Nodes in SWMM5
| Nodes |
Nodes are points of a conveyance system that connect conveyance links together. There are several different categories of nodes that can be employed:
| · | Junctions |
| · | Outfalls |
| · | Flow Dividers |
| · | Storage Units |
Nodes are also the points where external inflows can enter a drainage system and where removal of pollutants through treatment can occur.
| External Inflows |
In addition to inflows originating from subcatchment runoff and groundwater, drainage system nodes can receive three other types of external inflows:
Direct Inflows - These are user-defined, time-varying inflows (e.g., hydrographs or pollutographs) added directly into a node. They can be used to perform flow and water quality routing in the absence of any runoff computations (as in a study area where no subcatchments are defined).
Dry Weather Inflows - These are continuous inflows that typically reflect the contribution from sanitary sewage in sewer systems or base flows in pipes and stream channels. They are represented by an average inflow rate that can be periodically adjusted on a monthly, daily, and hourly basis by applying Time Patternmultipliers to this average value.
Rainfall-Dependent Inflow/Infiltration (RDII) - These are stormwater flows that enter sanitary or combined sewers due to "inflow" from direct connections of downspouts, sump pumps, foundation drains, etc. as well as "infiltration" of subsurface water through cracked pipes, leaky joints, poor manhole connections, etc. RDII can be computed for a given rainfall record based on set of triangular unit hydrographs (UH) that determine a short-term, intermediate-term, and long-term inflow response for each time period of rainfall. Any number of UH sets can be supplied for different sewershed areas and different months of the year. RDII flows can also be specified in an external RDII Interface file.
Direct, Dry Weather, and RDII inflows are properties associated with each type of drainage system node (junctions, outfalls, flow dividers, and storage units) and can be specified when nodes are edited. They can be used to perform flow and water quality routing in the absence of any runoff computations (as in a study area where no subcatchments are defined). It is also possible to make the outflows generated from an upstream drainage system be the inflows to a downstream system by using interface files.
See Also
| Junctions |
Junctions are drainage system nodes where links join together. Physically they can represent the confluence of natural surface channels, manholes in a sewer system, or pipe connection fittings. External inflows can enter the system at junctions. Excess water at a junction can become partially pressurized while connecting conduits are surcharged and can either be lost from the system or be allowed to pond atop the junction and subsequently drain back into the junction.
The principal input parameters for a junction are:
| · | invert (channel or manhole bottom) elevation |
| · | height to ground surface |
| · | ponded surface area when flooded (optional) |
| · | external inflow data (optional). |
See Also
| Storage Units |
Storage Units are drainage system nodes that provide storage volume. Physically they could represent storage facilities as small as a catchbasin or as large as a lake. The volumetric properties of a storage unit are described by a function or table of surface area versus height. In addition to receiving inflows and discharging outflows to other nodes in the drainage network, storage nodes can also lose water from surface evaporation and from seepage into native soil.
The principal input parameters for storage units include:
| · | invert (bottom) elevation |
| · | maximum depth |
| · | depth-surface area data |
| · | evaporation potential |
| · | seepage parameters (optional) |
| · | external inflow data (optional). |
| RDII Inflow Page |
The RDII Inflow page of the Inflows Editor dialog form is used to specify RDII (Rainfall Dependent Infiltration/Inflow) for the node in question. The page contains the following two input fields:
Unit Hydrograph Group
Enter (or select from the dropdown list) the name of the Unit Hydrograph group which applies to the node in question. The unit hydrographs in the group are used in combination with the group's assigned rain gage to develop a time series of RDII inflows per unit area over the period of the simulation. Leave this field blank to indicate that the node receives no RDII inflow. Clicking the button will launch the Unit Hydrograph Editor for the UH group specified.
Sewershed Area
Enter the area (in acres or hectares) of the sewershed which contributes RDII to the node in question. Note this area will typically be only a small, localized portion of the subcatchment area that contributes surface runoff to the node.
| Direct Inflow Page |
The Direct page on the Inflows Editor dialog is used to specify the time history of direct external flow and water quality entering a node of the drainage system. These inflows are represented by both a constant and time varying component as follows:
| Inflow at time t = | (baseline value)*(baseline pattern factor) +
(scale factor) * (time series value at time t) |
The page contains the following input fields that define the properties of this relation:
Constituent
Selects the constituent (FLOW or one of the project's named pollutants) whose direct inflow will be described.
Baseline
Specifies the value of the constant baseline component of the constituent's inflow. For FLOW, the units are the project's flow units. For pollutants, the units are the pollutant's concentration units if inflow is a concentration, or can be any mass flow units if the inflow is a mass flow (see Units Factor below). If left blank then no baseline inflow is assumed.
Baseline Pattern
An optional Time Pattern whose factors adjust the baseline inflow on either an hourly, daily, or monthly basis (depending on the type of time pattern specified). Clicking the button will bring up the Time Pattern Editor dialog for the selected time pattern. If left blank, then no adjustment is made to the baseline inflow.
Time Series
The name of the time series that describes the time varying component of the constituent's inflow. If left blank then no time varying inflow is assumed. Clicking the button will bring up the Time Series Editor dialog for the selected time series. The units of the time series values obey the same convention as described above for Baseline inflow.
Scale Factor
A multiplier used to adjust the values of the constituent's inflow time series. The baseline value is not adjusted by this factor. The scale factor can have several uses, such as allowing one to easily change the magnitude of an inflow hydrograph while keeping its shape the same, without having to re-edit the entries in the hydrograph's time series. Or it can allow a group of nodes sharing the same time series to have their inflows behave in a time-synchronized fashion while letting their individual magnitudes be different. If left blank the scale factor defaults to 1.0.
Inflow Type
For pollutants, this field selects the type of inflow data as being either a CONCENTRATION (mass/volume) or a MASS FLOW RATE (mass/time). This field does not appear for FLOW inflow.
Units Factor
A numerical factor used to convert the units of pollutant mass flow rate into concentration mass units per second. For example, if the inflow data were in lbs/day and the pollutant concentration was chosen as mg/L, then the conversion factor value would be (453,590 mg/lb) / (86,400 sec/day) = 5.25 (mg/sec) per (lb/day). This field does not appear for FLOW inflow, and for concentration-type inflows any value entered will be overriden to 1.0.
More than one constituent can be edited while the dialog is active by simply selecting another choice for the Constituent property. However, if the Cancel button is clicked then any changes made to all constituents will be ignored.
If a pollutant is assigned a direct inflow in terms of concentration, then one must also assign a time series inflow to flow, otherwise no pollutant inflow will occur. An exception is at submerged outfalls where pollutant intrusion can occur during periods of reverse flow. If pollutant inflow is defined in terms of mass, then a corresponding flow inflow is not required.
| Dry Weather Inflow Page |
The Dry Weather page of the Inflows Editor dialog is used to specify a continuous source of dry weather flow entering a node of the drainage system. The page contains the following input fields:
Constituent
Selects the constituent (FLOW or one of the project's specified pollutants) whose dry weather inflow will be specified.
Average Value
Specifies the average (or baseline) value of the dry weather inflow of the constituent in the relevant units (flow units for flow, concentration units for pollutants). Leave blank if there is no dry weather flow for the selected constituent.
Time Patterns
Specifies the names of the time patterns to be used to allow the dry weather flow to vary in a periodic fashion by month of the year, by day of the week, and by time of day (for both week days and week ends). One can either type in a name or select a previously defined pattern from the dropdown list of each combo box. Up to four different types of patterns can be assigned. You can click the button next to each Time Pattern field to edit the respective pattern.
More than one constituent can be edited while the dialog is active by simply selecting another choice for the Constituent property. However, if the Cancel button is clicked then any changes made to all constituents will be ignored.
| Inflows Editor |
The Inflows Editor dialog is used to assign Direct, Dry Weather, and RDII inflows into a node of the drainage system. It is invoked whenever the Inflows property of a Node object is selected in the Property Editor. The dialog consists of three tabbed pages that provide a special editor for each type of inflow:
| · | Direct Inflow |
| · | Dry Weather Inflow |
| · | RDII Inflow |
| Outfalls |
Outfalls are terminal nodes of the drainage system used to define final downstream boundaries under Dynamic Wave flow routing. For other types of flow routing they behave as a junction. Only a single link can be connected to an outfall node, and the option exists to have the outfall discharge onto a subcatchment's surface.
The boundary conditions at an outfall can be described by any one of the following stage relationships:
| · | the critical or normal flow depth in the connecting conduit |
| · | a fixed stage elevation |
| · | a tidal stage described in a table of tide height versus hour of the day |
| · | a user-defined time series of stage versus time. |
The principal input parameters for outfalls include:
| · | invert elevation |
| · | boundary condition type and stage description |
| · | presence of a flap gate to prevent backflow through the outfall. |
See Also
| Dry Weather Inflow Page |
The Dry Weather page of the Inflows Editor dialog is used to specify a continuous source of dry weather flow entering a node of the drainage system. The page contains the following input fields:
Constituent
Selects the constituent (FLOW or one of the project's specified pollutants) whose dry weather inflow will be specified.
Average Value
Specifies the average (or baseline) value of the dry weather inflow of the constituent in the relevant units (flow units for flow, concentration units for pollutants). Leave blank if there is no dry weather flow for the selected constituent.
Time Patterns
Specifies the names of the time patterns to be used to allow the dry weather flow to vary in a periodic fashion by month of the year, by day of the week, and by time of day (for both week days and week ends). One can either type in a name or select a previously defined pattern from the dropdown list of each combo box. Up to four different types of patterns can be assigned. You can click the button next to each Time Pattern field to edit the respective pattern.
More than one constituent can be edited while the dialog is active by simply selecting another choice for the Constituent property. However, if the Cancel button is clicked then any changes made to all constituents will be ignored.
| Ponding and Pressurization |
Normally in flow routing, when the flow into a junction exceeds the capacity of the system to transport it further downstream, the excess volume overflows the system and is lost. An option exists to have instead the excess volume be stored atop the junction, in a ponded fashion, and be reintroduced into the system as capacity permits. Under Kinematic Wave flow routing, the ponded water is stored simply as an excess volume. For Dynamic Wave routing, which is influenced by the water depths maintained at nodes, the excess volume is assumed to pond over the node with a constant surface area. This amount of surface area is an input parameter supplied for the junction.
Alternatively, the user may wish to represent the surface overflow system explicitly. In open channel systems this can include road overflows at bridges or culvert crossings as well as additional floodplain storage areas. In closed conduit systems, surface overflows may be conveyed down streets, alleys, or other surface routes to the next available stormwater inlet or open channel. Overflows may also be impounded in surface depressions such as parking lots, back yards or other areas.
In sewer systems with pressurized pipes and force mains the hydraulic head at junction nodes can at times exceed the ground elevation under Dynamic Wave routing. This would normally result in an overflow which, as described above, can either be lost or ponded. SWMM allows the user to specify an additional "surcharge" depth at junction nodes that lets them pressurize and prevents any outflow until this additional depth is exceeded. If both ponding and pressurization are specified for a node ponding takes precedence and the surcharge depth is ignored. Neither ponding nor pressurization applies to storage nodes.
| Treatment Editor |
The Treatment Editor is invoked whenever the Treatment property of a node is selected from the Property Editor. It displays a list of the project's pollutants with an edit box next to each as shown below.
Enter a valid treatment expression in the box next to each pollutant which receives treatment. Click the OK button to accept your edits or click Cancel to ignore them.
Any of the following math functions (which are case insensitive) can be used in a treatment expression:
| · | abs(x) for absolute value of x |
| · | sgn(x) which is +1 for x >= 0 or -1 otherwise |
| · | step(x) which is 0 for x <= 0 and 1 otherwise |
| · | sqrt(x) for the square root of x |
| · | log(x) for logarithm base e of x |
| · | log10(x) for logarithm base 10 of x |
| · | exp(x) for e raised to the x power |
| · | the standard trig functions (sin, cos, tan, and cot) |
| · | the inverse trig functions (asin, acos, atan, and acot) |
| · | the hyperbolic trig functions (sinh, cosh, tanh, and coth) |
along with the standard operators +, -, *, /, ^ (for exponentiation ) and any level of nested parentheses.
| Treatment |
Removal of pollutants from the flow streams entering any drainage system node is modeled by assigning a set of treatment functions to the node. A treatment function can be any well-formed mathematical expression involving:
| · | the pollutant concentration (use the pollutant name to represent its concentration)– for non-storage nodes this is the mixture concentration of all flow streams entering the node while for storage nodes it is the pollutant concentration within the node’s stored volume |
| · | the removals of other pollutants (use R_ prefixed to the pollutant name to represent removal) |
| · | any of the following process variables: |
- FLOW for flow rate into node (in user-defined flow units)
- DEPTH for water depth above node invert (ft or m)
- AREA for node surface area (ft2 or m2)
-
DT for routing time step (sec)
-
HRT for hydraulic residence time (hours)
| · | Any of the following math functions (which are case insensitive) can be used in a treatment expression: |
-
abs(x) for absolute value of x
-
sgn(x) which is +1 for x >= 0 or -1 otherwise
-
step(x) which is 0 for x <= 0 and 1 otherwise
-
sqrt(x) for the square root of x
-
log(x) for logarithm base e of x
-
log10(x) for logarithm base 10 of x
-
exp(x) for e raised to the x power
-
the standard trig functions (sin, cos, tan, and cot)
-
the inverse trig functions (asin, acos, atan, and acot)
-
the hyperbolic trig functions (sinh, cosh, tanh, and coth)
along with the standard operators +, -, *, /, ^ (for exponentiation ) and any level of nested parentheses.
The result of the treatment function can be either a concentration (denoted by the letter C) or a fractional removal (denoted by R). For example, a first-order decay expression for BOD exiting from a storage node might be expressed as:
C = BOD * exp(-0.05*HRT)
or the removal of some trace pollutant that is proportional to the removal of total suspended solids (TSS) could be expressed as:
R = 0.75 * R_TSS
Care must be taken to avoid circular references when specifying treatment functions. For example, the above expression would not be computable if it were used to compute fractional removal of TSS.
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Categories: Inside SWMM5, Rossman, SWMM5