Water Network (pipe network training)

Water Network Design and Analysis in Devotech iDAS

Devotech iDAS uses the EPANET engine for water network analysis. EPANET is software that models and analyses water network models. The Devotech iDAS Help File does not repeat the EPANET 2 User Manual [8], it only contains brief descriptions of each object type and how to work with these objects. It also explains differences between EPANET and Devotech iDAS, e.g. valves are treated as pipes in EPANET but treated as structures in Devotech iDAS. If you need more details about water network objects and analysis, the EPANET User Manual is a great source of information. The EPANET software as well as the EPANET User Manual can be downloaded from the following website (EPANET can be freely copied and distributed):

https://www.epa.gov/water-research/epanet

If you want to learn water network design, watch the water network overview videos first just to get a feeling how everything fits together.

Water reticulation overview videos:

https://www.devotechgroup.com/idas-water-reticulation

Bulk water pipeline overview videos:

https://www.devotechgroup.com/idas-bulk-water

Then watch the first nine stormwater videos which cover the pipe network basics (login is required, sign up is for free, we need to approve your account, use company email address, if you need to use private email address, let us know on support@devotechgroup.com, we will approve it):

https://www.devotechgroup.com/storm-water-training

You can also open the training videos from Devotech websites: https://www.devotechgroup.com/. Go to Education – Training Videos:

Sign in and go to the video channel Water Reticulation and Bulk Water:

Then you can continue with the water training videos.

Water reticulation training videos:

https://www.devotechgroup.com/water-reticulation-training

Bulk water pipeline training videos:

https://www.devotechgroup.com/bulk-water-training

You can also find some useful tips in the Pipe Networks (General) video channel:

https://www.devotechgroup.com/pipe-networks-training

Water Network Pipe and Structure Details

Reservoir

Reservoirs are nodes that represent an infinite external source or sink of water for the network. They are used to model things like lakes, rivers, groundwater aquifers, and tie-ins to other systems. Reservoirs can also serve as water quality source points (note: quality analysis is not supported within Devotech iDAS, and the network will need to be exported to EPANET in order to do a quality analysis). The primary input properties for a reservoir is the hydraulic head (equal to the water surface elevation if the reservoir is not under pressure) and the initial quality for the water quality analysis. Because a reservoir is a boundary point to a network, its head and water quality cannot be affected by what happens within the network. Therefore, it has no computed output properties. However, the head (Water Depth) can be made to vary with time by assigning a time pattern to it.

Tanks

Tanks are nodes with storage capacity, the volume of stored water can vary with time during a simulation. The primary input properties for tanks are:

• bottom elevation (where water level is zero)
• diameter (or shape if non-cylindrical)
• initial, minimum and maximum water levels
• initial water quality.

The principal outputs computed over time are:

• hydraulic head (water surface elevation)
• water quality

Tanks are required to operate within their minimum and maximum levels. The EPANET analysis engine stops the outflow if a tank is at its minimum level and stops inflow if it is at its maximum level. Tanks can also serve as water quality source points.

INITIAL LEVEL

Height in feet (meters) of the water surface above the bottom elevation of the tank at the start of the simulation. This is a required property.

MINIMUM LEVEL

Minimum height in feet (meters) of the water surface above the bottom elevation that will be maintained. The tank will not be allowed to drop below this level. This is a required property.

MAXIMUM LEVEL

Maximum height in feet (meters) of the water surface above the bottom elevation that will be maintained. The tank will not be allowed to rise above this level. This is a required property.

Pumps

Specify the Outgoing Pipe and pump Curve or Power (one of these two must be defined):

1. To define a pump Curve, go to the Library, sub- menu Curves and create a new curve. As a type use Pump, specify Number of Values and define the Flow and Head:

Valves

Devotech iDAS distinguishes between five valve groups from an analysis point of view:

1. Valves which limit pressure or flow, e.g.: pressure reducing valves, flow control valves
2. Valves which do not limit pressure or flow, e.g.: air valves, scour valves
3. Gate valves (isolating vales)
4. Non-return valves (check valves)
5. Other valves, e.g.: actuating valves, inline sluice valves

Valves which Limit Pressure or Flow [8]

The following valves belong to this group:

• Pressure Reducing Valve (PRV)
• Pressure Sustaining Valve (PSV)
• Pressure Breaker Valve (PBV)
• Flow Control Valve (FCV)
• Throttle Control Valve (TCV)
• General Purpose Valve (GPV)

The EPANET engine uses pipe objects to model the valves while Devotech iDAS uses node objects (structures), it reflects reality better. This is the reason why Minor Losses are included in the Valves tab otherwise the Minor Losses are a property of the pipe, see the Minor Losses chapter for details.

PRVs limit the pressure at a point in the pipe network. The EPANET engine computes in which of three different states the PRV can be in:

• Partially opened (i.e., active) to achieve its pressure setting on its downstream side when the upstream pressure is above the setting
• Fully open if the upstream pressure is below the setting
• Closed if the pressure on the downstream side exceeds that on the upstream side (i.e., reverse flow is not allowed)

PSVs maintain a set pressure at a specific point in the pipe network. The EPANET engine computes in which of three different states the PSV can be in:

• Partially opened (i.e., active) to maintain its pressure setting on its upstream side when the downstream pressure is below this value
• Fully open if the downstream pressure is above the setting34
• Closed if the pressure on the downstream side exceeds that on the upstream side (i.e., reverse flow is not allowed)

PBVs force a specified pressure loss to occur across the valve. Flow through the valve can be in either direction. PBV's are not true physical devices but can be used to model situations where a pressure drop is known to exist.

FCVs limit the flow to a specified amount. The program produces a warning message if this flow cannot be maintained without having to add additional head at the valve (i.e., the flow cannot be maintained even with the valve fully open). FCVs should be used with an open system downstream which means that there should be a tank or a reservoir downstream. For example, if there is a node with a fixed demand 50l/s downstream and the FCV can only deliver 30l/s, there is no other source to supply water for the required demand and it will return nonsense results.

FCVs pressure head loss is calculated as a difference between the pressure head at the valve and the pressure head of the first downstream structure. The first downstream structure's pressure head is calculated from the downstream tank (reservoir) plus losses in the pipeline. If the flow is very low, the losses in the pipeline are also very low therefore the head loss in the FCV is very high:

Increasing the reservoir pressure head does not have an impact and the first downstream structure hydraulic head (elevation + pressure head) because it is calculated backwards from the tank:

Reservoir with pressure head 10m

Reservoir with pressure head 15m

The FCV position along the pipeline has an impact on the HGL and EGL, see the image below for the example above with a 10m pressure head at the reservoir and FCV positioned closer to the end of the pipeline:

TCVs simulate a partially closed valve by adjusting the minor head loss coefficient of the valve. A relationship between the degree to which a valve is closed and the resulting head loss coefficient is usually available from the valve manufacturer.

GPVs are used to represent a link where the user supplies a special flow – the head loss relationship instead of following one of the standard hydraulic formulas. They can be used to model turbines, well draw-down or reduced-flow backflow prevention valves.

Shutoff (gate) valves and check (non-return) valves, completely open or close pipes, which are not considered as separate valve links but are included as a property of the pipe in which they are placed.

Each type of valve has a different type of setting parameter that describes its operating point (pressure for PRVs, PSVs, and PBVs; flow for FCVs; loss coefficient for TCVs, and head loss curve for GPVs).

Valves can have their control status overridden by specifying if they should be completely open or completely closed. A valve's status and its setting can be changed during the simulation by using control statements.

The following valve input parameters are available:

OUTGOING PIPE

It determines the valve direction.

DIAMETER

It is used to calculate the velocity through the valve. If minor losses are specified, this velocity is used for the head loss calculation. Open valves act as a smooth pipe (low friction coefficient) with a length twice the valve diameter.

SETTING

Each valve type requires different setting:

• Pressure Reducing Valve (PRV) – Maximum pressure (m)
• Pressure Sustaining Valve (PSV) – Sustaining pressure (m)
• Pressure Breaker Valve (PBV) – Pressure loss in the valve (m)
• Flow Control Valve (FCV) – Maximum flow (flow units)
• Throttle Control Valve (TCV) − Loss coefficient (dimensionless)
• General Purpose Valve (GPV) − GPV curve name

GPV CURVE

It describes the relation between headloss and flow rate for GPVs. It provides the capability to model devices and situations with unique headloss-flow relationships, such as reduced flow - backflow prevention valves, turbines, and well draw-down behaviour.

1. To define a GPV Curve go to the Library, sub-menu Curves, create or import new curve and as a type use Headloss:

MINOR LOSSES

To add a minor loss coefficient, see the Minor Losses chapter for more details.

The input parameters can be defined in the Water Manager, the vertical Structures tab, in the horizontal Valves tab:

The computed outputs for the valves are the flow rate and headloss.

If you export a Devotech iDAS water network model to EPANET the valve structures are converted to very short valve conduits with the following defined properties:

Valves which Do Not Limit Pressure or Flow

The following valves belong to this group:

• Air valve
• Scour valve

These valves behave like any other node.

Gate Valves (isolating valves, shutoff valves)

To close a gate valve, select the Outgoing Pipe and change the Initial Status to Closed:

It will automatically close the pipe in the Conduits tab:

The gate valve is actually a pipe property. This is how the EPANET engine was developed, the Devotech iDAS developers cannot change it. Any pipe can be opened or closed even if it is not connected to a gate valve. A gate valve structure is there just for a graphical representation and the quantities.

Non-return Valves (check valves, reflux valves)

To set the non-return valve, select the Outgoing Pipe and change the Initial Status to Check Valve:

The non-return valve is a pipe property. This is how the EPANET engine was developed, the Devotech iDAS developers cannot change it. Any pipe can be open or closed even if it is not connected to a non-return valve. The non-return valve structure is there just for a graphical representation and the quantities.

Other Valves

Any valves not listed in the chapters above are treated as any other node. If you do not want Devotech iDAS to treat a specific valve as any other node, change the mapping in the Pipe Manager ─ Mappings ─ Structures tab.

Devotech iDAS uses structure styles to distinguish between different structure types. For example, if you want to treat a Butterfly Valve as a Throttle Control Valve, go to the Structure Properties and change the Style name:

Roughness Coefficient

Specify the pipe's roughness coefficient in the Pipes tab**.** This coefficient must correspond with the head loss formula selected in the General settings. If the Darcy-Weisbach formula is used, the software computes the friction factor automatically by using different equations depending on the flow's Reynolds Number (Re):

• Re < 2 000: Hagen-Poiseuille formula,
• 2 000 < Re < 4 000: Cubic Interpolation from Moody Diagram,
• 4 000 < Re: Swamee and Jain approximation to the Colebrook-White equation (see the EPANET help file for detailed formulas).

The roughness can be set individually for each pipe or for the selected pipes or for all pipes (right-click on the grid cell to display right-click menu):

The typical values for roughness coefficients (use the Darcy−Weisbach values in millimeters for projects in metric units):

Minor Losses

Minor head losses (also called local losses) are caused by the added turbulence that occurs at bends and fittings. The importance of including these losses depends on the layout of the network and the degree of accuracy required. They can be accounted for by assigning a minor loss coefficient to the pipe. The minor headloss becomes the product of this coefficient and the velocity head of the pipe, i.e.:

HL = K (v2 / 2g),

where: HL = Head Loss (m),

K = Minor Loss Coefficient (dimensionless), see table below,

V = Flow Velocity (m/s),

g = Acceleration of Gravity (m/s2).

Minor loss coefficients for typical fittings:

As mentioned above, the minor loss coefficient is a pipe property which might a bit confusing because an elbow is actually a structure, not a pipe. On the other hand, the valves are treated as pipes in EPANET. Use the suggestions below to define which pipe should have a minor loss coefficient derived from the connected structure:

Pipes in which the flow direction can be determined:

• A structure with one incoming pipe and one outgoing pipe – add minor loss coefficient to the outgoing pipe
• A structure with two incomming pipes and one outgoing pipe – add minor loss coefficient to the outgoing pipe
• A structure with one incoming pipe and two outgoing pipes – add minor loss to the incoming pipe
• Use your engineering judgement for other scenarios

Pipes in which the flow direction cannot be determined (pipes in loops)

• Distribute the minor loss coefficient equally between all the connected pipes, e.g. for three connected pipes use 1/3 of the minor loss coefficient in each pipe

One pipe can contain minor loss coefficients from multiple structures.

1. To add a minor loss coefficient to a pipe, go to the Water Manager, Pipes tab and add the value in the Minor Loss column:

2. To add a minor loss coefficient to a valve, go to the Structures tab, Valves subtab and add the value in the Minor Loss column.

   IMPORTANT: Only valves that limit pressure or flow (PRV, PSV, PBV, FCV, TCV, GPV) have the minor loss column. Other valves do not have this setting and the minor losses must be set in the connected pipes. The reason behind is that EPANET engine only supports the valves that limit the pressure or flow and these valves are converted to links when iDAS creates EPANET INP file doring the analysis. All other valves are treated as structures in the EPANET engine.

Water Network Analysis Errors

Error Numbers [8]

Error 101 An analysis was terminated due to insufficient memory available.

Error 110 An analysis was terminated because the network hydraulic equations could not be solved. Check for portions of the network not having any physical links back to a tank or reservoir or for unreasonable values for network input data.

Error 200 One or more errors were detected in the input data. The nature of the error will be described by the 200-series error messages listed below.

Error 201 There is a syntax error in a line of the input file created from your network data. This is most likely to have occurred in .INP text created by a user outside of EPANET.

Error 202 An illegal numeric value was assigned to a property.

Possible Solution:

Check if any of the objects used in the analysis, such as pipes, structures, patterns,

curves etc. do not contain spaces in the names or if the names do not have more than fifteen (15) characters.

Error 203 An object refers to undefined node.

Error 204 An object refers to an undefined link.

Error 205 An object refers to an undefined time pattern.

Error 206 An object refers to an undefined curve.

Error 207 An attempt is made to control a check valve. Once a pipe is assigned a Check Valve status with the Property Editor, its status cannot be changed by either simple or rule-based controls.

Error 208 Reference was made to an undefined node. This could occur in a control statement for example.

Error 209 An illegal value was assigned to a node property.

Error 210 Reference was made to an undefined link. This could occur in a control statement for example.

Error 211 An illegal value was assigned to a link property.

Error 212 A source tracing analysis refers to an undefined trace node.

Error 213 An analysis option has an illegal value (an example would be a negative time step value).

Error 214 There are too many characters in a line read from an input file. The lines in the .INP file are limited to 255 characters.

Error 215 Two or more nodes or links share the same ID label.

Error 216 Energy data were supplied for an undefined pump.

Error 217 Invalid energy data were supplied for a pump.

Error 219 A valve is illegally connected to a reservoir or tank. A PRV, PSV or FCV cannot be directly connected to a reservoir or tank. Use a length of pipe to separate the two.

Error 220 A valve is illegally connected to another valve. PRVs cannot share the same

downstream node or be linked in series, PSVs cannot share the same upstream node or be linked in series, and a PSV cannot be directly connected to the downstream node of a PRV.

Error 221 A rule-based control contains a misplaced clause.

Error 223 There are not enough nodes in the network to analyze. A valid network must contain at least one tank/reservoir and one junction node.

Error 224 There is not at least one tank or reservoir in the network.

Error 225 Invalid lower/upper levels were specified for a tank (e.g., the lower lever is higher than the upper level).

Error 226 No pump curve or power rating was supplied for a pump. A pump must either be assigned a curve ID in its Pump Curve property or a power rating in its Power property. If both properties are assigned then the Pump Curve is used.

Error 227 A pump has an invalid pump curve. A valid pump curve must have decreasing head with increasing flow.

Error 230 A curve has non-increasing X-values.

Error 233 A node is not connected to any links.

Error 302 The system cannot open the temporary input file.

The possible solutions are listed below depending on the source of the problem:

Problem 1: A drawing might reside in a directory to which the user does not have write privileges.

Solution: Move the drawing to your desktop, open it from this new location and rerun the analysis. Some users report better success when moving the drawing to C:\Civil 3D Projects instead of using desktop.

Problem 2: Multiple Civil 3D instancess are causing the issue.

Solution: Close all running Civil 3D instances for all the Civil 3D versions and start up only one Civil 3D instance.

Problem 3: Civil 3D limits the access to the location where the drawing is saved.

Solution: Set the folder where the drawing is saved as a trusted location. Open Civil 3D Options:

Select the Trusted Location folder, click on Add and browse to the folder where the drawing is saved. If you want to include the selected folder as well as its subfolders, you must add three dots "…" at the end of the folder path:

Problem 4: Civil 3D does not have a privilage to create file in the location where the drawing is saved.

Solution: Run Civil 3D as administrator (right click on the Civil 3D icon and use Run as administrator command)

Problem 5: The user's antivirus is blocking the temporary file which is created by Devotech iDAS in the location where the drawing is saved when running the analysis.

Solution: Create an exception rule on the firewall to allow access to EPA SWMM and SSA.

Problem 6: The user is using Bentley Project Wise and it does not allow the user to create that file type on the system.

Solution: Move the drawing to the C drive and then run the analysis.

Error 303 The system cannot open the status report file. See Error 302 for the solution.

Error 304 The system cannot open the binary output file. See Error 302 for the solution.

Error 305 Cannot open hydraulics file. See Error 302 for the solution.

Error 308 Could not save results to file. This can occur if the disk becomes full.

Error 309 Could not write results to report file. This can occur if the disk becomes full.

System Ill-conditioned Error

The following issues might cause this error:

• Duplicate structures
• Duplicate pipes
• Disconnected pipes
• Zero length pipes

Negative Pressure Error

Reservoir does not provide enough head:

• Check reservoir pattern if used
• Increase water depth
• Move the reservoir to higher area
• Add pump to your system to increase the head

Tank does not provide enough head:

• Increase height above surface
• Move the tank to higher area
• Add pump to your system to increase the head

Tank does not deliver any water:

• Set initial depth above 0
• Make sure the tank is big enough so it does not get empty during the analysis

Demand is too high:

• Check the demands
• Check the demand patterns

Flow velocities are too high, therefore the losses are too high:

• Increase pipe size
• Use pipes with lower friction

Pump cannot deliver the head:

• Adjust pump curve
• Rerun system curve analysis to find out correct pump curve

Duplicate structures:

• use iDAS command Remove Duplicates

Disconnected pipes and structures:

• Use iDAS command Connect Pipes

Pressure reducing valve has too low maximum pressure:

• Increase maximum pressure in the valve settings

Pressure sustaining valve has too low set pressure:

• Increase set pressure in the valve settings

Pressure breaker valve has too high pressure loss:

• Set the pressure loss to lower value in the valve settings

Throttle control valve has too high minor head loss coefficient:

• Decrease head loss coefficient in the valve settings

General purpose valve has too high head loss:

• Decrease head loss by adjusting head loss curve

Pipe roughness is too high:

• Set the roughness to the correct value for the used head loss formula (Darcy-Weisbach or Hazen-Williams)

Pipe diameter is too small:

• Increase pipe diameter to decrease the velocity and losses

Zero length pipe

• Delete zero length pipes

Analysis Report and Input File

Once you run the analysis, you can go to Tab Ribbon to display Analysis Report as well as Input File. This input file can be imported into EPANET or any other software that can import EPANET .inp files:

Analysis Results Displayed in Graphs

The results from the analysis can be displayed in graphs. It is important to note that an analytical engine treats the valves and pumps as conduits therefore Flow, Headloss and Velocity are also shown under structures:

Horizontal and Vertical Bends

To order parts for pressure networks from a manufacturer, it is necessary to know what the bend angles are. Detailed bend information can be found in the Pipe Manager under Structures tab, Junctions subtab:

The Allocated Bends can also be found under BOM tab, Pipe and Structures subtab:

Export Pipe Data to Vent-O-Mat

Vent-O-Mat is software used to size air valves. To export data to Vent-O-Mat use the Water – Export Pipe Branch command. This command creates a .txt file which can be used to import data into Vent-O-Mat. The text file is created in the same folder where the drawing is saved.

File example:

Water Network Analysis in EPANET

1. The pipe network can be exported from Civil 3D to an EPANET .inp file. Open the Pipe Manager:

2. Run the Analysis and Devotech iDAS will create an EPANET .inp file in the location where the drawing is saved:

3. To open the .inp file in EPANET go to File ‒ Open and select *.INP for Files of type in the opened window.

4. Browse to the .inp file:

The imported network:

1. In EPANET, the pipes are called links and the structures are called nodes. If you double-click on a link or node you can change the properties in the Properties window.

2. Before starting the analysis, specify the analysis options for instance the Flow Units, Head loss Formula etc. Go to Project ‒ Analysis Options, in the opened window set the options according to the project requirements.

Hydraulics Options:

Flow Units ‒ units in which the nodal demands and link flow rates are expressed.

Choosing units in gallons, cubic feet, or acre-feet implies that the units for all the other network quantities are customary US.

Selecting litres or cubic meters causes all other units to be SI metric. Use caution when changing the flow units as it might affect all other data supplied in the project. (See Appendix A of the EPANET manual, Units of Measurement.)

Head loss Formula ‒ the formula used to compute the head loss as a function of flow rate in a pipe. Choices are:

Hazen-Williams

Darcy-Weisbach

Chezy-Manning

Because each formula measures the pipe roughness differently, switching formulas might require that all pipe roughness coefficients be updated.

1. As soon as you specify all properties and analysis options you can run analysis by using command Project ‒ Run Analysis.

2. You can display the results in a table by using the Report ‒ Table command. It opens a window where you can specify if you want a table for Nodes or Links and which parameters you want to see in the table.

3. Table settings - Type:

4. Table settings: − Columns:

Created table:

1. To display the results in the pipe network map, go to the Browser and specify which data you want to see for the links and nodes. A legend is added automatically.

2. You can also display values for the links and nodes in map. Go to View ‒ Options, in the Map Options window select Notation and tick Display Node Values and Display Link Values.

Values displayed in plan view:

There are two options available if you need to change the pipe diameter, slope etc. The first option is to do it in EPANET, as soon as the analysis is successful, go to Civil 3D and change all the values there. The second option is to change all the values in Civil 3D and then export it to EPANET and perform the analysis again.

Solving Problems When Importing Pipe Networks to EPANET

If you see errors during the import of a pipe network into EPANET, generally the problem is that some pipes are not connected or there are more structures on top of each other etc. As a result, you will not see the pipe network in EPANET, or you will only see a part of the network. To solve this problem, check your pipe network and see if there are any of the above-mentioned problems.