Water Statistics

For a probabilistic analysis you can define the following water pressure parameters as random variables in the Water Pressure Options dialog:

• Percent fill (percent fill option)
• Pressure head (phreatic surface option)

To define a water pressure random variable:

• In the Water Pressure Options dialog select the Quick-Stats button located beside the percent fill option or the phreatic surface option, choose a distribution, and enter the standard deviation, relative minimum and relative maximum.

Percent Fill Random Variable

If you are using the percent fill option, the random variable is simply the value of percent fill.

Phreatic Surface / Pressure Head Random Variable

For a Phreatic Surface the Random Variable (Change in Pressure Head) that you are defining is the Pressure Head DIFFERENTIAL, relative to the graphical location of the Phreatic Surface boundary on the model. It is NOT the absolute value of the Pressure Head. During the Probabilistic Analysis, the value of the Pressure Head random variable is added to the y-coordinate of each vertex of the Phreatic Surface. In this way, the entire Phreatic Surface is moved up (or down), according to the randomly sampled value of the Pressure Head differential.

NOTE: the Mean Value of the Pressure Head random variable is equal to ZERO. The Random Variable that you are defining is the Pressure Head DIFFERENTIAL, relative to the location of the phreatic surface.

See the Random Variables and Statistical Distributions topic for further information.