Making the NHD Flow:Adding Hydrology to the
Hydrography
ByTim Bondelid – RTI InternationalJeanne Game – RTI InternationalCindy McKay – Horizon Systems
Sponsored ByUSEPA
Office of Water
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
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
Study Area
Routing With the VAAs
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Hydrologic SequenceNumbers
Hydrologic Sequence Numbers
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) = 0Endif
End Loop
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
Drainage Area Estimates
Drainage Area Estimates
Drainage Area Estimates
USGS Gaging Stations
Drainage Area QA: Step 1NHD Pilot Drainage Area (Uncorrected)
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USGS Gage Drainage Area
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Drainage Area QA: Step 2NHD Pilot Drainage Area Comparison
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USGS Gage Drainage Area (km2)
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a (K
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Drainage Area QA: Log-LogNHD Pilot Drainage Area Comparison
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USGS Gage Drainage Area (km2)
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NWPCAM/RF3 Drainage Area QA: Similar Results
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
Flow QA: LinearNHD Pilot Flow Comparison
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USGS Gage Flow (cfs)
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Flow QA: Log-LogNHD Pilot Flow Comparison
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USGS Gage Flow (cfs)
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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
RF1 Vs. NHD VelocitiesRF1 vs NHD Velocities (corrected)
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RF1 Velocity (fps)
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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
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
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