Non-Visual Objects in SWMM5
In addition to physical objects that can be displayed visually on a map, SWMM utilizes several classes of non-visual data objects to describe additional characteristics and processes within a study area.
|·||Water Quality Data|
SWMM utilizes several forms of tabular data to describe the properties of its various objects. These include:
Curve objects are used to describe a functional relationship between two quantities. The following types of curves are used in SWMM:
|·||Storage – describes how the surface area of a Storage Unit node varies with water depth.|
|·||Shape – describes how the width of a customized cross-sectional shape varies with height for a Conduit link.|
|·||Diversion – relates diverted outflow to total inflow for a Flow Divider node.|
|·||Tidal – describes how the stage at an Outfall node changes by hour of the day.|
|·||Pump – relates flow through a Pump link to the depth or volume at the upstream node or to the head delivered by the pump.|
|·||Rating – relates flow through an Outlet link to the freeboard depth or head difference across the outlet.|
|·||Control – determines how the control setting of a pump or flow regulator varies as a function of some control variable (such as water level at a particular node) as specified in a Modulated Control rule. Is also used to adjust the flow from an LID unit’s underdrain based on head.|
|·||Weir – allows the discharge coefficient for a weir to vary with head.|
Each curve must be given a unique name and can be assigned any number of data points.
|Unit Hydrograph Editor|
The Unit Hydrograph Editor is invoked whenever a new Unit Hydrograph object is created or an existing one is selected for editing. It is used to specify the shape parameters and rain gage for a group of triangular unit hydrographs. These hydrographs are used to compute rainfall-derived inflow/infiltration (RDII) flow at selected nodes of the drainage system. A UH group can contain up to 12 sets of unit hydrographs (one for each month of the year), and each set can consist of up to 3 individual hydrographs (for short-term, intermediate-term, and long-term responses, respectively) as well as parameters that describe any initial abstraction losses. The editor, shown below, contains the following data entry fields:
Name of UH Group
Enter the name assigned to the UH Group.
Rain Gage Used
Type in (or select from the dropdown list) the name of the rain gage that supplies rainfall data to the unit hydrographs in the group.
Select a month from the dropdown list box for which hydrograph parameters will be defined. Select All Months to specify a default set of hydrographs that apply to all months of the year. Then select specific months that need to have special hydrographs defined. Months listed with a (*) next to them have had hydrographs assigned to them.
Select this tab to provide the R-T-K shape parameters for each set of unit hydrographs in selected months of the year. The first row is used to specify parameters for a short-term response hydrograph (i.e., small value of T), the second for a medium-term response hydrograph, and the third for a long-term response hydrograph (largest value of T). It is not required that all three hydrographs be defined and the sum of the three R-values do not have to equal 1. The shape parameters for each UH consist of:
|·||R: the fraction of rainfall volume that enters the sewer system|
|·||T: the time from the onset of rainfall to the peak of the UH in hours|
|·||K: the ratio of time to recession of the UH to the time to peak|
Initial Abstraction Depth
Select this tab to provide parameters that describe how rainfall will be reduced by any initial abstraction depth available (i.e., interception and depression storage) before it is processed through the unit hydrographs defined for a specific month of the year. Different initial abstraction parameters can be assigned to each of the three unit hydrograph responses. These parameters are:
|·||Dmax: the maximum depth of initial abstraction available (in rain depth units)|
|·||Drec: the rate at which any utilized initial abstraction is made available again (in rain depth units per day)|
|·||Do: the amount of initial abstraction that has already been utilized at the start of the simulation (in rain depth units).|
Note that any unit hydrograph or initial abstraction parameter left empty is assumed to be 0.
Right-clicking over the unit hydrograph and initial abstraction data entry grids will make a popup Edit menu appear. It contains commands to cut, copy, and paste text to or from cells that have been selected in the grid.
The Curve Editor dialog is invoked whenever a new Curve object is created or an existing Curve object is selected for editing. The Editor adapts itself to the category of curve being edited (Storage, Shape, Tidal, Diversion, Pump, Rating, Control or Weir). To use the Curve Editor:
|1.||Enter values for the following dialog items:|
|Name||Name of the curve.|
|Type||(Pump Curves Only) Choice of pump curve type (see Pumps for a description of each curve type).|
|Description||Optional comment or description of what the curve represents. Click the button to launch a multi-line comment editor if more than one line is needed.|
|Data Grid||The curve’s X,Y data.|
|2.||Click the View button to see a graphical plot of the curve drawn in a separate window.|
|3.||If additional rows are needed in the Data Grid, simply press the Enter key when in the last row.|
|4.||Right-clicking over the Data Grid will make a popup Edit menu appear. It contains commands to cut, copy, insert, and paste selected cells in the grid as well as options to insert or delete a row.|
|5.||Press OK to accept the curve entries or Cancel to cancel the edits made.|
You can also click the Load button to load in a curve that was previously saved to file or click the Save button to save the current curve’s data to a file.
Time Patterns allow external dry weather flow (DWF) to vary in a periodic fashion. They consist of a set of adjustment factors applied as multipliers to a baseline DWF flow rate or pollutant concentration. The different types of time patterns include:
|Monthly||one multiplier for each month of the year.|
|Daily||one multiplier for each day of the week|
|Hourly||one multiplier for each hour from 12 AM to 11 PM.|
|Weekend||hourly multipliers for weekend days.|
Each time pattern must have a unique name and there is no limit on the number of patterns that can be created. Each dry weather inflow (either flow or quality) can have up to four patterns associated with it, one for each type listed above.
Monthly time patterns can also be used to adjust the baseline values of the following hydrological parameters:
|·||subcatchment depression storage|
|·||subcatchment pervious surface roughness|
|·||soil infiltration recovery rate|
|Time Pattern Editor|
The Time Pattern Editor is invoked whenever a new Time Pattern object is created or an existing time pattern is selected for editing. The editor contains the following data entry fields:
Enter the name assigned to the time pattern.
Select the type of time pattern being specified.
Enter a value for each multiplier. The number and meaning of the multipliers changes with the type of time pattern selected:
|MONTHLY||One multiplier for each month of the year|
|DAILY||One multiplier for each day of the week|
|HOURLY||One multiplier for each hour from 12 midnight to 11 PM|
|WEEKEND||One multiplier for each hour from 12 midnight to 11 PM for weekend days|
In order to maintain an average dry weather flow or pollutant concentration at its specified value (as entered on the Inflows Editor), the multipliers for a pattern should average to 1.0.
|Time Series Editor|
The Time Series Editor is invoked whenever a new Time Series object is created or an existing time series is selected for editing. To use the Time Series Editor:
|1.||Enter values for the following standard items:|
|3.||If the external file option is selected, click the button to locate the file’s name. The file’s contents must be formatted in the same manner as the direct data entry option discussed below. See the description of Time Series Files for details.|
|4.||For direct data entry, enter values in the data entry grid as follows:|
|Date Column||Optional date (in month/day/year format) of the time series values (only needed at points in time where a new date occurs).|
|Time Column||If dates are used, enter the military time of day for each time series value (as hours:minutes or decimal hours). If dates are not used, enter time as hours since the start of the simulation.|
|Value Column||Time series numerical values.|
A graphical plot of the data in the grid can be viewed in a separate window by clicking the View button. Right clicking over the grid will make a popup Edit menu appear. It contains commands to cut, copy, insert, and paste selected cells in the grid as well as options to insert or delete a row.
|5.||Press OK to accept the time series or Cancel to cancel your edits.|
|Note that there are two methods for describing the occurrence time of time series data:|
|·||as calendar date/time of day (which requires that at least one date, at the start of the series, be entered in the Date column)|
|·||as elapsed hours since the start of the simulation (where the Date column remains empty).|
For rainfall time series, it is only necessary to enter periods with non-zero rainfall amounts. SWMM interprets the rainfall value as a constant value lasting over the recording interval specified for the rain gage which utilizes the time series. For all other types of time series, SWMM uses interpolation to estimate values at times that fall in between the recorded values.
Time Series objects are used to describe how certain object properties vary with time. Time series can be used to describe:
|·||water stage at outfall nodes|
|·||external inflow hydrographs at drainage system nodes|
|·||external inflow pollutographs at drainage system nodes|
|·||control settings for pumps and flow regulators.|
Each time series must be given a unique name and can be assigned any number of time-value data pairs. Time can be specified either as hours from the start of a simulation or as an absolute date and time-of-day. Time series data can either be entered directly into the program or be accessed from a user-supplied Time Series file.
For rainfall time series, it is only necessary to enter periods with non-zero rainfall amounts. SWMM interprets the rainfall value as a constant value lasting over the recording interval specified for the rain gage that utilizes the time series. For all other types of time series, SWMM uses interpolation to estimate values at times that fall in between the recorded values.
For times that fall outside the range of the time series, SWMM will use a value of 0 for rainfall and external inflow time series, and either the first or last series value for temperature, evaporation, and water stage time series.
|Data Series Selection Dialog|
|Object Type:||The type of object to plot (Subcatchment, Node, Link or System).|
|Object Name:||The ID name of the object to be plotted. (This field is disabled for System variables).|
|Variable:||The variable whose time series will be plotted (choices vary by object type).|
|Legend Label:||The text to use in the legend for the data series. If left blank, a default label made up of the object type, name, variable and units will be used (e.g. Link C16 Flow (CFS)).|
|Axis:||Whether to use the left or right vertical axis to plot the data series.|
As you select objects on the Study Area Map or in the Project Browser their types and ID names will automatically appear in this dialog.
Click the Accept button to add/update the data series into the plot or click the Cancel button to disregard your edits. You will then be returned to the Time Series Plot Selection dialog where you can add or edit another data series.
To make a precipitation time series display in inverted fashion on a plot, assign it to the right axis and after the plot is displayed, use the Graph Options Dialog to invert the right axis and expand the scales of both the left and right axes (so it doesn’t overlap another data series).
|Time Series Files|
Time Series Files are external text files that contain data for SWMM’s time series objects. Examples of time series data include rainfall, evaporation, inflows to nodes of the drainage system, and water stage at outfall boundary nodes. The file must be created and edited outside of SWMM, using a text editor or spreadsheet program. A time series file can be linked to a specific time series object using SWMM’s Time Series Editor.
The format of a time series file consists of one time series value per line. Comment lines can be inserted anywhere in the file as long as they begin with a semicolon. Blank lines are not allowed. Time series values can either be in date / time / value format or in time / value format, where each entry is separated by one or more spaces or tab characters. For the date / time / value format, dates are entered as month/day/year (e.g., 7/21/2004) and times as 24-hour military time (e.g., 8:30 pm is 20:30). After the first date, additional dates need only be entered whenever a new day occurs. For the time / value format, time can either be decimal hours or military time since the start of a simulation (e.g., 2 days, 4 hours and 20 minutes can be entered as either 52.333 or 52:20). An example of a time series file is shown below:
|;Rainfall Data for Gage G1
07/01/2003 00:00 0.00000
07/06/2003 14:30 0.05100
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