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Advanced water quality analysis with GIS

Advanced water quality analysis with GIS. RESM 575 Spring 2010 Lecture 11. Today. Part A Introduction to watershed analysis with GIS Part B Advanced water quality analysis Terrain analysis Lab 11a and 11b Basic hydro analysis tools Advanced watershed analysis with WCMS.

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Advanced water quality analysis with GIS

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  1. Advanced water quality analysis with GIS RESM 575 Spring 2010 Lecture 11

  2. Today Part A • Introduction to watershed analysis with GIS Part B • Advanced water quality analysis • Terrain analysis Lab 11a and 11b • Basic hydro analysis tools • Advanced watershed analysis with WCMS

  3. Part A.Introduction to Watershed Analysis with GIS

  4. Overview • GIS significance • Important datasets • Concepts • Analysis Tools

  5. Why watershed analysis with GIS? • Watershed analysis is a spatial issue • Used to analyze regional stressors

  6. Regional stressors • Stream sedimentation • Habitat loss • Forest fragmentation • Acid mine drainage • Acid rain • Flooding • Invasive and non-native species

  7. Watershed based frameworks • Integrative approach • Legislative roots in the 1972 Clean Water Act • Goal to clean up and protect US water bodies from point and nonpoint sources Designated uses – evaluated as part of the Clean Water Act

  8. Watershed cataloging units USGS Regions (2 digit) USGS Sub-regions (4 digit) USGS Sub-basins (8 digit) USGS 8-Digit sub-basins in WV

  9. Watersheds for WV NRCS 10 and 12 watersheds in WV (5th and 6th level) n=342 n=745

  10. Issues • More local watersheds needed • One to one relationship between land cover runoff and receiving stream segment • Track runoff from land to stream

  11. Example of scale differences DNR Stocked streams Tier 2.5 - Reproducing trout streams Impaired streams Watershed boundaries

  12. Solution • Delineate watershed boundaries using the topography to guide us

  13. Manual method

  14. Subwatersheds

  15. GIS and Water Resources • Geographic information systems (GIS) is a valuable tool in water resources management GIS in watershed management: • Elevation surface is key • Delineate watersheds • Track flow from a point • Find intermittent stream paths • Calculate drainage areas

  16. GIS use in the hydro cycle

  17. Surface hydrology • Determine where the water came from and where it is going • Describe the behavior of water as it moves over the surface of the earth • Analysis starts with the creation of a hydrologically correct surface (no sinks or peaks interrupting drainage direction) • Include the entire drainage

  18. Elevation surface or grid • The starting point for all hydrological modeling in GIS • USGS Digital elevation model 30m or 10m elevation cells, or 3m for WV • Each cell or grid represents a value for the elevation

  19. DEM sources for WV • 30m (1972) found in the c:/gis-data06/grids/ directory as wv_elev • Mosaic statewide • 10m (1972) derived from 1:24,000 hypsography on the WVU Tech center website • By 24K quad – partial state coverage • 3m (2003) derived from 2003 SAMB photos on the WVU Tech Center website • By 24k quad

  20. Helpful ArcGIS commands To combine dems If you have a *.dem file

  21. 3m to 30m DEM comparison

  22. National 30m seamless DEMs

  23. Other hydro products to note for WV • Segment level watersheds • 1:24K hydrology

  24. Sinks • Depressions in the DEM where water gets trapped • A sink prohibits calculating future flow direction grid values. • A sink occurs when all neighboring cells are higher than the processing cell. • Sometimes they are natural features!

  25. Flow direction • Created from an elevation surface • Direction values are assigned • Flow direction grids are used in many hydro GIS functions 32 64 128 16 1 8 4 2 Flow direction map

  26. 32 64 128 16 1 8 4 2 Flow direction • Created from an elevation surface • Direction values are assigned • Flow direction grids are used in the other flow functions Flow direction map

  27. Flow accumulation • The accumulated flow is based upon the number of cells flowing into each cell in the output grid. The current processing cell is not considered in this accumulation. • Output cells with a high flow accumulation are areas of concentrated flow and may be used to identify stream channels. • Output cells with a flow accumulation of zero are local topographic highs and may be used to identify ridges

  28. Summary of spatial techniques and tools available within a GIS Elevation grid Fill sinks Any sinks? Yes Flow direction No Flow accumulation Allows for additional landscape based analysis Stream order Stream delineations Riparian areas Watersheds

  29. Delineate watersheds Hydro toolbar in ArcGIS 9

  30. Delineate watersheds interactively Interactive delineation for a point

  31. Track flow from a point

  32. Track flow from a point

  33. Find intermittent stream paths Mapped streams from the 1:24,000 topomap

  34. Find intermittent stream paths Mapped streams from the 1:24,000 topomap

  35. Find intermittent stream paths Intermittent, debris slides, accumulators, path of easiest descent exist

  36. Find intermittent stream paths

  37. 5. Calculate drainage area Flow accumulation grid = tells us the number of cells of a certain area that flow to a point Drainage area?

  38. 5. Calculate drainage area Flow accumulation grid = tells us the number of cells of a certain area that flow to a point

  39. Calculate drainage area So, if there are 280,721 cells that flow to that location… and each cell is 3m by 3m in size (9sq meters) Then The total drainage area is (280,721) * (9) = 2,526,489 sq meters Or 2,526,489 sq meters * 0.00024718 = 624 acres

  40. Summary points • Watersheds are the key unit of analysis for examining water quality issues • Scale issues require us to delineate smaller watersheds for local issues • GIS can aid in watershed management by • Elevation grids • Delineate watersheds • Track flow from a point • Find intermittent stream paths • Calculate drainage areas

  41. For basic hydrological modeling • ArcGIS9 toolbar • Lab 12 Hydrological Analysis Basics

  42. Part B.Advanced Water Quality Analysis with GIS

  43. Overview • Terrain analysis • concave/convexity, moisture index • Finding potentially affected streams • Expected mean concentration modeling • WCMS (Watershed Characterization and Modeling System) ArcGIS 9 extension

  44. Surface hydrology • Rainfall - runoff relationships • Runoff - above curve • Losses - below curve • interception • depression storage • evapotranspiration • infiltration Runoff Time Runoff Rainfall Time

  45. Runoff curve from gauge Source: www.americanwhitewater.org

  46. Watershed characteristics affecting runoff • Watershed configuration • size • shape • orientation • stream network • Topography • Geology • soils, infiltration and erosion characteristics • Surface culture • agricultural practices • residential land use practices • Structures • hydrologic modification

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