Sewer Network Settings

This command sets up the working environment for the design and analysis of sewer, sanitary and utility networks and should be done before starting the construction of networks.

General Settings

Network Type: Indicate if the sewer network conveys storm runoff flow (Storm Sewer) or man-made flow (Sanitary/Utility). If the Sanitary/Utility network type is specified, the controls found in the Drainage tabare disabled.

Active Files: Select a new or existing sewer (.SEW) file to become the active sewer file and a "surface file" for ground cover calculations:

• Surface by Rim Elevations- When this option is enabled, the ground surface elevation is derived as an interpolated grade from structure rim elevation to structure rim elevation and the Surface Model option is disabled, or,
• Surface Model- When the Surface by Rim Elevationsoption is disabled, select a valid surface model (.TIN, .FLT, .GRD) that blankets the sewer network. The ground surface elevation is obtained from the surface model along the pipe reach.

Link Sewer Network to Reference Surface and Centerlines: Indicate the method of how the sewer network should react if there are changes to either the specified Surface Model or any related Centerlines that are specified in either the Create Sewer Structurecommand or the Edit Sewer Structurecommand. The following types of corrections can be made:

1. If the reference Surface Model changes, the structure rim elevation can be updated and there are two options for updating the invert elevation, discussed in the Elevation Update Methodsection below.
2. Each structure has the option to assign a reference centerline and the structure will record the station and offset from this centerline. When the reference centerline of a structure changes, the structure can be moved to the position of the recorded station and offset along the newly modified centerline.

Depending on the desired level of end-user control vs. automation, one of the following corrective options can be specified:

• Off- When a Surface Model or a Centerline changes, corrective action to the sewer network is notperformed. Any corrections to the sewer network will need to be performed manually or through the use of the Check Reference Centerlines and Surfacecommand which will compare the sewer network with the referenced file(s),
• Prompt- When a Surface Model or a Centerline changes, you will be offered a choice for a follow-up action of whether to update the structures or not.
• Auto- When a Surface Model or a Centerline changes, corrective action is automaticallyperformed on the sewer network and any elevation updates will be calculated based on the Elevation Update Method.

Elevation Update Method: Indicate how the invert elevation(s) should change as a result of a change to a Surface Model (when the "linking" method is set to Auto):

• Update Depth, Hold Inverts- When this option is selected, the former invert elevations are retained and new depth of cover amounts are re-calculated, or,
• Update Inverts, Hold Depth- When this option is selected, the former depth of cover amounts are retained and new invert elevations are calculated

The Inlet Library, Sewer Structure Library, Pipe Size Library, Pipe Manning's N Library, and Plan View Label Settings can be set to the current project file CURRENT or SPECIFIC. If specific is specified the user can SET the location of the library files to be used.

The SaveAs button saves all the settings to a .SNS file and Load button loads all the settings from a previously saved .SNS file.

Design Settings

Direction: The network can be designed from Downstream to Upstream or vice versa. If the design direction is from Downstream to Upstream, the first structure created is generally the outfall and the current structure and its downstream pipe are highlighted in the plan view. Otherwise, the network is created from one of its entrances toward the eventual outfall and the current structure and one of its upstream pipes are highlighted.

Auto Set All Sewer Pipe Sizes: When enabled, this option disables the Pipe Sizecontrol found on the Pipe tabof the Create/Edit Sewer Structurecommand and sizes the pipe(s) automatically to the closest available pipe size as specified in the Pipe Size Library.

Auto Set All the Invert Elevations of the Sewer Network: When enabled, this option:

1. calculates initial Invertelevations found on the Structure taband the Pipe tabof the Create/Edit Sewer Structurecommand, and,
2. enables the Add Step Up to Minimize Excavationcontrol, and,
3. disables the Auto Match Pipes at Junctioncontrol.

Add Step Up to Minimize Excavation: When enabled, this option allows pipe inverts to be placed above the current invert elevation up to the Max. Step Upvalue to minimize excavation and create a potential "drop manhole."

Auto Match Pipes at Junction: When enabled, this option sets the pipe inverts automatically when creating a new pipe in order to match it to other pipes at the same junction.

Auto Set Invert In When Change Invert Out So Invert Out Not Higher: When enabled, this option will adjust the invert in to the pipe to be higher than the invert out.

Use The Connection Wizard When Add Pipes: This will open the pipe connection wizard when the user selects the ADD or PICK an available pipe connection on the docked dialog box under the Pipe Tab.

Minimize Pipe Sizes in Design: When enabled and if the sewer network is being designed, this option will ensure the pipes are not oversized as extra calculation iterations are performed.

Automatic Watershed Analysis: When enabled, this option performs an automatic watershed analysis of the referenced Surface Filefound on the General tabto determine the drainage area serviced by the new structure. This action is the same as clicking the Drainage Area - Calcbutton found on the Drainage tabof the Create/Edit Sewer Structurecommand.

Auto Connect Structures: This option determines how to connect a newly created structure to the network:

• On- Automatically connects a pipe between the new structure and the closest structure, or,
• Off- Does not connect a pipe to the newly created structure (the structure would need to be manually connected to the network via the Connectioncontrol found on the Pipe tabof the Create/Edit Sewer Structurecommand or,
• Prompt- Provides an option as to whether or not a pipe should connect to the new structure.

HGL Computation Method: There are three methods to calculate HGL and EGL: FHWA Method, Virginia DOT Method and Just Full Capacity - Ohio Method. The differences are shown below.

1. FHWA Method

   The complete description can be found in "Drainage of Highway Pavement (HEC12) form the FHWA Hydraulic Engineering Circular 12. In this method, when the HGL at the downstream is above the critical depth, use the HGL elevation as the initial elevation and conduct non-uniform flow calculation; when the HGL is below the critical depth and normal depth is above critical depth (subcritical flow), set the HGL at critical depth and conduct non-uniform flow calculation; when the HGL is below the critical depth and normal depth is below critical depth (supercritical flow), set the HGL at normal depth and conduct uniform flow calculation.

2. Virginia DOT Method

   VDOT method is a simplified FHWA method. The first difference is the determination of the HGL at the downstream side of the pipe. In determining the HGL, begin with the actual tailwater elevation or an elevation equal to 0.8 times the diameter of the outlet pipe, whichever is higher. The second difference is that because the HGL is always greater than critical depth, non-uniform flow is conduct through all the pipes. Another difference is the velocity is normal flow velocity.
   

3. Just Full Capacity - Ohio Method

   One difference between FHWA method and this method is the optimal pipe size. The optimal pipe size is based on the smallest diameter pipe in which the design discharge for the selected storm frequency will not exceed the just full capacity of the pipe. This storm frequency is called Just Full Capacity Frequency. Just full capacity with a free water surface is considered to occur at 93.8% of the pipe diameter for circular conduits. Another difference is the determination of the HGL at the downstream side of the pipe, this method uses the tailwater elevation or critical depth plus half of the diameter of the pipe, whichever is greater, to determine the starting HGL.
   

   Friction Slope Averaging Method: Available methods are:

   • Arithmetic- S _fav= (S _fu+ S _fd)/2, or,
   • Conveyance- S _fav= ((Q _u+ Q _d)/(K _u+ K _d)) ², where
     • Q = Flow
     • K = Conveyance = (1.486/n)*a*r ^2/3(based on English units)
     • n = Manning's n-value
     • a = Flow area
     • r = Hydraulic radius
   • Geometric- S _fav= (S _fu* S _fd) ^1/2

   Tailwater Elevation At Outfall: Enter the water surface elevation at the outfall.

   HGL Offset from Rim Elev: This value is used to check the hydraulic grade line result. If some of the hydraulic grade lines are within this value from the rim elevation, alerts are presented to indicate the potential problem(s).

   

   Drainage Settings

   The drainage settings are used to set up the hydrology calculation method and rainfall information for the design of Storm Sewer networks.

   Hydro Methods: Select either the Rational method (the SCS Rainfall group becomes disabled) or SCS method (the Rational Rainfall group becomes disabled) for Peak Discharge calculations.

   Computation Methods: Indicate the computation method for the Storm Sewer network:

   • Peak Discharge- The Rainfall Durations are disabled and the peak flow of each drainage area is calculated by the selected Hydro Methodand the Storm Sewer network is designed to pass the peak flow, or,
   • Hydrograph- The Rainfall Durations are enabled and a runoff hydrograph of each area is generated and routed through the network.

   Adjust Rational Method Runoff Coefficient for Higher Frequency Storms this option would time the runoff coefficient with a constant to adjust the runoff coefficient. The constant for 25 year is 1.1, 50 year is 1.2 and 100 year is 1.25. The adjusted runoff coefficient is checked to make sure it's not greater than 1.0

   Use Different Rain Event for Inlet Gutter Spread and Ponding Depth Calculation: When enabled, this option enables an alternate rainfall event for either Rational or SCS calculation methods to determine inlet efficiency.

   Rational Rainfall: Specify the Rainfall, Return Period and Duration (if using the Hydrograph method) if using the Rational equation.

   SCS Rainfall: Specify the Antecedent Moisture Condition, Storm Type and rainfall map if using the SCS methodology.

   Always Capture All Inlet Flow (Bypass Disabled): You may elect to let the inlets to capture all drainage runoff.

   Min. Time of Concentration: This value will replace any calculated T _cthat is shorter than this value.

   Max. Gutter Spread: Indicate the largest allowable gutter spread for determining inlet effectiveness.

   

   Pipe Settings

   Cover: Enter the minimum and maximum depth of cover which is the distance from the surface elevation to the crown elevation along the pipes. Alternatively, enable either (or both) Librarytoggle(s) to use the value(s) specified in the Pipe Size Library.

   Velocity: Enter the minimum and maximum flow velocity for the pipes. The minimum velocity is about 2 to 3 ft/s (0.6 to 0.9 m/s) when the pipe is flowing full for self-cleansing. The maximum velocity should be less than approximately 15 ft/s (4.5 m/s) to prevent erosion of the pipe interior by suspended sediment and debris. Alternatively, enable either (or both) Librarytoggle(s) to use the value(s) specified in the Pipe Size Library.

   Slope: Enter the minimum and maximum slope range for the pipes in the network. The minimum slope should be sufficient to maintain the minimum velocity and the maximum slope is related to the maximum velocity. Alternatively, enable either (or both) Librarytoggle(s) to use the value(s) specified in the Pipe Size Library.

   Normal Slope: The normal slope is the initial slope used to place a pipe in the network.

   Max. Length: This is the maximum length between structures in a network before an alert is presented indicating a potential problem.

   Drop Across Junction: This is the drop across the inside of a junction. Depending on the Directionspecified on the Design tab, the Invert Up is either raised by this amount or the Invert Down is lowered by this amount.

   Pipe at Junction Match by: Indicate if pipes should be aligned by their inverts or crowns.

   Main Design Criteria: Indicate which criteria should be maintained if both the Minimum Coverand Minimum Slopecannot be satisfied. If Coveris selected, the Slope will yield and vice versa.

   Check Min. Cover: Define whether to check the minimum cover at the structures only or along the entire length of each pipe.

   Size Pipe At Target Flow Depth: When this option is enabled in design mode, the sewer pipes will be set to the sizes that are sufficient to maintain the target flow depth.

   
   
   

   Lateral Settings

   Lateral Slope: Allows the user to set a minimum and maximum lateral slope.
   

   Lateral Normal Slope: The normal slope is the initial slope used to place a lateral in the network.
   

   Hold All Lateral Pipe Slopes: This option sets how the lateral should change if mainline edits are made, and will hold the lateral slopes should the mainline be adjusted. Therefore both the connection and the cleanout elevation would change to hold the slopes.For more than one cleanout, all lateral slopes are preserved after modifying the main line pipe.
   

   Hold Slope of the Lateral Pipe Connected to Mainline: This option will adjust the first cleanout and lateral elevation if the mainline is adjusted.
   

   Hold Lateral Inverts At Cleanouts: This option will adjust the lateral connection to the mainline pipe and the cleanout invert would remain at the original elevation.
   

   Use Default Lateral Cleanout Symbol: Allows the user to select a symbol to be used as designation of the cleanout.
   

   Use Default Lateral Connection Symbol: Allows the user to select a symbol to be used as designation of the connection
   

   Initial Lateral Cleanout Name: The user can specify the initial cleanout name. A sequential numbers will start from this setting. For example CO1, CO2, CO3, etc.
   

   Initial Lateral Connection Name: The user can specify the initial connection name. A sequential numbers will start from this setting. For example CONN1, CONN2, CONN3, etc.

   Normal 0 false false false EN-US X-NONE X-NONE
   

   Error Check Settings

   Check Collision with Another Sewer Network During Design: When enabled, this option allows for potential conflict detection with another sewer network. Should the placement of a structure or pipe encroach on the Conflict Tolerance, an alert will be displayed to caution against the potential collision.

   Check Circular Manhole Size: When enabled, this option will check if the manhole is big enough to hold the incoming and outgoing pipes and will display an alert if any of the settings are violated.

   Show Pipe Crossings: When enabled, this option allows you to display the pipe crossings of current network opposed to any sewer networks or pipes that are drawn in the drawing.

   

   Display Settings

   Pipe Length: Specify how the pipe length should be displayed.

   Pipe Slope Annotation: Specify how the pipe slope should be displayed.

   Display Slope In: Specify to display slope in the unit of either distance/distance or %.

   Elevation Decimals: Indicate the desired amount of precision to display for elevation values.
   

   Show Circles:Places circles of max pipe length while placing structures.
   

   Pulldown Menu Location(s): Network > Sewer Network Setup
   Keyboard Command: swrconfig
   Prerequisite: None