infiltration modelling with

EROSION 2D/3D calibration factors (e.g. water repellency factor, skin-

factor, etc.) were determined in different steps by calibrating computer

modelled infiltration, respectively volume rate of flow to the measured

data.

Computer model

Model input-parameters:

Relief data (DEM)

Rainfall data

(duration, intensity)

Soil parameters

(e.g. bulk density, grain size

distribution, calibration factors,

etc.)

REFERENCES

Schmidt, J. (1991) A mathematical Model to Simulate Rainfall Erosion. Catena Supplement (19) 101-109 / Schmidt, J. (1992) Modeling long term soil loss and landform change. A.J. Parson and A.D. Abrahams (eds.) Overland flow - Hydraulics and Erosion

Mechanics. UCL Press. London. 409-433 / VON WERNER, M. (1995): GIS-orientierte Methoden der digitalen Reliefanalyse zur Modellierung von Bodenerosion in kleinen Einzugsgebieten. Dissertation Thesis, Freie Universität Berlin, Berlin / SCHINDEWOLF, M. &

SCHMIDT, J. (2012): Parameterization of the EROSION 2D/3D soil erosion model using a small-scale rainfall simulator and upstream runoff simulation, in: Catena 91, p. 47–55

Rainfall experiments on reclaimed lignite mine sites

- Event and raster-based physical soil erosion model (cellular automata

type) (Schmidt, 1991, 1992; v. Werner, 1995)

- Prediction of runoff and particle detachment, transport and deposition

- Infiltration modelling according to GREEN&AMPT (1911) approach

- Momentum flux approach by SCHMIDT (1996) describes particle

detachment and transport

- Validation of newly implemented calibration factor Fphob within this study

Study site 1 Study site 2 Study site 3

Non vegetated

Strongly water repellent

Soil crust

Water repellent

Vegetated

Non water repellent

METHODS

Influence of water repellency had to be considered and implemented

into soil ersion model EROSION 3D. Validation of new E3D-calibration

factor Fphob within this ongoing study. Required input data for soil erosion

modelling (e.g. physical soil parameters, infiltration rates, calibration

factors, etc.) were gained by soil sampling and rainfall experiments.

STUDY AREA

Non-vegetated as well as recultivated reclaimed mine sites in the

Lusatia lignite mining region (southeast of Berlin, Germany)

Rainfall simulator

- Three linked rainfall modules (height: 2 m, plot size: 3x1 m) with

oscillating nozzels

- Collection of runoff and sediment (SCHINDEWOLF, 2012)

OBJECTIVE

- Reliable assessment of soil erosion risks in post mining sites

- Modelling of effectiveness of different recultivation scenarios

- Model-based approach to conceptions of near-surface slope protection

measures as a result of this ongoing study

0,00

0,10

0,20

0,30

0,40

0,50

1 6 11 16 21 26 31 36 41 46 51 56 Rainfall duration [min]

Infiltra

tio

n [m

m/m

in]

Calibration of calculated infiltration rates by

water repellency factor

Infiltration [mm/min]: ● Rainfall experiment ― Simulation (with skin-factor) --- Simulation (with skin-factor and water repellency factor)

Effect of water repellency

CONCLUSION

Infiltration and runoff experiments on non-vegetated reclaimed lignite

mine sites showed that water repellency reduces infiltration to a

minimum. Wetting front infiltrates only few millimetres after 1 hour of rain

with an intensity of 0.6 mm/min (See figure “Study site 1”). Soil erosion

model EROSION 2D/3D is able to depict infiltration processes that are

limited by water repellency by using the new implemented water

repellency factor Fphob.

Results will be used for modelling different (recultivation) scenarios and

assessment of erosion risks of reclaimed lignite mine sites.

Model output-parameters:

Spatial parameters

(Erosion, Deposition, Sediment

concentration, Net erosion, etc.)

Cross section parameters

(Surface runoff volume, Outflow

from the catchment, Sediment

output from the catchment)