MODELLING SURFACE RUNOFF TO MITIGATE HARMFUL IMPACT OF SOIL EROSION Pavel KOVAR, Darina VASSOVA Faculty of Environmental Sciences Czech University of Life Sciences Prague HydroPredict Conference 2010 Prague, September 20 to 23, 2010
INTRODUCTION Problems Caused by Water Erosion – Loss of soil is an important issue worldwide, due to: • Increased frequency of hydrological extremes • Inexistent or insufficient erosion control measures • Improper land use • Improper agricultural/forest management – First steps for solving problems related to water erosion : • Empirical models: – USLE/MUSLE (Modified/Universal Soil Loss Equation, Delivery Ratio) • Simulation models: – CN-based models ( EPIC , CREAMS , AGNPS , ...) – Surface Runoff and Erosion Processes ( SMODERP , EROSION 2D , ...) • Advanced simulation models: – EUROSEM (European Erosion Model, http://www.cranfield.ac.uk/eurosem/Eurosem.htm) – WEPP (Water Erosion Prediction Project, http://milford.nserl.purdue.edu/weppdocs/)
INTRODUCTION CAN WATER EROSION BE PREDICTED USING A MODIFIED HYDROLOGIC MODEL? In this presentation we will try to determine the common principles of surface runoff and soil erosion analyses: – Physically-based models – Natural rainfall-runoff events data – Simulated rainfall-runoff data (using rain simulator) – Design rainfall data – Observed and computed rain erosivity data assessment – Soil loss analysis based on soil erodibility (rill and interrill erosion assessment)
EXPERIMENTAL RUNOFF PLOTS Area: TŘEBSÍN
EXPERIMENTAL SITES DESCRIPTION Soil characteristics: – Brown soil “Eutric Cambisol” on weathered eluvials and deluvials – Field capacity (average): 33.5% – Porosity (average): 48.3% Plot parameters and crops Plot No. Length Wide Slope Area Crop Crop Crop Crop (m 2 ) (m) (m) (%) 2007 2008 2009 2010 9 37.7 6.6 11.2 248.8 sunflower maize maize maize 6 37.8 6.7 12.8 253.3 sunflower maize maize maize 4 37.4 6.8 14.3 254.3 sunflower maize maize maize Average 37.6 6.7 12.8 250.0 2 So Soil hydraulic parameters SF 2 K s Plot No. Satur. hydraulic conductivity Sorptivity at FC Storage suction factor K s (mm · min -1 ) So (mm · min -0.5 ) SF (mm) 9 0.214 1.06 2.63 6 0.177 1.20 4.07 4 4.360 4.64 2.47
RAIN SIMULATOR
RAIN SIMULATOR
SHEET FLOW
DISCHARGE/LOAD MEASUREMENT DEVICE
GRANULARITY CURVE FOR EXPERIMENTAL RUNOFF AREAS AT TŘEBSÍN 100 1 2 3 80 4 5 Plot Grain Grain Grain Grain Grain 6 No. <0.002 <0.01 0.01- 0.05- 0.25- percent (%) 7 0.05 0.25 2.0 60 8 1 11.4 27.8 61.5 80.7 100.0 9 2 10.7 27.7 60.8 83.0 100.0 3 9.1 27.6 66.7 81.2 100.0 40 4 9.9 30.8 71.2 85.1 100.0 5 11.9 33.2 76.4 87.8 100.0 6 13.1 33.7 75.3 88.5 100.0 20 7 16.6 36.1 80.6 91.3 100.0 8 17.2 35.2 79.3 92.1 100.0 9 17.6 35.2 79.5 92.1 100.0 0 0.001 0.01 0.1 1 10 soil grain size
MODEL KINFIL – PRINCIPLES EINFIL Part H – Infiltration computation: s i f i K 1 s i t • Green Ampt (and Morel- p 2 Seytoux) So S H – Storage suction factor: f s i f K 2 s – Ponding time: S f t p i i 1 K s KINFIL Part – Computation of flow on slopes using kinematic y y m 1 my i ( t ) wave computation: e t x • (Lax-Wendroff numerical scheme)
THE KINFIL PARAMETERS ROOT depth of root zone (m) saturated hydraulic conductivity (m·s -1 ) KS sorptivity at field capacity (m·s -0.5 ) SO porosity ( – ) POR field capacity ( – ) FC SMC (or API) soil moisture content (mm) number of planes in cascade ( – ) JJ slope of plane ( – ) SLO LEN length of plane (m) t 1 WID width of plane (m) m 1 x my NM Manning roughness DS mean soil particle diameter (mm) D(i) soil particle category diameters (mm) – cascade of planes soil particle density (kg · m -3 ) – cascade of segments RO
IMPACT OF PHYSIOGRAPHIC CHARACTERISTICS ON SURFACE RUNOFF Length of slope Angle of slope Slope angle vers. time to peak Slope length vers. specific runoff (CN=88, slope α = 0,05, Manning n=0,100) (CN=88, length L=100m, Manning n=0,100) 1.5 1.5 Specific discharge Time to peak q (l s -1 m -1 ) 1 1 (hrs) 0.5 0.5 0 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0 50 100 150 200 250 300 350 400 450 500 Slope angle α (-) Slope length L (m) Hydraulic roughness Roughness vers. time to peak (CN = 88, length L=100m, slope α=0,05 ) 0.5 Manning n 0.4 0.3 0.2 0.1 0 0.4 0.6 0.8 1 1.2 Time to peak (hrs)
NATURAL RAINFALL-RUNOFF OBSERVATION DT = 30 min, area 250 m 2 (36.0 × 7.0 m), 10 August 2007 Rainfall-runoff events Depths, velocity and shear velocity Soil loss: Soil loss: 281 kg · ha -1 5330 kg · ha -1
SIMULATED RAINFALL-RUNOFF EVENTS TŘEBSÍN 9, DT = 1 min, area 30 m 2 (3.0 × 10.0 m) 26 Aug. 2009 (DRY, SMC o =23.4%, Maize) 26 Aug. 2009 (WET, SMC o =39.3%, Maize) Depths and Velocities 26 Aug. 2009 (DRY) 26 Aug. 2009 (WET)
DESIGN RAINFALLS Rain gauge Benešov: P t,N =P 1d,N · a · t 1-c i t,N =P 1d,N · a · t -c Design rainfall depths P t,N (mm): Rain depths P t,N for duration t d (10 to 300 min), N-years reccurance Benešov 90 80 70 60 P (mm) 50 40 30 20 10 0 0 50 100 150 200 250 300 t (min) 2 5 10 20 50 100 years
DESIGN RAIN INTENSITIES Design rain intensities i t,N (mm · min -1 ): Rain intensity it,N for duration td (10 to 300 min), N-years reccurence Benešov 4.0 3.5 3.0 i (mm · min -1 ) 2.5 2.0 1.5 1.0 0.5 0.0 0 50 100 150 200 250 300 t (min) 2 5 10 20 50 100 years
SURFACE RUNOFF FROM DESIGN RAINFALL Locality: TŘEBSÍN 9, area 30 m 2 , Maize
DESIGN RUNOFF: DEPTH, VELOCITIES AND SHEAR STRESS VALUES AT DIFFERENT TIME Locality: TŘEBSÍN 9, area 30m 2 , N = 2 years, TD = 10 min Time: 20 min Time: 10 min 2.50 0.06 2.50 0.06 0.05 -1 ) 0.05 VELOCITIES V (m.s 2.00 2.00 -1 ) VELOCITIES V (m.s SHEAR STRESS (Pa) SHEAR STRESS (Pa) 0.04 0.04 Depth (m) Depth (m) 1.50 1.50 0.03 0.03 1.00 1.00 0.02 0.02 0.50 0.50 0.01 0.01 Shear Stress Shear Stress 0.00 0.00 Depth 0.00 0.00 Depth Velocity 0 2 4 6 8 10 0 2 4 6 8 10 Velocity Length (m) Length (m) Shear Velocity Shear Velocity Time: 30 min Time: 40 min 2.50 0.06 2.50 0.06 -1 ) 0.05 -1 ) 0.05 VELOCITIES V (m.s VELOCITIES V (m.s 2.00 2.00 SHEAR STRESS (Pa) SHEAR STRESS (Pa) 0.04 0.04 Depth (m) Depth (m) 1.50 1.50 0.03 0.03 1.00 1.00 0.02 0.02 0.50 0.50 0.01 Shear Stress 0.01 Shear Stress Depth Depth 0.00 0.00 Velocity 0.00 0.00 Velocity Shear Velocity 0 2 4 6 8 10 0 2 4 6 8 10 Shear Velocity Length (m) Length (m)
DESIGN RUNOFF: POTENTIAL SOIL LOSS Locality: TŘEBSÍN 9, N = 2 years, TD = 10 min Grain size categories and their critical shear stress: 0.01 – 0.05 0.05 – 0.25 0.25 – 2.00 Category (mm) < 0.01 t c (Pa) 0.0076 0.0380 0.1900 1.6700 Effective medium grain size D s = 0.030 mm, t c = 0.5 Pa Experimental runoff area: Potential soil loss (for D s ) at 10 ’ Potential soil loss (for D s ) at 30’ Potential soil loss (for D s ) at 20 ’ 0.91 0.45 0.02 0.06 0.69 1.39 1.76 0.88 0.10 2.12 1.06 0.15 2.38 1.19 0.21 Pa
CONCLUSIONS ADVANTAGES OF THE KINFIL MODEL – provides results from the physically-based scheme. – provides possibilities to calibrate model parameters for natural rainfall-runoff event reconstructions. – simulates surface runoff discharges, depths, velocities and shear stress accurately enough to be compared with measured discharges and soil losses measured by rain simulator equipment. – simulates also the change of land use and farming management. MODELLERS AIM – to extend research in soil losses caused by rill erosion ( t 0 vers. t K for various granulometric spectra). – to compare the KINFIL and WEPP models results.
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