Data Series 412
U.S. GEOLOGICAL SURVEY
Data Series 412
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A suite of geospatial datasets have been compiled for estimating streamflow statistics in Idaho, to support statistical modeling of perennial streams and to support the Idaho StreamStats web application. Since the initial prototype application was developed in 2003, Idaho StreamStats has been based on 30-m resolution EDNA data. The new datasets developed for modeling perennial streams are well suited to providing an improved foundation of datasets for Idaho StreamStats, and will be used on the web site in the near future. Links are provided for metadata for the datasets. The metadata includes distribution information on obtaining these datasets for use outside the Idaho StreamStats web application.
In a collection as large as these geospatial datasets, errors may be detected and the data may need to be updated. Therefore, the data are distributed using a versioning system. Each download .ZIP file contains the version information in the filename in the form of “Vnn,” where “nn” is the data version number. In this manner, each data component may be versioned and distributed independently. The data is distributed in .ZIP files, one per 8-digit HUC, plus one .ZIP file for the ArcHydro Global dataset, one for the statewide layers, and separate files for the synthetic perennial streams shapefile and for the perennial streams event table. For example, the file “IDSS_17060201_V01.zip” would contain the entire folder for HUC 17060201. A file named “IDSS_17060201_V02.zip” would indicate that data have been updated, and that version 02 data should be used. If a change to one dataset results in the need to change others (adjacent datasets, for example,) all affected datasets will be updated, and the data distribution site will be maintained so it includes a complete set of compatible dataset versions.
Each .ZIP file includes a text file that indicates the version of the accompanying data component. For example, the “IDSS_17060201_V02.zip” file would contain a file named “IDSS_17060201_V02.txt,” which will extract into the archydro\17060201 folder. The name of this file will indicate the version of the data in the folder. The file itself contains an explanation of the versioning system, and a summary of edits made since the first version of the dataset was released.
When the .ZIP files are uncompressed, each file should be extracted to the same location. This ensures that all data files and version files are extracted to the appropriate locations relative to each other. If a new version of a data component is available, the previous component should first be deleted in its entirety before the new version is extracted. The examples in table 2 show how to remove each type of data component. In the examples, all original data components are assumed to have been extracted to the D:\id_ss\ folder.
Idaho StreamStats uses the ArcHydro Tools, developed by ESRI and enhanced under contract by ESRI for StreamStats. The ArcHydro Tools are available as a free download at http://support.esri.com/index.cfm?fa=downloads.dataModels.filteredGateway&dmid=15 (Environmental Systems Research Institute, Inc., 2007). The tools include documentation and a tutorial.
The Idaho ArcHydro datasets are organized and tiled by 8-digit HUC. These units also are known as subbasins in the WBD nomenclature. Some 8-digit HUC boundaries have changed since these datasets were developed, so these datasets should not be used as a substitute for WBD. The data structure within each HUC tile is identical, and consists of an ESRI personal geodatabase named for the HUC and several ESRI Grid-format datasets. The dataset structure for each HUC is listed in table 3.
A “global” database also is available for Idaho in the file “global.mdb.” This database contains the information needed to link the HUCs together to delineate watersheds that span more than one HUC. Selected data elements of the ArcHydro global geodatabase are shown in table 4.
To use these data with the ArcHydro Tools, users need to download the ds412_ArcHydroGlobal.zip and ds412_StatewideLayers.zip files, plus any 8-digit HUC datasets that overlap their area of interest. The 8-digit HUC datasets needed may be determined by overlaying the user’s area of interest with the “hucpoly” polygon feature class in the global geodatabase contained in the ds412_ArcHydroGlobal.zip file. A new folder should be created and all .ZIP files should be extracted into this folder. This procedure will ensure that the datasets are in their proper locations relative to one another.
Create a fresh ArcMap document (identified by the “.MXD” file extension) by starting ArcMap, loading the “Layers” feature dataset (including all component feature classes) from the global.mdb file, and saving the document with a new file name. The ArcHydro Tools use configuration information stored in Extensible Markup Language (XML) to define basin characteristics and other configuration options. XML code for the Idaho StreamStats configuration has been incorporated into versions of the ArcHydro Tools released after February 1, 2009. The ArcHydro Tools Configure Function Parameters tool may be used to load the configuration for StreamStats, using the configuration named “Idaho_10m.” This will load the XML configuration designed to work with these data. The Local Point Delineation or Global Point Delineation tools from the ArcHydro Tools may be used to delineate watersheds. The Compute Local Parameters or Compute Global Parameters menu options then may be used to compute watershed characteristics. For further explanation of the functions of the above datasets, and for instructions on using the tools, see the ArcHydro Tools documentation, available on the ArcHydro Tools download site.
A separate folder named “statewide” is created by extracting the DS412_StatewideLayers.zip file, and contains a personal geodatabase containing exclusion polygons, grids of the regression regions, and two grids used to compute basin characteristics. The peak flows regression regions grid is named “id_pkreg.” The regions grid for low flows, mean-annual, and monthly flow statistics is named “id_lowreg.” These grids are more detailed versions of the region maps in Hortness and Berenbrock (2001), Berenbrock (2002), Hortness and Berenbrock (2003), Hortness (2006), and Wood and others (2008). The grids named “forestg” and “precip_combo” may be used to compute percentage of forested area and mean annual precipitation, respectively, for watershed datasets edited by the user after the automated delineation process. (Continuous parameter grids in each HUC folder are available for unedited watershed datasets.)
The exclusion polygons in the ExcludePolys.mdb geodatabase are areas for which delineation is restricted in StreamStats, or for which additional information is provided. These exclusions consist of areas where software limits are exceeded and watershed delineation is not possible, and areas downstream of Canada, where no data were included, and the delineations are not valid. Also included are the Eastern Snake River Plain, an area for which no regression equations were developed, and a polygon covering the area outside a 1-km buffer of the state of Idaho, in which flow estimates may be computed, but are considered not valid.
Estimated perennial streams developed as described above are provided in ESRI shapefile format in two separate datasets. The dataset named “DS412_ SyntheticPerennialStreams.shp” contains the synthetic streams in ESRI shapefile format. The dataset named “DS412_PerennialStreamsEvents.dbf” contains linear event data indexed to the NHDPlus Version 01_02 (schema version 1, data version 2), in dBase format. See the NHDPlus User Guide (Horizon Systems Corporation, 2008) for more information about NHDPlus versions. The DS412_PerennialStreamsEvents.dbf file is known as an “event table.” The data in an event table are referenced to a route system to give them spatial context. The records in DS412_ PerennialStreamsEvents.dbf should be used in conjunction with the flowline route system in the NHDPlus Version 01_02.
Digital geospatial datasets are available for download as part of this report by following hyperlinks. The hyperlinks point to FGDC-compliant metadata for the datasets. Links in the Distribution_Information section of the metadata provide access to the download files.
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