U.S. Department of the Interior U.S. Geological Survey DEM Preparation Using the New England Method Streamstats Data Preparation Workshop Pete Steeves.

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

DEM Preparation Using the New England Method

Streamstats Data Preparation Workshop

Pete Steeves and Alan Rea

MA-RI and ID Districts

USGS

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NHD Watershed• DEM preparation using the New England method was

also used to create a watershed tool for NHD. For areas that were prepared for NHD Watershed, the resulting datasets can be used in StreamStats. Several overlapping objectives include:– Delineate a watershed from any point location on NHD

reaches quickly, reliably, and accurately– Relate the resulting watershed to the reach and measure of

the selected point (in essence, create a “polygon event”)– Horizontally integrate 3 earth-surface-based physiographic

datasets (hydrography, basin boundaries, and elevation data) through a series of pre-processing steps

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Overview• Projections• Tiling scheme (database design)• Developing datasets in neighboring

states• Preparing NHD and WBD• Preparing DEM data

– Topogrid – Walling and Burning

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Projections

• The Streamstats team has decided to go with a multi-projection environment.

• Every state will decide it’s own projection(s)

• This requires some upfront GIS planning for a given state:– Basemaps– DEM preparation– Basin characteristics

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Tiling Scheme

• Streamstats has adopted the 8-digit Hydrologic Unit as it’s tiling scheme

• This tiling scheme is also being used for NHD, WBD, and EDNA

• The ‘single outlet’ standard for hydrologic unit tiles is ideal for the ArcHydro/Streamstats environment

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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

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Tier 1 Consideration for Massachusetts

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Tier 2 Consideration for Massachusetts

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Developing Datasets in Neighboring States

• Tier 1 data needs to be developed in your State projection

• Tier 2 data can be developed in any projection. The final vector Global datasets can be projected without complications

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Preparation of NHD

• NHD acts as the backbone, upon which the other datasets are structured

• Keep in mind that the optimal goal is to have a dendrite network

• Only the centerline route features are used when preparing the NHD

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Preparation of NHD (cont)

• Determine if you have hi-resolution NHD for a given HUC

• Copy the NHD coverage out of the NHD workspace

• Convert the route.rch table to an Arc coverage

• Project the NHD coverage to your state projection

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Preparation of NHD (cont)

• Remove all isolated networks that are not part of the main network

• Flip all remaining arcs. NHD route features are oriented upstream by default, and they need to be oriented downstream for this procedure

• Extend the outlet arc

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Preparation of NHD (cont)

• A final step involves making a dendrite of the NHD

• A consequence of skipping this step may be incorrect watershed delineations for points on the braided section of a network

• Canals and other man made structures must be dealt with on a case by case basis

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Preparation of WBD

• WBD boundaries act as retainer walls for DEM preparation.

• By including WBD in the preprocessing, watershed delineations are forced to recognize these boundaries as truth

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Preparation of WBD (cont)

• Boundaries may need to be modified to make certain that they cross NHD in a single location for a given basin polygon.

• Boundaries can be added to WBD (i.e. basin boundaries delineated to gage station locations).

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Preparation of WBD (cont)

• For dense basin boundary datasets weed out any boundaries that do not work well with NHD, particularly in areas with man-modified structures (i.e. canals)

• This work needs to be done in coordination with NHD preparation. At times it may be more appropriate to weed out NHD features (i.e. canals)

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Preparation of NED

• Topogrid is a computation intensive step that enforces NED to recognize NHD as drainage truth.

• Subsequent walling and burning steps further enforce the Topogrid process by exaggerating elevation values along NHD and WBD features

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Preparation of NED (cont)

• Several preliminary steps include:– Projecting – Clipping the NED to a 4000 meter buffer area

around the basin– Converting zunits to centimeters– If your HUC has partial areas with 10 meter

DEMs (and you want to use them), this data needs to be developed separately from the NED for these preliminary steps

– Converting DEM values to points

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Topogrid

The Topogrid command is an interpolation method specifically designed for the creation of hydrologically correct digital elevation models (DEMs) from comparatively small, but well selected elevation and stream coverages. It is based upon the ANUDEM program developed by Michael Hutchinson (1988, 1989).

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Topogrid Represents the ‘Intermediate Step’

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Topogrid

• Resample cell size to 10 meters• Set your origin coordinates using the

subcommand ‘XYZlimits’• Buffer your HUC boundary 50 meters and

use for subcommand ‘Boundary’• Input layers include dendrite steams and

NED points• Save the resulting dataset after post

Topogrid processing

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Topogrid• For most HUCs, breaking up your

watershed may be necessary prior to running TopoGrid– The key factor is GridAllocation– Be sure to buffer each subset 4000 meters

(hence, overlap) for input NED points– Be sure to buffer each subset 50 meters (hence

overlap) for the subcommand ‘Boundary’– Use the full dendrite layer for each subset

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Walling and Burning

• Exaggerate the depth of the dendrite and height of the WBD boundaries

• Simply run the nedprocessing.aml (which runs the agree.aml as well)

• Agree.aml is used for burning: http://www.crwr.utexas.edu/gis/gishyd98/quality/agree/agree.htm#Part1

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