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File/s needed: 
Click to download the METRIC model files.

Open XP_Tutorial5.xpdx

You can carry on from the previous Chapter or switch to the Sizing of Treatment Phase by selecting from the drop-down list on the left Tree View panel if you have not already done so.

As you saw from reviewing the results, the treatment train is successfully mitigating the volume of water discharging from the site, however the flow rate is still too great compared to the existing site. As well as this we are getting flooding in our pipe networks which we do not want, therefore we will now carry out a sizing of the treatment system to fix these issues.

Pipe Auto Sizing

We are going to size our pipes in line with the Sewers for Adoption (SfA) UK guidance specifications. To meet these requirements we need to make sure that our network will not surcharge for a 1:2 year event and will not flood for a 1:30 year event. As we have already discovered, we have broken this rule for both cases so we will need to redesign our network. We can either do this by manually altering pipes individually, or we can use the Pipe Sizing Wizard found within the Preliminary Sizing Ribbon.

The Pipe Sizing Wizard works by using an Intensity Duration Frequency (IDF) curve for a particular storm event, for a particular area. We will specify this using FSR data. With this IDF curve a time of concentration and rainfall intensity is generated for individual pipes, this generates the expected flow the pipe will have to deal with (in the UK this is done using the Modified Rational Method). The connection is then sized accordingly. This is related to the Wallingford Procedure for the UK, and enables pipes to meet the Sewers for Adoption criteria or similar guidance documents in other countries on pipe surcharging and flooding for various events, as stated above.

  1. Open the Pipe Sizing Wizard by clicking on the icon in the Preliminary Sizing Ribbon.

    The Pipe Sizing Wizard should open and show the first step of the wizard, selecting the flow path to size. The only flow path in our system should be specified on opening the wizard, however there is the ability to also select the flow path from the Select Flow Path drop down menu. Make sure our flow path is selected and then click Next.

  2. The second stage of the Pipe Sizing Wizard allows us to enter the Pipe Sizing Criteria, within here are a variety of conditions that can be specified for our pipes to be designed to. We will be using the Modified Rational Method (as mentioned above), combined with the two-year return period FSR data from Oxford (UK) as the basis for our pipe design. Other factors that can be specified in the left-hand window have default values set, we will leave these as they are. In the right-hand window, we want to use the Lock drop down menu to maintain our slopes by selecting Slopes. We also want to tick on Min. Cover Depth and Synchronise Manhole Invert Levels.

  3. Now that we have completed our criteria specifications we can now click Next to see what changes the wizard has made. Highlighted in yellow are any changes that have automatically been made. Anything that remains with a white background has not been altered by the wizard, as shown by our pipe slopes since we locked them previously. Hovering your mouse over the highlighted fields will display the original values before the wizard made alterations, allowing a comparison between the two values.

  4. Make sure that Show the Pipe Sizing Report after finishing is selected, then click Finish to save and apply the changes that the wizard has made. Upon the wizard closing, the Pipe Sizing Report now shows. Here we can select the flow path we want to see the report for as well as the layout of the pipe sizing report. Furthermore, we can also export this Pipe Sizing Report to PDF by clicking the  icon. This pipe sizing report can be extremely useful in showing us total areas, predicted flows and depths within our pipes based off the pipe sizing wizard results.

  5. Now that the connections have been altered we can also go back to the Profile view to see how the system has been altered.

  6. If we zoom in on the Profile it shows that our Standard Pipe (4) invert level and Dry Pond invert level no longer match the connection invert levels, this is further confirmed by the values shown in the summary table at the base. To correct this, we will manually alter the base level of our pond to that of the Downstream Invert Level of Standard Pipe (4). Within the Profile view double click on the Dry Pond to open the pond form. In the dimensions tab we can now manually edit the Base Level to match that of the preceding pipe DS IL. If the Base Level is greyed out then we can fix this by using the radio button to set the Depth to automatically calculate as opposed to the Base Level. We can now type in our new Base Level, which in this case is 561.362. This has now extended the depth to 1.705 metres, resulting in a deeper pond and therefore providing more capacity for storage which we will review again later.

  7. Now that we have altered our pond Invert Level we also want to make sure that our outflow control Invert Level is also correct. As discussed in an earlier Chapter, the outlets are set at 300mm above the base to allow infiltration to occur. Simply go into our Outlets tab and alter the Invert Level of the control so that it sits 300mm above the Pond Invert Level at 561.662m. Click OK to close the form and apply the changes. The profile will be updated to show the levels matching.

  8. The simulation can now be re-run by selecting Go from the Analysis ribbon to show how the pipe sizing function has successfully altered the pipes so that they now don’t surcharge for 1:2 year storms except immediately upstream of the pond. To check that the pipes do not Flood for 1:30 year storms open the Analysis Criteria on the Analysis ribbon and change the rainfall to FSR 30 then rerun the Analysis.

Note: There is surcharging in the lower pipe for the 1:2 year critical storm, is due to the water depth in the pond being greater than the soffit of the pipe (as can be seen in profile view).

Pond Sizing

Now that we have resized our pipes we want to alter our Dry Pond so that we are meeting the same discharge flow rate as the existing site. As we saw from our phases report for the developed site we are discharging at higher rates than the existing site. To successfully decrease the flow rates we will alter the outflow control and also the pond size, as reducing the flow rate will lead to a higher storage volume required.

  1. Open the Dry Pond by double clicking on the icon in plan view. Before we size the pond we want to alter the depth column in the table, so that it now matches the depth of the pond (in our example this is 1.705 m). This depth change is due to us altering the pond in the previous section to make sure that pipe (4) connected invert to invert.

  2. Within the Dry Pond window open the Sizing Calculator. Within the Sizing Calculator select Quick Storage Estimate from the Method drop down menu and change the Design Level to Exceedence.

  3. Now click on the calculator button next to Volume (m3) to open the Quick Storage Estimate window. Input the data as shown below, then press Calculate. This produces a storage volume estimate based on our desired discharge rate.

  4. Displayed is the quick storage estimate that xpdrainage has provided from the parameters that we used in the Input tab. We can see that the software has estimated that we require 908m3 to 1237m3 of storage to manage the volume of water effectively. You will also notice that due to us specifying an infiltration rate in the pond we are given a second estimate, 350m3 to 782m3, this is the storage required if we have an effective infiltration rate

  5. Click OK to the calculator forms to close and apply the volume, the software will automatically take the average of the infiltration storage value, the volume within Sizing Calculator has now increased to 565.949m3. Although the software has automatically chosen this for our pond we will manually alter this to 908m3 to provide a more conservative approach.

    We can now see that the pond has updated its areas and volume based on what was specified in the Sizing Calculator

  6. Now that we have sized our pond we will also alter the outflow on our system to better mitigate the flow running off of our developed site. To do this we will go to the Outlets tab. Select Edit, select the  button and change the flow of the orifice to 15 l/s, and weir to 22.5 l/s, then click the Solved for displayed controls calculator button to alter the diameters. Click OK to close the form.

  7. Click OK to apply the changes and close the pond form.

  8.  Save the file as Metric_Tutorial6.xpdx

Results and Fine Tuning 

You can carry on from the previous Chapter or open XP_Tutorial6.xpdx and switch to the Completed Design phase by selecting from the drop-down list on the left Tree View panel if you have not already done so.

  1. Now that we have finished the sizing of our network we can run an analysis to compare results between the Existing and Completed Design. We will re-run the simulation to see how effective our changes have been. Open Analysis Criteria and make sure the fields are as below, then run the simulation.

  2. Just as with previous simulations the Stormwater Controls Summary will be the first window we see, select Critical Storm to show the worst event experienced by the Dry Pond, this will allow us to see if our storage upsizing has been effective.

  3. As we can see from the window above we have no flooding from the pond, with some excess storage available, as stated in the Percentage Available (%) column. We could continue refining the design to downsize the pond to a smaller volume to decrease the area it takes up and save on construction costs. For the purpose of this tutorial we will leave the pond as it is.

  4. Further to this we can open the Connections Summary from the Results ribbon to see if our pipes were able to take the flow of the 1:30 year events without flooding. Click the Critical Storm icon again.

    As we can see from this window our pipes are only experiencing surcharged conditions and are not flooding for the critical 1:30 year storm. This means that we are meeting the UK standard Sewers for Adoption criteria for drainage design.

  5. You can also navigate to the profile view for any storm to visually inspect how our updated system is coping with the critical storms. The 240 mins Winter storm is critical for the Dry Pond. The different storms can be selected using the Storm Selection menu at the base of this window.

  6. We can also view the Phases report to make sure that our flow rates and outflow volumes are now satisfactory when compared to the Existing Site conditions. Open Phases Report from the Results ribbon and select the options as shown below, then select Update Preview. You may need to drag the box around the legend to expand it to show the legend for both phases.

  7. The effect of our storage and flow control meant that we were not initially capturing the peak of the hydrograph or the whole drain down for the shorter duration storms in the Completed Design Phase. We have extended the Run Time for the shorter duration storms in the Rainfall Manager.

  8. We can check all storms in the Phase Report and see we are successfully mitigating the run-off from this developed site. Further refinement the treatment train is possible by altering the size of our outlets and the size of the pond, as we have some leeway between our runoff rates and volumes. For the purpose of the tutorial we will not be editing the treatment train any further, however you can refine the Results comparison to the Existing Phase flows if desired.

  9. The finished layout can be exported to AutoCAD file (*.dxg or *.dxf ). Go to the Export ribbon, and then select the To CAD button.

  10. Within xpdrainage there is also the ability to export your completed pipe network. This can be done within the Export Ribbon, select Export Pipe Network(s) to save the network as a LandXML (*.xml) file. This allows the connections and junctions within the current phase to be shared with other applications, such as Autodesk® AutoCAD® Civil 3D®, as well as allowing networks designed outside of xpdrainage to be imported into the software for analysis and editing.

  11. Within the Import Ribbon you can also import pipe networks, if they are presented as a LandXML (*.xml) file.

  12. It is important to note that xpdrainage contains some information that is not supported by the LandXML file format. As such they are approximated within the LandXML file exported. These are:

Stormwater Controls:

  1. These are not supported by LandXML so a simple structure (i.e. node with no volume) is provided at these locations with a label explaining what they are.
  2. In addition to the Stormwater Control, the Inlet and Outlet attachment points shown on Plan cannot be represented. To maintain the layout the export will contain a 'connection', or null, structure for each of the inlet and outlet locations. Connections (pipes) will then be shown to/from these locations.

  1. Number of Barrels – If a value of more than 1 is specified the export will contain multiple versions of the same pipe/channel with the name post fixed with  _X_Ø, where X is the number of the barrel.
  2. Triangular Channels – These will be exported as an equivalent ‘v’ shaped channel (.
  3. Conceptual Connections (No Delay, Simple Time Delay and Lagged Flow) – These will be saved as a Circular Pipe with a nominal diameter, as specified on the Export Options.

More information on the Export Pipe Function can be on Export Pipe Network.