1. Relations homme/environnement et transports
solides : une approche spatialisée
7th- 8th June 2011, Algeria
Experimental analysis of sediment transported from a bare soil with rill
Hafzullah Aksoy, N. Erdem Unal, Sevket Cokgor, Abdullah Gedikli, Jaeyoung Yoon, Kaan Koca, S. Boran Inci, Ebru Eris & Gijung Pak

2. Various combinations of slope steepnesses and rainfall regimes
OBJECTIVES
Experimental analysis of rainfall-induced erosion with rill.
Developing soil loss relationships between slope steepness and flow rate.
In This Study
Experimental
studies
2-D sediment
transport
Various combinations of slope steepnesses and rainfall regimes

3. 1 2 3 4 5 6 OVERVIEW OF EROSION Definition of erosion
Why erosion is concerned?
Types of erosion on hillslope
Erosion models
Rainfall simulator
Experiments

4. 1 Definition of Erosion
Erosion is detachment and transport of soil particles by the agents such as rainfall, runoff and wind. Water erosion by rainfall and consequent runoff is the most destructive form of erosion!
Detachment: Removal of soil particles by raindrop impact.
Sediment load: Rate of sediment transported downslope by runoff
Soil
Sediment load
Sediment Transport
Detachment
*Detachment by rainfall / runoff
*Transportation by rainfall / runoff

5. 2 Why erosion is concerned?
Estimating the amount of erosion is important because runoff along with sediments and contaminants;
Degrade water quality
Carry soil to the lakes and sea
Can accumulate in rivers and reservoirs.
There is a need for modelling and quantitative estimation of erosion!

6. 3 Types of erosion on hillslope
Splash erosion
Interrill-rill erosion (sheet-rill)
Gully erosion

7. Rill and inter-rill erosion in the field Image by M. Mamo
Gully erosion
image by NRCS.
Rill and inter-rill erosion in the field Image by M. Mamo
ITU, image by H.Aksoy (2004)
Bonn, image by H.Aksoy (2009)

8. 4 Erosion models Empirical models Conceptual models
Physically based models

9. CONSTANT RAINFALL INTENSITY! (211.8 mm/h)
BUT TOO HIGH!
Present study is required!

10. Rainfall Simulators Norton rainfall simulator, 2002 Rainulator
Indiana, US
Rainfall simulator (Swanson)
Rainfall Simulators

11. Erosion flume used in the experiments

12. ITU Rainfall Simulator

13. Rainfall Intensity Nozzle type Flow rate Pressure on nozzles
VeeJet
(l/min)
(bar)
(mm/h)
8070
32.05
0.4
105
8060
26.47
0.3 85
8050
22.70 65
8030
19.50 45

14. Christiansen Uniformity Coefficient (CuC) (Christiansen, 1942).
CuC = Christiansen Uniformity Coefficient (%)
xi = The amount of water measured in each container (cm3)
= Average amount of water (cm3)
N = The number of water accumulation containers
CuC (%)
Classification
≥90
Very good
80-89
good
70-79
low
≤69
very low
Uniform rainfall distribution over the entire plot is important for erosion studies!

15. Rainfall uniformity test

16. Values calculated for ITU Rainfall Simulator
Nozzle type
Spacing between the nozzles
Rainfall
intensity
Christiansen Uniformity
Coefficient
VeeJet
(cm)
(mm/h)
(%)
8070
125
105
87.3
8060 85
83.0
8050
145 65
82.2
8030 45
82.0
CuC (%)
Classification
≥90
Very good
80-89
good
70-79
low
≤69
very low

17. Erosion experiments 1 2 3
Four rainfall intensities (45, 65, 85, 105 mm/h) Certain slopes (Longitudinal (Sy) & lateral slope (Sx)) Uniform bare sand with a median grain size (D50=0.45mm)

18. Rill that is created prior to each experiment.
Interrill area
Rill that is created prior to each experiment.

19. Samples of the flow and sediments were collected manually at downslope end of the flume.
Interval: 15 s – 1 min

20. Sediment weight measurements
Flow samples V W W
Water and sediment weight
Sediment weight

21. Calibration for sediment measurement

22. Overview of results
1 The effect of rainfall intensity on erosion and volumetric sediment concentration
2 The effect of slope on erosion and volumetric sediment concentration
3 Development of sediment load equations

23. 45 mm/h mm/h 85 mm/h 105 mm/h

24. 45 mm/h mm/h 85 mm/h 105 mm/h

25. Logarithmic scale

27. Empirical equations
Julien 2010, p.23

28. Conclusions The effect of rainfall intensity on the sediment weight
The effect of slope on the sediment weight
Longitudinal slope exponential increase
Lateral slope linear increase and less dominant
Resulting slope exponential increase
The effect of rainfall intensity on the sediment weight
Negligible in mild slopes.
Non-negligible with increasing slopes
(i.e., a linear relation between rainfall intensity and sediment weight)

29. Conclusions The effect of rainfall intensity on the concentration
The effect of slope on the volumetric sediment concentration
Longitudinal slope linear increase, more effective
Lateral slopes linear increase
Resulting slope linear increase, similar to longitudinal slope
The effect of rainfall intensity on the concentration
not an effective factor

30. Future
Validating physically-based rainfall-runoff-sediment transport mathematical models.
Soil with vegetation or stones embedded can be used instead of using a bare sand.
Repeat the experiments for different conditions such as different rainfall intensities and finer sand. Also natural soil can be examined.

31. Thank you Working group of the project
KimChee Eating group of the project
Prof. Dr. Hafzullah AKSOY
Technical University of Istanbul
Hydraulics Laboratory
Maslak-Istanbul/TURKEY
Tel :