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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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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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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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