Model Setup

A GeoSWMM model for Tutorial 08 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 08 e.g. Tutorial_08.gdb. Users should keep a backup of Tutorial_08.gdb before working with it.

When opened in ArcGIS Pro, the model geo-database 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). Additionally, 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.

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- Rain gage. Property Editor of this gage is shown below.

A 2-hour synthetic storm event of volume of 0.1918 inch and 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 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 0.1918-in. This series is created under Time Series block in the Model Object Panel (see Transect Properties for details). To learn more on rainfall data types that can be assigned to a rain gage in GeoSWMM, review the user’s manual.

Subcatchment Properties

There are 16 subcatchments in the GeoSWMM model of Tutorial 08. 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. The junctions are added in the same locations as they were added in Tutorial_02. Besides, new junctions have been added to connect the interceptors into the main conveyance system and they have been denoted as JI in the model. To represent the desired storm water conveyance pipes, which were previously created in Tutorial_02, as combined sewer pipes in GeoSWMM, dry weather wastewater flows have been added into their inlet junctions. To learn more about combined sewer system and their representation in GeoSWMM, please see the Appendix-A. Locations of all of these junctions in this tutorial are shown in Figure 2.1. Their invert elevations and inflows status are listed in Table 2.4.

Table 2.4 : Invert Elevation and inflow status of junctions

NB:

1. 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

Two outfalls have been used in this model; one for receiving the stormwater from the entire study area and another one to receive the wastewater (dry weather flow) from the interceptors and to send it to the hypothetical WWTP (Waste Water Treatment Plant). The physical properties of the outfalls are provided in Table 2.5.

Table 2.5 : Outfall properties

Storage Unit Properties

The interceptors, in the long run, convey the wastewater to a pump station comprising a storage unit, which represents a wet well, and a pump. The storage unit is named as Well. It has an invert elevation of 380.27 feet and the storage curve has been set as FUNCTIONAL.

Conduit Properties

In total 35 conduits have been used in the model which can be categorized into three major types:

1. Combined sewer conduits: carry both the stormwater and the wastewater
2. Stormwater conveyance conduits:  carry only the stormwater
3. Interceptors: carry only the wastewater (dry weather flow)

The physical properties of the conduits are provided in the following Table 2.6.

Table 2.6 : Conduit properties

NB:

1. For irregular channels, maximum depth is used for area calculation of the conduits that represents vertical distance of top width level from the invert in the cross section. For a circular pipe, it’s 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.

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 Viewer of conduit C4 should look like Figure 2.4.

Pump Properties

Pump is a device used to lift water to higher elevations and in SWMM model it is represented as a link between two nodes. The pump added in this model discharges the wastewater flow to a constant head outfall (O2) representing the inlet to a hypothetical WWTP and the Inlet and Outlet nodes have been set as the Well and JI1 respectively. The pump curve assigned to the pump is named as “Pump1” and its properties have been described in the following section. The startup and shutoff depths of the pump have been set as 5ft and 2ft respectively. The initial status is provided “OFF”.

Pump Curve Data

A pump’s operation is defined through its characteristic curve that relates the flow rate pumped to either the water depth or volume at its inlet node or to the lift (i.e., hydraulic head) provided. In pump curve editor, these data can be inserted manually, or can be directly imported from an external file. For this tutorial, Pump Type “TYPE 3” has been used that relates the flow rate to the hydraulic head Note that a CSV files as listed in Table 2.1 contain this pump curve data. After the data has been inserted, the Pump Curve Editor and Viewer of pump “Pump1” should look like Figure 2.5.

Weir Properties

Four weirs of same type (i.e. TRANSVERSE) have been used in the model to divert the wastewater flow to the interceptors from the outlet nodes of four combined sewer pipes. Weirs are also represented as links in SWMM. To know detail about weirs and their representations in SWMM, see Appendix-B. The physical properties of the weirs are provided in the following Table 2.7:

Table 2.7 : Weir properties

Time Series Data

In the project file- Tutorial_08.gdb, four time series datasets are provided under Time Series block in the Model Object Panel. These datasets represent a 2-hour synthetic storm event with the 0.1918 in. water quality storm defined in Tutorial 03 and the 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 four analysis scenarios. The rain format is “Intensity” with time interval of 5 minutes. The Time Series Editor and the chart viewer for Tutorial 08 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 1 minute time step to compare the peak-runoffs for different hydraulic routing methods. Table 2.8 lists the primary simulation settings which are set for Tutorial 08.

Table 2.8 : Simulation options for Tutorial 08

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 2.9 : 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.