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Enhancing NHD with Hydrological Data Analysis

This presentation outlines a pilot study to enrich hydrography with hydrology data in the NHD, using simplified techniques. The study area routing, drainage area estimates, flow and velocity computations, and QA processes are detailed. Advantages, conclusions, and recommendations are discussed for the national-scale application. Key insights include validating NHD VAAs and the efficacy of the methods for hydrologic parameter estimation.

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Enhancing NHD with Hydrological Data Analysis

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  1. Making the NHD Flow: Adding Hydrology to the Hydrography By Tim Bondelid – RTI International Jeanne Game – RTI International Cindy McKay – Horizon Systems Sponsored By USEPA Office of Water

  2. Project Objectives • Pilot Study to develop drainage area, mean annual flow, and velocity estimates for NHD • Apply simplified techniques originally developed for the National Water Pollution Control Assessment Model (NWPCAM) • Use the Pilot as a test application of the NHD VAAs • QA the results using USGS gaging stations and RF1 velocities

  3. NWPCAM • Acknowledgements: EPA OW, NCEE, OPEI • A national-scale modeling system for policy analysis • RF3-based with VAA’s • Large ORACLE system • Several models are integrated into the system • Includes the hydrologic methods shown in this presentation

  4. Study Area

  5. Routing With the VAAs

  6. Hydrologic Sequence Numbers

  7. Routing With the VAAs The Reach File Routing Algorithm: Accumulating/Modeling some “Value”: DIM VAL(10) Sort Reach File in SEQNO Order **** The Actual Routing Algorithm: **** Loop on Reaches: If SFLAG=1 then VAL(LEV) = 0 ***Reach-specific Value or Modeling here *** VAL(LEV) = VAL(LEV) + RCHVALUE ***Put Accumulated Value into Reach Table*** RCH!VALUE = VAL(LEV) ***Check for end of Stream Level Path*** If J>0 and J = (LEV-1) then VAL(J) = VAL(J) + VAL(LEV) VAL(LEV) = 0 Endif End Loop

  8. Drainage Area Estimates • Associate 1 sq. km. AVHRR grids with the nearest Drain • Provides an estimate of incremental drainage area by Drain • Sum up total drainage areas using VAA routing algorithm • QA using USGS gaging station drainage areas: two steps

  9. Drainage Area Estimates

  10. Drainage Area Estimates

  11. Drainage Area Estimates

  12. USGS Gaging Stations

  13. Drainage Area QA: Step 1

  14. Drainage Area QA: Step 2

  15. Drainage Area QA: Log-Log

  16. NWPCAM/RF3 Drainage Area QA: Similar Results

  17. Flow Estimates • Estimate average annual unit runoff by HUC • Apply distance-weighted unit runoff using NCD gages; simplified “zone of influence” • QA Using USGS runoff isopleth map • Compute incremental Drain runoff – multiply incremental drainage area times unit runoff • Route and accumulate incremental flows to estimate mean annual flow by Drain • QA by comparing to USGS gage mean annual flows

  18. Flow QA: Linear

  19. Flow QA: Log-Log

  20. Velocity Estimates • Use “No Slope” Method of Jobson • Compare to RF1 velocities • Does not measure accuracy • Provides an order-of-magnitude cross-check • Need time-of-travel studies to test accuracy • Could possibly be enhanced with Drain slope estimates • First steps taken to test this

  21. RF1 Vs. NHD Velocities

  22. Advantages Of This Method • Uses simple yet effective methods for bringing key hydrologic attributes into the NHD • Can be developed quickly for the national NHD • Linkages to land cover can bring in NPS loading estimates for large-scale water quality modeling • The VAAs combined with these hydrologic attributes provides a time-tested modeling framework

  23. Conclusions • The simplified methods for estimating NHD hydrologic parameters worked quite well • This Pilot Study validated the NHD VAAs as an efficient and effective application tool • The performance of the simplified methods is comparable to the national-scale results from NWPCAM • Many of the databases and tools are now developed for application in other areas

  24. Recommendations • Repeat the pilot application in other areas • Compare with other NHD hydrologic pilots • Test in arid areas • Compare the simplified velocity estimation techniques to site-specific time-of-travel studies • Do a cost-benefit evaluation of the various NHD hydrologic methods under development • National-scale application to get first-order hydrology estimates into the NHD

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