Watershed Modeling

This forum contains all archives from the SD Mailing list (go to http://www.systemdynamics.org/forum/ for more information). This is here as a read-only resource, please post any SD related questions to the SD Discussion forum.
Locked
"Jacob J Jacobson/JAKE/CC01/INEE
Junior Member
Posts: 2
Joined: Fri Mar 29, 2002 3:39 am

Watershed Modeling

Post by "Jacob J Jacobson/JAKE/CC01/INEE »

Bill,

I have been working on watershed modeling for sometime now. In the
situation that you describe, I would most definitely use two stocks.
One for the level in the reservoir and one for the storage of water
in the soil. The most compelling reason is that there will always
be a flow from the reservoir to the soil when there is water in the
reservoir but that flow will go to zero when the reservoir is dry.
Any addition of water (i.e. rainfall or as is usually the
case here in Idaho, snowfall) would start in the reservoir and infiltrate
to the soil reservoir.

By using only one stock, you would lose this interesting part of the model
(different infiltration rates, saturation of soil, lining the reservoir...)

Just my one thought for the day.

Jake Jacobson
Idaho National Engineering & Environmental Laboratory
email: jake@inel.gov
(:>)
Jay Forrest
Junior Member
Posts: 12
Joined: Fri Mar 29, 2002 3:39 am

Watershed Modeling

Post by Jay Forrest »

Good question Bill!

I would say, no, that it is still not a desirable case for allowing a
negative stock... My logic is based on the fact that the dynamics of
depleting the water in the pond bed is very different than the dynamics of
evaporation, animal drinking, etc. in the above zero state. While the
different dynamics can clearly be handled in a single stock model, I tend
to prefer models where are transparent and the logic clear. Combining
different dynamics in a single stock IMO tends to mask the complexity of
the situation and hide logic.

Thanks for asking!
Jay Forrest
From: Jay Forrest <jay@jayforrest.com>
Locked