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National Hydrography Dataset

The National Hydrography Dataset (NHD) is a comprehensive set of digital, spatial data that contains information about surface water features such as lakes, ponds, streams, rivers, springs and wells. The United States Geological Survey (USGS) is the central repository and a key agency for the NHD.

Within the NHD, surface water features are combined to form "reaches," which provide the framework for linking water-related data to the NHD surface water drainage network. These linkages enable the analysis and display of these water-related data in upstream and downstream order. The NHD is based upon the content of USGS Digital Line Graph (DLG) hydrography data integrated with reach-related information from the EPA Reach File Version 3 (RF3).

While initially based on 1:100,000-scale data, the NHD is now complete at the 1:24,000-scale nationwide. The dataset is also designed to incorporate and encourage the development of higher resolution data required by many users.

NHD Stewardship

Much of the data for the NHD will come increasingly from local sources, necessitating a management and oversight at an intermediary level. These intermediaries, or ‘data stewards’, will be required throughout the country on a statewide basis. In some cases, multiple stewards may be required in a given state. For the San Diego region, SanGIS is the NHD sub-Steward.

NHD Stewards coordinate and assume responsibility for the NHD for their region, and perform a number of responsibilities. For more information on these responsibilities or the program, please visit the USGS NHD Stewardship website, or contact SanGIS. Procedurally, local agency staff will maintain the NHD within their jurisdiction and provide the updated dataset to SanGIS who will then deliver the dataset to USGS for incorporation into the larger dataset.

NHD Tools and Tutorials

The NHD is a spatial dataset whose features and attributes are maintained graphically with GIS and ESRI’s ArcGIS using the NHD Geo Edit tools and tutorials that were custom-built by the USGS. Tools are for use by NHD stewards and those other persons trained by USGS in using the toolset.

NHD Data Availability

NHD in San Diego County
NHD data are available at both the 1:24,000 and 1:100,000 scales for the entire county. The data consist of numerous surface water features and are very detailed. The data for San Diego, like the rest of the U.S., are organized by a specific type of watershed called a subbasin. All the NHD features - points, lines, and polygons - in each subbasin are packaged together and available as a personal geodatabase or as shapefiles. The graphic below shows the distribution of the six subbasins across San Diego County.

Figure 1. Locations of NHD subbasins across San Diego County

• new ponds or reservoirs
• new irrigation canals or ditches
• complementary hydrography networks such as municipal storm drain networks
• adding features that may have been missed in the original NHD production

Examples of changes to existing features include:

• updating a stream or river channel using newer and/or higher resolution imagery
• changing an incorrect hydrographic feature name
correcting a feature that may have been altered by natural events or construction
ensuring features are integrated into the NHD model (flow direction, reach codes)

We're asking that NHD users help identify places where the data need updating. Your knowledge of local hydrography can reveal instances like those listed above where updates need to be made. SanGIS has instituted a process whereby those changes can be made easily.

Process for Updating NHD Data
There a six NHD subbasins covering different portions of San Diego County. These subbasins have been downloaded from the NHD website and are available here at SanGIS. Updates to NHD data are made by making changes to feature geometry or attribution using GIS software and then applying custom NHD tools to integrate the changed data back into the national database. The NHD tools, however, are complex and require training in their application. Thus, the tools will only be used by NHD stewards who have received training, like SanGIS, and USGS.

The most important part in any updates, however, is simply knowing what needs to be changed. And this is where you can help. We are making all the San Diego NHD available as ESRI shapefiles. Basic changes to feature geometry and attribution are easily made using ESRI and other GIS software packages. In addition to applying your knowledge about the local hydrography, recent imagery can be compared to NHD to find changes.

1. Download the NHD shapefiles for the subbasin of interest from SanGIS
2. Some contributors may just want to use the NHD data as part of their normal GIS work and update the data as they come across errors and some people may want to access NHD with the main purpose of updating the dataset. Either way, start working with the data.
3. Other GIS datasets can aid in evaluating the detail and currency of NHD. Newer and higher resolution imagery data are of particular value in checking NHD. Other data include elevation data and transportation.
4. Select features that need attention. This includes both existing features already in NHD and new features that should be added to NHD. These new features can as simple as a spring or as complex as a storm drain network. If you have questions as to what features comprise NHD, see the NHD standards page (rockyweb.cr.usgs.gov/nmpstds/nhdstds.html)
5. Save only the relevant features in a shapefile and sent them to SanGIS. If you are sending existing features, go ahead and make the changes to the feature geometry or attribute table and then save them as a new shapefile. If you submitting entirely new features, just save them in a new shapefile. If possible, please include any comments as a separate text or readme file.
6. Send the edits to: fjessie@sangis.org.

Reference: Data Sources
Many of the commonly used San Diego GIS datasets can be found right here at SanGIS (www.sangis.org/Download_GIS_Data.htm). Other sources of public domain data include:

• NHD data downloads (nhd.usgs.gov)
• National and local basemap data (seamless.usgs.gov)
• Local and State of California data (gis.ca.gov)

Reference: How is NHD Organized?

NHD data are available at scales of 1:24,000 (high resolution) and 1:100,000 (medium resolution) nationwide. The higher scale 1:24,000 data is the primary dataset to which most improvements and updates are being made. NHD data are not organized by political units like county maps or grids like the 7.5-minute quad maps. Rather, the data are organized by watersheds because water flow and distribution is affected by terrain and not by boundaries. A watershed can be defined to be the region drained upstream of a point selected along a stream or river. Since the watershed drainage basin size can vary so widely, we need a set of defined watershed boundaries which can contain hydrographic data, like in NHD.

The U.S. Geological Survey, the Natural Resources Conservation Services, and the Environmental Protection Agency have developed a structure for naming and designating watersheds or various sizes. The table below provides information on six different levels of watersheds.

NHD data are made available by subbasin and will have an eight digit reference number. For California, more detailed subdivisions of the subbasins are currently being developed. In the above example, the San Diego River subbasin would be divided into smaller basins representing the drainage areas of tributaries of the San Diego River.

San Diego NHD Contacts

USGS Geospatial Liaison
Drew Decker, ddecker@usgs.gov, 619-225-6430
Carol Ostergren, costergren@usgs.gov, 916-278-9510

SanGIS sub-Steward
Andrew Abouna, aabouna@sangis.org, 858-874-7020
Frank Jessie, fjessie@sangis.org, 858-874-7010

Local Agency Staff
Liz Staudenmayer, Cleveland National Forest, estaudenmayer@fs.fed.us
Jack Hurlburt, City of Chula Vista, JHurlbut@ci.chula-vista.ca.us
Lili Hidalgo, City of Encinitas, LHidalgo@ci.encinitas.ca.us
Richard Cortopassi, City of San Diego, RCortopassi@sandiego.gov
Frederick McCamic, County of San Diego, Fredrick.Mccamic@sdcounty.ca.gov
Becky Schaffner, Southern California Coastal Water Resource Project Authority, beckys@sccwrp.org

NHD and Related Links

ESRI’s ArcGIS

NHD Data Availability

NHD Geo Edit tools and tutorials

NHD Homepage

NHD Newsletters

NHD Stewardship

NHD Viewer

CalWater Watershed Dataset

National Standards for Watershed Delineation

National Hydrography Dataset Standards

SanGIS Homepage

What is GIS?