Model Setup

GeoSWMM model for both scenarios (e.g. undeveloped and developed) can be prepared using the GIS shape files supplied with this manual (Table 2.1), by applying Import Layer model setup technique. Details of these techniques are demonstrated in the User's Manual of GeoSWMM. It is assumed that readers have sufficient knowledge on model developing procedures in GeoSWMM. Hence, the contexts of this section start with the models provided for Tutorial 01 i.e. Tutorial_01U.gdb (for undeveloped site) and Tutorial_01D.gdb (for developed site). It is recommended that backups of these project files should be stored separately before beginning this exercise.

Figure 2.3 and Figure 2.4 illustrate the models of undeveloped and developed scenarios in GeoSWMM in ArcGIS Pro.

Both the Geodatabase and Model Object Panel contain network element information (e.g. rain gages, subcatchments, and outfalls). In the GeoSWMM models, an interconnected storm drainage system has been formed by assigning the rain gage to the subcatchment(s) and assigning the subcatchment(s) to discharge at the common site outfall. There is no conveyance network considered. The subcatchment(s) are assumed to drain directly to the site outfall.

Before the models are simulated, provide (or check) 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 Model Object Panel (see Time Series Data for details). To learn more on rainfall data types that can be assigned GeoSWMM, review the User’s Manual.

Subcatchment Properties

The undeveloped site is represented by only one subcatchment in Tutorial_01U.gdb. On the other hand, the developed site is delineated with 16 subcatchments in Tutorial_01D.gdb. Table 2.3 summarizes the physical properties of these drainage areas under both conditions. Other hydrologic properties (e.g. roughness, depression storage etc.) can be found in the Property Editor of these subcatchments. Most of these properties are calculated using the Tools of GeoSWMM. For details on how to estimate these physical and hydrologic properties using GeoSWMM, see the User’s Manual.

Table 2.3 : Subcatchment Properties

Notice that in developed condition, average surface imperviousness of the drainage areas is increased to a large extent from the undeveloped condition.

Outfall Properties

The entire study catchment drains to the FREE type outfall O1 under both scenarios. Invert elevation of this outfall is 385.12 feet.

Time Series Data

Three rainfall 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. Figure 2.6 shows the distribution of rainfall over 2 hours duration for the abovementioned storms.

Rainfall time series are assigned as a Rain Gage property in three storm event scenarios. The Rain Format is Intensity with Time Interval of 5 minutes. The Time Series Editor and the View options should appear as in Figure 2.7.

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

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 12-hour long simulation has been carried out at 5 minutes Time Step to compare the peak-runoffs for both undeveloped and developed scenarios. Table 2.4 lists the primary simulation settings.

Table 2.4 : Simulation Options for Tutorial 01

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 2.5.

Table 2.5 : Horton Infiltration Model Parameters

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