Where are the wet areas

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Assessment Approaches/GIS Tools Predictive Tool
for Determining Likelihood of Isolated Wetlands
on the Landscape
Where are the wet areas
John R. Richardson, Ph.D. US EPA Region 4
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Wetlands are convergent systems in the landscape
Cohen, Matt J., and Mark T. Brown, A model
examining hierarchical wetland networks for
watershed stormwater management, Ecological
Modelling, Volume 201, Issue 2, 24 February 2007,
Pages 179-193
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Wetlands Diagram
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How to determine wet areas on a landscape
scale Wetlands Floodplains Lakes Rivers Flood
prone areas Ephemeral Wet Areas
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Computed Topographic Index Beven 1979 Moore,
Grayson and Ladson 1991 Verdin and Greenlee 1996
(Hydro1k) Wilson and Gallant 2000 Wise 2007
Depends on Digital Elevation Model (DEM)
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R4 Topography DEM / Zoom to Savannah River
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NHD water bodies and Flowlines
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• Process DEM with Streams from NHDPlus
• Burn in Process
• Insure streams are where the Flowlines are

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Hydrologic conditioning

• Identify sinks and pour points
• Fill sinks and depressions
• Burn NHD streams into DEM

Horizon Systems NHDPlus
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Horizon Systems NHDPlus
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Grid Calcuation

• On a pixel by pixel basis (30 m) for USA
• Requires Flow accumulation and Slope
• Derived from hydrologically conditioned Digital
  Elevation Model (DEM)
• Compound Topographic Index
• ln(Flow Accumulation/tan(slope))

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DEM
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Calculate Slope
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Calculate Flow Accumulation
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NHDPlus 1st order Streams / DEM
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• Previous work based on
• 1000 meter cell size (Hydro1k)
• 100 meter cell size (R4Hydro)
• 30 meter cell size (NHDPlus Dem)

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DEM
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Hydro1Km / DEM
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DEM
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R4Hydro (100m) / DEM
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Wetness Index (30m) / DEM
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Edisto River
Georgia NWI / DEM
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Zoom DEM
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Hydro1k / DEM
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R4hydro 100m / DEM
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Wetness Index (30m) / DEM
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Zoom to 124000 TOPO
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Hydro1k / TOPO
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R4Hydro 100m / Topo
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Wetness Index (30m) / TOPO
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NWI Wetlands / TOPO
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2001 NLCD
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Wetness Index (30m) / 2001 NLCD
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What is the relationship of Wetness Index to
known wet areas

• Tabulate wetness index (GIS analysis)
• 2001 NLCD USA
• Region 4 FEMA Flood maps
• Georgia NWI
• 03 NHD Flowlines
• 03 NHD Water bodies
• Burke County GA hydric soils

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Georgia NWI
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NHD Flowlines
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Zoom to Burke County Ssurgo Hydric soil data
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TOPO / Zoom Burke County
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Wetness Index 30m / TOPO
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Wetness Index 30m /Hydric soils/ TOPO
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Wetness Index 30m /Hydric soils/NWI wetlands/ TOPO
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Wetness Index 30m / TOPO
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Next Steps

• Further analysis and comparisons to existing data
• ORD use of Wetness Index to develop new NLCD
• DEMs are not always consistent across the US
• Better data - Shuttle Radar, 10m DEMS, LIDAR
• Combine use of Flow accumulation and Wetness
  Index
• richardson.john_at_epa.gov

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Calculate Flow Accumulation
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Wetness Index (30m) / DEM