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Garden with Insight v1.0 Help: Soil params water group

Time for sub-surface water to flow from watershed edge to center: The number of days it takes water lost from the soil patch from lateral (horizontal) subsurface flow to return based on some other topographical feature of the watershed the soil patch is in. Ranges from 0 to 2000; a reasonable estimate is 10 days.

Furrow dike fraction of volume available for water storage: This parameter reduces the volume between furrow dikes that is available to store water to simulate limits on furrow dike effectiveness.

Water table minimum depth: The minimum depth below the soil surface to which the water table can rise. Ranges from 0 to 200 meters.

WTMN - Minimum depth to water table (1) * (m) 

In areas where the water table enters the root zone, the minimum water table depths from the surface are input. EPIC simulates water table fluctuation between WTMN and WTMX according to 30-day accumulations of rainfall and potential evaporation.

Water table maximum depth: The maximum depth below the soil surface to which the water table can fall. Ranges from 0 to 300 meters.

Fraction of wilting point to which plants can pull water out of top 0.5m of soil: In the top half-meter of soil, plant roots can pull more water from the soil than below, mostly because their root mass is greater. This parameter determines how much plants can pull water out of the topmost soil as a fraction of wilting point.

Parameter for rainfall in time of concentration: Affects the proportion of rain in one rainfall event (storm) that falls during the time of concentration (when it is raining the hardest). Ranges from zero to about two; the higher this number, the harder it rains (and the greater the erosion).

Method for estimating peak runoff rate: The method used to calculate the peak rate at which water runs off the soil surface during a rainstorm. The modified rational equation and the SCS TR-55 method are slightly different. Within the SCS method the four sub-types use different parameters.

Adjustment factor for peak runoff rate: This parameter is not used in this version of the simulation.

Method for estimating potential evaporation: The method used to calculate the potential amount of soil evaporation before considering snow, vegetation cover and plant transpiration.
S Curve - effect of soil depth on soil evaporation: Proportion of total potential soil evaporation (Y) coming out of the soil down to and including a given depth (X). For example, 50% of all soil evaporation might occur down to a depth of 10 mm, and 95% of all soil evaporation might occur down to 100 mm.

S curve shape: Soil evaporation - depth. 

Soil evaporation - depth. The number to the left of the decimal is depth (mm), and the number to the right of the decimal is fraction of soil evaporation between soil surface and specified depth.

S Curve - effect of rainfall amount on degree of soil settling: The proportion by which the soil settles (the soil bulk density moves closer to the settled bulk density) (Y) for a given amount of rainfall (X). The amount of rainfall used here is adjusted by runoff, soil depth, and soil texture for each soil layer.
S curve shape: Soil settling - rainfall. 

Soil settling - rainfall. The number to the left of the decimal is rainfall-runoff adjusted for soil texture and depth (mm), and the number to the right of the decimal is soil settling fraction caused by rainfall.

Vary curve numbers randomly: If yes, generate daily curve number parameter for rainfall runoff equation from triangular distribution around average curve number. Simulates daily variation in curve number. If no, use same average curve number every day.

Average SCS II curve number for runoff (not adjusted for slope): Parameter for average SCS curve number used to calculate runoff before adjustment for slope. Ranges from 30 to 95; lower means better water retention capacity. Average curve number used daily is derived from this parameter by adjusting for soil slope.

CN2 - Runoff curve number 

The runoff curve number is the SCS antecedent moisture condition 2
curve number. Table II.1 is the SCS table used in estimating CN2.
Land Use Hydrologic Group
Crop Cover Cond. ---A--- ---B--- ---C--- ---D---*
Fallow Straight Row ---- [ 77.0][ 86.0][ 91.0][ 94.0]

Row crops Straight Row Poor [ 72.0][ 81.0][ 88.0][ 91.0]
" " Good [ 67.0][ 78.0][ 85.0][ 89.0]
Contoured Poor [ 70.0][ 79.0][ 84.0][ 88.0]
" Good [ 65.0][ 65.0][ 82.0][ 86.0]
Cont. and Terraced Poor [ 66.0][ 74.0][ 80.0][ 82.0]
" " " Good [ 62.0][ 71.0][ 78.0][ 81.0]

Small grain Straight Row Poor [ 65.0][ 76.0][ 84.0][ 88.0]
" " Good [ 63.0][ 75.0][ 83.0][ 87.0]
Contoured Poor [ 63.0][ 74.0][ 82.0][ 85.0]
" Good [ 61.0][ 73.0][ 81.0][ 84.0]
Cont. and Terraced Poor [ 61.0][ 72.0][ 79.0][ 82.0]
" " " Good [ 59.0][ 70.0][ 78.0][ 81.0]

Close-seeded Str.Row. Poor [ 66.0][ 77.0][ 85.0][ 89.0]
legumes* or " " Good [ 58.0][ 72.0][ 81.0][ 85.0]
rotation Contoured Poor [ 64.0][ 75.0][ 83.0][ 85.0]
meadow " Good [ 55.0][ 69.0][ 78.0][ 83.0]
Cont. and Terrace Poor [ 63.0][ 73.0][ 80.0][ 83.0]
" " " Good [ 51.0][ 67.0][ 76.0][ 80.0]
* close-drilled or broadcast

Pasture or range Poor [ 68.0][ 79.0][ 86.0][ 89.0]
Fair [ 49.0][ 69.0][ 79.0][ 84.0]
Good [ 39.0][ 61.0][ 74.0][ 80.0]
Contoured Poor [ 47.0][ 67.0][ 81.0][ 88.0]
" Fair [ 25.0][ 59.0][ 75.0][ 83.0]
" Good [ 6.0][ 35.0][ 70.0][ 79.0]

Meadow Good [ 30.0][ 58.0][ 71.0][ 78.0]

Woods Poor [ 45.0][ 66.0][ 77.0][ 83.0]
Fair [ 36.0][ 60.0][ 73.0][ 79.0]
Good [ 25.0][ 55.0][ 70.0][ 77.0]

Farmsteads ---- [ 59.0][ 74.0][ 82.0][ 86.0]

Roads(dirt)** ---- [ 72.0][ 82.0][ 87.0][ 89.0]
Roads(hard surface)** ---- [ 74.0][ 84.0][ 90.0][ 92.0]
**including right-of-way
See table II.1.b and II.1.c. for other hydrologic soil-cover complexes.
* A. (Low runoff potential). Soils having high infiltration rates even
when thoroughly wetted and consisting chiefly of deep, well to
excessively drained sands or gravels. These soils have a high
rate of water transmission.
B. Soils having moderate infiltration rates when thoroughly wetted and
consisting chiefly of moderately deep to deep, moderately well to
well drained soils with moderately fine to moderately coarse
textures. These soils have a moderate rate of water transmission.
C. Soils having slow infiltration rates when thoroughly wetted and
consisting chiefly of soils with a layer that impedes downward
movement of water, or soils with moderately fine to fine texture.
These soils have a slow rate of water transmission.
D. (High runoff potential). Soils having very slow infiltration rates
when thoroughly wetted and consisting chiefly of clay soils with a
high swelling potential, soils with a permanent high water table,
soils with a claypan or clay layer at or near the surface, and
shallow soils over nearly impervious material. These soils have a
very slow rate of water transmission.

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Updated: May 4, 1998. Questions/comments on site to
Copyright © 1998 Paul D. Fernhout & Cynthia F. Kurtz.