TMC (h) is the main channel travel time or the average amount of time for a molecule of water to
travel down the main channel of a watershed.
TOC (h) is the off-channel travel time or the average amount of time for a molecule of water to
travel down the smaller side channels that run into the main channel.
Inputs for CHNLRTNG
K (h) is the linear reservoir lag from the Muskingum technique. Viessman et al. (1977) describes
how K is determined.
X (unitless) is the Muskingum wedge storage weighting coefficient. Viessman et al. (1977) also
describes how X is determined.
QB (m2/s) is initial baseflow in the watershed. In the absence of subsurface flow (when a rainfall
event has not occurred in the last few days), QB is equal to the initial discharge from the watershed
outlet. When subsurface flow is present, QB is equal to the initial discharge from the watershed
outlet minus subsurface flow.
QSS (m3/s) is the initial subsurface flow in the watershed. If the simulation period begins a few
days after a significant rainfall, set QSS to zero. If the simulation period begins after a significant
rainfall event, QSS is equal to the initial discharge from the watershed outlet minus QB.
EXAMPLE SIMULATIONS
Table 2. Description of the input para-
meters used to generate the three simu-
Now that you are familiar with the input parameters
lations.
of Object-GAWSER, the following simulations will
Input
Simulations
demonstrate some basic programming strategies. This
parameter Forested Agricultural Suburban
section will show how Object-GAWSER can be used to
DS_IMPs
0.00
0.00
0.50
simulate the behavior of a fictitious forested, agricul-
DSs
2.50
0.00
0.00
tural, and suburban watershed. The hydrologic behavior
DSs_2
7.50
5.00
2.50
among these three watersheds was varied by changing
KEFFs
4.00
2.00
1.00
KEFFs_2
12.00
6.00
3.00
the values of the input parameters that regulate depres-
PCT_1
0.05
0.10
0.20
sion storage, hydraulic conductivity, the amount of im-
PCT_2
0.35
0.25
0.40
pervious area, and the amount of pervious area in the
PCT_3
0.60
0.65
0.40
watershed. Table 2 shows these input parameters and
This table shows the values of eight input param-
their corresponding values for each simulation. Re-
eters for three different simulators.
member that DS_IMPs, DSs, and DSs_2 determine the
amount of depression storage for zones 1, 2, and 3, respectively. KEFFs and KEFFs_2 determine the
permeability of the soil in zones 2 and 3, respectively. PCT_1 determines the area of zone 1 (which
represents the amount of impervious area in the watershed), and PCT_2 and PCT_3 determine area
of zones 2 and 3 (which represent the amount of pervious area in the watershed). All other input
parameters are representative of a completely snow-covered watershed in southwestern Ontario in
early April (Schroeter 1989).
Forested watershed simulation
This watershed was assigned a large value of depression storage to account for the large amount
of depressions found in forest floors that have not been mechanically smoothed for development.
Please note that DS_IMPs (the depression storage for impervious surfaces) was assigned a value of
zero because this watershed was assumed not to contain large impervious surfaces (like large parking
lots) in which water ponds. The forested watershed was also assigned the largest values for hydraulic
conductivity because of the presence of extensive root systems that increase the permeability of
forest soils (Walt 1989, Schroeter 1995*). Finally, this watershed was assigned the least amount of
* Personal communication with H. Schroeter, Schroeter and Associates, 1995.
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