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4. Select Area of Interest (AoI)

A suite of tools (within the left menu area) are available to select areas within the lower 48 United States and begin the modeling process by summarizing land use, hydrologic soil groups, and other statistics. Options include: Select by BoundaryFree Draw, and Delineate Watershed.

Modeling options are described in Section 7.0 and some modeling workflows require that specific Area of Interest tools are used (as noted below):

  • In order to use the “Sub-basin Attenuation” sub-routine within the “Watershed Multi-Year Model“, the user must define/select an Area of Interest using either the HUC8 or HUC10 “Select by Boundary” choice.
  • In order to use the “Watershed Multi-Year Worksheet” (a.k.a., BMP Spreadsheet Tool), the user cannot use the HUC12 “Select by Boundary” choice.
  • Note: the most appropriate size (total area/acreage) of your Area of Interest for use with the Site Storm Model (Technical Documentation here and Guide here) is from 1 to several hundred acres and it is recommended that the model not be run for areas much large than about 1 square mile (640 acres; although modeling larger areas are possible).
  • Note: the most appropriate size (total area/acreage) of your Area of Interest for use with the Watershed Multi-Year Model (Technical Documentation here) is from several hundred acres to ~1,500 square miles (HUC 8 scale; although modeling larger areas are possible).

4.1 Select by Boundary

Choose a predefined boundary from several boundary types as described above in Section 2.3 Boundaries. First select the boundary type, then use this selection tool enable a “hover over” function to see the name of each bounded area. Once activated, the user can click on their desired area to generate land use and hydrologic soils analysis within the area (among other statistics).

Available boundary types for area selection are a subset of the boundary types viewable in the Layers Selector in the lower left of map. For more information and data sources for these layers, see Section 2.3 Boundaries of this guide.

4.2 Draw Area

Note: This Area of Interest tool can also be used to identify a smaller subarea within a larger HUC12 basin for more specialized use of the Watershed Multi-Year Model for developing a Pollution Reduction Plan (PRP) in Pennsylvania as described in Section 7.3.

4.2.1 Free Draw

A tool any user can deploy to draw a polygon and, upon closing the polygon (double click to close), clip land use and hydrologic soil groups (among other statistics) for the area within the polygon.

4.2.2 Square Kilometer

A single click anywhere on the map will result in a 1 km2 area that will clip land use and hydrologic soil groups (among other statistics) for the area within the polygon.

4.3 Delineate Watershed

Note: This Area of Interest tool can also be used to identify a smaller subarea within a larger HUC12 basin for more specialized use of the Watershed Multi-Year Model for developing a Pollution Reduction Plan (PRP) in Pennsylvania as described in Section 7.3.

This tool selects an Area of Interest by automatically delineating a watershed from a point on a stream network using topographic data represented as a digital elevation model (DEM).

Once the user clicks on the map, the tool moves downhill from that point to “snap” onto a second point on the nearest stream flowline. The tool then calculates the watershed upstream of this second point using the Rapid Watershed Delineation algorithms. The methods for moving downhill to the stream and watershed delineation both use a grid of flow directions derived from a digital elevation model (DEM).

The tool returns the delineated watershed area and boundary, which are provided to the Analyze Area of Interest functions. Two DEMs and stream networks are presently available for watershed delineation as listed below.

4.3.1 Continental U.S. Medium Resolution Streams and NHDPlus DEM

Selecting “Snap to Continental US medium resolution streams” moves downhill from the point you click to snap onto the nearest point on the medium resolution National Hydrography Dataset (NHDPlus flowline) and calculates the watershed upstream of this point using the 30 m resolution NHDPlus flow direction grid for the continental US.

If the point you click does not have a NHDPlus flowline downstream of it (e.g. is in an internally draining area) the watershed is calculated from the point you click. Learn more about NHDPlus. The Model My Watershed watershed delineation uses NHDPlus version 2.1 data model with latest content version accessed 11/22/16.

4.3.2 Delaware High Resolution Streams and 1/3 Arc Sec (10 m) Resolution DEM

Selecting “Snap to Delaware high resolution streams” moves downhill from the point you click to snap onto the nearest point on the Delaware high resolution stream network and calculates the watershed upstream of this point using a 1/3 arc second (10) m resolution digital elevation model for the Delaware River Basin obtained from the National Elevation Dataset.

The stream network snapped to was delineated using TauDEM as described above (Delaware River Basin High Resolution Stream Network overlay).

4.4 Upload File

Note: This Area of Interest tool can also be used to identify a smaller subarea within a larger HUC12 basin for more specialized use of the Watershed Multi-Year Model for developing a Pollution Reduction Plan (PRP) in Pennsylvania as described in Section 7.3.

Upload a polygon for your area.

  • Must be a shapefile (zip containing shp and prj files) or geojson.
  • Only the first feature is used.

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