Model setup

GeoSWMM model for this tutorial can be prepared by incorporating continuous rainfall and evaporation records into the existing model stored in Tutorial_03.gdb. This geodatabase already contains the detention pond (Storage Unit SU1) and its associated control structures (three orifice Or1, Or2, Or3 and one weir Wr1). Figure 2.2 illustrates the model in GeoSWMM in ArcGIS Pro.

Both the Geodatabase and Model Object Panel contain network element information (e.g. rain gages, subcatchments, junction, conduits, orifices, weirs, storage units, and outfalls). Additionally, the model object panel provides access to non-spatial model components, including time series, treatment functions and transect data.

Before the models are simulated, provide (or check) the following input data.

Rain Gage Properties

A rain gage provides precipitation input to the GeoSWMM model. In this tutorial, rainfall for the study area is sourced from a designated rain gage. Continuous precipitation data can be supplied to GeoSWMM by referencing an external rainfall data file. The properties of the rain gage can be viewed and edited in the Property Editor, as illustrated in Figure 2.3. Note that the File Name field will vary depending on the location where the rainfall file has been saved on your computer. Additionally, the Station ID must match the station name specified within the rainfall data file to ensure correct linkage. See Outfall Properties for more information on the continuous rainfall data.

Climatology Editor Properties

In this tutorial, evaporation for the study area is defined using the Climatology settings in GeoSWMM. A continuous temperature record is provided via an External Climate File, as shown in the Temperature tab of the Climatology Editor (Figure 2.5). Note that the File Name entry in the Temperature tab will vary depending on the location where the climate file is saved on your computer. In the Evaporation tab, the Source of Evaporation Rate is set to “Use Climate File”, which instructs GeoSWMM to compute evaporation directly from the temperature data specified in the Temperature tab.

Subcatchment Properties

There are 16 subcatchments in the GeoSWMM model of Tutorial 09. Table 2.3 summarizes the physical properties of the drainage areas.

Table 2.3 : Subcatchment Properties

Junction Properties

Junctions represent the endpoints of conduits and the locations where multiple pipes converge within the drainage network. In this tutorial, the locations of all junctions are illustrated in Figure 2.1. A complete list of junctions along with their corresponding invert elevations is provided in Table 2.4.

Table 2.4 : Invert Elevation of Junctions

NB: Maximum Depth of all junctions is set to zero. This will allow GeoSWMM to set the depth of each junction as the distance from the junction’s invert to the top of the highest conduit connected to it. Thus, junction flooding will occur as soon as flow exceeds the channel capacity.

Outfall Properties

The entire study catchment ultimately drains to a FREE type outfall O1. It is connected to the dendritic conduit network, and acts as the outlet node for subcatchment W1. The invert elevation of this outfall is 320.00 ft.

To facilitate the proper design of orifice Or1, the drainage system is initially configured so that Conduit C23 is not directly connected to Storage Unit SU1. Instead, a temporary outfall is used as the outlet for C23. Once the orifice design is finalized, the temporary outfall will be removed, and Storage Unit SU1 will be assigned as the new outlet of C23, thereby establishing full hydraulic connectivity within the model.

Conduit Properties

Figure 2.1 shows the layout of the runoff conveyance network for the study area. In this tutorial, the conduit sizes are designed to prevent flooding under expected flow conditions. A total of 24 conduits have been modeled in this Tutorial, among which two are natural channels with irregular cross section and the remaining 22 conduits have circular cross section. The physical properties of all the conduits are listed in the following Table 2.5.

Table 2.5 : Conduit Properties

NB:

• Maximum Depth represents the vertical distance of the top width level from the invert in the cross section for an irregular channel. For a circular pipe, it is the internal diameter.
• Except for conduit C23, inlet and outlet offsets of the conduits are set to zero i.e., conduit bottoms coincide with the invert of inlet and outlet nodes.
• The length of the conduits used in this model is 2D i.e., elevation differences in inlet and outlet nodes are not considered in length computation.
• Note that no minor loss, storage, and transport are considered in the conveyance network to keep the analysis simple.

Transect Properties

The Transects section in the Hydraulics block in Model Object Panel contains cross sectional data for the irregular channels. In this Tutorial, two irregular channels are used with transect data named TRSECT4 and TRSECT12. In the Transect Editor, these data can be inserted either manually or directly imported from an external file. Note that the excel file as listed in Table 2.1 contain these transect data. After the data has been inserted, the Transect Editor and Viewer of conduit C4 should look like Figure 2.6.

Time Series Data

The 10-year daily rainfall record provided for Bellingham is linked into the model as explained previously. The name of this file is USW00024217.dat. The period of record for these rain data extends from 2000 to 2010. Figure 2.7 shows the precipitation record for this period of time. For details on working with continuous time series data in GeoSWMM, see the User’s Manual.

Loss Parameters

In a catchment hydrologic process, major water losses accounted are infiltration and evapotranspiration. To account for Infiltration loss from the subcatchments, Horton model has been applied. Parameter values used in the models are listed in Table 2.6.

Table 2.6 : Horton Infiltration Model Parameters

Simulation Options Setting

The Options block in the Model Object Panel enables simulation settings. There are five tabs in Options editor. In this tutorial, a 10-year long simulation has been carried out at 1 day Time Step to compare the peak-runoffs for both undeveloped and developed scenarios. Table 2.7 lists the primary simulation settings.

Table 2.7 : Simulation Options for Tutorial 07