U.S. Department of the Interior U.S. Geological Survey Processing ArcHydro Datasets with NHDPlus Version 2, Emphasizing StreamStats Data Development Webinar

U.S. Department of the InteriorU.S. Geological Survey

Processing ArcHydro Datasets with NHDPlus Version 2, Emphasizing StreamStats Data Development

Webinar Series

Alan Rea and Pete Steeves

ID and MA-RI Water Science Centers

USGS

Webinar Series Overview

• May 9—Concepts and Preprocessing

• May 23—ArcHydro Data Development

• June 6—Basin Characteristics

• June 19—StreamStats-specific Datasets and Tools

NHDPlusV2—StreamStats Webinars May-June, 2012 Page 1-2

Course Web Site

http://streamstats09.cr.usgs.gov/DataPrepWorkshop/Workshop2012/


Today’s Agenda

• ArcHydro Concepts

• Using NHDPlus V2 for ArcHydro/StreamStats

• Tools for removing sinks

• Take-home assignment: Exercise 1


ArcHydro Concepts

• “Global” directory structure

• Terrain Preprocessing Steps

• Data structures




Developing Datasets in Neighboring States

• Define your study area• Study areas are 2 tiered– Tier 1 includes full or partial 8-digit

Hydrologic Units (HUCs) where a complete set of ArcHydro datasets need to be produced

– Tier 2 includes full HUCs upstream of your state and not overlapping your state


Tier 1 Consideration for Massachusetts


Tier 2 Consideration for Massachusetts

NHDPlusV2—StreamStats Webinars May-June, 2012 Page 10

Global Data Sets• All in Global.mdb geodatabase– hucpoly (tile boundaries)– streams (network to connect tiles)– huc_net_junctions (node points at

‘streams’ confluences and outlets for tile hucpolys)

– huc_net (geometric network)– hucpoint (point locations at outlets)• not used in StreamStats


Global Network


Directory Structure

ArcHydro Terrain Preprocessing Steps


1414

Flow Direction Grid (FDR)

• A 30 meter grid in national Albers projection

• Each cell points down hill to the neighboring cell with the lowest elevation• Supports “rain drop” tools

32 64 128

16 1

8 4 2

NHDPlusV2—StreamStats Webinars May-June, 2012

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Flow Direction Grid


161616

Flow Accumulation Grid (FAC)

• A 30 meter grid in national Albers projection

• Each cell contains the number of grid cells that drain to that cell

• Used to generate an elevation-based “synthetic” stream network

• NHDPlus V2 improvement accumulation numbers only include cells within the RPU



Stream Definition

NHDPlusV2—StreamStats Webinars May-June, 2012StreamStats Data Prep Workshop August 5-7, 2008 Page 18


Stream Segmentation



Catchment Grid Delineation



Catchment Polygon Processing


Drainage Line Processing


Adjoint Catchment Processing


Adjoint Catchment 151


Compact DataBase

NHDPlus Version 2 Concepts

• Overview of NHDPlus V2

• Version 2 is new, not publicly released yet (soon, though)

• How NHDPlus V2 compares to typical StreamStats datasets


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HydroDEM

• Process uses an AML called AGREE developed by University of Texas to “burn” NHD streams into the NED (NHDPlus V2 uses python and geoprocessing tools)

• Needed since NHD streams do not always match the NED flowpaths – “DEM Flowpath Displacement”


30

How the Agree AML works “stream burning”

- 5000


31

NED versus HydroDEM


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HydrologicallyConditioned

DEM

WBD

NHD

NHD ReachCatchments

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Only Certified WBD used in “walling” process

• NHDPlus V1

– NHDPlus – V2

Now available for entire US!


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NHDPlus Refinements

• Further modified the DEM surface within waterbodies to create a “Bathymetric Gradient”

• Catchments were generated for the NHD coastal reaches and sinks


35

Bathymetric Gradient in Waterbodies (also dropped in NHDPlus V2)

Wall

Waterbodies lowered


36

Standard DEM Flow lines


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Flow lines with Bathymetric Gradient


Key NHDPlus V2 Terms

• Vector Processing Unit (VPU)– Generally hydrologic regions– A few exceptions

• Raster Processing Unit (RPU)– Smaller units for raster processing



NHDPlus V2 Structure

We will use theseWe will

use these

40

NHDPlus V2 Structure

\NHDPlusBurnComponentsBurnlineEvent.shpBurnAddLine.shpBurnWaterbody.shpBurnAddWaterbody.shpWall.shpSink.shpLandSea.shp

NHDPlusV2—StreamStats Webinars May-June, 2012 41

NHD Snapshot

NHD Data Improvements for NHDPlus V2– More names, correct placement– More lakes– Lakes split by quad lines merged– Isolated networks connected– Real sinks (non-contributing areas) identified– Duplicate geometry removed– Microgaps closed– Great Lakes drainage connected

NHDPlusV2—StreamStats Webinars May-June, 2012 42

ArcHydro Catchments vs. NHDPlus Catchments

• Both define catchments, but differently

• NHDPlus catchments are generated for each MedRes NHD flowline

• ArcHydro catchments are generated from a fac threshold, and are much BIGGER

• StreamStats uses ArcHydro catchments


Comparisons

NHDPlus

• DEM resolution: 30-m• NHD scale: 1:100K• WBD scale: 1:24K• Tiles: RPUs

Typical StreamStats Implementation

• DEM resolution: 10-m• NHD scale: 1:24K• WBD scale: 1:24K• Tiles: 8-digit HUCs


Sinks in NHDPlus V2

• A sink causes the raster representaion of flow to stop

• Actually created by inserting a NODATA cell in the HydroDEM grid

• There are many more sinks in NHDPlus V2 than there were in V1

• Sinks inserted wherever streams stop


Sink Examples


Reasons to remove sinks

• Map errors or omissions

• Seasonal flow differences

• “Swiss cheese” watersheds

• Mapping sink watersheds (non-contributing areas)

• Differing interpretations, e.g. peak flows vs. low flows


Tools for removing sinks

• NHDPlus User Tools

• Only for ArcHydro, does not do a full update of NHDPlus


Sink Removal Process

1. Identify which sinks to remove, store in a separate shapefile

2. Run Remove NHDPlus sinks tool (spits out “overlapping” sinks)

3. Check results, make sure no problems4. Run Update fdr tool5. Repeat #2 - 4 for overlapping sinks,

iterate until no more overlaps6. When all done, update fac


Take-home Exercise

• First do Exercise 0—Installing the Tools

• Exercise 1—Removing Sinks from NHDPlus V2– First look at NHDPlus V2 data structures– Remove a sink using the tools– Update fdr and fac


Exercise 1


Documents

U.S. Department of the Interior U.S. Geological Survey Processing ArcHydro Datasets with NHDPlus Version 2, Emphasizing StreamStats Data Development Webinar