Criticality of Point Features in NHD-Based Hydrologic Modeling

1. Criticality of Point Features in NHD-Based Hydrologic Modeling Budhendra Bhaduri Geographic Information Science & Technology Oak Ridge National Laboratory PO Box 2008 MS 6237 Oak Ridge, TN 37831-6237 Phone: (865) 241 9272; Email: bhaduribl@ornl.gov www.ornl.gov/gist

2. Acknowledgements • Ron Parker, Jim Cowles (EPA/OPP) • Joel Blomquist, Mike Wieczorek (USGS) • Ed Bright, Phil Coleman, Bill Hargrove (ORNL) • “The Crosswalk Enthusiasts”

3. 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

4. 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

5. 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

6. 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

7. CWS intakes

8. CWS intakes 8-digit HUC

9. CWS intakes

10. 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

11. 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

12. CWS Intakes and NHD

13. CWS Intakes and NHD

14. Balancing Priorities Point Features NHD RF1 Crosswalk

15. NHD-RF1 Crosswalk • Objectives • Vastly automated algorithm • Relatively quick to implement • Reasonably comprehensive • Estimation of certainty/error

16. NHD-RF1 Crosswalk Create Buffer around RF1 RF1

17. NHD-RF1 Crosswalk Spatial join to link RF1 attributes to buffer polygons

18. NHD-RF1 Crosswalk Overlay of RF1 buffer polygons with NHD reaches

19. NHD-RF1 Crosswalk Spatial join to select NHD reaches completely enclosed in RF1 buffers

20. NHD-RF1 Crosswalk RF1 and NHD reaches linked with attributes via the buffer

21. NHD-RF1 Crosswalk Some reaches do not get selected Break in RF1 Unselected NHD reaches

22. Unselected NHD reach NHD reach crosses over buffer boundary NHD-RF1 Crosswalk

23. NHD-RF1 Crosswalk Select RF1 reaches individually

24. NHD-RF1 Crosswalk Select NHD reaches with the same name as the selected RF1 reach

25. NHD-RF1 Crosswalk Using midpoints of close NHD reaches find distance to the selected RF1 reach

26. NHD-RF1 Crosswalk Eliminate reaches with larger distances to select and associate the relevant NHD reaches

27. NHD-RF1 Crosswalk RF1 watershed boundary Using upstream trace or point-in-polygon algorithm other points can be associated

28. 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 Navigate NHD Nearest RF1

29. Buffer 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 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 Select RF1 reaches individually Using midpoints of close NHD reaches find distance to the selected RF1 reach NHD-RF1 Correlation Using point-in-polygon algorithm other points can be associated NHD-RF1 Crosswalk

30. 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