Models in Irrigation andWater Management - Practices of Irrigation and On-farm Water Management - page 400

are closed. Matrix infiltration and crack infiltration at a given rainfall intensity is
calculated as follows (Oostindie and Branswijk, 1992 ) :

P < I max : I = A m × P

A c P I c =

P > I max : I = A m × I max

(10.24)

A m ( P I c.1 = − I max )

A c P I c.2 =

I c = I c.1 + I c.2

In which

P Rainfall intensity (m/s)

I max =

=

maximum infiltration rate (m/s)

I Infiltration rate in soil matrix (m/s)

I c =

=

Infiltration rate in crack (m/s)
A m , A c =

Relative areas of soil matrix and cracks respectively

I c.1 = The part of total crack infiltration caused by rainfall intensity exceeding

maximum infiltration rate (m/s)
I c.2 = The part of total crack infiltration caused by rain falling directly into the

crack (m/s)

Defined in this way, all infiltration rates are based on total surface area.

Conductivity

To enable the analytical solution of the Darcy equation, the K ( h ) relation is
expressed by an exponential relation. One k ( h ) relation is described by three
different exponential k ( h ) sections, as for many soils an exponential k ( h ) relation is
valid only for a narrow range of pressure heads. Each line segment is described by

k 0 e ah

k ( h ) = (10.25)

In which,

k = calculated hydraulic conductivity (cm/d)

α = gradient

h pressure head (cm)

k 0 =

=

saturated hydraulic conductivity (cm/d)

The pressure heads that each line covers are specified. That is, the model input is the
intersection of the first and second line segment and the intersection of the second
and third line segment.