be set to one because PCT_1 represents the aerial fraction of zone 1 in the watershed (see Inputs for
GROFF1). To simulate a watershed with impervious areas and one soil type, set NZONE to two. If
NZONE equals two, the sum of PCT_1 and PCT_2 (the aerial fraction of zone 2 in the watershed, see
Inputs for GROFF2) should equal one. To simulate a watershed with impervious areas and two soil
types, set NZONE to three. If NZONE equals three, the sum of PCT_1, PCT_2, PCT_3, the aerial
fraction of zone 3 in the watershed (see Inputs of GROFF4) should equal one.
RAINs (mm of water), rainfall on the watershed, is programmed differently than the other input
parameters in that it contains a graphical function. RAINs should be programmed with hourly rain-
fall data. Instructions for programming graphical functions are located at the end of Data Inputs
Sector.
Inputs for SNOMLT
"A" (1/C) and "B"(h) are the compaction coefficients for the snowpack. Schroeter (1989) uses
values of 0.1 and 96 for A and B respectively. A sensitivity analysis of the liquid water released from
the snowpack (LIQ_WTR_REL, the main output from the SNOMLT sector) showed that Object-
GAWSER is almost completely insensitive to changes in the values of A and B.
INIT_LWC (mm of water) is the initial liquid water content of the snowpack. If a sufficient period
of below-freezing air temperatures precedes the simulation period, the snowpack is assumed to be
completely frozen and this parameter should be set to zero. Otherwise, INIT_LWC can be set to a
value that is greater than zero (Schroeter 1989).
ISDEP (mm of depth) is the initial snowpack depth. This value represents the average depth of the
snowpack in the entire watershed. This parameter only needs to be programmed if the watershed is
partly or completely covered by snow, because snow-free conditions are modeled by setting BARE
(from the "GENERAL INPUTS" box) equal to one (when BARE is equal to one, the parameters in
the SNOMLT sector are ignored by Object-GAWSER).
ISWC (mm of water) is the initial solid water content of the snowpack. Like ISDEP, this pa-
rameter only needs to be programmed if the watershed is partly or completely covered by snow.
MRHO (vol/vol) is the maximum dry density of the snowpack. MRHO usually occurs between
0.35 and 0.45 (Chard 1983, Schroeter 1988).
NEWDEN (vol/vol) is the relative density of newly fallen snow. NEWDEN occurs between 0.02
and 0.15, but usually occurs at a density of 0.1 (Schroeter 1989).
SNOWs (mm of depth) is the fluffy new snow that lands on the existing snowpack. SNOWs
should be programmed with hourly snowfall data. SNOWs is programmed similarly to RAINs from
the "GENERAL INPUTS" box because it is also programmed using a graphical function.
SWI (decimal) is the maximum fraction of pore space in the snowpack available to store liquid
water. SWI is commonly found to be 0.07 (Chard 1983).
TEMPs (C) is the air temperature and is programmed like RAINs in the "GENERAL INPUTS"
box. TEMPs should be programmed with hourly temperature data.
Inputs for GROFF1
DS_IMPs (mm) is the maximum depth of depression storage for impervious areas. To simulate
ponding in large impervious areas like parking lots, set DS_IMPs to 0.5 (Schroeter 1989). If no
ponding occurs on the impervious areas, set DS_IMPs to zero.
INIT_IMP_STOR (mm) is the initial amount of water in depression storage on impervious sur-
faces. To simulate a dry impervious surface, set INIT_IMP_STOR to zero. To simulate an impervi-
ous surface whose depression storage is completely filled with water, set INIT_IMP_STOR equal to
DS_IMPs. To simulate a pervious surface in which depression storage is partially filled, assign
INIT_IMP_STOR a value between zero and the value of DS_IMPs. If INIT_IMP_STOR is greater
than DS_IMPs, Object-GAWSER will convert the amount by which INIT_IMP_STOR exceeds
DS_IMPs to runoff.
PCT_1 (decimal) is the aerial fraction of zone 1 in the watershed. Remember, zone 1 is the imper-
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