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![Burn-in streams: method 1
1. Create a standardized DEM with standardized
values in the range [0,1]
2. For the cells in the river network subtract the
value 1, this will shift those cells to the range [-
1,0]
• This procedure will maintain the lowest neighbour
relation between cells except for those cells where
one neighbour is in the river network and the
other one is not.
31](https://image.slidesharecdn.com/demanalaysisandcatchmentdelineation-151001093918-lva1-app6892/75/Dem-analaysis-and-catchment-delineation-using-GIS-31-2048.jpg)
Uploaded byHans van der Kwast
Dem analaysis and catchment delineation using GIS
This document outlines the concepts and methods related to Digital Elevation Models (DEMs) and the delineation of catchments, detailing the definitions of Digital Terrain Models (DTM) and Digital Surface Models (DSM). It explains various DEM acquisition methods, data derived from DEMs, and the GIS procedures for delineating streams and catchments, including steps for processing DEMs such as filling sinks and calculating flow direction. The document also provides examples of DEM applications, including landscape analysis and contour mapping.
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Dem analaysis and catchment delineation using GIS
- 1. DEM analysis andcatchment delineation Dr. Hans van der Kwast OpenCourseWare ocw.unesco-ihe.org
- 2. Learning objectives After thislecture you are able to: • define DEM, DTM, DSM • describe different methods of DEM acquisition • give examples how DEMs can be used • describe what data can be derived from DEMs • explain the GIS procedure for delineating streams and catchments 2
- 3. Digital Elevation Models •Digital Terrain Model (DTM): a quantitative model of a part of the Earth’s surface in digital form (Burrough & McDonnel, 1998) • Digital Surface Model (DSM): DTM + all natural or human-made features 3
- 4. DEM acquisition • Groundsurveying • DGPS measurements • Stereo photogrammetry • Digitizing contour lines • LIDAR • Radar interferometry 4 INS laser- scanner
- 5. Use of DEMs •Determining the catchment area • Delineate drainage networks • Slope • Aspect • Identify geological structures 5 • Viewshed analysis • Orthorectification • 3D simulations • Change analysis • Creating contour maps
- 6. Use of DEMs:Example French Alpes 6
- 7. Use of DEMs:Example French Alpes 7
- 8. Use of DEMs:Raster map 8
- 9. Use of DEMs:Hillshade 9
- 10. Use of DEMs:DEM 10
- 11. Use of DEMs:DEM + hillshade 11
- 12. Use of DEMs:Contour lines 12
- 13. Use of DEMs:2.5D 13
- 14. Use of DEMs:DEM + orthophoto 14
- 15. Use of DEMs:Slope 15
- 16. Use of DEMs:Aspect 16
- 17. Use of DEMs:Plan and profile convexity • http://courses.soil.ncsu.edu/resources/soil_classifi cation_genesis/soil_formation/hill_shapes.swf 17
- 18. Use of DEMs:Topographic Wetness Index 18
- 19. Catchments (terminology) UK US Catchmentor Watershed drainage basin Watershed Drainage divide Drainage basin: An extent or an area of land where surface water from rain, melting snow, or ice converges to a single point at a lower elevation, usually the exit of the basin, where the waters join another waterbody , such as a river, lake, reservoir, estuary, wetland, sea, or ocean 19
- 20.
- 21. Stream and catchmentdelineation 21 Download DEM tiles Mosaic DEM tiles Reproject DEM Subset DEM Interpolate voids Fill sinks / remove spikes Burn-in the stream network Calculate the flow direction map Derive streams Define outflow point Derive catchment Convert dataset to model format
- 22. Download DEM tiles •Open access data: • SRTM 1 Arc-Second Global (~30 m) • SRTM Void Filled −~30 m for USA −~90 m global • ASTER Global DEM (GDEM) (~30 m) • Resolution ≠ accuracy! • Download at http://earthexplorer.usgs.gov 22
- 23.
- 24. Reproject DEM • Globaldatasets are usually in EPSG:4326 (Geographic Coordinate System, Lat/Lon) • For correct calculation of DEM derivatives, the DEM should be reprojected to a Coordinate Reference System 24
- 25. Calculation of slope 25 MovingWindow or Kernel (3 x 3) x slope = arctan(Δz/ Δx) z In a grid slope is calculated as a focal operation. The steepest slope in the window is assigned to the cell
- 26. Subset DEM • DEMtoo large: calculation times for the following steps can become too large or computer runs out of memory • DEM too small: catchment boundaries are cut off 26
- 27. Interpolate voids • Voidsare pixels with NODATA in your DEM as a result of the acquisition procedure • Voids can be interpolated using the values of surrounding cells 27Source: Markus Neteler
- 28. Fill sinks • DEMcreation results in artificial pits in the landscape • A pit is a set of one or more cells which has no downstream cells around it • Pits are removed using the fill sinks function in GIS software • If landscape contains real sinks (e.g. lakes), these need to be added after pit removal 28 Source: GITTA (2006) Water trapped in a pit
- 29. Fill sinks • Pitscan be removed by: • Cutting through • Filling up 29 Source: GITTA (2006)
- 30. Burn-in the streamnetwork • When a river network layer exists it can be used to force the flow direction algorithm to follow the river network 30 Source: Brad Hudgens (1999)
- 31. Burn-in streams: method1 1. Create a standardized DEM with standardized values in the range [0,1] 2. For the cells in the river network subtract the value 1, this will shift those cells to the range [- 1,0] • This procedure will maintain the lowest neighbour relation between cells except for those cells where one neighbour is in the river network and the other one is not. 31
- 32. Burn-in streams: method2 32 Source: ILWIS
- 33. Calculate flow direction •D8 algorithm: uses 8 discrete directions to calculate flow direction (0, 45, 90, 135, 180, 225, 270, 315 degrees) to steepest cells downwards • Dinf algorithm: uses continuous directions 33 D8 Dinf
- 34. Calculate flow directions:D8 34 80 74 63 69 67 56 60 52 48 30 4 5 6 3 7 2 1 8 45.0 230 4867 50.0 30 5267 Slope = Drop/Distance Steepest down slope direction
- 35. Calculate flow directionD8 35 D8 for each cell Stream link
- 36. Derive streams: Flowaccumulation 36 1 1 11 1 1 1 2 1 1 1 1 1 1 3 3 3 11 2 1 25 15 202 1 1 111 1 1 2 1 1 1 1 1 13 3 3 11 2 1 5 22 20 15 The area draining each grid cell includes the grid cell itself.
- 37. Derive streams: Flowaccumulation 37 1 1 11 1 1 1 2 1 1 1 1 1 1 3 3 3 11 2 1 25 15 202 Flow Accumulation > 10 Cell Threshold Stream Network for 10 cell Threshold Drainage Area
- 38. Define outflow point •Outlet needs to be defined in a delineated river that corresponds with the flow directions that have been calculated • Outlets can be: • Location in river with discharge measurement • Outlet of a tributary • … 38
- 39.
- 40. Effect of differentstream threshold values 40
- 41. Stream and catchmentdelineation 41 Download DEM tiles Mosaic DEM tiles Reproject DEM Subset DEM Interpolate voids Fill sinks / remove spikes Burn-in the stream network Calculate the flow direction map Derive streams Define outflow point Derive catchment Convert dataset to model format
- 42. Boundary condititions • ThisGIS workflow for stream and catchment delineation does not work when applied to: • Flat areas • Human controlled environments 42
- 43.