Edit/Create Sewer Structure is a very powerful program for the design and analysis of storm sewer networks. A network is generally made up of pipes, structures and inlets. There may be more than one pipe entering a structure, but only one can exit. This command allows you to construct a graphical representation of a pipe network in active drawing, which contains all your design data, such as pipe and structure data, inlet characteristics, watershed information, and rainfall details.
The following is an sewer network example. The Edit/Create Sewer Structure dock dialog is on the left, while the network plan view in the active drawing is on the right with current structure and pipe highlighted. When you modify the edit fields on the dock dialog and click on Apply button, the network plan view will be updated automatically. Furthermore, you are allowed to work on the active drawing while the dock dialog is open.
|
| Edit/Create Sewer Structure
Dialog and Dynamic Editing in the Active Design Drawing |
The storm sewer network is solved using the standard step gradually
varied flow methods. This is an iterative procedure
used to determine the energy and hydraulic terms at the end of each
pipe. The direction of computation is from the most downstream pipe of
the network to the most upstream pipe. The following steady state
energy equation is used between the upstream and downstream ends of
every pipe.
Zu + Vu2 / 2g = Zd + Vd2
/ 2g + Hf
where: Zu = upstream water surface elevation
Vu2 / 2g
= upstream velocity head
Zd
= downstream water surface elevation
Vd2
/ 2g = downstream velocity head
Hf
= friction loss
The Manning's equation is applied to determine the friction slope.
Q = (M/n) A R2/3 Sf1/2
where: Q = discharge
M = 1.49 for
English unit, 1.0 for Metric units
n = Manning's
roughness coefficient
A = cross-sectional
area
R = hydraulic radius
Sf =
friction slope
Then the friction loss along the pipe is computed by the following
equation:
Hf = SfL
where: L = pipe length
With the friction loss calculated, the elevation of the upstream
water surface can be determined.
First set up a sewer file and surface model for current project. The sewer file can either be an existing file or a new one. From the Network > Sewer Network Setup menu in the Hydrology Module, choose Set Sewer File and Set Surface File. From the Network menu in the Hydrology Module, select Edit/Create Sewer Structure. If you are creating a sewer structure, pick a location in the plan view where you want to locate the structure, otherwise click on an existing structure symbol. After a structure has been located, the dock dialog displays, and the current structure symbol is highlighted in the drawing. Following is an example of the dock dialog.
 |
| Edit/Create Sewer Structure |
This dialog window has four tabs, Structure, Drainage, Pipe and Hydraulic Calc, which are used to enter structure data, watershed information, pipe data and display hydraulic calculation results respectively. The rainfall information is displayed on the top of the dialog. The following is the description of the functionalities of the buttons for designing sewer network.
Rainfall Library: This
function allows you to choose a rainfall from the rainfall library.
Please
refer to the documentation on Rainfall Library for details.
Settings: A function that opens
the settings dialog to set up the sewer network design and display
settings.
Design: After constructing the
sewer network, this function designs the sewer lines, such as pipe
inverts and sizes, depending on the given information and design
settings.
Analysis: This function
conducts a hydraulic calculation on the existing sewer network.
Analyze by Hydro: A Hydro
Processing method from Pizer is used to perform a hydraulic analysis on
the existing sewer network. Please refer to the documentation on Hydro
Processing.
Add: Adds a new structure to
the network at the location you pick in the plan view. Then the new
structure will become the active structure for editing.
Edit: This function allows you
to pick an existing structure symbol in the plan view to make the
structure
active for editing.
Remove: This function removes
the structure that you pick, and also removes the corresponding pipes
and then reconstruct the network.
Apply: Save the changes of
sewer network.
Up: Moves to the upstream
structure and makes it active.
Down: Moves to the downstream
structure and makes it active.
Close: Quit the sewer network
dock dialog.
The sewer network settings should be set up before starting the construction of a sewer network. The design and pipe settings will determine how the network is laid out. Click on Settings button, the Settings dialog displays.
 |
| Sewer Network Settings |
Design Direction: The
network can be designed from downstream to upstream or vice verse. If
the design direction is from downstream to upstream, the first
structure defined is generally the outfall, and the current structure
and its downstream pipe are highlighted in the plan view;
otherwise the network is designed from one of its entrances to the
outfall, and the current structure and one of its upstream pipes are
highlighted.
Auto Set All Sewer Pipe Sizes:
This toggle will disable the pipe size edit fields. When designing the
network, if this toggle is on, all the pipes will be sized
automatically to the closest available pipe sizes.
Auto Set All the Invert Elevation:
This toggle will disable the pipe and structure invert elevation edit
fields. When designing the network, if this toggle is on, all the pipe
and structure inverts will be set automatically.
Minimize Pipe Sizes in Design:
If pipe sizes are being designed, toggling this option will insure the
pipes are not over sized. Extra calculation iteration are performed.
Automatic Watershed Analysis:
Enables the automatic watershed analysis when adding and editing the
sewer components.
Friction Slope Averaging Method:
Available methods are Arithmetic, Conveyance and Geometric.
Tailwater Elevation At Outfall:
Enter the water surface elevation at the outfall.
Minimum and Maximum Cover:
Enter the minimum and maximum depth of cover, which is the minimum or
maximum distance from the surface elevation to the crown elevation all
along the pipe.
Minimum and Maximum Velocity:
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.
Minimum and Maximum Slope: The
minimum slope should be sufficient to maintain the minimum velocity,
and the maximum slope is related to the maximum velocity.
Normal Slope: The normal slope
is the initial slope used to place a pipe in the network.
Maximum Length: This is the
maximum length of pipes that could be used in the network. A warning
would pop
up when this setting is violated.
Pipe at Junction Match by: Two
methods are available to align the pipes at the junctions: Inverts
elevation and Crown elevation.
Drop Across Inverts: This is
the drop across inverts inside of a junction. The upstream inverts in
the junction are raised by the value entered here.
Rainfall Return Period: The
available options are 2, 5, 10, 25, 50 and 100 Year. This value is used
to obtain the corresponding IDF curve for calculating intensities.
Rainfall Duration: The
available options are 1, 2, 3, 6, 12, 24, 48 hour, which is used to
generate the rainfall hyetograph.
Display Slope In: An option to display slope either in ft/ft (m/m) format or % format.
The structure data is entered through the Structure tab.
Structure Name: An identical
name for the structure in the network.
System Name: A name for
current network. All the structures in the same network have the same
system name.
Structure ID: This is the ID of
a predefined structure in the structure library. The Library
button
next to it allows you to
select or define a sewer structure in the structure library. Once you
select the structure, the dimension of the structure are retrieved from
the library. Please refer to the documentation of the Sewer Structure
Library for details.
Inlet: This is the ID of a
predefined inlet in the inlet library. The
Library button next to it allows you
to select or define an inlet in
the inlet library. Once you select the inlet, the parameters of
the inlet are retrieved from the library. Please refer to the
documentation of the Inlet Library for details.
Reference CL: The reference
centerline is used to locate the structure by station/offset of the
centerline points, and align the structure
symbol in the graphic. The Select
button allows you to select a centerline from either a centerline file
or a
polyline.
Location: This button allows to
relocate the structure by pick a position in the drawing.
Symbol Name: This is the name
of the symbol that represents the structure in the network plan view.
The
Symbol button allows you to
select a symbol from a list of symbols.
Symbol Rotate: There are 10
options to rotate the structure symbol for displaying in the drawing.
Symbol Angle: When the Symbol
Rotate value is set to Enter Azimuth Angle, this edit field is enabled
for
entering an angle.
Symbol Size: Three options to
determine the size of the structure symbol.
Rim Elevation: The rim
elevation for the structure, it's usually the surface elevation.
Depth: The distance between the
rim elevation and the base elevation of the structure.
Invert-Out Elev: The invert
elevation of the pipe that exits the structure.
Sump Height: The distance
between the base elevation and the invert-out elevation.
 |
| Sewer Network Edit Structure |
The Rational Method is used to determine the flow rate from a
single
catchment or from multiple catchments at upstream. Please refer to
HEC-22 manual for details. The Pavement parameters along with the
catchment flow are used to design the size of the inlet device that
collects ground flows. Drainage and pavement information is entered
through Drainage tab.
 |
| Sewer Network Edit Drainage |
Area Units: Choose
a unit to
display the area values.
Drainage Area: The drainage
area that contributes to this inlet only.
Draw: Click this button, then
the watershed analysis program is conducted on the surface model, and
the drainage area that contributes to this inlet is hatched in the
drawing.
Pick: This button allows you to
select a closed polyline that represents the boundary of the drainage
area.
The area will be calculated and displayed.
Calc: This function triggers
the watershed analysis program to calculate the drainage area and
displays the value.
Time to Inlet: Time of
concentration.
Runoff Coeff.: The composite
runoff coefficient for the drainage area.
Select: This button opens a
Drainage Runoff Areas dialog, where you can define a few of area types
with different runoff coefficients and area portions. The program will
compute the composite runoff coefficient for you. Please refer to the
documentation on Define Runoff Layers for details.
Long Slope: Enter
the
longitudinal slope of the pavement. This edit field is only available
if this inlet is on grade.
Cross Slope: Enter the pavement
cross slope.
Calc: This function triggers
the watershed analysis program to analyze
the pavement and extract the longitudinal slope and cross slope.
Manning's n: Pavement Manning's
n value.
After you Design or Analyze the network, the
inlet
calculation results are displayed. The inlet result helps you to
observe
if the inlet is sufficient for conveying the ground flow into the
network and make corrections.
The pipe data is entered through the pipe tab. The Downstream/Upstream list contains the connection that exits the structure or the connections that enter the structure, depending on the design direction. The Available list contains all the structures that are not connected to the current structure, i.e. the potential structures that can be connected to the current structure. There is two ways to add a connection. The first one is clicking on the Add button to connect the highlighted structure in the Available list to the current structure. The other one is clicking on the Pick button and then select a structure symbol in the plan view to connect it. If the connection is unable to be performed, a warning massage pops up. The Remove button allows you to remove the highlighted connection from the Downstream/Upstream list.
The pipes can have four different cross-sectional shapes: circular, box, horizontal ellipse and vertical ellipse. The Pipe Material has nine options. The Pipe Size can be specified or you can toggle the pipe to be in design. Pipe Size Library button allows you to store commonly used pipe sizes. When the pipe is in design, the program calculates the appropriate pipe size based on the flow and design settings and picks the closest available pipe size from the library. Please refer to the documentation on the Pipe Size Library for details.
In the Manning's n box, enter the Manning's n coefficient for calculating the friction loss of the pipe. The Library button allows you to select a Manning's' n value. Please refer to the documentation on the Manning's N Library for details. Down Invert and Up Invert are the downstream invert and upstream invert elevations of the pipe. You can enter the values directly or toggle them to be in design. When the Design toggle is on, the edit fields are disabled. The Slope is usually the normal slope. After the Design or Analysis, the slope is the pipe slope base on its upstream and downstream invert elevations, as while as its length. Invert elevations can be changed by specifying the slope.
After you Design or Analyze the network, the pipe calculation result is displayed. Length is the real pipe length. Total Flow is the flow that is being carried by the pipe. Total Area is the total of all the drainage areas that contribute to the flow inside the pipe. Min. Cover is the minimum distance from the surface elevation to the crown elevation all along the pipe.
 |
| Sewer Network Edit Pipe |
The energy losses through a pipe junction are specified in the
Hydraulic Calc tab. There are four methods to calculate the junction
losses: Approximate Method, Dynamic Method, Fixed Head Loss and
Energy-Loss Method.
Approximate Method uses the
difference between the downstream velocity head and the upstream
velocity head multiplied by the junction loss coefficient.
Dynamic Method uses the
downstream velocity head multiplied by the junction loss coefficient.
Fixed Head Loss uses the actual
head loss you specified.
Energy-Loss Method, similar to
the Dynamic Method, uses the downstream velocity head multiplied by the
adjusted junction loss coefficient. The adjusted junction loss
coefficient is defined as the initial head loss coefficient based on
relative size of structure multiplied by the correction factors for
pipe diameter, flow depth, relative flow, plunging flow and benching.
Please refer to the HEC-22 manual for details.
After you Design or Analyze the network, the hydraulic calculation results are displayed. The hydraulic grade line, energy grade line, flow depth and flow velocity at both downstream and upstream ends are reported. A graphic box also shows the hydraulic and energy grade lines, pipe outlines and the ground surface, which help you to observe the design result easily.
 |
| Sewer Network Hydraulic Result |
When you have input all necessary data to describe the sewer network system and the watershed drainage system, you can let the program to compute the hydraulic grade line in the system or to design the pipes to sufficiently convey the drainage flow. The drainage flow is determined using the Rational Method. Please refer to HEC-22 manual for details. You can design the sewer system with one rainfall return period, and analyze it with another return period.
There is a variety of design options in hydraulic calculation, such as designing pipe sizes, setting the invert elevations or designing both. You can also specify to design all pipe lines, or only a portion of pipes. When designing pipe sizes, the program first estimates the design flow for each pipe in the system and make an initial selection of the size required for each pipe. Typically, pipe slope is set to the actual invert slope. If the pipe invert elevations are to be designed, pipe slope is assumed as the same as the normal slope. The Manning equation is then used to solve the required pipe size given the pipe Manning's n coefficient, design discharge and slope. The calculated size is then rounded up to a available size in the pipe size library. When designing pipe invert elevations, the criterion of minimizing ground cover at all locations along pipe lines is used.
After initial design, the program analyzes gradually varied flow with the standard step method for a few iterations. It uses the actual velocity from the previous calculation to determine the actual flow and hydraulic grade line, modifys the pipe sizes and invert elevations based on the design constraints, and then performs next iteration of computation, until the result is stable and meets the design constraints. Any violations of the design settings will be displayed in a warning message dialog window.
The program analyzes gradually varied flow with the standard step method and reports the results such as hydraulic grade line, energy grade line, flow velocity, drainage flow rate and inlet interception etc. Any violations of the design settings will be displayed in a warning message dialog window.
Select sewer structure to edit: pick a manhole symbol
Sewer Structure Data dialog
Select sewer structure to edit: press Enter to end
Pulldown Menu Location: network > Edit/Create Sewer
Structure
Keyboard Command: editswr/putswr
Prerequisite: a sewer file (.SEW), a surface file (.TIN, .GRD,
.FLT)
File Name: \lsp\cntr_grd16.arx