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Introduction to GIS and Hydrology

Introduction to GIS and Hydrology. Steve Kopp ESRI Dean Djokic ESRI Al Rea USGS. Outline. Hydrology overview Data GIS tools for hydrology – the building blocks GIS data models and specialized tools Hydrologic modeling Hydraulic modeling Overview of NHD-Plus. Water Resources Overview.

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Introduction to GIS and Hydrology

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  1. Introduction to GIS and Hydrology Steve Kopp ESRI Dean Djokic ESRI Al Rea USGS

  2. Outline • Hydrology overview • Data • GIS tools for hydrology – the building blocks • GIS data models and specialized tools • Hydrologic modeling • Hydraulic modeling • Overview of NHD-Plus

  3. Water Resources Overview • 2 broad categories of water • Surface water • Groundwater • 2 broad categories of water modeling • Quantity • Quality • Today’s focus surface water quantity

  4. Surface Water Quantity • How much water is there? • Rainfall runoff modeling, a type of hydrologic modeling, determines for a given storm on a landscape, how much water will become runoff. • Where will it go? • Hydraulic modeling takes the quantity of water and the shape of the landscape and stream channel and determines how deep the water will be and what area it will cover in the event of a flood.

  5. Hydrologic Modeling • Goal: Find stream discharge, Q, at a location for a given precipitation. • GIS is used to summarize terrain and hydrologic characteristics of the watershed for input to a model. • Many ways to calculate Q. • Statistical methods • USGS regression equations (NFF, StreamStats) • “Physical” modeling (rainfall-runoff models) • HEC-HMS (successor to HEC-1), TR-20, etc.

  6. Hydrologic Modeling • Map natural processes onto software tasks • Aggregate landscape characteristics to simplify • “Lumped parameter model”

  7. Hydraulic Modeling • Goal: to predict water surface elevations for the creation of flood inundation maps. • Also velocity, sedimentation, quality • Input: channel and floodplain geometry with hydraulic characteristics, plus discharge and initial water surface level. • Output: water surface elevation at each cross section and other characteristics.

  8. GIS Data for Hydrologic and Hydraulic Modeling • Digital Elevation Model • http://seamless.usgs.gov/ • http://edna.usgs.gov/ • Watershed boundaries • http://www.ncgc.nrcs.usda.gov/products/datasets/watershed/ • Hydrography • http://nhd.usgs.gov/ • Soils • http://www.ncgc.nrcs.usda.gov/products/datasets/statsgo/ • http://soildatamart.nrcs.usda.gov/ • Landcover • http://seamless.usgs.gov/ • Current and historic water records • http://waterdata.usgs.gov/nwis • http://www.epa.gov/STORET/index.html • Climate, weather, rainfall • http://www.ncdc.noaa.gov/oa/ncdc.html • http://www.nws.noaa.gov/ndfd/ • Channel geometry (cross sections)

  9. Elevation Data • Types • DEM : Digital Elevation Model • DSM : Digital Surface Model • Data Structure • Raster • TIN

  10. Where do you get DEM data? • Sources • USGS DEM, NED, DTED, ETOPO30, SRTM • Interpolated from points and lines • Generated photogrammetrically • LiDAR • Created with interpolation tools • especially TOPOGRID, TopoToRaster • What cellsize and accuracy? • Horizontal and Vertical resolution must be appropriate for the landscape and scale being modeled.

  11. DEM Construction • DEM construction issues • Resolution and extent • Projection (for hydrology - equal area) • Source elevation data • Interpolation techniques (IDW, spline, via TIN) • Problems with contour input • Specialized DEM construction software/components (ANUDEM, TOPOGRID, TopoToRaster)

  12. DEM Constructioncontinued • Hydrologically correct DEM • Sinks • Do not fill in the Great Salt Lake • Streams in the correct place? • To burn or not to burn • Watershed boundaries in the correct place? • To fence or not to fence

  13. Watershed (Basin, Catchment, Contributing area) Watershed Boundaries (Drainage Divides) Pour Points (Outlets) Drainage System

  14. GIS Tools for Describing Surface Water Movement DEM FLOW ACCUMULATION FLOW DIRECTION STREAM ORDER Apply Threshold STREAM LINE SINK STREAM LINK No DepressionlessDEM Are there any sinks? FLOWLENGTH Yes FILL SNAP POUR WATERSHED

  15. 2 2 2 4 4 8 2 2 2 4 4 8 1 1 2 4 8 4 1 2 4 8 128 128 2 2 1 4 4 4 1 1 1 1 4 16 32 64 128 16 1 8 4 2 78 72 69 71 58 49 74 67 56 49 46 50 69 53 44 37 38 48 64 58 55 22 31 24 68 61 47 21 16 19 74 53 34 12 11 12 Flow Direction Flow Direction Elevation Direction Coding

  16. 32 64 128 16 1 8 4 2 0 0 0 0 0 0 0 1 1 2 2 0 0 3 7 5 4 0 0 0 0 20 0 1 0 0 0 1 24 0 0 2 4 7 35 2 Flow Accumulation Direction Coding

  17. Function Processing DEM FLOW ACCUMULATION FLOW DIRECTION STREAM ORDER Apply Threshold STREAM LINE SINK STREAM LINK No DepressionlessDEM Are there any sinks? FLOWLENGTH Yes FILL SNAP POUR WATERSHED

  18. Value = No Data NET_GRID 1 1 1 2 2 2 2 2 2 2 2 Creating Vector Streams StreamToFeature RasterToFeature

  19. Stream Link • Assign a unique value to each stream segment. • Can be used as input to Watershed

  20. 1 1 1 1 1 1 1 1 1 1 1 2 2 1 1 1 2 2 2 3 4 2 2 3 7 3 Stream Ordering Shreve Strahler

  21. Watershed • Delineate the contributing area to a cell or group of cells.

  22. Snap distance Stream Cell you clicked on The cell that will be selected(cell with highest flow accumulation) SnapPour • Snap the “pour point” of a watershed to the cell of highest flow accumulation within a neighborhood. • Prevents accidental creation of tiny watersheds on channel side slopes.

  23. Flow Length • Calculate the length of the upstream or downstream flow path from each cell.

  24. Filled sink Sink DEM Errors – Sinks and Spikes • Sinks: when sinks are (or are not) sinks – lakes, depressions, … • Global fill • Dealing with internal basins • Selective fill • Depth • Area

  25. DEM Editing • Streams: when streams are not where they “should” be • Flat areas – difficulty in determining the flow pattern • Barriers (roads) diverting the flow paths • How to “model” bridges and culverts in DEM • How to model dams • Imposing the flow pattern - to burn or not to burn (beware of the scale issues and artifacts – Saunders, 2000) • Simple burn • AGREE • OMNR

  26. DEM Editing (cont.) • Boundaries - when watershed boundaries are not where they “should” be • To fence or not to fence • Ineffective flow areas

  27. DEM Editing (cont.) • Tools • Global operators • Fill • Agree (burn/fence) • OMNR (when it becomes available) • SWFWMD • Custom – model builder • Micromanagement • DEM Editing tools • Custom – model builder

  28. Enhanced Flow Direction (OMNR – Kenny & Matthews) • Main steps • Standard flow directions (D8) • A hybridized raster/vector topological analysis to assign D8 flow directions to cells that intersect the network. • An iterative raster single cell dilation and D8 assignment from within water bodies to focus flow towards the virtual segments. • A merging of results from steps 1, 2 and 3 to produce a final “enhanced flow direction grid”.

  29. Summarizing Watershed Characteristics(Zonal Statistics) • A zone is all the areas/cells with the same value. • Calculate a statistic within the zones for each cell in a raster. • Input zones can be feature or raster. • Output as a raster, summary table, or chart. • Max flow length per watershed • Average slope per watershed • Average curve number per watershed

  30. Mean Slope per Watershed Watersheds Zonal Overlay (cont.) Slope

  31. Where is this functionality? • ArcInfo GRID Functions • ArcView 3.x Spatial Analyst • Avenue requests • Sample extension • ArcGIS Spatial Analyst 8.x • HydrologyOp containing VB methods • Sample Toolbar on ArcObjectOnline • Arc Hydro data model tools • ArcGIS Spatial Analyst 9.x • Tools in the Spatial Analyst Toolbox

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