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Content: They are  transport, coastline and area reaches. Transport Reach
A transport reach represents the pathway for the movement of water through a drainage network. They provide a basis on which locations of observations can be geocoded and linked to the drainage network. Transport reaches must be assigned to all NHDFlowline features. Coastline Reach
A coastline reach represents a section of coastline along the Atlantic, Pacific, or Arctic Oceans, the Great Lakes, the Gulf of Mexico, or the Caribbean Sea. These reaches provide a basis for geocoding locations of observations along the coastline. Coastline features provide the lines used for coastline reach delineation. The delineation of a coastline reach may follow one or more coastline features. A coastline reach always follows the entire delineation of the underlying coastline feature(s); the delineation of a coastline feature is not split among reaches.