Re: RFI - Bridges again.

[Ian Harvey <ian_harvey@do.not.spam.me>]

Derick Wuen wrote:
> 
> "All other things being equal" (which they usually are not) railways follow
> the "grain" of the country. Water drains to the lowest part of the country
> and then follows the least inclined passage to the next lowest portion, and
> so on. Thus the lowest graded routes (most effective) follow watercourses.

Water follows the most inclined passage.  I guess the reason that
following a watercourse can give low grades is tied in with erosion and
the energy of the flow (steeper slope -> faster flow -> erosion -> cuts
a channel until the slope in the channel results in a slow flow with
less erosion, cutting of the channel gradually works its way upstream).  

Then again I'm no hydrologist.
...
-- 
IanH
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