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.

What makes Louisiana different? ► “Backwards” distributary basins ► Heavy marsh area (Southeastern LA) ► Hurricane prevalence ► Subsidence issues

“Backwards” Distributary Basins

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

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?

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

Pilot Project – Lake Maurepas ► First “Coastal Louisiana” experience – Pass Manchac

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

East Central LA Coastal

Revision ► Initial Photorevision process begun in summer 2008 with Q (post-Katrina) imagery ► January 2009, production halted due to lack of resources ► Fall 2009 – Discussions begin regarding the future of ► NHDGeoEdit Tool Workshops Feb. & Jun. 2010

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

Questions ► How do we revise a HUC containing over 60,000 complex features efficiently? ► Future needs ► What tools are available to expedite process?

Solutions Step 1 ► Methods for reducing revision complexity  Assessment of problem areas  Resolutions  Classification of problem areas

Solutions Step 1

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

East Central LA Coastal

Solutions Step 2

Solutions Step 3 ► NHD GeoConflation Toolset  Workshops in Jul and Apr  Allows for mass dataset revisions  Helps automate NHDStatus, NHDReachCrossReference, etc., generation

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

Final Results ► Remaining Concerns  XML Extract size  Machine Limitations  Durability of Standards

Looking Forward ► Reduction of initial revision time ► Partial HUC12 assessment / revision, following catastrophic events ► Regularly scheduled HUC8 maintenance