how do scientists determine headwater of a river?

Hello happywoodpecker,

Here is a good response to your question:

"How do you know you are at the furthest upstream tributary or
headwaters?  They are the first collection points for rainwater
flowing across the ground surface. Once rainwater can no longer soak
into the soil, either because the soil is saturated or it is raining
very hard, it flows downslope as a sheet of water. You can see this
happen in parking lots during a heavy rain.  The sheet of water flows
downslope - geologists like to call this sheet flow - and is directed
into small streams.  These first, small streams are the upper
tributaries, or headwaters, of a river.  Therefore, headwaters are not
the highest elevational point in a watershed; they are fed by sheet
flow that originates further upslope!"

"Re: How are the headwaters of a river determined or defined?" by
Diane Hanley, Staff, geologist, Science Center of NH (Jun 19, 1999)
MadSci Network
http://www.madsci.org/posts/archives/jun99/929916571.Es.r.html

- justaskscott


Search strategy --

After trial and error in searching for various terms on Google, I
found this answer by searching for:

"headwaters are"

Superfast answer.  Great job!  Well be back with more questions.

Happywoodpecker,
There is something else implied by your question  (and expressed in the answer:
"How do you know you are at the furthest upstream tributary or headwaters?")

Generally, one tends to think of a named river being "that" river from
its "furthest upstream tributary" to its mouth, but most rivers get
named before their headwaters or their mouths are found.  Thus the
headwaters of the Mississippi are not the furthest upstream tributary
of the river that flows past New Orleans, since the headwaters of the
Missouri River are a much greater distance upstream (and maybe also
have another local name).

Myoarin