vious portion of the watershed and is simulated entirely by GROFF1. Highly developed watersheds
are simulated by setting PCT_1 close to one. Undeveloped watersheds are simulated by setting
PCT_1 close to zero. Because all watersheds contain streams, PCT_1 should not be set to zero
because Object-GAWSER characterizes stream beds as impervious surfaces. Make sure that the sum
of PCT_1, PCT_2 (from GROFF2), and PCT_3 (from GROFF4) equals one.
Inputs for GROFF2
Before the inputs for GROFF2 are discussed, please recall that GROFF2 and GROFF3 are used to
simulate zone 2 which consists of one soil type. Please also recall that GROFF2 simulates that water
from zone 2 that goes to subsurface storage and that GROFF3 simulates that water from zone 2 that
goes to groundwater storage. Therefore, GROFF2 and GROFF3 share those inputs which represent
the soil characteristics of zone 2 except those inputs that determine whether the water from the
bottom soil layer goes to subsurface or groundwater storage. Therefore, GROFF3 uses the value of
every input parameter for GROFF2 except FATR and H_II.
CSs (mm/h) is the maximum seepage rate for zone 2. Values for CSs can be derived from field
measurements or from the literature (Mein and Larson 1973, Ghate and Whiteley 1982, Haan et al.
1982, Schroeter 1989). Relatively large values for CSs should be used to simulate relatively quick
seepage of water from the top to the bottom soil layer and vice versa.
Ds (mm/h) is the maximum percolation rate for zone 2. Values for Ds can be derived from field
measurements or from the literature (Mein and Larson 1973, Haan et al. 1982, Ghate and Whiteley
1982, Schroeter 1989). Relatively large values for Ds should be used to simulate relatively quick
percolation of water from the bottom soil layer into subsurface and groundwater storage and vice
versa.
DSs (mm) is the maximum depth of depression storage on the soil surface for zone 2. DSs should
have a relatively large value to minimize runoff and maximize subsurface flow and baseflow. DSs
should have a relatively small value to maximize runoff and minimize subsurface flow and baseflow.
FATR (decimal) is the percentage of zone 2 simulated by GROFF2. This parameter determines
the amount of water in zone 2 that will percolate into subsurface storage. To route all water from zone
2 to subsurface storage, set FATR to one. To prevent any water from entering subsurface storage, set
FATR to zero. Please note that the sum of FATR and FATR_2 (from GROFF3) does not have to equal
one.
FCAP_I (mm) is the field capacity soil water content for the top layer of soil for zone 2. Relatively
high values of FCAP_I will simulate soils capable of storing larger amounts of water and vice versa.
For Object-GAWSER to accurately simulate gravity drainage of water, FCAP_I must be less than
SMC_I (saturated moisture content of the soil, which is discussed later in this section).
H_I (mm) is the thickness of the top soil layer in zone 2. To simulate a thick upper soil layer with
a large amount of soil water storage, assign H_I a relatively large value. To simulate a thin upper soil
layer with a small amount of soil water storage, assign H_I a relatively small value.
H_II (mm) is the thickness of the bottom soil layer for the portion of zone 2 simulated by
GROFF2. Because GROFF2 simulates the flow of water to subsurface storage, H_II should be as-
signed a relatively small thickness. If GROFF2 simulated the flow of water to groundwater storage
(like GROFF3 and GROFF5), H_II would be assigned a relatively large thickness. Therefore, the
value of H_II includes an implicit third layer of subsurface storage.
IMC_Is (vol/vol) is the initial moisture content for the top layer of soil in zone 2. To simulate a top
layer of soil that is saturated, set IMC_Is equal to the saturated moisture content of the upper soil
layer (SMC_I, which is discussed later in this section). To simulate a top soil layer that is dry, set
IMC_Is is equal to the wilting point of the upper soil layer (WILT_I , which is discussed later in this
section). Do not assign IMC_Is a value greater than SMC_I or less than WILT_I.
IMC_IIs (vol/vol) is the initial moisture content for the bottom soil layer in zone 2. To simulate a
bottom soil layer that is saturated, set IMC_IIs equal to the saturated moisture content of the bottom
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