Problem

How can you model aquifers in SewerGEMS and CivilStorm using the SWMM solver?

How can you model the interaction between groundwater / water table and a perforated pipe?

Solution

With the SWMM Extensions, it is possible to model aquifer or groundwater flow in SewerGEMS and CivilStorm when using the SWMM solver. By going to Components > SWMM Extensions > Aquifer, you can apply the needed parameters for the aquifer.

For more information on these parameters, please refer to the SWMM hydrology sections of the SWMM 5 documentation, which has detailed information on these.

Once this is completed, go to the catchment properties and set "Apply Groundwater" to True and set the receiving node, which is the node that groundwater flow will drain too. Typically this is the same outflow node for the catchment. You will then select the aquifer from the pulldown menu. Once this is completed, you will need to assign some parameters that are used to derive the groundwater flow. The equation used for this is:

Qgw = A1*(Hgw - E)^B1 - A2*(Hsw - E)^B2 + A3*(Hgw*Hsw)

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).

There are also a number of coefficients with this: A1, A2, B1, B2, A3. If lateral 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. For more information on these, please refer to the SWMM 5 documentation.

Custom groundwater equation: Starting with CONNECT Edition Update 3, a custom groundwater equation can be applied. When "apply groundwater" is set to "true" in the catchment properties, you will see fields for "Apply custom deep flow equation" and "Apply custom groundwater lateral equation". See more in the help topic "SWMM hydrology"

For modeling a perforated pipe, you would need to determine the appropriate values for the above coefficients based on the perforated pipe's openings. If you are looking for a more detailed and comprehensive analysis of groundwater, OpenFlows FLOOD may be a suitable option.