The beginning and ending points may be selected for geographic, historical or other reasons. – and the name may be based on landmarkssuch as gauging stations, river miles, natural features, and topography . In fluvial hydrology, a reach is a convenient subdivision of study; it may be any length of river of fairly uniform characteristics, or the length between gauging stations, or simply the length of a watercourse between any two defined points.Hydrologic Definitions, Science in Your Watershed, USGS 
Reaches are often named by those using the river, and a reach may be named for landmarks, natural features, and historical reasons (see, for instance, Gallions' Reach, named after the family that once owned its banks) . In fluvial hydrology, a reach is a convenient subdivision of study; it may be any length of river of fairly uniform characteristics, or the length between gauging stations, or simply the length of a watercourse between any two defined points.Hydrologic Definitions, Science in Your Watershed, USGS These may be measured in terms of river miles.
R
The beginning and ending points may be selected for geographic, historical or other reasons. – and the name may be based on landmarkssuch as gauging stations, river miles,
Reaches are often named by those using the river, and a reach may be named for landmarks,
R
topography
historical reasons (see, for instance, Gallions' Reach, named after the family that once owned its banks)
A
These may be measured in terms of river miles.