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

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

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

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

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!

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

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)

4 Erosion models Empirical models Conceptual models Physically based models

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

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

Erosion flume used in the experiments

ITU Rainfall Simulator

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

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!

Rainfall uniformity test

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

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)

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

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

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

Calibration for sediment measurement

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

45 mm/h 65 mm/h 85 mm/h 105 mm/h

45 mm/h 65 mm/h 85 mm/h 105 mm/h

Logarithmic scale

Empirical equations Julien 2010, p.23

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)

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

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.

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 E-mail: haksoy@itu.edu.tr Tel : +90 212 285 6577