Model Setup

A GeoSWMM model for Tutorial 07 can be developed using the GIS shape files supplied with this manual (Table 2.1) by applying Import Layer model setup technique. Detailed model development techniques are demonstrated in the User's Manual of GeoSWMM. It is assumed that readers have sufficient knowledge on model developing procedure, hence contexts of this section start with the GeoSWMM model geodatabase provided for Tutorial 07 e.g. Tutorial_07.gdb. Users should keep a backup of Tutorial_07.gdb before working with it.

When opened in ArcGIS Pro, the model geodatabase should appear like following Figure 2.2.

Both the Geodatabase and Model Object Panel contain network element information (e.g. raingage, subcatchments, junctions, conduits and outfall). In addition, Model Object Panel contains non-visual object information (e.g. transects, time series, time patterns, land use, pollutants, calibration data etc.). Users can read or edit object attributes either from the GIS feature attribute table or from the element table of the model object panel.

Before model simulation, users need to provide (or check) following input data.

Rain Gage Properties

Rain gage provides precipitation or rainfall data to a GeoSWMM model. Rainfall in the study area in this tutorial is measured at gage- Raingage. Property Editor of this gage is shown below.

A 2-hour synthetic storm event with three return periods e.g. 2-year, 10-year and 100-year have been assigned as the rainfall Data Source to the rain gage in three analysis scenarios. To set rainfall data in the gage, the type of Data Source (e.g. time series or external file) and the data name need to be assigned in its property editor. For example, in above figure, the source is specified as TIMESERIES and the series name is specified as 2-yr. This series is created under Time Series block in the Model Object Panel (see Time Series Data for details). To learn more on rainfall data types that can be assigned to a rain gage in GeoSWMM, review the user’s manual. In SWMM, every subcatchment must be linked to a rain gage for the model to simulate.

Subcatchment Properties

There are 16 subcatchments in the GeoSWMM model of Tutorial_07. Table 2.3 summarizes the physical properties of these drainage areas.

Table 2.3: Subcatchment properties

Junction Properties

Conduit ends and their confluences are represented by simple junctions. Locations of these nodes in this tutorial are shown in Figure 2.1. List of these junctions and their invert elevations are listed in Table 2.4.

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 drains to the FREE type outfall O1. It is connected to the dendritic conduit network, and acts as the outlet node for subcatchment W1. Invert of this outfall is 385.12 ft.

Conduit Properties

In a SWMM model, generally, the roadside gutters are represented as irregular conduits (links); their cross sections will be that of a typical street, representing the surface “channel” through which water would flow if the pipe system surcharged and flooded the street. To learn details about gutters and their design criteria, see Appendix-A.

Figure 2.1 shows the layout of the runoff conveyance network in the study area. A total of 33 conduits have been modeled in this tutorial, among which two are natural channels and eleven are roadside gutters with irregular cross section. Remaining 20 conduits have circular cross section. Physical properties of all conduits are listed in the following table.

Table 2.5 : Conduit properties

NB:

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

Transect Properties

Transects section in the Hydraulics block in Model Object Panel contains cross sectional data for the irregular channels and gutters. In this tutorial, two channels and eleven gutters are used with transect data. The location of the left bank, the right bank and the channel section is defined by entering the corresponding station locations in the Bank Stations. In this tutorial, the gutters have the same roughness throughout so the Left and Right bank stations are set as default in the Transect Editor. These data can be inserted manually, or can be directly imported from an external file. Note that two CSV files as listed in Table 2.1 contain these transect data. After the data has been inserted, the Transect Editor and Viewer of conduit C4 and C3_Sreet should look like Figure 2.4 and Figure 2.5.

Time Series Data

In the project file Tutorial_07.gdb, three time series datasets are provided under Time Series block in the Model Object Panel. These datasets represent a 2-hour synthetic storm event with three return periods e.g. 2-year, 10-year and 100-year. And they are assigned as a Rain Gage property (e.g. rainfall data) in three analysis scenarios. The rain format is “Intensity” with time interval of 5 minutes. The Time Series editor and the chart viewer for Tutorial 07 should appear like the following figure.

Under Time Series block, users can create, import or edit time series data for any object (e.g. node inflow) as well. For details on working with time series data in GeoSWMM, see the User’s Manual.

Simulation Option Setting

The Options block in the Model Object Panel enables to provide simulation settings in GeoSWMM. There are five tabs in Options editor. In this tutorial, a 12-hour simulation has been carried out at 5 minutes time step to compare the peak-runoffs for different hydraulic routing methods Table 2.6 lists the primary simulation settings which are set for Tutorial 07.

Table 2.6 : Simulation options for Tutorial 07

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 in this tutorial. Parameter values, which have been assigned to all subcatchments, used in this model are listed below.

Table 2.7 : Horton infiltration model parameters

Note that evapotranspiration and other loss properties are not assigned to the current model. For details on these loss parameters, review the User’s Manual.