level
cloud
converter
valve
connector
Figure 2. Basic STELLA II diagram.
Open circles are referred to as "converters" and function to convert inputs to outputs. The inputs may
be equations or logical statements (open circles) or numerical relationships (circles containing tildes).
Converters do not accumulate but change instantaneously over the simulation run.
A "cloud" represents sources or sinks. If an arrow points into the cloud it must be a sink. Conversely,
an arrow pointing away from a cloud implies that the cloud must be a source. [In Figure 2, the cloud
represents a source.]
Valves represent rates (differentials). The object is meant to symbolize a plumber's valve that opens
or closes depending on physical conditions. When the valve opens, water will `flow' from the cloud (the
source) into the level.
Solid arrows are referred to as "connectors" or information flows, and function to depict the causal
linkages among the objects (variables) in the model. Connectors have no numerical value.
The combination of a cloud, valve, and arrow is referred to as a "flow" (McKim et al. 1993,
Richmond and Peterson 1994).
Sector organization of Object-GAWSER
FRAIN
Object-GAWSER's concept of the watershed is
expressed using 12 interconnected compartments
RAINa
BARE NZONE LIQ WTR REL
called "sectors." A sector is a grouping of related
INIT IMPERV STOR
STELLA II objects that simulates the hydrologic
processes in a given part of a watershed (Fig. 3). The
RAIN
~
12 sectors are interconnected in that the output from
RI1
IMP EVAP
one sector can become the input to another sector.
Figure 3 is a sample Object-GAWSER sector. This
sector, called GROFF1, simulates storage and runoff
SURF1
in impervious areas.
The 12 sectors in Object-GAWSER are entitled
IMPERV STOR
the following:
SURF1w
SNOMLT (snowmelt)
DSa
GROFF1 (first generation of runoff sector)
SDEP
DSNOW
GROFF2 (second generation of runoff sector)
GROFF3 (third generation of runoff sector)
GROFF4 (fourth generation of runoff sector)
PCT 1
DS IMPs
FDS
EDAY
GROFF5 (fifth generation of runoff sector)
SBS_STOR_&_FLOW_1 (first subsurface stor- Figure 3. Example Object-GAWSER sector
in Object-GAWSER. The sector shown is
age and routing),
GROFF1 and contains the objects that cal-
GDWTR_STOR_&_BASFLW_1 (first ground-
culate the hydrology of impervious surfaces.
water storage and baseflow routing sector)
SBS_STOR_&_FLOW_2 (second subsurface
storage and routing sector),
GDWTR_STOR_& BASFLW_2 (second groundwater storage and baseflow routing sector)
SRFRNF (surface runoff routing), and CHNLRTNG (channel routing).
SNOMLT simulates the hydrology of the snowpack, which lies above the soil surface. SRFRNF
simulates the water that flows over the soil surface and through channels to the watershed outlet.
GROFF1 simulates the hydrology of impervious surfaces in the watershed (or zone 1). GROFF2,
GROFF3, GROFF4, and GROFF5 collectively represent the hydrology of pervious surfaces in the
3
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