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Creating Local Resolution NHD: Similarities and Differences in Three State Projects
Susan Phelps, CFM, GISP
March 29, 2012
Local Resolution NHD in Mississippi
• 2010 – Ongoing
• Managed by Mississippi Department of Environmental Quality (MDEQ)– Work conducted by Mississippi Geographic Information (MGI), of
which AECOM is a member
• Stewards:– MDEQ: Steve Champlain – Mississippi Automated Resource Information System (MARIS):
Jim Steil– USGS POC Region 4: Elizabeth McCartney– USGS Geospatial Liaison: George Heleine
Background Overview• Purpose and Goal
– 1 of 7 statewide framework data layers identified as priority by MDEQ• Increase accuracy, content of
hydrography layer in Mississippi Digital Earth Model (MDEM)
– Pilot local-resolution NHD project to define accuracy, specifications for collection of hydrography statewide• Coordination with Arkansas,
Tennessee NHD stewards regarding edge-matching
Project Scope• Source Data Used:
– Statewide 2 ft orthos • Supplemented by NAIP
– Terrain • USACE LIDAR• Statewide 5 ft contours and DTMs
– 18 acre guide streams– Breaklines from terrain processing– 24K NHD– FEMA National Flood Hazard Layer (NFHL) for dams and levees – MDEQ Safe Dams database– FEMA Mid-Term Levee Inventory (MLI)– USACE Vicksburg district levee database
Digitization
Project Scope• Horizontal Alignment
– Streams up to 18-acre drainage area upstream limit collected• if 24K extended further
upstream and visible in imagery, it was maintained
– Water bodies draining 1 acre or greater collected• if less than that but included
in 24K NHD and visible in imagery, it was kept
– All 24K NHD Area, Lines and Points collected• New dams and levees also
digitized
Digitization
Project Scope
• Conflated 24K NHD attributes to local-resolution hydrography, attributes populated for new features– USGS NHD toolset utilized– Reach codes, ComIDs, GNIS info conflated– Feature level, FGDC compliant metadata
generated for each sub-basin deliverable
Conflation and Attribution
• Pre-conflation steps completed using combination of USGS scripts and ArcGIS 9.3 tools
• Following were checked:– Topology – Flow direction– Artificial paths
• All within Area or WB features
– Stream/rivers • All outside of Area or WB features
Project Scope• Conflation complete in Lower Mississippi, Upper Big Black sub-basins
– Now available on The National Map
• Conflation in progress for remaining two sub-basins, Coldwater and Upper Pearl – Using .NET version of conflation tools
Status
Similarities with Local Resolution NHD Projects in Indiana, Mississippi and North Carolina
Similarities
• All 3 projects included some form of pilot study
• Upstream drainage limit used to determine scale of mapping– Guide streams generated from terrain sources, used
for general stream location
• Streams and water bodies digitized from combination of imagery and terrain
• Intermittent/Perennial designations –conflating over 24K attributes, but not attributing for new features
• Urban areas most challenging– No stormwater data to incorporate as of yet
• None included coastal component as of yet
Differences with Local Resolution NHD Projects in Indiana, Mississippi and North Carolina
Differences
Indiana Mississippi North Carolina
USGS NHD Tools Used? X X
Customized Geodatabase? X
HUC 8-Based Submittals? X X
6 Acre Upstream Limit? X X
¼ Acre Water Body Size Limit? X X
Differing Applications of Ftypes? X X X
Value-Added Attributes included with Local Resolution NHD Projects in Indiana, Mississippi and North Carolina
Value-Added Attributes / Data
• Catchment areas (IN)
• Metadata shapefile tracking source data (IN)
• Flow accumulation and flow direction grids (IN)
• Collection of new dams, levees (MS)
• Drainage areas (NC)
• Point events (NC)
Conclusions
Conclusions
• Differing upstream limits b/w states not necessarily a bad thing– Topography different in every state; can have different needs w/in same state– Pilot study can help determine best path forward
• Clear guidance and documentation on Ftypes and procedures a must– Can’t always rely on what’s in 24K– Certain info such as perennial vs intermittent vs ephemeral or canal/ditch
versus stream/river very difficult to discern without field visits or additional local data
– Urban areas very difficult to digitize w/out local stormwater data (surface vs subsurface?)
• Never too early to start thinking about maintenance– If phased approach is used, should it start prior to completion of local res
NHD statewide?– Consider priorities when budgeting
Conclusions
• Support from Workgroup and/or Advisory Council is helpful– Ensures that local res NHD product is useful to greater number of end users– Can provide local knowledge and resources
• Support from USGS POCs, NHD Stewards a must!!!– NHD tools and training– Guides and standards– Funding opportunities
• Coordination with surrounding states recommended– Potential cost-sharing opportunities
