#INFOSWMM

How to model Natural Groundwater (NG) interflow in InfoSWMM and InfoSWMM SA using the SWMM5 Engine


How to model Natural Groundwater (NG) interflow in InfoSWMM and InfoSWMM SA using the SWMM5 Engine

The Groundwater Editor dialog is used to specify the groundwater property of a Subcatchment. It is used to link a Subcatchment to both an aquifer and to a node of the drainage system that exchanges groundwater with the aquifer. It also specifies coefficients that determine the rate of groundwater flow between the aquifer and the node.

These coefficients (A1, A2, B1, B2, and A3) appear in the following equation that computes groundwater flow as a function of groundwater and surface water heads:

where

Qgw = groundwater flow (cfs per acre or cms per hectare)

Hgw = elevation of groundwater table (ft or m)

Hsw = elevation of surface water at receiving node (ft or m)

E = elevation of node invert (ft or m)

To initiate the Groundwater editor, do one of the following:

1. To edit Groundwater inputs for one Subcatchment at a time:

o Select Subcatchment, click on the icon located at the second row of the top of the attribute browser, and then select Groundwater from the initiated pop up menu. This will initiate the following editor.

Note: Once groundwater properties are specified, the user needs to click on the button to save the properties or on the or button to cancel the changes and close the editor.

2. To edit Groundwater inputs for multiple Subcatchments at a time:

· Select one of the group editing features (i.e., Group Editing on Selection () or Group Editing on Domain ()).

· On the initiated Group Editing dialog, click on . These steps would activate the Groundwater Editor shown below.

Note:

· Once groundwater properties are specified, the user needs to click on the button to save the properties, or on the or the buttons to cancel the changes, the button to close the editor.

· The button deletes groundwater data for the selected Subcatchments only. The button empties groundwater data for all Subcatchments, not just the selected ones, in the drainage system.

The properties listed in the editor are as follows:

Name Description
Aquifer Name Name of aquifer object that supplies groundwater. Leave this field blank if you want the Subcatchment not to generate any groundwater flow.
Receiving Node Name of node that receives groundwater from the aquifer.
Surface Elevation Elevation of ground surface for the Subcatchment that sits above the aquifer (ft or m).
Groundwater Flow Coefficient Value of A1 in the groundwater flow formula
Groundwater Flow Exponent Value of B1 in the groundwater flow formula.
Surface Water Flow Coefficient Value of A2 in the groundwater flow formula.
Surface Water Flow Exponent Value of B2 in the groundwater flow formula.
Surface-GW Interaction Coefficient Value of A3 in the groundwater flow formula.
Fixed Surface Water Depth Fixed depth of surface water at receiving node (ft or m) (set to zero if surface water depth will vary as computed by flow routing).
Threshold Groundwater Elevation The aquifer water table elevation which must be reached before any ground water flow occurs (feet or meters). The default setting when the field is left blank is the receiving node’s invert elevation.

Note

  • The values of the flow coefficients must be in units that are consistent with the groundwater flow units, which can either be cfs/acre for US units or cms/ha for metric units.
  • If groundwater flow is simply proportional to the difference in groundwater and surface water heads, then set the Groundwater and Surface Water Flow Exponents (B1 and B2) to 1.0, set the Groundwater Flow Coefficient (A1) to the proportionality factor, set the Surface Water Flow Coefficient (A2) to the same value as A1, and set the Interaction Coefficient (A3) to zero.

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