Overland flow and erosion in agricultural lands

Transcription

1 Overland flow and erosion in agricultural lands Structure a. Introduction, processes and factors b. Impacts c. Models and applications FORM-OSE Post-Graduate Training School Living with hydro-geomorphological risks : From theory to practice Process, model, assessment Paul van Dijk A.Véronique Auzet 1 2 Structure a. Introduction, processes and factors b. Impacts c. Models and applications Soil erosion is an old problem on steep slopes in semi-arid regions Recognised more recently In loess regions in the European temperate climate zone with moderate relief Focus of today s course 3 4 The french example, inventory based on reports Source : Auzet A.V., In Le grand atlas de la France rurale. (Eds INRA). J.P. de Monza, Paris

2 Background of erosion problems in temperate climate Change from forest/pasture towards arable land use << org.matter on the surface << supply of org. matter in the soil >> Temp (exposure of the soil surface) >> Aeration (tillage) >> activity of soil micro-biology >> decomposition of mat. org. by mineralisation et oxidation Exposure of the soil surface to raindrop impact during part of the year Why in areas with loessderived soils (1)? << organic bounds in the soil << aggregate stability >> crust formation << infiltration >> overland flow >> splash erosion >> erosion 7 Source : Kihlbom Why in areas with loess-derived soils (2)? Soil surface conditions, crusting F F1 Low structural stability Scodro (21) F29 1 Spring: a quick soil desagregation Timing aspects : climat and agriculture (ex: Bretagne C. Gascuel, 21) Rainfall characteristics Vegetation cover Soil conditions: roughness and infiltrability Sowing Weeding harvesting Successive agricultural operations Soil and hydrologic conditions Winter: hydrologic conditions Two The processes Splash erosion Overland flow generation Hortonien (rainfall intensity > infiltration cap) Rainfall intensity, soil surface state Saturation (soil pore space is filled with water, additional rainfall cannot infiltrate) Rainfall quantity, soil moisture storage capacity, impeding layer Exfiltration Snowmelt (on frozen soil) Soil detachment by overland flow Transport Deposition key-periods 2

3 Spatial aspects, scales Upstream overland flow formation and diffuse erosion Erosion Transport Sediment delivery Deposition Overland flow concentration and rill erosion Transport phase Photos: A.V. Auzet 15 Photos: A.V. Auzet 16 Sediment deposition Photos: P.M. van Dijk Sediment delivery to streams

4 Structure a. Introduction, processes and factors b. Impacts c. Models and applications Impacts On site Soil loss, reduced soil depth Loss of nutrients Modified physical and chemical properties, AWC Destruction of crop In case of gullies : problematique access with agr. machines Off site Sediment and pollutants transfers Surface water quality and ecosystem degradation Damage to infrastructure and built-up areas (muddy flows) Direct and indirect economical costs for communities and individuals 19 2 Damage in fields Blotzheim, juin 23 R. Armand Damage depends on the land occupation Damage to infrastructure P. van Dijk Blotzheim, juin 23 ( R. Armand)

5 Damage in built-up areas Landser, 25 mai 21 Lemmel M., Scodro E. 25 Blotzheim, juin 23 R. Armand 26 Water quality impacts and effects on aquatic ecosystems La Dijle (Belgique) Mai Structure a. Introduction, processes and factors b. Impacts c. Models and applications Models, in order to : Identify problem areas (target areas for measures) Increase our knowledge Evaluate and predict (effects of measures, catchment management, climate/land use change) At different spatial scales (field, catchment, region ) At different time scales (minutes to years)

6 Model types Models, objectifs, scales empirical USLE, RUSLE, MUSLE deterministic CREAMS, AGNPS, SWAT, SWIM physically-based WEPP, KINEROS, EUROSEM, LISEM, SHE stochastic RillGrow LISEL, 4 km2 Rillgrow, 3 m Two models, two spatio-temporal scales LISEM: the Limburg Soil Erosion Model Event (time step : seconds) Physically-based Distributed Catchment-scale (raster cell size 5 to 5 m) Model 1 : LISEM RECODES: climate and land use change impacts on sediment delivery to streams in the Rhine basin Time step : 1 month Distributed, (raster cell size : 1 km 2) To reply to water management questions for the Netherlands in the period untill Model 1 LISEM : GIS embedded catchment model Flowchart of LISEM Input DEM Land use Output Erosion Overland flow Soil Hydrogramme Rainfall Deposition

7 Rain of ruturn period 5 years duration (min) rain of return period 5 years LDD (Local Drainage Direction) Basic data DEM Soil The LDD defines flow direction in all cells and thus spatial structures Prec. pluviometry (mm) 37 Land use 38 Model parameters derived from soil type Model parameters derived from land use LISEM SOIL TYPE D5 (mu) 22,3 23,65 22,42 26,3 23,12 22,3 KSAT F() (mm/h) 21,1 22,5 2,7 28,6 21,5 22, KSAT F(1) (mm/h) 1, 1, 1, 1, 1, 1, KSAT F(2) (mm/h) 2, 2, 2, 2, 2, 2, KSATCRST (mm/h) / / / / / / KSATWT (mm/h) 2,11 2,25 2,7 2,86 2,15 2,2 PSI (cm) SOILDEP (mm) THETAI (-),3,3,3,3,3,3 THETAS (-),48,5,51,47,49,5 39 LISEM OCCUPATION DU SOL Mais Bande Plan d'eau Betterave Blé Jachère Verger Forêt enherbée/prairie et habitat AGGRSTAB (-) 19 18, CH (m),35, COH F() F(1) (kpa),69,47,91,51 3,32 1,93 1, COH F(2) (kpa),75,52,95,57 3,32 1,93 1, COHADD (kpa),8 3,32 1,45 1, LAI (m2/m2) 1,1 1, n (-) ,1 PER (-),4,95,95,95 STONEFRAC (-),5,5,1,5,5,5,5 et 1 RR F() (cm),89 1,48,97,7,73 1,36 RR F(1) (cm),29,35,48,97,7,73 1,36 RR F(2) (cm),12,25,48,97,7,73 1,36 Les chiffres en italique sont ceux proposés par la table de LISEM pour la deuxième quinzaine du mois de mai. Les chiffres en gras correspondent à des valeurs que nous avons mesurées, observées ou bien choisies en fonction de critères prédéfinis. 4 F Runoff Application of LISEM, no. 1 Effects of soil surface conditions (Mickaël Lemmel, 21) F

8 Erosion G1AF -Initial soil surface state Application of LISEM, no. 2 G1AF1 - Moderate degradation LISEM + TCRP (tillage controlled runoff pattern) Accounting for tillage structures effects on runoff patterns and erosion G1AF2 -Strong degradation Dead furrow Headlands Effects of tillage direction LDD topographique TCRP Structures de drainage de la partie amont du BV GUTZ

9 Runoff distribution over the catchment LDD topographique LDD modifié avec TCRP Takken et al., 1999 Lame d eau ruisselée (mm) N mètres 5 Different spatial structure topography tillage Overland flow concentration often occurs at field boundaries 49 5 Application of LISEM, no. 3 Secteur de l Outre Forêt Scenarion studies at the catchment scale (Marc Pichaud, 21)

10 Scenarios with different combinations of : - grass strips - reduced tillage - retention structures (dikes) reduction of peak discharge 45 reducting factor(%) reduction of eroded surface (<.5tonne/ha) bande enherbée tcs à 2 % 15 digues be+tcs2% be+di15 tcs1+di15 tcs2+di15 be+tcs2+di15 2 years 5 years 1 years reduction factor (%) grass strips (gr) mulch (2%) 15 dams gr + mul. gr + mul.(1%)+dams scenarii mul.(2%)+dams gr+mul.+dams 2 years 5 years 1 years scenarii THE NETHERLANDS 1 km Model 2: RECODES (GAMES + USLE) Climate and land use change : impacts on sediment delivery in the Rhine basin (Van Dijk, 21) Andernach Cochem LUXEMBURG FRANCE GERMANY Kalkofen Schweinfurt Kaub Viereth Kleinheubach Worms Rockenau Rheinfelden Diepoldsau 57 SWITZERLAND AUSTRIA 58 Approach fully distributed model with a time step of one month a sediment production module to quantify mobilisation of sediment by soil erosion at the hillslope scale a module accounting for sediment storage through a delivery ratio expression The basic modules Sediment production: USLE, RUSLE, ABAG Delivery ratio: GAMES, the fraction of mobilised sediment that actually reaches the stream depends on: proximity of source to stream the probability of overland flow occurrence the character of the terrain along the route towards the channel (roughness, slope angle) sediment supply: between or within cells written in PCRaster dynamic modelling language 6 1

11 R-factor K-factor Snowmelt effects are taken into account Hydrological coefficient described the availability of overland land to transport sediment towards streams Local annual erosion Sediment delivery to streams Sediment source to stream distances are estimated using a detailed drainage network map 65 Source: Van Dijk (21) 66 11

12 Temporal variations Results of scenario calculations érosion (t/km2) Neckar Aare (UL) Mosel N D J F M A M J J A S O mois Effet sur l'apport de sédiment (%) Source: Van Dijk (21) Source: Van Dijk (21) climate and land use change only climate change only land use change CPC+UKHI (high) best estimate CPC+UKHI (central) CPC+UKHI (low) UKHI (high) UKHI (central) UKHI (low) CP scenario Attention! Errors and uncertainty! 25 Total Discharge (m3) Errors in input data Model errors Never consider model output as the truth Uncertainty analyses! (such as Monte Carlo analyses) simulated cal val measured Example of Govers and Jetten 7 Peak Discharge (l/s) Total Soil loss (ton) 7 4 simulated cal val simulated 3 2 cal val Example of Govers et Jetten measured 71 Example of Govers et Jetten measured 72 12

13 Why do erosion models perform poorly? Deterministic, spatio-temporal models require many input parameters which all contain some degree of errors. Model output can be very sensitive to some of them (non-linearity) Source: Govers et Jetten 73 Source: Govers et Jetten 74 Error propagation 4. error propagation h->v->q In case rainfall or infiltration has an error of 5,1,15 et 2%... relative error output (%) relative error input (%) Q V h Source: Govers et Jetten 75 the error in modelled catchment discharge can be > 3%! 76 Source: Govers et Jetten Example: sensitivity to Ksat Incertainty / model complexity Source: De Roo et al (1995) 77 Source: Grünwald (1997) 78 13

14 Thanks! 79 14