1 criticality of point features in nhd-based hydrologic modeling budhendra bhaduri geographic...

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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: bhaduribl@ornl.gov

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