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U.S. Department of the InteriorU.S. Geological Survey
Processing ArcHydro Datasets with NHDPlus Version 2, Emphasizing StreamStats Data Development
Webinar Series
Alan Rea and Pete Steeves
ID and MA-RI Water Science Centers
USGS
Webinar Series Overview
• May 9—Concepts and Preprocessing
• May 23—ArcHydro Data Development
• June 6—Basin Characteristics
• June 19—StreamStats-specific Datasets and Tools
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-2
Course Web Site
http://streamstats09.cr.usgs.gov/DataPrepWorkshop/Workshop2012/
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-3
Today’s Agenda
• ArcHydro Concepts
• Using NHDPlus V2 for ArcHydro/StreamStats
• Tools for removing sinks
• Take-home assignment: Exercise 1
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-4
ArcHydro Concepts
• “Global” directory structure
• Terrain Preprocessing Steps
• Data structures
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-5
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-7
Developing Datasets in Neighboring States
• Define your study area• Study areas are 2 tiered– Tier 1 includes full or partial 8-digit
Hydrologic Units (HUCs) where a complete set of ArcHydro datasets need to be produced
– Tier 2 includes full HUCs upstream of your state and not overlapping your state
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 10
Global Data Sets• All in Global.mdb geodatabase– hucpoly (tile boundaries)– streams (network to connect tiles)– huc_net_junctions (node points at
‘streams’ confluences and outlets for tile hucpolys)
– huc_net (geometric network)– hucpoint (point locations at outlets)• not used in StreamStats
1414
Flow Direction Grid (FDR)
• A 30 meter grid in national Albers projection
• Each cell points down hill to the neighboring cell with the lowest elevation• Supports “rain drop” tools
32 64 128
16 1
8 4 2
NHDPlusV2—StreamStats Webinars May-June, 2012
161616
Flow Accumulation Grid (FAC)
• A 30 meter grid in national Albers projection
• Each cell contains the number of grid cells that drain to that cell
• Used to generate an elevation-based “synthetic” stream network
• NHDPlus V2 improvement accumulation numbers only include cells within the RPU
NHDPlusV2—StreamStats Webinars May-June, 2012
NHDPlusV2—StreamStats Webinars May-June, 2012StreamStats Data Prep Workshop August 5-7, 2008 Page 18
NHDPlusV2—StreamStats Webinars May-June, 2012StreamStats Data Prep Workshop August 5-7, 2008 Page 20
NHDPlusV2—StreamStats Webinars May-June, 2012StreamStats Data Prep Workshop August 5-7, 2008 Page 22
NHDPlus Version 2 Concepts
• Overview of NHDPlus V2
• Version 2 is new, not publicly released yet (soon, though)
• How NHDPlus V2 compares to typical StreamStats datasets
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-28
29
HydroDEM
• Process uses an AML called AGREE developed by University of Texas to “burn” NHD streams into the NED (NHDPlus V2 uses python and geoprocessing tools)
• Needed since NHD streams do not always match the NED flowpaths – “DEM Flowpath Displacement”
NHDPlusV2—StreamStats Webinars May-June, 2012
33
Only Certified WBD used in “walling” process
• NHDPlus V1
– NHDPlus – V2
Now available for entire US!
NHDPlusV2—StreamStats Webinars May-June, 2012
34
NHDPlus Refinements
• Further modified the DEM surface within waterbodies to create a “Bathymetric Gradient”
• Catchments were generated for the NHD coastal reaches and sinks
NHDPlusV2—StreamStats Webinars May-June, 2012
35
Bathymetric Gradient in Waterbodies (also dropped in NHDPlus V2)
Wall
Waterbodies lowered
NHDPlusV2—StreamStats Webinars May-June, 2012
Key NHDPlus V2 Terms
• Vector Processing Unit (VPU)– Generally hydrologic regions– A few exceptions
• Raster Processing Unit (RPU)– Smaller units for raster processing
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-38
NHDPlus V2 Structure
\NHDPlusBurnComponentsBurnlineEvent.shpBurnAddLine.shpBurnWaterbody.shpBurnAddWaterbody.shpWall.shpSink.shpLandSea.shp
NHDPlusV2—StreamStats Webinars May-June, 2012 41
NHD Snapshot
NHD Data Improvements for NHDPlus V2– More names, correct placement– More lakes– Lakes split by quad lines merged– Isolated networks connected– Real sinks (non-contributing areas) identified– Duplicate geometry removed– Microgaps closed– Great Lakes drainage connected
NHDPlusV2—StreamStats Webinars May-June, 2012 42
ArcHydro Catchments vs. NHDPlus Catchments
• Both define catchments, but differently
• NHDPlus catchments are generated for each MedRes NHD flowline
• ArcHydro catchments are generated from a fac threshold, and are much BIGGER
• StreamStats uses ArcHydro catchments
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-43
Comparisons
NHDPlus
• DEM resolution: 30-m• NHD scale: 1:100K• WBD scale: 1:24K• Tiles: RPUs
Typical StreamStats Implementation
• DEM resolution: 10-m• NHD scale: 1:24K• WBD scale: 1:24K• Tiles: 8-digit HUCs
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-44
Sinks in NHDPlus V2
• A sink causes the raster representaion of flow to stop
• Actually created by inserting a NODATA cell in the HydroDEM grid
• There are many more sinks in NHDPlus V2 than there were in V1
• Sinks inserted wherever streams stop
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-45
Reasons to remove sinks
• Map errors or omissions
• Seasonal flow differences
• “Swiss cheese” watersheds
• Mapping sink watersheds (non-contributing areas)
• Differing interpretations, e.g. peak flows vs. low flows
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-47
Tools for removing sinks
• NHDPlus User Tools
• Only for ArcHydro, does not do a full update of NHDPlus
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-48
Sink Removal Process
1. Identify which sinks to remove, store in a separate shapefile
2. Run Remove NHDPlus sinks tool (spits out “overlapping” sinks)
3. Check results, make sure no problems4. Run Update fdr tool5. Repeat #2 - 4 for overlapping sinks,
iterate until no more overlaps6. When all done, update fac
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-49
Take-home Exercise
• First do Exercise 0—Installing the Tools
• Exercise 1—Removing Sinks from NHDPlus V2– First look at NHDPlus V2 data structures– Remove a sink using the tools– Update fdr and fac
NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-50
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