In GeoSTORM, the combination of different infiltration methods with the EPA SWMM hydrology method changes the contents of the General Specifications data panel of the Subbasin Data dialog box. Understanding this behavior helps the user correctly define subbasin parameters. Refer to this article in our knowledge base to learn more about the EPA SWMM infiltration methods supported by GeoSTORM.
Follow the steps below to define subbasin data while selecting different infiltration methods along with the EPA SWMM hydrology method:
- From the Input ribbon menu, click the Scenario Manager dropdown menu and select the Scenario Manager command.
Alternatively, the user can click the Scenario Manager icon to open the Scenario Manager dialog box.
- The Scenario Manager dialog box will be displayed.
- Now, from the EPA SWMM infiltration method dropdown combo box, select an infiltration method.
Note: The EPA SWMM infiltration method dropdown combo box will only be enabled when EPA SWMM is selected as the Hydrology analysis engine. Otherwise, this dropdown box will be displayed as disabled.
The following sections explain how the General Specifications data panel of the Subbasin Data dialog box changes based on the type of infiltration method selected for the EPA SWMM hydrology method.
Infiltration Method – Green Ampt
The following General Specifications data panel is displayed when the Green Ampt infiltration method is selected in the Scenario Manager dialog box.
General Specifications
This section allows the user to define the general parameters of the defined subbasin.
The following parameters are available in this section.
- Drainage area
This entry field defines the area of the selected subbasin. The user can click the […] button to measure the subbasin area from the Map View. Clicking the [Recalc] button will cause the software to recalculate the area of the digitized subbasin. Similarly, the [Recalc All] button will cause the software to recalculate the area of all the digitized subbasins.
- Downstream connection
This read-only entry field defines the downstream element that the selected subbasin drains to. The user can click the […] button to select the subbasin downstream connection from the Map View.
The following elements can be selected:
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- Manhole
- Routing Junction
- Storage Area
- Subbasin (only when using EPA SWMM hydrology)
- Terminal Outfall
The user can click the [Clear] button to remove the downstream element connection.
- Soil capillary suction head
This entry field defines the average value of the soil capillary suction along the wetting front. Clicking the […] button will display the Soil Properties dialog box, as shown below.
- Soil hydraulic conductivity
This entry field defines the soil-saturated hydraulic conductivity. Clicking the […] button will display the Soil Saturated Hydraulic Conductivity dialog box, as shown below.
- Soil initial deficit
This entry field defines the difference between soil porosity and initial moisture content. For completely drained soil, this is the difference between the soil porosity and field capacity. Clicking the […] button will display the Soil Properties lookup table dialog box as shown below.
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TOC equivalent width
This entry field defines the equivalent width used to calculate the rectangular runoff plane dimensions that are used in the kinematic wave Time of Concentration (TOC) computations for sheet flow and shallow concentrated flow.
The user can click the [Calc] button to compute the TOC equivalent width for the current subbasin by computing the contributing drainage areas on both sides of the longest flow path bisecting the subbasin. Similarly, the user can click the [Calc All] button to compute the TOC equivalent width for all subbasins.
Note: The user can compute this value automatically using the Compute TOC Widths command. Refer to this article in our knowledge base to learn more about this command.
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TOC average slope
This entry field defines the average slope of the runoff plane used in the kinematic wave Time of Concentration (TOC) computations for sheet flow and shallow concentrated flow.
Note: The user can compute this value automatically using the Compute Slopes command. Refer to this article in our knowledge base to learn more about this command.
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Internal routing
This dropdown combo box defines how runoff from the impervious and pervious subareas contained within the subbasin is internally routed.
The following internal routing options are provided:
- Direct to Outlet
- Impervious to Pervious
- Pervious to Impervious
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Internal runoff routed
This spin control entry field defines the percentage of subarea runoff that flows from impervious to pervious (or pervious to impervious).
Note: This entry becomes a read-only field and displays a value of 100% when the Direct to Outlet option is selected in the Internal routing dropdown combo box.
Impervious Subarea Parameters
This section allows the user to define the impervious area parameters of the defined subbasin.
The following parameters are provided in this section:
- Impervious surface area
This spin control entry field defines the percentage of the subbasin area that is impervious (i.e., roadways, sidewalks, driveways, roofs, etc.).
- No depression surface area
This spin control entry field defines the percentage of the impervious surface area that has no depression storage.
- Average depression depth
This entry field defines the average depth of depression storage for the impervious portions of the subbasin (i.e., roadways, sidewalks, parking, roofs, etc.). Clicking the […] button will display the Average Depression Depth lookup table dialog box, as shown below.
- Impervious area Manning’s
This entry field defines Manning’s roughness coefficient for overland flow over the impervious portion of the subbasin (i.e., roadways, sidewalks, parking, roofs, etc.) for very shallow flow depths. Clicking the […] button will display the Overland Flow Roughness lookup table dialog box, as shown below.
Pervious Subarea Parameters
This section allows the user to define the pervious area parameters of the defined subbasin.
The following parameters are provided in this section:
- Average depression depth
This entry field defines the average depth of depression storage for the pervious portions of the subbasin (i.e., grass, wooded, open space, etc.). Clicking the […] button will display the Average Depression Depth lookup table dialog box, as shown below.
- Pervious area Manning’s
This entry field defines Manning’s roughness coefficient for overland flow over the pervious portion of the subbasin (i.e., grass, wooded, open space, etc.) for very shallow flow depths (typically less than 1 inch). Clicking the […] button will display the Overland Flow Roughness lookup table dialog box, as shown below.
Computational Results
After successfully computing the analysis, this section provides a summary of the computational results for the defined subbasin.
The following results are provided in this section:
- Peak runoff rate
This read-only field displays the peak runoff rate that occurred from the defined subbasin during the storm event. Another read-only field, adjacent to the Peak runoff rate read-only field, displays the date and time at which the peak runoff occurred from the defined subbasin during the storm event.
- Total precipitation
This read-only field displays the total precipitation that falls onto the defined subbasin during the storm event.
- Total losses
This read-only field displays the total losses (i.e., infiltration, depression, etc.) for the defined subbasin during the storm event.
- Total runoff
This read-only field displays the total runoff for the defined subbasin during the storm event.
Infiltration Method – Horton
The following General Specifications data panel is displayed when the Horton infiltration method is selected in the Scenario Manager dialog box.
General Specifications
This section allows the user to define the general parameters of the defined subbasin.
The following parameters are available in this section:
- Drainage area
This entry field is similar to the Drainage area entry field available in the General Specifications section for the Green Ampt infiltration method.
- Downstream connection
This entry field is similar to the Downstream connection entry field available in the General Specifications section for the Green Ampt infiltration method.
- Maximum infiltration rate
This entry field defines the maximum infiltration rate on the Horton curve. Clicking the […] button will display a Maximum Infiltration Rates lookup table dialog box, as shown below.
- Minimum infiltration rate
This entry field defines the minimum infiltration rate on the Horton curve, which is equal to the soil hydraulic conductivity. Clicking the […] button will display a Soil Saturated Hydraulic Conductivity lookup table dialog box as shown below.
- Horton decay constant
This entry field defines the infiltration rate decay constant for the Horton curve. Typical Horton decay constants range between 2 and 7.
- Maximum infiltration volume
This entry field defines the maximum infiltration volume. Clicking the […] button will display a Soil Properties lookup table dialog box.
- Saturated soil drying time
This entry field defines the number of days required for fully saturated soil to dry. Typical values range between 2 to 14 days, depending on soil type and climate-related factors.
- TOC equivalent width
This entry field is similar to the TOC equivalent width entry field available in the General Specifications section for the Green Ampt infiltration method.
- TOC average slope
This entry field is similar to the TOC average slope entry field available in the General Specifications section for the Green Ampt infiltration method.
- Internal routing
This entry field is similar to the Internal routing entry field available in the General Specifications section for the Green Ampt infiltration method.
- Internal runoff routed
This entry field is similar to the Internal runoff routed entry field available in the General Specifications section for the Green Ampt infiltration method.
Impervious Subarea Parameters
This section is similar to the Impervious Subarea Parameters section available in the General Specifications data panel for the Green Ampt infiltration method. Refer to the Impervious Subarea Parameters section as explained above.
Pervious Subarea Parameters
This section is similar to the Pervious Subarea Parameters section available in the General Specifications data panel for the Green Ampt infiltration method. Refer to the Pervious Subarea Parameters section as explained above.
Computational Results
This section is similar to the Computational Results section available in the General Specifications data panel for the Green Ampt infiltration method. Refer to the Computational Results section as explained above.
Infiltration Method – Modified Green Ampt
The following General Specifications data panel is displayed when the Modified Green Ampt infiltration method is selected in the Scenario Manager dialog box.
Note: The contents of the General Specifications data panel for the Modified Green Ampt infiltration method are similar to those for the Green Ampt infiltration method. Refer to the General Specifications section of the Green Ampt infiltration method.
Infiltration Method – Modified Horton
The following General Specifications data panel is displayed when the Modified Horton infiltration method is selected in the Scenario Manager dialog box.
Note: The contents of the General Specifications data panel for the Modified Horton infiltration method are similar to those for the Horton infiltration method. Refer to the General Specifications section of the Horton infiltration method.
Infiltration Method – SCS Curve Number
The following General Specifications data panel is displayed when the SCS Curve Number infiltration method is selected in the Scenario Manager dialog box.
General Specifications
This section allows the user to define the general parameters of the defined subbasin.
The following parameters are available in this section:
- Drainage area
This entry field is similar to the Drainage area entry field available in the General Specifications section for the Green Ampt infiltration method.
- Downstream connection
This entry field is similar to the Downstream connection entry field available in the General Specifications section for the Green Ampt infiltration method.
- Curve number
This entry field defines the curve number for the defined subbasin. Clicking the […] button will display a SCS Curve Number lookup table dialog box as shown below.
- Saturated soil drying time
This entry field is similar to the Saturated soil drying time entry field available in the General Specifications section for the Horton infiltration method.
- TOC equivalent width
This entry field is similar to the TOC equivalent width entry field available in the General Specifications section for the Green Ampt infiltration method.
- TOC average slope
This entry field is similar to the TOC average slope entry field available in the General Specifications section for the Green Ampt infiltration method.
- Internal routing
This entry field is similar to the Internal routing entry field available in the General Specifications section for the Green Ampt infiltration method.
- Internal runoff routed
This entry field is similar to the Internal runoff routed entry field available in the General Specifications section for the Green Ampt infiltration method.
Impervious Subarea Parameters
This section is similar to the Impervious Subarea Parameters section in the General Specifications data panel for the Green Ampt infiltration method. Refer to the Impervious Subarea Parameters section for the Green Ampt infiltration method.
Pervious Subarea Parameters
This section allows the user to define the pervious area parameters of the defined subbasin.
This section is similar to the Pervious Subarea Parameters section displayed in the General Specifications data panel for the Green Ampt infiltration method. Refer to the Pervious Subarea Parameters section for the Green Ampt infiltration method.
Computational Results
After successfully computing the analysis, this section provides a summary of the computational results for the defined subbasin.
This section is similar to the Computational Results section in the General Specifications data panel for the Green Ampt infiltration method. Refer to the Computational Results section for the Green Ampt infiltration method.