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

08090301 East Central LA Coastal

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

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

08090301 Questions

►How do we revise a HUC containing

over 60,000 complex features

efficiently?

►Future needs

►What tools are available to expedite

process?

08090301 Solutions Step 1►Methods for reducing revision

complexity

Assessment of problem areas

Resolutions

Classification of problem areas

08090301 Solutions Step 1

08090301 Solutions Step 1

08090301 Solutions Step 1

08090301 Solutions Step 1

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

08090301 East Central LA Coastal

08090301 Solutions Step 2

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

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

08090301 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