Hi Jason,
On the wish list or not, it's a fantasy. Any one who tells you they can do
it has no knowledge of TIN models.
Unless you pick a point which is exactly on a line in the model where the
two triangles on each side of the line slope towards the line forming a
valley, the catchment area to a point is a line. And, as you know a line
has zero area.
You could make some sort a guess and get a catchment area which drains to
the triangle which you pick - or some other convention such as an assumption
of water depth at the point, or a nominal length of gutter at the point, but
would you rely on something like this without knowing what the convention
was and whether that would be realistic in the circumstances of your design?
The watersheds defined for the TIN model are areas bound by "ridge lines" in
the model. They are a guide to the user in as much as water from outside a
catchment cannot get into the catchment because it would have to flow over a
ridge line to do so.
Obviously in practice, water in flat country can cross catchment boundaries
as the water depth can exceed height of the ridge line above the invert in
the catchment area.
As an example of this, I once had to analyse a "maximum probable rainfall"
event. A rail embankment varying from 3 to 7m high (nominally horizontal
for the trains) ran across several valleys with 6m by 4m culverts at the
valleys. These culverts were no where near adequate for the event I was
analysing and water would have flowed between the valleys had the storm
event occurred.
At it's peak, it is likely the water would have flowed about a metre deep
over the rail line over a length of about 6km and washed significant
portions of the embankment away.
--
Laurie Comerford
CADApps
www.cadapps.com.au
www.civil3Dtools.com
"Jason Hickey" wrote in message
news:5462837@discussion.autodesk.com...
sdevin wrote:
> I just tried using the watershed analysis routine. It left me
> somewhat confused. The model is in mountainous terrain and was
> developed from 24k contours. I would like to be able to pick a spot
> on the surface and have the software delineate the drainage basin
> discharging at this point. Can this be done?
It's on the wishlist.
--
Jason Hickey
Civil 3D 2007, SP3
Dell Precision M70
2 GIG RAM, 256 MB nVidia Quadro FX Go1400
Intel Centrino 2 gHz Processor
www.civil3d.com
