Noun
thalweg (plural thalwege or thalwegs)
(geology, geography, cartography) The line that connects the lowest points in a valley or river channel, and thus the line of fastest flow or deepest water along a river’s course.
Similarly, an expected thalweg of where surface water would want to travel in intermittent and permanent streams can be computed from elevation data in the GIS. Source: Internet
The water boundaries are still set to be the original thalweg of the rivers. Source: Internet