soil layer (SMC_II, which is described later in this section). To simulate a bottom soil layer that is
dry, set IMC_IIs equal to the wilting point of the bottom soil layer (WILT_II, which will be discussed
later in this section). Do not assign IMC_IIs a value greater than SMC_II or less than WILT_II.
KEFFs (mm/hr) is the effective hydraulic conductivity of the top soil layer in zone 2. High values
of KEFFs simulate high permeability soils and low values of KEFFs simulate low permeability soils.
Zone 2 can be changed to an impervious area (like zone 1) by setting KEFFs to zero.
PCT_2 (decimal) is the aerial fraction of zone 2 in the watershed. Set PCT_2 to one to model the
entire watershed with zone 2. Set PCT_2 to zero if zone 2 does not represent any part of the water-
shed. Finally, if zone 2 represents only part of the watershed, set PCT_2 to a value between zero and
one which represents the percentage of the watershed represented by zone 2. Make sure the sum of
PCT_1, PCT_2, and PCT_3 (from GROFF4) equals one.
SAVs (mm) is the average suction at the wetting front in the top soil layer of zone 2. Larger values
of SAVs are associated with larger amounts of infiltration into the top layer of soil and vice-versa.
SMC_I (vol/vol) is the saturated soil water content for the top layer of soil in zone 2. To simulate
a large storage capacity in the top layer of soil, assign SMC_I a relatively large value. To simulate a
small storage capacity in the upper soil layer, assign SMC_I a relatively small value.
SMC_II (vol/vol) is the saturated moisture content for the bottom soil layer in zone 2. To simulate
a large storage capacity in the bottom soil layer, assign SMC_II a relatively large value. To simulate
a small storage capacity in the bottom soil layer, assign SMC_II a relatively small value.
WILT_I (mm) is the wilting point for the top layer of soil in zone 2. WILT_I differs from SMC_II
in that relatively small values of WILT_I are used to simulate a large storage capacity in the top layer
of soil and relatively large values of WILT_I are used to simulate a small storage capacity in the top
layer of soil.
WILT_II (mm) is the wilting point soil-water content for the bottom soil layer in zone 2. Like
WILT_I, small values of WILT_II simulate large amounts of storage in the bottom soil layer and
large values of WILT_II simulate small amounts of storage in the bottom soil layer.
Inputs for GROFF3
GROFF3 contains less programmable objects than GROFF2 because GROFF3 uses the values of
all the input parameters from GROFF2 except FATR and H_II. Therefore, duplicates of the objects
representing the input parameters shared by GROFF2 and GROFF3 exist in GROFF3.
FATR_2 (decimal) is the percentage of zone 2 simulated by GROFF3. This parameter determines
the amount of water in zone 2 that will percolate into groundwater storage. To route all water from
zone 2 to groundwater storage, set FATR_2 to one. To prevent any water from zone 2 from entering
groundwater storage, set FATR_2 to zero. Please note that the sum of FATR and FATR_2 (from
GROFF3) does not have to equal one.
H_II_2 (mm) is the thickness of the bottom soil layer for the portion of zone 2 simulated by
GROFF3. Because GROFF3 simulates the flow of water to groundwater storage, H_II should be
assigned a relatively large thickness. Therefore, the value of H_II includes an implicit layer of
groundwater storage.
Inputs for GROFF4
Before discussing the inputs for GROFF4, please recall that GROFF4 and GROFF5 are used to
simulate zone 3, which consists of one soil type. Please also recall that GROFF4 simulates that water
from zone 3 that goes to subsurface storage and that GROFF5 simulates that water from zone 3 that
goes to groundwater storage. Therefore, GROFF4 and GROFF5 share those inputs which represent
the soil characteristics of zone 3 except those inputs that determine whether the water from the
bottom soil layer goes to subsurface or groundwater storage. Therefore, GROFF5 uses the value of
every input parameter for GROFF4 except FATR_3 and H_II_3.
CSs_2 (mm/h) is the maximum seepage rate for zone 3. Values for CSs_2 can be derived from
field measurements or from the literature (Mein and Larson 1973, Ghate and Whiteley 1982, Haan et
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