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The Reach Address Database (RAD) stores the reach address of each Water Program feature that has been linked to the underlying surfacewater features (streams, lakes, etc) in the NHD. These reach addresses record the geographic extent of Water Program features in both tabular and spatial formats. Using Geographic Information System (GIS) terminology, the reach addresses are implemented as event tables and associated event shapefiles. The reach addresses link to a static copy of the NHD obtained from the USGS, which also resides in the RAD. Periodically, EPA retrieves an updated version of the NHD from USGS and migrates all reach addresses in the RAD to this new version.
The only information about an individual Water Program feature stored in the RAD is its reach address. Additional descriptive information for each feature is stored in separate Water Program databases. A unique Water Program feature ID is used to relate the reach address for each Water Program feature found in the RAD with the other detailed data for that feature found in the separate databases. This unique Water Program feature ID is also called the Entity ID. Using Geographic Information System (GIS) terminology, the Water Program feature ID is the key for relating the event tables and shapefiles with the corresponding attribute information for that feature.
The following diagram shows how the Water Program feature ID links the reach addresses in the RAD to the Water Program databases.
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