GIS-based modeling of landscape processes: erosion

1. Geospatial Analysis and Modeling: Lecture notes Helena Mitasova, NCSU MEAS GIS-based modeling of landscape processes:erosion Geospatial Analysis and Modeling MEA592 – Helena Mitasova

2. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Outline • geospatial modeling and simulations : using erosion and sediment transport as example of concepts and applications • methods for geospatial modeling of erosion, sediment transport and deposition • simulating impact of land use

3. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Erosion processes: examples 0 0.5m 0 10m

4. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Erosion processes Erosion, sediment transport and deposition: driven by water, wind and gravitation • hillslope erosion/deposition : sheet, rill, gullies • fluvial processes: channel evolution, meandering • coastal erosion: waves and storm surge • wind erosion and sand transport, dune migration • debris flows and land slides • glacial erosion Learn more in GIS elective: MEA592-002 Quantitative Earth Surface Processes

5. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Modeling erosion and sediment flow Motivation: sustainable land use management - analysis of spatial pattern of sediment flow, - identification sediment sources and sinks, - design of conservation measures Applications ?

6. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Geospatial erosion modeling: Applications Agriculture and forestry tourism and recreation

7. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Geospatial erosion modeling: Applications Construction and military training

8. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Geospatial erosion modeling:GIS role - efficient management of georeferenced data

9. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Geospatial erosion modeling:GIS role - efficient management of georeferenced data, - computation of input parameters - run model: integrated or linked - spatial analysis - visualization of results - simulation of management alternatives - assessment and validation from imagery and lidar Linking with GIS ?

10. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Geospatial erosion modeling Linking with GIS • simple models (RUSLE): workflow using GIS tools • fully integrated process-based models - SIMWE • linked external models - SWAT + MapWindows • on-line tools with webGIS components - GeoWEPP • stand alone models RUSLE2, WEPP, … Modeled time period: average annual rates, event-based steady state and dynamic continuous time simulations (days to years) More in MEA792 Advanced Geospatial modeling

11. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Erosion and deposition by water Modeled quantity: Configuration space and interactions: modeled quantity as function of Governing equations:

12. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Erosion by overland water flow Modeled quantity: soil erosion / deposition rate [mass per area, per time] Configuration space and interactions: sediment erosion and deposition as function of • rainfall intensity, • runoff, • soil erodibility • land cover • topography Governing equations: • empirical (USLE) • physics-based (continuity, transport capacity: WEPP, SIMWE)

13. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Governing equations general sediment transport continuity equation change in qs over time + change in qs in space = = sources - sinks = net erosion/deposition see http://courses.ncsu.edu/mea582/common/GIS_anal_lecture/giserosion5.pdf page 11 simplified steady state equation: change in qs over time = 0 change in qs in space = net erosion/deposition estimateqs: many empirical and process-based equations, can be generalized as qs = K qm Sn K - coefficient for rainfall, soil and cover properties q - overland water flow, S - slope, m,n - empirical parameters

14. Sediment flow modeling 1993 photogrammetric DEM Sediment flow at NCSU experimental field N Spatial pattern of sediment flow rate

15. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Geospatial erosion models Examples of erosion models at different levels of complexity Erosion only: USLE/RUSLE2D USLE/RUSLE3D 0 t/ha y 6 12 18 24 300m physics-based: WEPP, SIMWE Erosion/deposition: USPED, RUSLEII

16. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Geospatial erosion models: RUSLE Revised Universal Soil Loss Equation USLE, RUSLE2D, RUSLE3D: • based on standard plot experiments • annual or event-based soil detachment rate [mass/(area.time] L function of length E=R.K.L.S.C.P empirical factors/coefficients R - rainfall intensity K - soil erodibility L - hillslope length or contributing area S - slope steepness C - cover P - protection measures all parameters can be derived in GIS from landuse, soil and elevation layers using published values and equations L function of contrib. area - captures impact of concentrated flow

17. Sediment transport modeling soil detachment with spatially variable land use estimated by RUSLE 3D

18. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Assignment - erosion Erosion in [m] subtracted from DEM: when you properly adjust light from SW and z-exag the nviz image should look something like this

19. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Geospatial erosion models Erosion/deposition: change in sediment flow in space USPED, RUSLEII: • based on physical interpretation of USLE LS factor as sediment transport capacity • erosion/deposition: change (divergence) of sediment flow WEPP, SIMWE • solve continuity equation for sediment flow • include relation between sediment transport capacity and sediment flow (clean water erodes more than water filled with sediment) • captures transition in regimes from detachment limited erosion (no deposition) and transport capacity limited erosion and deposition (max. extent of deposition)

20. Sediment transport modeling soil detachment by RUSLE 3D net erosion and deposition by USPED

21. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Net erosion and deposition Net erosion and deposition is computed as a divergence of sediment flow. erosion depos. Erosion/deposition as change in sediment flow along 1D flowline Erosion/deposition as divergence of 2D sediment flow Observed colluvial deposits

22. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Detachment and transport capacity limited transport capacity of surface water flow is much higher than its capacity to detach soil (e.g. due to soil compaction) > erosion everywhere transport capacity of surface water flow is lower > deposition starts higher on hillslopes

23. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Impact of soil erodibility on pattern of sediment flow and erosion/deposition Changing detachment capacity while transport capacity stays constant: with increasing detachment deposition increases and sediment output remains the same (DCL -> TCL case, C~0.01 -> C~10)

24. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Sediment flow for different soils sand C ~1 clay C ~0.1 detachment capacity limited case DCL transport capacity limited case TCL

25. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Path sampling method Net erosion/deposition as change in sediment flow • sediment flow computed using path sampling • accuracy depends on the number of particles used in simulation

26. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Impact of change in land use pattern Original LU sediment flow net erosion/deposition Optimized LU: estimate erosion for uniform bare ground and put grass on the highest erosion areas

27. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Landcover impact on water flow current 49% forest construction 24% forest 0.7m3/s 0.002m3/s discharge m3/s Spatial distribution of water discharge for 1hr steady rainfall at 46mm/hr (2 year design storm)

28. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Net erosion/deposition change main impact of disturbance is outside construction site: stream erosion within protective buffer 0.01-6.0kg/ms erosion=968kg/s 0.001kg/ms erosion=87kg/s erosion deposition /m2s erosion deposition

29. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Net erosion/deposition within buffer impact of disturbance caused by concentrated water flow that is not sufficiently reduced by the buffer, maximum erosion rates are within the protective buffer Discharge m3/s /m2s Erosion deposition

30. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Net erosion/deposition: extended buffers total erosion kg/s Extended, high infiltration buffers can reduce the impact forest buffer no extended buffer grass buffer current

31. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Modeling impact of hedges slope elevation at pins 1996 1993 erosion deposition Seth M. Dabney et al. 1999 Lanscape Benching from Tillage Erosion Between Grass Hedges

32. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Evolution of hedge slope without tillage Evolution of erosion and deposition pattern growing impact of small artifact Seth M. Dabney et al. 1999 Lanscape Benching from Tillage Erosion Between Grass Hedges

33. WebGIS modeling tools: both data and models provided 30m DEM GeoWEPP Geospatial Analysis and Modeling MEA592 – Helena Mitasova

34. On-line tools: GeoWEPP Geospatial Analysis and Modeling MEA592 – Helena Mitasova

35. Geospatial Analysis and Modeling MEA592 – Helena Mitasova Geospatial erosion modeling:Summary - computation of input parameters: rainfall, runoff, soil erodibility, land cover, topography - equations:empirical (USLE), physics-based (continuity, transport capacity: WEPP, SIMWE) - computing:flowtracing+map algebra within GIS, PDE solvers (linked to GIS) - spatial analysis: global/zonal statistics, overlays for impacts and risk assessment - visualization of results - simulation of management alternatives

36. Geospatial Analysis and Modeling MEA592 – Helena Mitasova References • Neteler 2008 (GRASS book): ch. 5.5 for GRASS implementation, Appendix for equations • Mitasova et al.: Geospatial Erosion Modeling, review for upcoming Treatise in Geomorphology (see link on the Lectures web site) • Harmon et al. 2001: Landscape erosion and evolution modeling. Springer.