Abstract:
Mathematical models of hydrologic and agricultural systems require knowledge
of the relationships between soil moisture content (8), soil water pressure (h) and
unsaturated hydraulic conductivity (K). To model the retention and movement of
water and chemicals in the unsaturated zone, it is necessary to know the relationships
between soil water pressure, water content and hydraulic conductivity. It is often
convenient to represent these functions by means of relatively simple parametric
expressions. The problem of characterizing the soil hydraulic properties then reduces
to estimating parameters of the appropriate constitutive model. A number of models
for water retention function and unsaturated hydraulic conductivity are well reported
in literature, the most popular being van Genuchten model and Brooks-Corey model.
In general, the van Genuchten model matches experimental data more satisfactorily
than Brooks-Corey model. However, the functional form of van Genuchten model is
complicated and limits its usefulness for large number of analytical solutions available
for infiltration and drainage problems. On the other hand, Brooks-Corey model yields
conductivity and water retention functions that are easy to manipulate mathematically.
For this study, 27 soil samples were collected from various locations as well as
depths in different villages, namely Aurangabad, Kamalpur, Budhakhera, Gagalheri,
Dudhil Bukhara in the upstream part of Hindon river catchment and laboratory
investigations were carried out to determine bulk density and grain size distribution.
Using these data as input to the SOILPROP software, van Genuchten and BrooksCorey
parameters (a and n & hd and A.) were determined to derive the retention
characteristic and unsaturated hydraulic conductivity. The values of a and n (van
Genuchten parameters) were found to vary from 0.00004 to 0.00078 and 1.19 to
1.65 respectively. The values ofhd and A. (Brooks-Corey parameters) were found to vary from 860 to 20200 em and 0.189 to 0.538 respectively. These results (as necessary
input for unsaturated zone modelling) will be helpful for prediction of soil moisture
flow and groundwater recharge in the Hindon river catchment.