What is HydroAdd?

The Hydrography Addressing Tool, or HydroAdd, is a web-based tool that allows you to address your data to the National Hydrography Dataset (NHD). Addressing, also referred to as indexing, linking, or linear referencing, is a means to align your data features to be coincident with National Hydrography Dataset (NHD) features. The HydroAdd process also spatially joins some NHD flowline attributes to your data features.

Addressed data greatly contributes to the power of the NHD to serve not just as spatial data but also as a geospatial information infrastructure, or infostructure, and further as a base for analysis and knowledge. Any kind of hydro-related observations can be addressed to the NHD with HydroAdd, such as observations relating to hydrology, water quality, biology, regulations, etc.

Benefits

Benefits of hydro addressed data are numerous. For example, USGS has estimated stream flow and velocity for every flowline in the NHDPlus High Resolution (NHDPlus HR). These estimates are possible because the USGS addressed streamgages to NHD flowlines. Stream flow and velocity estimates in the NHDPlus HR allow many kinds of modeling and analysis, such as time of travel studies for point source pollutants.

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Addressed data is also useful for tracking and reporting assets on the NHD. For example, section 303(d) of the Clean Water Act requires states identify impaired waterbodies. Every two years, every state is required to submit a list of impaired waters to EPA. Many states submit hydro addressed data to the EPA to comply with the CWA.

Because HydroAdd is a web-based tool, multiple users can collaborate on shared projects. HydroAdd also allows you to keep your data synchronized as the NHD is updated, so you can track and manage your geospatial assets in relation to the NHD.

How to Access

To use HydroAdd, you must have an active ArcGIS Online (AGOL) account. HydroAdd displays your data as an editable web features service from AGOL. Note that you cannot edit the NHD with HydroAdd—you can only address your own data with HydroAdd.

Federal agencies can use HydroAdd now! The Office of Management and Budget (OMB) is currently reviewing an application under the Paperwork Reduction Act to release HydroAdd to the public. The Paperwork Reduction Act process and OMB’s approval to collect information through the HydroAdd application is an important and legally necessary step in releasing this tool to the public. USGS will send a notification to users through the NHD listserv when HydroAdd becomes available to everyone.

►For a demonstration, training, or questions about HydroAdd, contact hydroadd@usgs.gov.

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