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Criticality of Point Features in NHD-Based Hydrologic Modeling
Budhendra Bhaduri
Geographic Information Science & Technology
Oak Ridge National LaboratoryPO Box 2008 MS 6237
Oak Ridge, TN 37831-6237
Phone: (865) 241 9272; Email: [email protected]
www.ornl.gov/gist
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Acknowledgements
Ron Parker, Jim Cowles (EPA/OPP)
Joel Blomquist, Mike Wieczorek (USGS)
Ed Bright, Phil Coleman, Bill Hargrove (ORNL)
“The Crosswalk Enthusiasts”
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Overview
What’s the “point”? Importance of point features
What are we doing now? Ongoing initiatives
What are the problems? The joys and the sorrows
What are the (possible) solutions? Make “joys” inversely proportional to time and money
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What’s the Point?
Point features Dams, Lakes, Reservoirs, Community Water System (CWS)
Intakes, Monitoring Stations
Point features are critical in hydrologic modeling Serve as critical junctions on a hydrologic system where flow
and velocity characteristics change May impact contaminant concentrations at a downstream
location through retardation and/or storage of runoff and stream flow
Serve as pour points in estimating upstream contributory area
Point-Reach association is important
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Ongoing Initiatives
Overall objective is the estimation of distributions of pesticide concentrations in surface water for exposure/risk assessments
The main tool for estimation of concentrations is the SPARROW regression model developed by USGS SPARROW modeling needs dams and CWS intakes on RF1
Contributory upstream watershed characterization tool for estimating pesticide impact Watershed characterization tool needs CWS intakes on
NHD
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Ongoing Initiatives
Georeferencing Community Water System (CWS) intakes to NHD Location verified to 6 seconds using DeLORME Data 2,243 intakes (serving populations > 10,000) available 7,000-10,000 will be available shortly
Georeferencing National Inventory of Dams (NID) to RF1 No accuracy estimate 1,800 dams currently located on RF1 75,000-80,000 dams in NID
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CWS intakes
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CWS intakes
8-digit HUC
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CWS intakes
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Georeferencing Point Features
A vastly automated algorithm involves Proximity analysis (distance snapping) Attribute (name) matching
CWS intakes to NHD Find 2 closest NHD reaches Match names to select the correct reach Use alphanumeric flags for certainty Verify and validate problematic set
NID to RF1 Find nearest reach and match names For no-match, find RF1 watershed and Hydro1K grid cell
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Georeferencing Point Features
Name-matching CWS intake source and NHD Reach names Naming conventions and abbreviations
river & rv.; creek & cr.; south & s.; use GNIS data
Flag-raising Names match to satisfaction
Closest reach chosen (names don't match)
Closest reach chosen, no other nearby streams
Verified using DRG, GNIS, or other ancillary data
Not verifiable, and others as appropriate
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CWS Intakes and NHD
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CWS Intakes and NHD
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Balancing Priorities
Point Features
RF1 NHD
Crosswalk
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NHD-RF1 Crosswalk
Objectives
Vastly automated algorithm
Relatively quick to implement
Reasonably comprehensive
Estimation of certainty/error
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NHD-RF1 Crosswalk
RF1
Create Buffer around RF1
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NHD-RF1 Crosswalk
Spatial join to link RF1 attributes to buffer polygons
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NHD-RF1 Crosswalk
Overlay of RF1 buffer polygons
with NHD reaches
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NHD-RF1 Crosswalk
Spatial join to select NHD reaches completely enclosed in RF1 buffers
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NHD-RF1 Crosswalk
RF1 and NHD reaches linked
with attributes via the buffer
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NHD-RF1 Crosswalk
Break in RF1
Unselected NHD reaches
Some reaches do not get selected
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NHD-RF1 Crosswalk
Unselected NHD reach
NHD reach crosses over buffer boundary
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NHD-RF1 Crosswalk
Select RF1 reaches individually
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NHD-RF1 Crosswalk
Select NHD reaches with the same name as the selected RF1
reach
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NHD-RF1 Crosswalk
Using midpoints of close NHD reaches find distance to the selected RF1 reach
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NHD-RF1 Crosswalk
Eliminate reaches with larger distances
to select and associate the relevant NHD
reaches
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NHD-RF1 Crosswalk
Using upstream trace or point-in-
polygon algorithm other points can be
associated
RF1 watershed boundary
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NHD-RF1 Crosswalk
What should be the final x,y locations of
the points?
Nearest point on RF1 reach
Use NHD topology to navigate downstream till a NHD reach with the same name as the RF1 reach is found, and then find the nearest point on RF1
Nearest RF1
Navigate NHD
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NHD-RF1 CrosswalkBuffer RF1 and
Spatial join to link RF1 attributes to buffer polygons
Spatial join to link RF1 reaches with
their buffers
Overlay of RF1 buffer polygons with NHD
reaches
Spatial join to select NHD reaches completely enclosed in RF1
buffers
RF1 and NHD reaches linked with attributes via the buffer
Using midpoints of close NHD reaches find distance to the
selected RF1 reach
Using point-in-polygon algorithm other points
can be associated
Select RF1 reaches individually
Select NHD reaches with the same name as the
selected RF1 reach
Eliminate reaches with larger distances to select and associate
the relevant NHD reaches
NHD-RF1 Correlation
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Conclusions
Point features are important
It is critical to develop associations of point features to NHD and/or RF1 for hydrologic modeling
Multiple pathways to solution
No “best” georeferencing technique
Focus on reasonable answers