Cress Help - Ground water flow - Complete tailwater - B26.2

Long parallel channels

This calculation rule calculates the groundwater levels or hydraulic heads of some basic situations in areas with confined and unconfined aquifers and with phreatic water. The theory behind these calculation examples is also examined, by means of which complex situations can be manually calculated. Darcy’s law can also be shown and it is possible to use them to make a calculation. The WATEX and MODUFLOW computer programs can also be used to calculate groundwater flow.

Confined aquifer (complete tailwater)

    equation 1

The general differential equation for flow in two directions is:

    equation 2

in which :

f: local hydraulic head [m]

Long parallel channels:

    figure 1

The flow parallel to the channel can be neglected. The differential equation now becomes:

    equation 3

The general solution is:

    equation 4

The boundary conditions for this are:

    equation 5

The solution is then:

    equation 6

in which:

  • H1 en H2: water levels in the two channels [m]
  • L: length of the strip of soil [m]
  • x: distance from edge [m]
  • fx: remote hydrostatic head
  • x [m] Note.

The line does not show the groundwater level (which runs to the underside of the clay layer), but the line of the hydraulic head. In a piezometric gauge though the clay layer the water would rise to fx .