PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

Watershed Stratification :
A Problem on Watershed 10 4
W e have also begun to structure the
hydrologic model for watershed 10 concurrently
with the simulation study underwa y
for watershed 2 and the watershed system s
analysis. Our objective here is to prepare a
fine-resolution hydrologic model which in -
corporates the transpiration model from th e
Primary Producers, the evapotranspiratio n
model from Meteorology, and provides soi l
moisture and subsurface water flow for th e
Primary Producer and Bio-Geochemical Processes
groups . The first step in structuring suc h
a model is system stratification .
One key to the analysis of complex system s
is the compartmentalization of the syste m
into homogeneous subsystems which can the n
4 Authored by George W . Brown, Associate Professor,
Oregon State University, Corvallis .
be isolated for study . This should be done in
such a way that the linkage between compartments
is simple and direct .
Another key is placement of compartmen t
boundaries in such a way that the cells ar e
easily uncoupled, or are coupled as a simpl e
linear cascade . To do otherwise would complicate
the modeling considerably. A hydrologic
model that consists of a series of compartments
arranged as a branching cascade is
extremely difficult to manage . Water flow
from an upper compartment must be some -
how divided between lower compartments in
the cascade. The basis for such division i s
generally obscure and usually arbitrary .
In our attempt to structure the hydrologi c
model for watershed 10 at the next level o f
resolution, we began by setting compartmen t
boundaries along stream courses . This automatically
decoupled the compartments, sinc e
water does not cross the channel (fig . 11) .
Next, it was necessary to consider the arrangement
of the plant communities within
Figure 11. Initial and secondary stratification of watershed 10, H . J. Andrews Experimental Forest, Oregon .
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