Lesson 15c: Introduction to the National Hydrography Dataset

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Detailed Description

This lesson will provide a brief overview of the National Hydrography Dataset (NHD), describe what features make up NHD, show how NHD functions as a national hydrographic network, and provide information on accessing data and additional resources.


Date Taken:

Length: 00:15:33

Location Taken: Augusta, ME, US


The National Map is a collection of mapping products and services produced by the USGS National Geospatial Program.   The products and services are accessed via the internet through service calls and graphical user interfaces.  The National Geospatial Program has released a series of “how to” videos for people who are working with The National Map data and services.  The videos show how to use the services and interfaces to access data and tools for viewing, analyzing and printing geospatial data.   The training materials are a mixture of video and PowerPoint-based lessons.  Lessons 1 and 2 serve as an introduction to the training materials.  The remaining lessons are designed as quick “how to’s” and may be viewed as needed, in any order, depending on the user.

Lesson 15c: Introduction to the National Hydrography Dataset.

This lesson will provide a brief overview of the National Hydrography Dataset, describe what features make up NHD, show how NHD functions as a national hydrographic network, and provide information on accessing data and additional resources.

The National Hydrography Dataset or NHD is a digital geospatial dataset that includes the surface water features within the United States.  It is one of three Hydrographic Dataset components of the National Map.

NHD is closely related to the Watershed Boundary Dataset and the NHDPlus layer but this lesson will focus on the background, content, and access to NHD.  The other hydrographic datasets have their own lessons. Lesson 15a covers the Watershed Boundary Dataset and Lesson 15b covers NHDPlus.

NHD and the other hydrographic datasets support numerous science applications at the USGS and other organizations.  These include ecological flows, drought, flooding, spill response, StreamStats, modeling and prediction, watershed condition reporting and analysis, resource reporting and analysis, and more.  In addition, NHD serves as the national network and database for surface water features.  All National Map data are available in the public domain for users outside of USGS.

In 2016 USGS released a report on the Hydrography Requirements and Benefits Study (abbreviated as HRBS).  HRBS was initiated to review and understand current and future user requirements and the associated benefits for improved hydro data.  An online questionnaire was completed by over 500 USGS hydrography data users from local, state, federal, tribal, nonprofit, and private sector organizations.  This image shows some details on the current and potential benefits that can be realized from hydro data.  More information on HRBS, plus access to the complete report, can be found on the National Map homepage.

NHD represents the nation’s surface water drainage network and related features.  These features include rivers and streams, canals, lakes and ponds, coastlines, dams, glaciers, and marshes as seen here.  Note that lake feature contains artificial path features. These permit hydro network connectivity to be maintained through water bodies.

Although other scales are available, the NHD High Resolution, at 1:24,000 scale or better in some locations, is the most up-to-date and detailed hydrography dataset for the nation.  This illustration shows the NHD for an area in Colorado and many of the features found in NHD are labeled.

NHD has its origins in the original 1:100,000- and 1:24,000-scale USGS topographic maps.  These maps included numerous hydrography features made up of point features (such as wells), line features (such as stream segments), and area features (including lakes).  The topographic map features were later digitized and become digital line graph (or DLG) vector data.  The surface water DLGs became the initial version of NHD.

These images show a portion of the Lone Pine, California 1:24,000-scale quadrangle.  First you see a topographic map from 1994 and note the blue water feature lines.  Next, you can see the digital NHD features as thicker blue and green lines – note how they match the lines on the topographic map.  NHD data are being updated, and USGS has processes and tools for updates, but this illustrates the origin of the data.

NHD is a vector dataset and so is composed of point, line, and polygon features.  The following images provide some detail on the content included with NHD.

This image shows the different NHD features comprising NHD waterbodies and NHD flowlines.  Flowlines are important line features that represent water channels where flow occurs.  NHD waterbody polygons relate to flowlines by containing artificial path features to enable network connectivity through waterbodies.

Similar to NHD Waterbodies are NHD Areas.  These are also polygon features and they represent landmarks that provide additional detail to waterbody and flowline features.  For example, the “Inundation Area” can outline a region subject to periodic flooding that is part of a waterbody.

NHDLines are linear features that are not a part of the flow network.  Like the NHDAreas, these features provide further descriptive information to the NHD network, in this case NHD Flowlines.  The NHD line “rapids,” for example, can be placed congruent to a flowline to show where rapids are found.  Many of the NHD features are included for cartographic purposes.

Finally, let’s look at point features.  NHD Point features provide further descriptive information.  “SpringSeep” is one such feature and can be placed by an NHD Flowline or by itself.  Some NHD features can be depicted as points or as lines or polygons depending on the size of the features and the intended data scale.  For example, “rapids” is a point feature, as well as an NHD Line features as pointed out earlier. 

Certain NHD features can be further subdivided by type, each with its own feature code.  This table shows just some of the different types of NHD Waterbody features.  In addition to different varieties of different feature types, each feature will include a limited amount of attribution.   

Complete documentation on NHD data and the earlier content can be found on the NHD website.  This includes the NHD Feature Catalog, NHD Feature Rules, and the NHD model.  We will cover the NHD website shortly.

NHD is more than a map.  It serves as the national hydrography network for mapping and modeling.  The NHD network includes flow direction and connectivity upstream, downstream, and through waterbodies.  The following images show what gives NHD its network capabilities.

Characteristics of the NHD network include: flow direction, the black arrows are showing the direction water is flowing. Because of flow direction, now we have the ability to navigate upstream and downstream from any point on the network.

NHD flowline features are given a 14 digit “Reachcode.”  The reachcode serves as a unique code for every flowline, regardless of whether a stream is named or not.  Any point along a flowline can be identified based on its percentage distance upstream of the end of the segment.  This percentage, combined with the reachcode, serves as a stream address schema.

This addressing capability is known as linear referencing.  NHD also has tools to relate outside features to NHD as “events.”  Together, this means that other data can, in effect, become part of the NHD network and the interactions of water on these features can be studied.  

We can see the streamgage, in this Colorado example, now tied to the NHD network.

When other features are added as event to NHD, their attribute information in integrated with NHD.  This adds geospatial context to the streamflow data and enables a range of applications.  This image shows average water flow at the streamgage, which is information that be added to NHD at this location.

Now we will look at how NHD is stored and provided and related resources.

The area of land between ridges on the land surface that collects all the precipitation that falls in it and drains to a common outlet is called a watershed.  The watershed boundary dataset, or WBD, represents the watersheds of the country in eight nested hierarchical levels or hydrologic units.  This graphic shows large watersheds across the US and note each is given a two digit code.  Let’s focus on the Pacific Northwest Hydrologic Unit Code level 1 or ‘HUC-2.’

Large watersheds can be divided into smaller ones.  Each large 2-digit hydrologic unit can be divided into 4-digit units.  The Lower Snake is one of 13 HUC-4’s in the Pacific Northwest HUC-2.  Each of these can subdivided into smaller hydrologic units now given a 6 digit code, and so forth.  This is important to know because NHD is organized and distributed by hydrologic units.  Please see Lesson 15a for a more thorough explanation of the Watershed Boundary Dataset.

NHD data are provided by 2-digit, 4-digit, 8-digital hydrologic units.  This illustration shows how the 4- and 8-digit units fit within the Pacific Northwest.  NHD can also be downloaded by state or for the entire country.

This image shows how the flow network and hydrologic units are fully integrated in the National Hydrography Dataset.

Full details on NHD and access to the data can be found on the NHD homepage.  The NHD homepage can be found here.

 About National Hydrography Data Products provides basic details on medium- and high-resolution NHD.

Access National Hydrography Data Products provides links to accessing NHD.  We will visit this page in a moment.

Documentation and Specifications contains links to the NHD User Guide, Feature Catalog, and Feature rules, among other resources. We mentioned the Feature catalog earlier in this lesson.

Under resources, Tools has add-on applications designed to work with NHD data.  NHD tools are listed here.  The tool at the top, Markup Application, allows data users to suggest edits, or “markups”, to NHD, as well as WBD and NHDPlus High Resolution.  Suggested edits will be reviewed by the USGS and the NHD state stewards before they are approved for incorporation into the NHD and WBD datasets and future NHDPlus High Resolution Refresh products. 

Stewardship and Community” refers to the group of NHD partnering organizations that help maintain NHD content.   This page has contact links and information on stewardship.  Stewards are local, state, and federal groups that assist USGS in updating NHD by applying their expert local knowledge of hydrography conditions in their region to updating geographic and attribute data. 

and finally “News” and “Connect” have links for the NHD Points of Contact and the NHD newsletters.

Now we will show you how to access the NHD data.  Click on the “Access National Hydrography Product” button. 

People typically either download NHD through the National Map Downloader or directly download via FTP link.  

This shows the different hydrography datasets that can be downloaded, including NHDPlus High Resolution, the NHD data discussed in this lesson, and the Watershed Boundary Dataset.  You can also see the data extent options for accessing hydrography products, based on different hydrologic units.  Note that you can use the Download Viewer to see the different hydrologic unit codes on the screen.  This can help you in directly downloading NHD from the Direct Download Links which will be discussed next. You can see the hydrologic unit codes here within the Viewer display.

The Download Viewer provides access to many other USGS datasets beyond NHD.  Lessons 3a through 3e provide details on different operations using the Viewer.

The links shown here provide quick access to NHD. The State and Entire Nation downloads are self-explanatory, and these allow for rapid access to very large NHD datasets.  Downloading by watershed, however, requires you to know the hydrologic unit code for your area of interest.  You may need to download the Watershed Boundary Dataset or consult the National Map Downloader (as mentioned) to see these codes.

Let’s see how the data are presented.  Geodatabase is the format typically used for NHD. See the very long list here.   All HUC-4 units are listed here in numerical order.  The compressed data file, xml geodatafiles, and thumbnail jpg can be easily downloaded.  Again, you will need to know the hydrologic unit code to find the area you want.

USGS also makes NHD available through internet map services.  This allows NHD data to be displayed using GIS software along with other data layers without needing to download data.  Please note that the USGS offers both cached (or tiled) and dynamic map services for NHD.


In this lesson you learned about, the National Hydrography Dataset and its content, how NHD functions as the national hydrographic network, and methods to access NHD and information on related tools, documentation, news, and contacts.