![Page 1: Mapping Coastal Wetlands in the National Hydrography Dataset James Mitchell, Ph.D. Information Technology GIS Manager Louisiana Department of Transportation](https://reader037.vdocuments.us/reader037/viewer/2022103004/56649c785503460f9492d051/html5/thumbnails/1.jpg)
Mapping Coastal Wetlands in the National Hydrography
Dataset
James Mitchell, Ph.D.
Information Technology GIS Manager
Louisiana Department of Transportation and Development
Sean Deinert
Director of Technical Operations
GDM International Services, Inc.
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What makes Louisiana different?
►“Backwards” distributary basins
►Heavy marsh area (Southeastern LA)
►Hurricane prevalence
►Subsidence issues
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“Backwards” Distributary Basins
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Current NHD
►High Resolution NHD built from “best
available” data
►Contemporaneous issues related to
original inconsistencies
►Keeping up with the rapidity and
frequency of change in the Louisiana
landscape
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Red features are from the NHD. Orange polygons are areas represented by NOAA as land in 1940 (most current data). These are now open water in the NHD.
Where Has All the Coastline Gone?
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GDM and NHD
►STRATMAP Revised over 4,400 quadrangles of
hydrographic data
Created HR NHD for Texas
►LA Seamless Basemap Project Collection, creation and revision of
basemap data
HR NHD Revision
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Pilot Project – Lake Maurepas
►First “Coastal Louisiana” experience – Pass Manchac
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Pilot Project – Lake Maurepas
►Using the NHD GeoEdit tool for large scale revisions
►Manual process of NHD Revision process Photorevision Manual deletion of all features and
accompanying NHDStatus records Manual allocation of reachcodes Manual tabulation of NHDCrossReference Appropriate Add / ModifyGeometry
NHDStatus records
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08090301 East Central LA Coastal
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08090301 Revision►Initial Photorevision process begun in
summer 2008 with Q4 2005 (post-Katrina) imagery
►January 2009, production halted due to lack of resources
►Fall 2009 – Discussions begin regarding the future of 08090301
►NHDGeoEdit Tool Workshops Feb. & Jun. 2010
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08090301 Major Concerns►Time
Why do these revisions take so long?
►The amount of change
►The rapidity of change
►The dataset size and complexity
►Tools for large-scale revision unavailable
►Cost
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08090301 Questions
►How do we revise a HUC containing
over 60,000 complex features
efficiently?
►Future needs
►What tools are available to expedite
process?
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08090301 Solutions Step 1►Methods for reducing revision
complexity
Assessment of problem areas
Resolutions
Classification of problem areas
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08090301 Solutions Step 1
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08090301 Solutions Step 1
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08090301 Solutions Step 1
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08090301 Solutions Step 1
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08090301 Solutions Step 2►Development of Standards for Coastal
Areas
“Estuary” features
Classification of Bays within Estuary
Classification of Swamp/Marsh in Estuary
as a separate feature
NHDFlowline pruning / redevelopment,
maintaining essential features
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08090301 East Central LA Coastal
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08090301 Solutions Step 2
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08090301 Solutions Step 3►NHD GeoConflation Toolset
Workshops in Jul. 2010 and Apr. 2011
Allows for mass dataset revisions Helps automate NHDStatus,
NHDReachCrossReference, etc., generation
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08090301 Final Results►Old methods:
60,000+ features revised
8 months+ to update and revise
Manual table generation
►New Methods 31,000+ features revised
~5 months to update and revise
Automated table generation
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08090301 Final Results
►Remaining Concerns
XML Extract size
Machine Limitations
Durability of Standards
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Looking Forward
►Reduction of initial revision time
►Partial HUC12 assessment / revision,
following catastrophic events
►Regularly scheduled HUC8
maintenance
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