Lesson 15: the Watershed Boundary Data Set

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In this lesson, we will describe the Watershed Boundary Dataset, show how the data are organized, and explain how the data are improved and maintained. Finally, we will show how the data can be accessed by download and as a map service.


Image Dimensions: 1280 x 720

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Length: 00:13:13

Location Taken: US


“Lesson 15: the Watershed Boundary Dataset.”
“In this lesson, we will describe the Watershed Boundary Dataset, show how the data are organized, and explain how the data are improved and maintained.  Finally, we will show how the data can be accessed by download and as a map service.”
“The Watershed Boundary Dataset (abbreviated as WBD) is the national collection of nested watersheds, called hydrologic units.  It is a component of The National Map, a collection of eight base map data themes with related products and services.  WBD is part of the hydrologic foundation layers.  These hydrologic units form the framework upon which surface water features are organized.
“The Watershed Boundary Dataset defines the areal extent of all or part of surface water drainage to a point on a stream and may represent all or only part of the total drainage area to that point.  The intent of defining Hydrologic Units (HU) within the Watershed Boundary Dataset is to establish a base-line drainage area framework for the Nation.  Water features generally do not cross hydrologic unit boundaries except to receive flow from an upstream unit and to provide flow to a downstream hydrologic unit.  Exceptions are sometimes made with manmade water features such as aqueducts and canals.”
“This illustration shows how elevation data define a small hydrologic unit around the hydrography contained within.  Note how the water features in this example do not cross unit boundaries except to flow to the next hydrologic unit downstream.”
 “WBD serves as a seamless collection of nested hydrologic units for the nation.  This illustration helps demonstrate its multilevel hierarchical structure.  The largest hydrologic units are identified by a two digit code.  This is called the Hydrologic Unit Code (or HUC).  These large units are divided into a collection of smaller hydrologic units.  These smaller divisions gain an additional two digits on their HUC code.  Each subsequent level of subdivision adds a progressive two digit code.  There are six required subdivision levels within WBD - the smallest required unit has a 12 digit code.  WBD is complete for the nation to the 12 digit hydrologic unit code, with provisions for 14- and 16-digit delineations.  14- and 16-digit hydrologic units are optional and quite rare (except for Alaska which has 14-digit hydrologic units on Forest Service lands).”  
“WBD includes both polygons and line features that provide information.  The HUC 12 polygons contain a “ToHUC” field that identifies the downstream flow of the units.  All polygons contain information about the type of drainage area and areas where the boundary itself or flow between units is modified.  For instance, a levee that interrupts natural flow, or a canal that transfers water from one unit to another.  This info is provided as codes in the data.  The line dataset holds information about the sources used to delineate the hydrologic unit, such as 1:24,000-scale topographic maps or 3DEP elevation data.”
 “WBD units are referred to by their hydrologic unit code – such as an “8-digit HU” as highlighted here.  Note that most hydrologic units (though not all) also have a common name, (such as “Death Valley” in this example) in addition to its numeric code.  The names are based on features in the Geographic Names Information System”
“WBD was developed by a local, State, and national effort headed by the Natural Resources Conservation Service, Environmental Protection Agency, and USGS.  WBD became a companion dataset to the National Hydrography Dataset in 2012, both hosted by USGS.  Efforts have been made since then to improve spatial integration between NHD and WBD.”
“WBD is built on elevation data and as elevation data are reviewed and improved, changes are made to WBD.  The example shows a simple WBD update.  The original WBD (orange line) is cutting across the NHDFlowline (blue line).  This intersection can be avoided by moving the WBD to the ridgeline north of the end of the flowline (pink line).”
“WBD names are another maintenance task.  A review and revision of the names for the 4-, 6-, and 8-digit hydrologic units is underway.  The 2- to 8-digit hydrologic unit attributes originate from USGS Hydrologic Unit Maps that were first published in 1987.  You can see the link for the report here.  These maps precede the WBD and therefore also precede the guidance that is now used when naming Hydrologic units. The current name format for the 2- to 8-digit units does not align with the WBD Standards, Geographic Names Information System (GNIS), or the 10- to 14-digit names.  Note the link to the WBD standard here.  One example shown is: “Upper Snake” vs “Upper Snake River.”  The WBD National Technical Coordinators are reviewing the level of effort and implications for updating the 4- to 8-digit names to match the WBD standards.”
“Throughout WBD’s history, it has been recognized that the scope of a national dataset is more than a one agency effort.  Local knowledge is important so that the WBD is useful to the large community that uses it.  Rather than creating local, project-specific, or state-specific hydrologic units, we encourage stewardship of the WBD so that there is a nationally consistent dataset available for everyone’s use for any project.  A nationally consistent dataset aids in interconnectedness and the ability to compare and share scientific research.”
“USGS houses the data and makes it available, but many agencies from local, State, and federal goernments, as well as the private sector, come together to maintain the data and make it useful.  As such, a stewardship program was developed, including the development of editing tools, to support stewards editing the data.  Each State has a designated WBD Principal Steward, who serves as the main point of contact for all other stakeholders and users in the State.  Each WBD Principal Steward can either be sole editors of the WBD, or they can approve other partners and editors to also edit the data, which is encouraged.  There can be many substewards and editors that coordinate with the WBD Principal Steward and WBD National Technical Coordinators.”
“Hydrologic units do not follow political boundaries and regularly cross international borders.  The next slides illustrate how WBD data are being standardized across the border with Canada.  A similar process was also employed for units along the border with Mexico.”
“The WBD team and Canadian partners are working on completing delineation of hydrologic units on our shared border.  The U.S. shares approximately 5,500 miles of border with Canada.  Forty percent of this is made up of shared lakes and rivers.  Each country has its own suite of hydrologic datasets that, in the past, stopped at the border so that political boundaries defined the extent of the hydrologic data.  The International Joint Commission formed a task force to develop seamless hydrographic data across the border to assist with reporting and analysis needs.  The task force is made up of members from the International Joint Commission, U.S. Geological Survey, Environment and Climate Change Canada, and Natural Resources Canada.“
“Two fundamental geospatial datasets are being harmonized, Drainage Areas or ”hydrologic units” and Hydrography.  Within the United States and Canada, drainage areas are defined by the Watershed Boundary Dataset (WBD) and Sub-sub-drainage areas (SSDA) respectively.  Surface hydrography represents the drainage network and contains features such as streams, rivers, and lakes.  Within the United States and Canada, hydrography is defined by the National Hydrography Dataset (NHD) and National Hydro Network (NHN) respectively.  The IJC Task Force is using a phased approach to harmonize these two geospatial datasets.  This leads into next three slides.”
“Phase 1 work included development of the working area along the international border that is coposed of WBD 8-digit equivalent drainage areas.  This was accomplished by matching and reconciling the WBD 8-digit Hydrologic units with Canada’s 4th level Sub-sub-drainage areas.  This phase has been completed and the harmonized data are available within the WBD.”  
“Phase 2 includes the development of harmonized hydrography.  This was accomplished by synhronizing the geometry and cross-stepping attribution between the U.S. NHD and Canada’s NHN.  The harmonized hydrography includes network navigation on the flowlines that allows users to trace the network up- and down-stream across the international border through multiple hydrologic units as shown in the animated graphic.  This phase has been completed and is in maintenance.  Note that before data harmonization, the raindrop trace used to stop at the border.”   
“Phase 3 includes the development of two additional nested levels of drainage areas within the cross border 8-digit hydrologic units.  These levels already existed within WBD as the 10- and 12-digit hydrologic units but are new units for Canada.  Existing units within the U.S. are reviewed, modified, and updated where necessary to harmonize with the new units that are being developed in Canada.  Best available base data (elevation, streams, imagery, etc.) are used to develop these new hydrologic units.  Phase 4 of the effort is the development of attribution (codes and names) for the two additional nested levels of drainage areas.  Both phases are still in progress and will be incorporated into the WBD as they are completed.  
“Most National Map digital products are typically used either by viewing the data through an online mapping service or by downloading the actual data files.  WBD adds a third option as it is also packaged with hydrography data.  Online map services allow you to view data in your GIS software (such as ArcMap or Global Mapper) or on map viewer websites without needing to download data files. Stand-alone WBD (without NHD data) can be easily downloaded from the USGS FTP site or from the Amazon Cloud.  Data are ready to use in GIS software.  WBD is also included with NHD data downloads.  Since NHD is organized by watershed, WBD is a natural accompanying dataset.”
“USGS has a list of map services providing data from The National Map.  The service list link is shown here.  WBD has its own standalone map service within the Theme Overlays group.  The National Map also hosts a standalone NHD map service which can be used together with the WBD service.
“Sometimes it’s preferable to download the data files.  This is especially true, for example, if you need to manipulate or analyze the data content.  WBD data can be downloaded from a number of source sites.  This list provides the site names and links.  The first site listed, The National Map Download Client, is the primary repository for digital USGS mapping data.  You can download the WDB as its own dataset or packaged with the National Hydrography Data.  Lesson 4a, in this instructional series, provides further details on using the Download Client.”
“WBD is an integral part of the USGS hydrography program and a companion dataset to NHD. The WBD is managed jointly by the USGS and Natural Resources Conservation Service and is part of USGS’s The National Map.  Data improvements are ongoing and interested parties can contact the WBD team for updates, information, or to become involved.”
“In this lesson, we described the Watershed Boundary Dataset and its role in the national collection of hydrography data.  We covered the different levels of WBD and how the dataset is a nested hierarchal system.  We also showed how the data are continuously improved and provided a special focus on cross border hydrologic units.  Finally, we listed a number of data resources within USGS and other federal sites for WBD data access.  Further information can always be found on the Watershed Boundary Dataset homepage link shown below.”