Re: RFI - Bridges again.

["Derick Wuen" <cullend@webone.com.au>]

Ian Harvey wrote in message <3789FE67.9CE49D65@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.

Obviously neither am I!

Incontrovertable truth is that watercourses are least graded part of
country, hence rail line following watercourse is usually least graded route
and/or requires least earthworks. Trade off comes when the watercourse
meanders or wanders from straight, expensive bridges may be required to
maintain both straight and low graded route.

Example: NSW west along Solitary Creek (Rydal - Tarana) on original
alignment had many bridges across creek in order to maintain grades and
relatively straight alignment.

>...
>--
>IanH
>Comments and questions welcome at ian_harvey at bigpond dot com
>However, do _not_ send me unsolicited commercial email.