Soil hydraulic conductivity calculator using data measured in subsurface drainage systems.
Entirely free download of software


When in a subsurfafe drainage system measurements were made on drain discharge and level of the ground water table, the soil's hydraulic conductivity can be determined with the free HydrCond calculator.


The calculator program gives the possibility to find the conductivity above an below drain level.

For examples see this hydaulic conductivity chapter.


Screenprint of the HydrCond calculator model:

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               conductivity software image    
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MATHEMATICS

Parameters of a suburface drainage system:

    drainage system image

The Hooghoudt equation for groundwater flow to subsurface drains reads:
        Q = {8.Kb.d.(H-E) + 4.Ka.(H-E)^2} / S^2
where:
Q = drain discharge (m/day), Kb = hydraulic conductivity below drain level (m/day), Ka = hydraulic conductivity above drain level (m/day), d = the equivalent depth of the impermeable layer below drain level (m), H = height of the water table above drain level midway between the drains (m), E = height of the water table above drain level near the drain (m), S = drain spacing (m).

The equivalent depth d depends on the actual depth D, the drain radius R,and the drain spacing S. It can be calculated using the method described by W.H. van der Molen and J, Wesseling 1981. A solution in closed form and a series solution in Hooghoudt's drain spacing formula. In: Agricultural Water Management 52, pp 336 - 346.

Rewriting the quation as:
        Q.S^2/(H-E) = 8.Kb.d + 4.Ka.(H-E)
gives the opportinity to determine the values of 8.Kb.d and 4.Ka from a linear regression of Q.L^2/(H-E) on H-E, so that the values of Ka and Kd.d are found, while with the value of d, the Kb value can be determined,


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