Model setup

GeoSWMM model for Tutorial 02 can be developed using the GIS shape files supplied with this manual (Table 2.1) by applying Import Layer technique. Details of these techniques are demonstrated in the User's Manual of GeoSWMM. It is assumed that readers have sufficient knowledge of model developing procedures, hence the contexts of this section start with the GeoSWMM model geodatabase provided for Tutorial 02 i.e. Tutorial_02.gdb. A backup of Tutorial_02.gdb should be stored separately 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. raingages, subcatchments, junctions, conduits and outfalls). In addition, GeoSWMM Object Panel contains non-visual object information (e.g. time series and transect data). Users can read or edit object attributes either from the GIS feature attribute table or from the element table of the model object panel. In a SWMM model, generally, natural channels are represented as conduits (links); manholes as junctions (nodes); while weirs can be represented as both links and nodes. To learn details about the network representation in GeoSWMM, see Appendix-A.

Before model simulation, provide GeoSWMM with the following input data.

Rain Gage Properties

A rain gage provides precipitation or rainfall data to a GeoSWMM model. In this Tutorial, rainfall in the study area is measured at a Rain Gage. The Property Editor of this gage is shown below.

A 2-hour synthetic storm event with three different return periods i.e. 2-year, 10-year and 100-year has been assigned as the rainfall Data Source. To set rainfall data in the rain gage, the type of Data Source (e.g. time series or external file) and the Series Name need to be assigned. For Tutorial, in the above figure, the Data Source is specified as TIMESERIES and the Series Name is specified as 2yr. This series is created under Time Series block in the GeoSWMM Model Object Panel (see Outfall Properties for details). To learn more on rainfall data types that can be assigned GeoSWMM, review the User’s Manual.

Subcatchment Properties

There are 16 subcatchments in the GeoSWMM model of Tutorial 02. Table 2.3 summarizes the physical properties of these drainage areas.

Table 2.3: Subcatchment Properties

Junction Properties

Conduit endpoints and their confluences are represented by simple junctions. Locations of these nodes in this Tutorial are shown in Figure 2.1. A list of these junctions and their invert elevations are listed 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 drains to the FREE type outfall O1. It’s connected to the dendritic conduit network and acts as the outlet node for subcatchment W1. The Invert of this outfall is 385.12 feet.

Conduit Properties

Figure 2.1 shows the layout of the runoff conveyance network in the study area. In this Tutorial, the conduit sizes will be designed to avoid flooding. A total of 22 conduits have been modeled in this Tutorial, among which two are natural channels with irregular cross section. The remaining 20 conduits have circular cross sections. The physical properties of all conduits are listed in Table 2.5. Here, the Diameter is taken by adding 0.5 Feet with the Maximum Depth of the corresponding conduits.

Table 2.5: Conduit Properties

NB:

• Maximum Depth for an irregular channel represents the vertical distance of top width elevation from the invert elevation. For a circular pipe, it’s the internal diameter.
• Diameters listed in Table 2.5 are the initial values. These values will be hydraulically designed in this Tutorial (see Conduit Sizing).
• 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 difference 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

Transects section in the Hydraulics block contains cross-sectional data for the irregular channels. In this Tutorial, two irregular channels are used with transect data named TRSECT4 and TRSECT12. In 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 View of conduit C4 should look like Figure 2.4.

Time Series Data

In the GeoSWMM model (Tutorial_02.gdb), three different 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 i.e. 2-year, 10-year and 100-year. They are assigned as a Rain Gage property (e.g. rainfall data) in three analysis scenarios. The rain format is ‘Intensity’ with the time interval of 5 minutes. The Time Series editor and the chart viewer for Tutorial 02 should appear as Figure 2.5.

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 Options Setting

The Options block in the GeoSWMM 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 02.

Table 2.6: Simulation options for Tutorial 02

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.