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Table of Contents

Notes to be worked into pages

Use this upper part for temporary notes that ask questions or supply text or reminders that need to be developed.

  • NAWQA, Streamstats and NWIS are having a discussion on ways to serve basin boundaries internally and externally. Conference calls and more information over at the NAWQA ADIAS wiki.
  • talk topic: Ariel & Larry on generalization of hydrography.
    • Interesting data processing and programming content
    • Use of a generalization service allowing users to go from the high-res NHD to any desired scale could be addressed. This is important in that it might get folks away from thinking that if they need less detail in their hydrographic data, they do not need (necessarily anyway) to use the now unsupported NHD medium res or the NHDPlus offshoot. 
    • Need to develop or educate about NHD plans for giving users a clear, easy way to specify and recreate a version of NHD. This not only implies having metadata about how NHD was generalized in a previous usage, but also the base version of the NHD high-res that was used.
    • Stress that NHD high-res isn't really a single scale anymore (24K some places, 2400K in others, just best-available). This point should probably be made in other parts of the wiki, too.
  • Conference call between SPARROW/NAWQA, StreamStats, NRP MoWS, NHD/WBD, NHDPlus
    • folks to talk about different watershed delineations. Curtis Price and Al Rea have been talking about building a geodatabase to centralize versions of watersheds associated with gages and other points of interest because there are many versions that pre-date both WBD and those to be created by NWIS. Although these earlier versions are not considered the "delineation of record," they have very much been used to create publications and are worthy of archival and making accessible. Building metadata catalogs on a common metadata standard would be an important piece for supporting this vision, particularly if these data were not actually physically centralized.
      • should we talk internally first and then try to engage EPA, or should we just bring EPA into the mix for the first cut (don't want to waste their time)?



Basic information - comparison of NHD vs. NHDPlus

The National Hydrography Dataset (NHD) is the surface water (rivers, streams, lakes, reservoirs, canals) component of The National Map, created by joining the efforts of many Federal, State, and local agencies (link for some history). It is composed of several products, notably in medium (1:100,000) and high resolution versions of the national stream network. The high resolution hydrography is generally 1:24,000, although this is truly a multi-resolution data set. High-resolution NHD should really be thought of as a spatially-variable best-available resolution rendering of hydrography. Alaska is covered by a 1:63,360 scale product, Puerto Rico by a 1;20,000-scale product. There are spots where 1:2,400-scale vectors have been developed, but this is not national. These local resolutions (greater than 1:24,000-scale) are usually limited to county or municipality scale; however, there is a growing need to increase the collection scale and a few states have moved to statewide local resolution. NHD is available in a number of formats, including the personal geodatabase (referred to as NHDinGEO), the file geodatabase (*.fgdb), and the ESRI shapefile format (referred to as NHDGEOinShape). There are number of GIS tools for working with these data, notably the Hydrography Event Management (HEM) Tool, an ArcMap toolbar, which can manage localized point, line, and area information based on feature reachcodes and providing addressing for these events.

  • NHD high resolution data is living (dynamic) data that is continually being maintained and improved at all levels. Extracts (downloads from The National Map or NHD Viewer) are snapshots of the production database at a given time. The NHD HR contains a feature date (FDate) and feature-level metadata that defines date and the process in which a feature was created or changed.

  • No new work is being done on the medium resolution product (static, 2004 snapshot of hydrographic data from the USGS topographic product) by the NHD team, but extensive edits to vectors and attributes are being made by the NHDPlus team. Changes from the NHDPlus team are NOT currently planned to be in subsequent releases of the medium resolution NHD (although changes will be in subsequent NHDPlus releases). This could use some discussion because the longer we wait, the harder it will be to harmonize these two data sets. The NHD team has evolved how it manages the medium-resolution data and it seems like a complex and expensive proposition to take edits from NHDPlus and integrate into the new NHD system.

  • Although NHD high-res is collected for the country in a seamless data set, these data are being continually evolved by the state cooperators. This means that density and quality of data, while improving in general, varies in different states. This also means that many new reaches are being added and pre-existing ones are being split. An impact of this is that the indices of user-defined events which reference data to high-res NHD reaches need to be updated on an ongoing basis. The HEM is designed for this purpose.  
    • This process might be worth discussing here as many users might be shying away from NHD high-res out of fear/uncertainty about complexity and cost of this process.
      • HEM indexes a spatial object (event) to specific reach(es) and measure(s) (percentage of the reach). When a steward changes the feature that an event is assigned to the measures are updated, and if a feature has been moved to a different 8-digit HUC region or the steward is separating these features it may receive a different reachcode. In such cases the event must have it's "address" updated. HEM allows a user to find these changes based on the reach modification attributes, such as ReachSMDate, and allows the user to do batch updates of all changes if the user is confident in the data.

  • In 2012-2014, NHD high resolution is being edited to provide the best possible base for a future version of NHDPlus HR, including a network improvement project nationwide, hydro-image integration project, and engaging in partner activities.

NHDPlus, originally released in 2006, offers a number of new kinds of integration and content on top of the 1:100,000 NHD. The main additions are extra attributes and a set of raster topographic derivatives with the NHD "burned in." A notable product of the integration of hydrography and elevation data is that NHDPlus contains catchments for each reach, which are not a part of the original NHD content (not even in the high-res NHD 2.1 stuff). The NHDPlus project is largely funded EPA Office of Water to enhance the EPA WATERS application, notably by deriving streamflow volume and stream velocity for each stream segment . NHDPlus also integrates the 2001 National Land Cover Dataset (NLCD) and the Watershed Boundary Dataset (WBD). Cindy McKay of Horizon Systems is the main contractor and is part of a team (link to team member list). Al Rea is a good USGS point of contact for this work. This set of data products are distributed in workspaces with shapefiles, dbf tables, and ArcInfo Grids. There are a number of tools built to work with this specific data model, including those for ArcMap 9.3. The tools have not been ported for ArcGIS 10 yet. NHDPlus has released version 2.0 in 2012, which is still 1:100,000-scale product. An important aspect of what is planned for NHDPlus is that it will, in addition to publishing a data product, be publishing methodology and tools for creating NHDPlus data from NHD medium resolution content.

  • If NHD has moved to version 2 of its geodatabase design, will the NHDPlus 2.0 tools be able to use it as input? If the NHD being asked about is the medium res, then there might be a hope.
  • If not, what do the NHDPlus 2.0 tools use as input? NHD medium res. Not sure of the version number.
  • Is NHDPlus 2.0 a supported USGS data product? No.

  • NHDPlus has limited tools available for the 2.0 product (Horizon Systems has limited funding to move forward with some of the tool development)
  • NHDPlus 2.0 adds a number of attributes and integrated data that can be very useful in analysis
  • Attribution in NHDPlus 2.0 relies on a pristine geometric flow network that meets specific criteria and quality. Certain types of flow modeling are not considered in either NHD high res or NHDPlus (tidal induced, backflow, divergence quantity, etc)
  • NHDPlus is a snapshot in time and is currently based off the 2004 NHD Medium Res - although has been highly edited to meet the requirements of the NHDPlus VAA attribution and integration tools.

Watersheds, catchments, basins, and contributing areas are all synonyms in general English, but tend to get used to differentiate products in this field (unfortunately/confusingly). While there are watershed-like features associated with each reach in NHDPlus, referred to as a "reach catchments," there are a number of other data sets offering differing delineations. Hydrologic Units refers to an earlier generation of GIS data representing hierarchy of successively smaller, nested watersheds for the country. These features were generally much larger than NHDPlus reach catchments and were derived by an entirely different process. Each unit was given a hydrologic unit code (HUC). There were four levels of nesting and each has a HUC with a specific number of digits (more digits being higher resolution/more deeply nested). The data set or spatial units from it are often, somewhat erroneously, referred as "HUCs." These have been superseded by a new generation product, the Watershed Boundary Dataset (WBD), which shares the nesting structure and approach to assigning identification numbers. The WBD is a joint effort by folks like the USGS, EPA, and USDA and has been more rigorously constructed to honor hydrology and DEM data than the original HUCs. The country has been subdivided into 12-digit units. The identification numbers are sometimes still referred to as HUCs (just to confuse everyone). 6-digit units are referred to as "basins." 8, 10, and 12 digit units are referred to as "sub-basins," "watersheds," and "sub-watersheds," respectively. WBD are supposed to be the watershed maps of record for Federal work. Note that an NHDPlus reach-catchment does _not_ correspond with any level of WBD unit.

  • One of the main enhancements to the NHD data model data model associated with its version 2.1 is it's inclusion of WBD. Not only are all WBD units planned to be indexed to a high-resolution NHD reach, but the actual geometry and attributes of these watersheds is included (note that WBD is also available as a standalone product, too). 
    • Can NHDPlus reach catchments be aggregated to form WBD units? No.
  • A number of folks have either built tools for deriving contributing areas associated with arbitrary features, or released the resultant datasets. The StreamStats program has such a tool that takes user input via a web page application. Mike Wieczorek and James Falcone have derived delinations based on a selection of several thousand points of interest to the NAWQA program, most of which are USGS stream gages. These are (verify?) have been used for the SPARROW program. NWIS has indexed all current and historical gages (> 100,00 points) to NHD and is apparently planning to derive contributing areas to these points. Not sure about their methodology.

  • WBD is a certified data set and based on the requirements set forth in Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD)

Other Topics

  • Border Harmonization Projects
    • US-Canada International Joint Commission effort to harmonize NHD & WBD with Canadian counterpart datasets
      • IJC Contact: Mike Laitta;, o:202-736-9002, c:202-341-1487
      • Peter Steeves has been working the data for Canadian Harmonization (
      • Project is complete with the exception of Lake Superior and one HUC-8 drainage as of 7/2013. The data exhibit a big need for maintenance since certain agreements to maintain synchronization with NHN data are not as expected.
    • US-Mexico
      • USGS Programmatic Contact: Paul Kimsey;
      • Project completed as of 02/2013
    • Ideas for serving the harmonized products via TNM seamlessly w/NHD or via EPA WATERS w/NHD-Plus
  • (proposed) National riverways portal--good for recreation (rafters, fishers, etc), aquatics science, maybe innundation studies. Could be initially set up based on NHD, but could expand to include imagery, LIDAR-based geomorphological classifications, riparian cover type, stream temperature and flows. Could be a shared Fed project (in line with the recent NOAA/USGS/COE MOU). EPA has got a number of products along these lines; probably worth talking with them about overlap/differences in concepts.
  • NWIS is looking to index all 100+K points they've ever had to NHD and then derive watersheds for these points--a very large undertaking. Sounds like they plan to use a WBD-based approach. Karen Hanson is likely the main person defining methodology. Jean Dupree has a geodatabase template for tracking topological relations for overlapping basins "from points" (question)
  • Curtis Price is pushing for the development of a way to track, find, serve/access, document different versions of the contributing area associated with given points. This is being driven by the fact that many watershed studies for NWIS (and other) points pre-date the NWIS standardization effort and he wants to ensure that those spatial data are available. For example, there were probably analyses done using Thiessen polygons from these points as early approximations of watersheds. These will definitely not be used in future, but the data should be available somewhere.

  • Jeff Simley (NGP Hydro Product Lead) is discussing a new phase for data delivery of NHD HR data by integrating an elevation product such as TIN (triangulated irregular network). Product current titled Ele-Hydro.
  • NGTOC has developed a partner support wiki for the NHD, WBD, HEM, and GeoConflation projects located in the MyUSGS Hydrographic Data Community. This is specific to the NGTOC data sets and primarily focused on providing information to USGS partners and stewards.


Viger, Roland 8900
Doumbouya, Ariel T. 2100
Benson, Abigail L. 200
Anderson, David S. 100
Langseth, Madison Lee 100

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