Groundwater Flow Equation Editor (SWMM)

This editor is displayed when the button is selected from either the Lateral groundwater flow equation or the Deep groundwater flow equation field in a subcatchment's properties.

It is used to define either a custom:

• lateral groundwater flow equation - which is used to calculate the groundwater flow between the saturated sub-surface zone of a subcatchment and its associated aquifer node
• deep groundwater flow equation - which is used to calculate the groundwater flow between the saturated sub-surface zone of a subcatchment and its associated aquifer

An example of a lateral groundwater flow equation specified in the editor is shown below.

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In this example, a step function is specified to ensure that flow only occurs when the groundwater level is above a threshold of 5.

If no equation is specified in the editor, the standard lateral or deep groundwater flow equation is used by ICM.

 

The editor consists of the following items:

• A pane in which you can specify a new or edit an existing custom equation.

  The following symbols and mathematical functions can be used in a lateral or deep groundwater flow equation:

• Hgw - the height of the groundwater table relative to the aquifer's bottom elevation
• Hsw - the height of the surface water relative to the aquifer's bottom elevation
• Hcb - the height of the channel bottom relative to the aquifer's bottom elevation
• Hgs - the height of the ground surface relative to the aquifer's bottom elevation
• Phi - the porosity of the subsurface soil
• Theta - the moisture content of the upper unsaturated zone
• Ks - the saturated hydraulic conductivity
• K - the hydraulic conductivity at the current moisture content
• Fi - the infiltration rate from the ground surface
• Fu - the percolation rate from the upper unsaturated zone
• A - subcatchment area
• abs(x) - the absolute value of x
• sgn(x) - which is +1 for x >= 0 or -1 otherwise
• step(x) which is 0 for x <= 0 and 1 otherwise
• sqrt(x) - the square root of x
• log(x) - logarithm base e of x
• log10(x) - logarithm base 10 of x
• exp(x) - e raised to the x power
• The standard trig functions (sin, cos, tan, and cot)
• The inverse trig functions (asin, acos, atan, and acot)
• The hyperbolic trig functions (sinh, cosh, tanh, and coth)
• Standard operators, +, -, *, /, ^ (for exponentiation)
• Any level of nested parentheses
• An OK button, which saves any changes and closes the editor.
• A Close button, which discards any changes and closes the editor.