Agriculture Reference
In-Depth Information
10.3.2 Model for Upward Flux Estimation
10.3.2.1 Model UPFLOW
UPFLOW is a software tool developed to estimate the expected upward flow
from a shallow water table in a given soil profile and to evaluate the effects of
environmental conditions on the upward flow (Raes, 2002 ; Raes and Deproost,
2003 ) .
The input in the UPFLOWmodel are average evapotranspiration (ET) during the
time period, expected mean soil water content, average depth of water table (WT)
below the soil surface, crop type, the characteristics of the various layers of the soil
profile and their thickness, and the salt content of the groundwater (if groundwater
contains salts).
For the given environmental conditions, UPFLOW displays the expected steady
upward flow [mm/day] from the water table to the topsoil, the soil water content
[vol%] expected in the topsoil, the amount of salt transported upward during the
given period [t/ha-year, if the water table contains salts,], the degree of water logging
[%] in the root zone (if any), and a graphical display of the soil water profile above
the water table.
In the model, the steady upward flow to the topsoil is estimated according to De
Laat ( 1980 , 1995 ) :
h
K ( h )
z
=
K ( h ) d h
(10.20)
q
+
0
where z (m) is the vertical co-ordinate, q the constant upward flux (m 3 /m 2 /d) of
water, h the soil matric potential per unit weight of water (m), and K ( h ) the hydraulic
conductivity (m/d).
Given the K - h and
-h relation for the various soil layers of the profile above
the water table, UPFLOW is able to determine the maximum flux that can flow
to the top soil by checking that the simulated soil water content (derived from the
moisture profile) remains below the specified mean water content in the top soil.
UPFLOW calculates the amount of water that the plant roots extract according to
Feddes et al. ( 1978 ) . Since the water flow inside the soil profile is assumed to be
steady, the capillary rise from the water table to the topsoil can never exceeds the
ET demand of the atmosphere. Mean soil evaporation or crop evapotranspiration for
a given period from climate, soil, and crop parameters are calculated in the model
according to Allen et al. ( 1998 ) .
θ
10.3.3 Model for Flow Estimation in Cracking Clay Soil
In clay soils swelling and shrinkage have important consequences for water trans-
port. Several models have been developed to simulate water transport in clay
soils.
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