To input or edit the attribute or model hydraulic node data, either double click on a node, or select the node and press the Enter key while in Hydraulics Mode.


The Hydraulics mode uses a link-node network to describe the collection/conveyance system and thereby the mathematical solution of the gradually varied unsteady flow equations that form the basis of the solution. 

Nodes are the storage elements and correspond to manholes or pipe and channel junctions. The calculated variables associated with the node are volume, head and surface area. Inflows such as hydrographs and outflows such as weir diversions, pumps and flooding take place at the nodes.

Node data are required for every node in the network including regular nodes, storage and diversion (orifice and weir) nodes, pump nodes, and outfall nodes.

Occasionally it is necessary to perform routing on the water that floods onto the ground. A new conduit is constructed by the user to transport the flooded water from the ground elevation of the upstream junction to the ground elevation of the downstream junction. It is not necessary to simulate manholes as vertical pipes in order to transport water. With this arrangement, water may surcharge (move vertically out of a “manhole-pipe”) and return to the sewer system at a downstream location through another “manhole-pipe” after traversing an overland channel.

Inlet Capacity can be invoked to limit the amount of water received by the node from the interface file and overland conduits as a maximum capacity or a rating of approach vs. captured flow. In this construct dual drainage can be simulated with flow overland and only partial flow in subsurface conduits.

Inflow constrictions by inlets etc. can also be simulated as orifices or rating curves if their hydraulic characteristics are known. With this extra effort, dual "major" (street surface) and "minor" (sub-surface sewer network) drainage systems can be simulated using a parallel system restricting flow in both directions.

Spill Crest

The spill crest (ground elevation) of a node (ft or m) is the physical top of the junction. This may be either a real or conceptual upper limit to the junction.

The surcharge elevation of a node is computed automatically by the Hydraulics mode during the simulation. For a node connected only to closed top conduits (i.e. pipes), it is defined as the crown elevation of the highest connecting pipe.

If an open channel is connected to a node, the spill crest (elevation where surface flooding occurs) should be set at the elevation where the HGL exceeds the defined maximum depth of the cross-section. A run time error will be generated if it is not. If the spill crest elevation is higher than the top of the bank of a connecting open channel and the water level is above the top of the channel, Table E10 of the output file a warning indicating this as a source of model error. It is important that cross-sections are defined to be large enough to convey the peak flow.

The configuration parameter VERT_WALLS causes XPSWMM to add vertical walls to the ground elevation specified by the spill crest of the nodes.

The spill crest is used to define upper boundary of HGL in the network. Normally this is the street or ground elevation; however, if the manholes are bolted down the spill crest” should be set sufficiently high so that the simulated water surface elevation does not exceed it. This can be automated at the node by selecting the Sealed option for Ponding and no adjustment of the spill crest is required.

When the hydraulic head must exceed the spill crest to maintain continuity at the node, the program allows the excess flow to overflow onto the ground and depending on the Ponding value selected it may become lost to the system for the remainder of the simulation period. These assumptions may be modified using the surface ponding options in this dialog.

Inlet Capacity

 

The Inlet Capacity option allows for flow to subsurface conduits downstream of a node to be restricted by an Inlet Rating Curve (IRC). For these calculations, inlet flow is the sum of the Times Series Inflow (User Inflow + Gauged Inflow + Dry Weather Flow) + Interface File Flow + flow routed to node in open channels).

The Inlet Rating Curve works as follows:


    • If Ponding None and no surface conduits - Divert flow according to the selected IRC method and lose excess.
    • If Ponding None with surface conduits - Divert flow according to the selected IRC method and excess distributed according to hydraulic properties of surface conduits. Any excess that cannot be re-distributed is lost.
    • If Ponding Allowed and no surface conduits - Divert flow according to the selected IRC method with excess ponding at the surface. Ponded surface water is added to the diverted flow at a flow rate equivalent to the volume of surface waterdivided by the time step. The maximum total diverted flow however is capped at either the "Maximum Capacity" or at the maximum value entered in the rating curve so do not enter unrealistically high capture rates even if they have equally unrealistic approach flows because the approach flow is ignored when determining the absolute maximum allowed. 
    • If Ponding Allowed with surface conduits - Divert flow according to the selected IRC method and excess distributed according to hydraulic properties of surface conduits. Any excess that cannot be re-distributed is ponded as per 3 above with the total diverted flow increased accordingly.
    • If the underground conduit has a constriction that causes reverse flow through the inlet then all the excess underground flow discharges back to the surface regardless of the inlet's maximum capacity (it blows its lid).


Whenever Inlet Capacity is turned on at a node, a second node is created, for computational purposes, with the text $I appended to the name. This new node is connected to the closed conduit and receives flow by an internal rating curve based on the inlet capacity. Results for this node are reported in the output file. In the Review Results graphical display, the new node is labeled as [Subsurface]. When inlet capacity is selected, it is possible that two HGL profiles will be shown in the long section results view. This is due to the second node which is created.

When using Inlet Capacity without both a closed conduit and an open channel (sub-surface and surface flows), or Dual Drainage, the following occurs:

  1. The original node has an invert equivalent to the Spillcrest less 0.01 ft (0.001 m).

  2. A new node is created using the original invert and Spillcrest equal to the original Spillcrest less 0.01 ft (0.001 m).

  3. A Rating Curve applies between the nodes base on the defined Inlet Capacity

With respect to the results for inlet capacity subsurface nodes: The depth calculation now considers the surface area for the surcharged case. Backward compatibility can be obtained by entering the configuration parameter IR_PRE2013. Refer to the list of configuration parameters for more information.

Maximum Capacity

The Inlet Capacity of a manhole or pit may be constrained to a Maximum Capacity whereby all flow is captured up to the entered value after which all excess flow bypasses, ponds or is lost from the system depending on what type of Ponding is enabled and the existence of overland flow conduits. If there is ponded water at the surface and no approach flow, water will be captured at this capacity.

Efficiency Factor

The Inlet Capacity of a manhole or pit may affected by blocking (an efficiency factor < 1) or installing multiple inlets (an efficiency factor > 1). Enter the appropriate factor here.

Inlet Capacity Type:

The Inlet may be defined by Maximum capacity only, by approach flow, by approach depth or by a HEC-12/HEC-22 equation. 

    • For the Approach Flow and HEC-22 options, when flow = 0, the Maximum Capacity value is used.
    • When node is linked to a 2D cell use the Rated by Approach Depth and the Calculate Depth by Node Storage Characteristics options.

Rated by Maximum Capacity Only. If this option is selected flow up to the Maximum Capacity entered above is captured. Flow in excess of this amount will be lost or diverted according to the type of Ponding is selected.

Rated by Approach Flow. The Inlet Capacity may be entered as a manhole or pit rating curve of Approach Flow versus Captured Flow. The “Captured” component of the rating curve is adjusted by the Efficiency Factor entered in this dialog.

A couple of side effects are that, firstly, if ponding is allowed the maximum diverted flow may be greater than expected particularly if using an inlet rating curve, and secondly, the flow in the conduit may be greater than the diverted inflow.  This is because a volume of water (equivalent to the flow rate) is diverted and this water is then converted to a flow rate in the conduit according to the pipes hydraulic characteristics. If the pipe is initially dry you might see a higher peak in the pipe flow rate than the flow rate being diverted. Secondly, the rating curve should have a zero, zero pair so that with no approach flow there will not be any captured flow. A non zero value for captured flow will be introduced with no approach flow resulting in continuity error if the first pair of data is 0, X with X being a non zero captured flow.

In versions prior to 9.0 the configuration parameter DEPTH_IRC was used to re-define the Approach Flow vs Captured Flow curve to be Approach Depth vs Captured Flow. This parameter is still active.

Rated by Approach Depth. The Inlet Capacity may also be entered as a manhole or pit rating curve of Approach Depth versus Captured Flow. The “Captured” component of the rating curve is adjusted by the Efficiency Factor entered in this dialog.

The depth may be defined by:

        1. the storage capacity of the node; either the depth of the storage node if Storage is selected, or by the ponding area/depth defined under Junction Defaults, or
        2. the Pavement Characteristics used to calculate gutter depth in the Calculate Gutter Spread option.

Note: the rating curve should have a zero, zero pair so that with no depth there will not be any captured flow. A non zero value for captured flow will be introduced with 0 depth resulting in continuity error if the first pair of data is 0, X with X being a non zero captured flow.

HEC-22. The third alternative utilizes the HEC-12/HEC-22 inlet capacity procedures. This requires the selection of an HEC-22 Inlet and a Pavement Crossfall from the Global Database. 

Calculate Gutter Spread

If this option is selected the gutter width, depth and velocity is calculated according to the pavement crossfall characteristics.

A separate addendum consisting of the complete FHWA documentation for HEC-12 "Design of Highway Pavements" is provided as part of the documentation for user training courses. Contact your account representative for additional information.

HEC-12 Combination Grate and Curb Inlets

 

This type of inlet consists of both a curb-opening inlet and a grate inlet usually located side-by-side, although the curb opening may be partially located upstream of the grate.

Curb Length (Lc). The length (ft, m)of the curb opening.

Curb Height (H). The height (ft, m)of the curb opening. The inlet operates as a weir at depths up to the curb opening height and as an orifice at depths greater than 1.4 times the height. At depths between 1.0 and 1.4 times the height the flow is transitioned. For curb openings other than vertical see the separate HEC-12 documentation for the effective height.

Grate Length (Lg). The nominal length (ft, m) of the grate.

Grate Width (W). The nominal width (ft, m) of the grate.

Grate Offset (Dg). The distance (ft, m) between the downstream end of the curb opening and the downstream end of the grate.

Type of Grate

P-1-7/8-4Parallel bar grate with bar spacing 1-7/8-in on center and 3/8-in diameter lateral rods spaced at 4-in on center (see figure 8 of the HEC-12 documentation).

P-1-7/8. Parallel bar grate with bar spacing 1-7/8-in on centre (See figure 8 of the HEC-12 documentation).

P-1-1/8. Parallel bar grate with 1-1/8-in on centre bar spacing (see figure 9 of the HEC-12 documentation).

30 degree Tilt Bar. 30 degree tilt bar grate with 3-1/4-in and 4-in on centre longitudinal and lateral bar spacing respectively (see figure 12 of the HEC-12 documentation).

45 degree Tilt Bar. 45 degree tilt bar grate with 2-1/4-in longitudinal bar and 4-in transverse bar spacing on centre (see figure 11 of the HEC-12 documentation).

Curved Vane. Curved vane grate with 3-1/4-in longitudinal bar and 4-1/4-in transverse bar spacing on centre (see figure 10 of the HEC-12 documentation).

Reticuline. "Honeycomb" pattern of lateral bars longitudinal bearing bars (see figure 13 of the HEC-12 documentation).

HEC-12 Curb Inlet

Curb-opening inlets are vertical openings in the curb covered by a top slab.

Height (H). The height (ft, m) of the curb opening. The inlet operates as a weir at depths up to the curb opening height and as an orifice at depths greater than 1.4 times the height. At depths between 1.0 and 1.4 times the height the flow is transitioned. For curb openings other than vertical see the separate HEC-12 documentation for the effective height.

Length (L). The length (ft, m) of the curb opening.

 HEC-12 Grated Inlet

A grated inlet consists of an opening in the gutter covered by one or more grates, usually metal.

Width. The nominal width (ft, m) of the grate.

Length. The nominal length (ft, m) of the grate.

Type of Grate

P-1-7/8-4. Parallel bar grate with bar spacing 1-7/8-in on centre and 3/8-in diameter lateral rods spaced at 4-in on centre (see figure 8 of the HEC-12 documentation).

P-1-7/8. Parallel bar grate with bar spacing 1-7/8-in on centre (See figure 8 of the HEC-12 documentation).

P-1-1/8. Parallel bar grate with 1-1/8-in on centre bar spacing (see figure 9 of the HEC-12 documentation).

30 degree Tilt Bar. 30 degree tilt bar grate with 3-1/4-in and 4-in on centre longitudinal and lateral bar spacing respectively (see figure 12 of the HEC-12 documentation).

45 degree Tilt Bar. 45 degree tilt bar grate with 2-1/4-in longitudinal bar and 4-in transverse bar spacing on centre (see figure 11 of the HEC-12 documentation).

Curved Vane. Curved vane grate with 3-1/4-in longitudinal bar and 4-1/4-in transverse bar spacing on centre (see figure 10 of the HEC-12 documentation).

Reticuline. "Honeycomb" pattern of lateral bars longitudinal bearing bars (see figure 13 of the HEC-12 documentation).


Note: A separate addendum consisting of the complete FHWA documentation for HEC-12 "Design of Highway Pavements" is provided as part of the documentation for user training courses. Contact your account representative for additional information.

HEC-12 Slotted Inlet

A slotted inlet is a special type of gutter inlet consisting of a pipe cut along the longitudinal axis with a grate of spacer bars to form slot openings.

Slot Length (Lg)The length (ft, m) of the slot.

Slot Width (W). The nominal width (ft, m) of the slot. Slotted inlets function in essentially the same manner as curb opening inlets, ie. as a weir with flow entering from the side.

Ponding

Ponding is the management of the water when the HGL reaches the spill crest (ground elevation). The available ponding options are:

None

The default mechanism is for surcharged water that breaks the ground surface to be lost from the network. The duration and amount of water lost is tabulated in the output file in Table E20 and is also available using most of the Results decision support tools (DSS) located in the Results menu.

Allowed

This option is for junction flood storage. Using this option, the flooded water will be stored at this node until the connected conduits can handle the excess flow.

By enabling this check box an artificial storage is created at the surface level of this node. The storage is of the form:

Ponding Area = A e ^ (B * Surface Depth)

Water is allowed to pond until there is sufficient hydraulic capacity within the system for it to rejoin the network. The coefficient A and exponent B for the above equation may be modified in the Junction Defaults section of the Job Control dialog. The values are reported in the Job Control Section of the output file.

This should only be used as a quick estimate of flood storage. If a significant volume of water is ponded then a more detailed Storage Node should be entered at this location to represent the actual storage relationship.

Sealed

Using this option the hydraulic grade line will rise above the ground surface spill crest but no volume is lost. It is accomplished internally by projecting the default node area upward to contain the water, which allows the HGL to rise above the surface, which creates pressure but no flow is lost. It is most commonly used for the connection of pumps to force mains and nodes that are placed for welded joints in siphons.

Link Spill Crest to 2D

Using this option the water that would normally spill out of the system is linked and passed to the 2D grid for overland flow routing. At this location there is a continuity balance with the 2D grid as the water leaving the node is the amount of water received by the grid at the common cell. In addition 2D grid flows can enter the node if the HGL is below the surface level of the node. Flows can be restricted into the node using the 2D Inflow Capture. It is important in this type of model construct that the spill crest of the node match the cell elevation. This ensures that the node does not rise above the 2D grid like a smokestack preventing water to be captured unless a very large depth is on the surface. A tool is available to generate ground elevations from a TIN.

Note: When a node is linked to a 2D cell and Inlet Capacity option is invoked, the Rated by Approach Depth and the Calculate Depth by Node Storage Characteristics are recommended options.

This option must also be selected in 1D/2D river simulations. If there is a node with 1D/2D Connections then the Link Spill Crest to 2D must also be selected in order to create a valid 2D boundary condition with the node. Simply connecting the node with the 1D/2D Connection polyline is not enough.

Link Invert to 2D

This special case is used to connect culverts to the 2D Grid. The water that is flowing on the 2D Grid can directly enter the upstream node of the culvert using the node invert. Ideally this invert matches the cell elevation. The culvert upstream invert can be above this level if it is perched above the ground. To link the culvert exit to the 2D grid the downstream node would also have the Link Invert to 2D. The invert elevations can be set to the TIN elevation using the Tools->Modify Elevations->Read Inverts from TIN files.

Node Invert Elevation

The junction invert elevation (ft or m) is defined as the physical bottom of the junction. It is not necessary to have one conduit with an invert elevation equal to the node invert elevation. However, the conduits must not have invert elevations below the node invert.

The node invert elevation is usually defined as the invert elevation of the lowest link connected to the junction. Below this level water would need to accumulate before flow could leave the junction.

2D Inflow Capture

The 2D Inflow Capture equation is a basic orifice equation and this dialog is used to specify a power curve to represent the capture of 2D flow at a node.

Q (cfs, cms) = coefficient × 2D cell depth (ft, m) ^ exponent

  • coefficient > 1
  • 2D Inflow Capture setting for node overrides default setting in 2D Job Control.

*Please note: global 2D Inflow Capture which can be specified within the 2D Job Control settings will apply to all nodes which DO NOT have local settings applied and the 2D Inflow Capture option checked. If you have checked the 2D Inflow Capture option selected at a node whatever inflow capture parameters/configuration that is specified locally will be used, WHETHER OR NOT the 2D job control setting is selected. If no sharing of flow between the 1D node and the 2D surface is desired the 1D node should not use either Link Spillcrest to 2D or Link Invert to 2D (see Ponding) option as well as not check the 2D Inflow Capture option at the given node.

Initial Depth

Enter the Initial node depth ( in ft or m). Initial water depths at junctions are optional. They are depths from the node invert and not an elevation value. If they are entered they will be used to begin the simulation in conjunction with initial flows entered for the conduit in the "Conduit Data" dialog box. If initial heads are omitted but initial flows are entered, then initial heads will be estimated on the basis of normal depth in adjacent conduits.

Globally all nodes in a model can be initialized to the same elevation by using the Configuration Parameter ZREF or by having a fixed backwater elevation outfall that does not have a tide gate. Data entered in

Constant inflows may be input to the system and the "initial conditions" established by letting the model run for enough time steps to establish steady-state flows and heads. The hot start capability may then be used to store these initial conditions for use at the beginning of additional simulations.

Inflow Data

Constant Inflow

Flow. Use this field to input constant flow information to a hydraulics node (in ft3/s or m3/s. 

Pollutant Loads. Net constant flow entering (positive) or leaving (negative) the node (ft³/s or m³/s). Using a negative value results in a withdrawal from the node. Negative constant inflows can only work if the flow rate being demanded exists.

If the Pollutant List check box is enabled under Hydraulics Job Control you will also be able to enter constant pollutant concentrations at this location in the dialog shown below. This allows for hourly and/or daily peaking factors to be used. With this dialog a second diurnal pattern can be added to a single node.

A common application for constant inflows is to represent a base flow in storm water systems and infiltration/inflow to manholes in Sanitary Systems.

Time Series Inflow

Time series inflow may be added to a node using any or all of the following options:

User Inflow

The Hydraulics layer provides for manual input of inflow hydrographs in cases where you wish to run the Hydraulics layer alone without the use of an Interface

 

Time

Time of day in decimal hours, 0 is midnight on the starting day of the simulation entered in the Hydraulics Job Control dialog. The time does not re-start at zero and should increase past 24 if necessary.

Flow Rate

Flow rate for the corresponding time (ft³/s or m³/s).

It may also be used to add additional input hydrographs, either at the same or different nodes to those available in the Interface File. Hydrograph time input points can be specified at any convenient time. Only one user hydrograph is permitted per node. When multiple flows must enter a node they must be summed external to the program or passed to the node through an interface file or other pathway.

If the Pollutant List check box is enabled under Hydraulics Job Control you will also be able to enter pollutant concentrations at the corresponding time as shown in the dialog below.


Gauged Inflow

Use this dialog to define a file containing gauged data .

 


Filename. This can be any name, however the file type must be a text file, fixed space or free format (space or comma delimited).

Station. The data is considered valid if the station name entered in this dialog matches the station field entered in the file format. If the station is blank all data in the file will be used.

File FormatThis is a Global Database record used to define the structure of the file. When you click on the select button you will be presented with a list of available records from which you should make a selection. Select the file format of the file containing the inflow data.

Edit will show the data, as it will be interpreted from reading the text file.


Dry Weather Flow

Multiple DWF patterns Dry weather flows can be calculated using hourly and weekly peaking factors. These flows may be constant for the hour by using the configuration parameter INTERP_DWF=OFF or interpolated from one hour to the next (default). Dry weather flow can be generated using one of three methods:

Direct Flow

The Flow Rate, Peaking Factor and Temporal Variation are the only mandatory data required. The flow rate is in the units specified in this dialog. The peaking factor is dimensionless. The flow rate and peaking factor are multiplied together to give the total flow, which is multiplied by the hourly and daily temporal variation to give the model flow for the current time step.

Unit Flow Rate

The Flow Rate, Area and Peaking Factor and Temporal Variation are the only mandatory data required. The flow rate is in the units specified in this dialog per area unit. The area is in the same units as the flow rate and the peaking factor is dimensionless. The flow rate, area and peaking factor are multiplied together to give the total flow, which is multiplied by the hourly and daily temporal variation to give the model flow.

Census-Based

The Flow Rate, Area, Density, Peaking Factor and Temporal Variation are all required for this method. The flow rate is in the units specified in this dialog per area unit. The area is in the same units as the flow rate and the peaking factor is dimensionless. The flow rate, area and peaking factor are multiplied together to give the total flow, which is multiplied by the hourly and daily temporal variation to give the model flow.

For example, using the data from the dialog above:

If the method was Direct Flow, then Q

= 300 liters/day x 1 (peaking factor)

If the method was Unit Flow Rate, then Q

= 300 liters/day/hectare x 4.21 hectares x 1

= 1,263 liters/day

If the method was Census-Based, then Q

= 300 liters/day/person x 4.21 hectares x 21 persons/hectares x 1

= 26,523 liters/day

The units presented in the output after the simulation will be ft³/s or m³/s. 

Interface File Flow

This item is inactive unless an interface file is selected for the Hydraulics Mode. When checked the node is permitted to receive inflows from the interface file. Entering a percentage of 0 to 100 percent allows the user to limit the amount of flow entering a node. 

Storage Node Data

Storage devices may be in-line or off-line and act as flow control devices by providing for storage of excessive upstream flows, thereby attenuating and lagging the hydrograph from the upstream area. A storage node may be placed at any number of junctions in the network. The elevation of the top of the storage (Node Surcharge Elevation) must be at least as high as the highest crown at the junction. In most cases when modeling open storage i.e. ponds, lakes, wetlands the spill crest level is the top of bank. For the case of underground storage the spill crest level is the crown or top of the storage.

The only difference between a storage node and a regular node is that an additional surface area of the amount entered here is added to that of the connecting pipes. All nodes have a default surface area defined in the Job Control > Junction Defaults. Note also that the crown is set at the top of the storage "tank". When the hydraulic head at a node exceeds this crown, the node goes into surcharge. Unless the "Ponding" flag is enabled, flow is lost from the system when the water level reaches the spill crest.

If ponding is Allowed then the invert elevation of the Storage Node set at the Spill Crest elevation and the spill crest is set to the original spill crest plus the maximum depth specified for the storage node.

If surcharge level is defined below ground level, storage function does not work once water level reaches above this level and default manhole area is used from here on. Water is lost at HGL > node Spill Crest and if Ponding is set to None. Water is not lost and HGL continue rising using default manhole area if Ponding is Allowed. These conditions are summarized in the table below.

Ponding

HGL

Result

None

< Surcharge Elevation

Water stored according to Storage Method

None

> Spill Crest

Water lost from network

Allowed

< Surcharge Elevation

Water stored according to default manhole area

Allowed

> Surcharge Elevation

Water stored according to Storage Method

The default ponding curve is not used for the storage node.

Basin Optimization

 

The Basin Optimization tool has four design options which are discussed below. To use the Basin Optimization design tool select an optimization option, enter the value(s), and click on OK. The result including new conduit size, if applicable, will appear after the next model solve.

The Limit d/s discharges optimization is not allowed if the Available Pipes option is enabled in the Design Constraints dialog.

Basin/storage optimization is related to the starting values and the solution finds a local optimum value, and may not find an overall optimum. Therefore, you should be starting with reasonable values for storage volume and outlet size.

Design Option 1: Resize d/s pipes

Required Input: Maximum Water Level of Storage Node Basin

Method Result: The software will design (resize) the downstream pipe(s) such that the Maximum Water Level at the storage node is ≤ the user defined value. The algorithm will increase the pipe size and restart the simulation when the Maximum Water Level is exceeded. If the water level exceeds the specified maximum HGL, the size of basin outlet conduit(s) are increased. If pipe sizes are available from Available Pipes dialog in Hydraulics Job Control settings, the next larger pipe will be selected. If no pipe sizes have been defined, the diameter (width for rectangular and trapezoidal pipes) will be increases by the following offset values.

Metric units:

US units:

5cm if the diameter is < 0.15m

7.5cm if the diameter is < 0.9m

15cm in all other cases

1 inch if the diameter is < 4 inches

2 inches if the diameter is < 1ft

3 inches if the diameter is < 2.5ft

6 inches in all other cases

Design Option 2: Limit d/s discharges

Required Input: Maximum Flow Values for Outlet conduits

Method Result: The software will limit the discharge from the storage node to be ≤ the user defined Max Flow. All links directly downstream of storage node appear in the Outlet Pipe table. The resulting maximum outflow from the storage node is the sum of the flows in the conduits in this table. If the maximum flow is exceeded, the outlet pipe size(s) will be decreased.

The optimization will only reduce the conduit size when the flow rate is exceeded and it will not be increased from the original size. Keeping this in mind it may be advantageous start with a larger conduit size to ensure the starting conduit size is large enough to pass the peak flow.

If pipe sizes are available from Available Pipes dialog in Hydraulics Job Control settings, the next smaller pipe will be selected. If no pipe sizes have been defined, the diameter (width for rectangular and trapezoidal pipes) will be decreased by the following offset values

Metric units:

US units:

5cm per default

7.5cm if the diameter is ≥ 0.9m

1 inch per default

2 inches if the diameter is ≥ 1ft

3 inches if the diameter is ≥ 2.5ft


Note: If no smaller pipes are available or the offset decrease would result in a negative diameter, no further decrease will be conducted. Further, this option will only reduce the original pipe size entered, it will not increase the pipe size. Therefore the user should ensure that the original pipe size is larger than needed so the program can reduce/optimize the size as expected. 

Design Option 3: Resize Basin

Required Input: Maximum Water Level of Storage Node Basin

Method Result: If the basin’s maximum HGL is exceeded, the basin will be resized. For the different storage types the following resizing operations are performed:

Constant area:

The Constant Storage Area will be multiplied by the increasing factor

Power function:

The Power function coefficient will be multiplied by the increasing factor

Stepwise linear:

Each surface Area will be multiplied by the increasing factor

The basin resizing algorithm runs in two phases, the exponential search phase and the fine tuning phase. In the exponential search phase the increase factor is 2. If a sufficient basin size is found, the algorithm will revert to the last insufficient size (divide by 2) and switch to the fine tuning phase. If the basin size is found to be insufficient in the fine tuning phase, the basin will be increased by 5%.The increase in the fine tuning phase can be controlled via a configuration parameter: BASIN_INCRFAC=1.05 would correspond to 5%. The lower limit is 1.001 and the upper limit is 1.25. 

Design Option 4: Resize of d/s Pipes and Basin

Required Input: Maximum Water Level of Storage Node Basin and Maximum Flow Values for Outlet conduits

Method Result: This method first designs the basin as outlined in Design Option 3 (Resize Basin). If a sufficient size is found, the flows on the out conduits are checked. If a flow limit is exceeded, the pipe size is decreased as in Design Option 2 (Limit d/s Discharges) and the method restarts with designing the basin. The complete restart is necessary since decreasing the outflow will cause an increase of the HGL.

This method can require a lot of restarts. However, asymptotically it will produce results that come close to the specified values. If the pipes were replaced every time a flow limit is exceeded, less restarts would be required; however, this replacement might not have been necessary as the basin could have been replaced later, causing the HGL to fall and subsequently the outflow making the replacement unnecessary. That is the reason why the above method has been chosen.

Basin Infiltration

Basin Infiltration has been added for storage nodes, in the 2013 version and beyond. Infiltration rates can vary with depth and are reported in xptables. Table E19 of the output file, and the detailed printout for a node reports the amount of infiltration occurring in the time interval.

After toggling the Infiltration flag, the basin infiltration dialog appears:

 

Here, the user can define the infiltration parameters for the basin.

In the Review Results Properties dialog, Basin Infiltration can be selected and displayed in the Review Results graphs as well. 

 

Storage Method

Stepwise Linear Storage

  

Click on Insert to add blank rows to table. Enter data as:

Depth. This is the depth above the node invert or (spill crest) as defined in the Storage Node Data dialog.

Area. Surface area of storage node (acres or hectares).

The depth-area data are integrated to determine the depth-volume relationship for the junction. The first area value should be a non-zero value. To approximate zero, use a small value, such as 0.0001.

There are a number of Configuration Parameters that can be used to define how the area and depth variables are used during the analysis, these include:

AS

Use area (acres or hectares) and stage (ft or m) to define the storage node (default).

VS

Use volume (ft³ or m³) and stage (ft or m) to define the storage node.

AE

Use area (acres or hectares) and elevation (ft or m) to define the storage node.

VE

Use volume (ft³ or m³) and elevation (ft or m) to define the storage node.

Area refers to the area of the reservoir at the given stage or elevation.

Volume is the total volume between the datum and the given elevation.

Power Function Storage

A power function is given by

Area = Coeff x DepthExponent

Where:

Area =

Surface Area (ft² or m²).

Depth =

depth above junction invert (ft or m).

Coeff and Exponent

are supplied by the user.


Coeff. 
The coefficient of the power function for determining storage volume.

Exponent. The exponent of the power function for determining storage volume.

Constant Area Storage

Constant surface area (units used are ft² or m²), refers to storage volume per ft (or m) of depth.

Conceptually, storage junctions are "tanks" of constant surface area over their depth. A storage tank may be placed at any node in the system, either in-line or off-line.

Measure Depth From

The elevation at which the storage node becomes effective may be set to either the node invert or the spill crest depending on which radio button is selected.

If Node Invert is selected the storage volume is effective starting from the node invert. If Spill Crest is selected, then the default manhole area is used until the water elevation reaches the spill crest whereupon the additional storage volume is added (with the default manhole area no longer included).

Surcharge Elevation

Elevation of upper limit of storage as calculated by the Storage Method. Above this level the surface area of the node is the default manhole surface area. This must be higher than the crown of the highest pipe connected to the storage junction (ft or m). If this value is 0 it is set equal to the Spill Crest Elevation.

The Node Surcharge Elevation is set below the ground elevation for an underground storage tank.

Outfall

Four types of outfall configurations can be simulated in the Hydraulics layer:

  • a single conduit with or without a tide gate,

  • and a diversion (orifice, weir, pump etc.) with or without a tide gate.

You can have any number of outfalls and you can have multiple conduits connected to the same outfall.  The latter can be accomplished with a mutlilink or any number of links terminating at the node.  The governing rule for a node to be allowed to be an outfall is that it must have at least one active link in to the node and no conduits leaving the node.

The outfall boundary condition can be described in different ways, as shown below:

The outfall is a conduit which discharges to a receiving water body under given backwater conditions. The free outfall may be truly "free" if the elevation of the receiving waters is low enough, or it may consist of a backwater condition. In the former case, the water surface at the free outfall is taken as critical depth, normal depth or whichever is less. If backwater exists, the receiving water elevation is taken as the water surface elevation at the free outfall unless the normal or critical depth is greater.

A weir outfall is a weir which discharges directly to the receiving waters according to relationships given in the weir section. This outfall type is further described in Hydraulics Multiple Conduit and Diversion Link Data

Type 1 - Free Outfall (NTIDE = 1)

No water surface at an outfall (elevated discharge). The elevation of the receiving waters is low enough that a backwater condition may be disregarded. The water surface at the free outfall is taken as critical or normal depth or whichever is less as specified in the above dialog. The default (preferred) condition is to use the minimum of Yc or Yn.

Type 2 - Fixed Backwater ( A1)

The elevation of a fixed backwater condition (feet or metres) is entered in the user entry field located to the right of the "Type 2, Fixed Backwater" button. The elevation actually used is the maximum of the value entered and the Normal/Critical depth criterion entered above.

If the tide gate is not checked and the user has selected the Fixed Backwater condition then the entire model will be initialized to the fixed backwater level at the beginning of the simulation.

Type 3.1 - User Tide Coefficients (NTIDE=3)

A tide whose period and amplitude are described by user supplied tide coefficients.

The function form used by the Hydraulics layer for the tide is:

TIDE = A1+A2*sin(wT)+A2*sin(2wT)+A4*sin(3wT)

+A5*cos(wT)+A6*cos(2wT)+A7*cos(3wT)

where

TIDE = elevation of outfall water surface (feet or metres)

T = current time (hours)

w = angular frequency 2*pi/W (radians/hr)

W = tidal period (hours)

A1 - A7 = coefficients (feet or metres)

Type 3.2 - Computed Tide Coefficients (NTIDE=4)

A tide which will be computed by the Hydraulics layer based on a curve fitted to a specified number of stage-time points describing a single tidal cycle.

Convergence Criterion (DELTA)

The convergence criterion used for iteratively fitting the tidal function (feet or metres).

Tidal Period (W)

The tidal period in hours.

Echo Results (NCHTID)

Print control for tidal information. Echo the information on stage/history to the text output file.

Stage History (J3 - K0=0)

The type of tidal input. Input is in the form of a time series of tidal heights. The tidal coefficients are calculated iteratively achieve a best fit using the equation shown above.


Time (TT)

Time of day in hours. Increase past 24 hours if necessary.

Stage (YY)

Tidal stage for the time shown in the adjacent cell (feet or meters).

Low/High Tide (K0=1) -

The type of tidal input. Input is in the form of high and low water values found in the tide tables (HHW, LLW, LHW and HLW). The tidal coefficients are calculated iteratively to achieve a best fit using the above equation.

Type 3.3 - User Stage History (NTIDE=5)

A stage-history of water surface elevations input by the user. The program uses linear interpolation between data points. This is a common option for outfalls in rivers, especially when modeling high return period events when the level of the receiving water will impact the outfall.


Echo Results (NCHTID)

Print control for tidal information. Information on stage/history will be echoed to the text output file if this flag is enabled.

Coordinates 


Time (TT). Time of day in decimal hours. Increase past 24 hours if necessary.

Stage (YY).  Tidal stage for the time shown in the adjacent cell (feet or meters).

Type 4 - Flow History (NTIDE=6)

 

Time (TT)

Time of day in decimal hours. Increase past 24 hours if necessary.

Flow

The flow rate corresponding to the adjacent time (ft3/s or m3/s).

A flow history Boundary Condition may be used as a demand function on the drainage system. Examples of this would be wastewater treatment plants, pumps or water diversion for irrigation.

Type 5 - User Rating Curve (NTIDE=7)

Flow

Flow rate in (m^3/s or ft^3/s).

Stage

The elevation corresponding to the flow entered in the adjacent cell (ft or metres). If the USE_OUT_RC_DEPTH Configuration Parameter is set then the stage can be entered as a depth rather than an elevation.

A rating curve Boundary Condition is used to fix both the stage at the outfall node and the flow in the connecting conduit. The model will iterate until the flow and stage are in balance. It can be used to connect two Hydraulics layer models together.

Type 6 – Natural Section

This outfall type can be used when a HEC RAS model has been imported, for example.  The final downstream cross section, in conjunction with the user’s choice of critical, normal, or the minimum of the two depths, acts as the downstream boundary condition in the model.  Please see image below. 

Tide Gate (JFREE orJGATE)

If this flag is enabled the outfall is assumed to have a tide (flap) gate and back-flow is not permitted. When there is a tide gate on an outfall conduit, a check is made to see whether or not the hydraulic head at the upstream end of the outfall pipe exceeds that outside the gate. If it does not, the discharge through the outfall is equated to zero. If the driving head is positive the water surface elevation at the outfall junction is set in the same manner as that for a free outfall subjected to a backwater condition.

If the tide gate is not checked and the user has selected the Fixed Backwater condition then the entire model will be initialized to the fixed backwater level at the beginning of the simulation.

Options

The Node Data Options dialog allows you to flag nodes that will have individual hydrograph results saved and whether to plot water levels in the output file that will be created from the Hydraulics layer simulation.  

Detail Printout - Nodes with this flag enabled in the Hydraulics layer will have a comprehensive list of results such as depth, stage, area, volume, inflow, outflow etc. for all saved time steps. The saved time steps is set in the HDR: Job Control > Output Control >Summary Interval.  A value of 5 there means every 5th time step.

Plot Water Levels - Nodes with this flag enabled in the Hydraulics layer will plot water levels and will be saved to the output file created from the Hydraulics layer simulation.  This option creates a rudimentary graphic plot using text characters in that file and is typically not required since a high quality and color graphic exists using Review Results.