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Enhancements in DEM Derivatives for NHDPlus Version 2: A Comprehensive Guide

This document outlines the improvements made in the Digital Elevation Model (DEM) derivatives for NHDPlus Version 2. Key components include flow direction grids, flow accumulation grids, catchment grids, and HydroDEM. The HydroDEM integrates a process to "burn" streams from the National Hydrography Dataset (NHD) into the National Elevation Dataset (NED), resolving discrepancies in flowpaths. Additional refinements include the creation of bathymetric gradients, improved handling of water bodies, and the introduction of more sink points. This comprehensive overview serves as a vital resource for understanding the latest advancements.

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Enhancements in DEM Derivatives for NHDPlus Version 2: A Comprehensive Guide

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  1. Improved DEM Derivatives in the NHDPlus Version 2 Alan Rea Craig Johnston Richard Moore

  2. DEM Derivatives included in NHDPlus Version 2 • Flow direction grid • Flow accumulation grid • Catchment grid and shapefile • Catchment seed grid (rasterized NHD, sinks) • HydroDEM (burned and walled) • Filled areas grid (diagnostic) • fdrnull grid (for computing flowlength)

  3. Burn Components used to create HydroDEM • BurnLineEvent (lines) • BurnWaterbody (polygons) • Sink (points—not directly in NHD) • Wall (lines) • LandSea (polygons) • BurnAddLine (lines not in NHD) • BurnAddWaterbody (polys not in NHD)

  4. HydroDEM development • Process uses an AML called AGREE developed by University of Texas to “burn” NHD streams into the NED (NHDPlus V2 uses python and geoprocessing tools) • Needed since NHD streams do not always match the NED flowpaths – “DEM Flowpath Displacement”

  5. Hydro Enforcement for streams: “stream burning”

  6. NED versus HydroDEM

  7. NHDPlus Refinements • Further modified the DEM surface within waterbodies to create a “Bathymetric Gradient” • Version 2 also burned in all water bodies, even isolated ones • Catchments were generated for the NHD coastal reaches • Catchments also were generated for sinks in Version 2 • Used VAA to enforce hydro stepping

  8. Standard DEM flow paths

  9. Flow paths with Bathymetric Gradient

  10. Victoria Reservoir Michigan NHD Flowline FTYPE = Pipeline Catch Burn Attributes Catchment = N Burn = N

  11. Sinks in NHDPlus V2 • A sink causes the raster representation of flow to stop • Actually created by inserting a NODATA cell in the HydroDEM grid • There are many more sinks in NHDPlus V2 than there were in V1 • Sinks inserted wherever streams stop

  12. Sink Examples

  13. Summary • Burned and walled HydroDEM and derivatives • Improvements to the flow direction grids • Improved input data (especially WBD) • Many more sinks than V1 • Catchments generated for sinks • HydroDEM and Burn Components included in distribution

  14. Questions? ahrea@usgs.gov http://www.horizon-systems.com/nhdplus/

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