The use of the program to model gravity flow in closed conduit networks is described in Tutorial 3 - Surface Water Hydraulics. This lesson extends on the runoff collection system with additional features common to drainage systems. These include:
  • Open topped channels and natural streams (in Part 1)
  • Detention ponds and outlet control structures (in Part 2)
  • Inlet capacity and street flow (in Part 3)

Part 1 – Trapezoidal and Natural Channels


Introduce the steps required to:

  • Model open topped conduits
  • Use shapes to define channel cross sections
  • Add vertices to the layout of channels
Time1 hour
Data files

Yarra31m.xp (from Mod 2)



  1. Launch the program:
    1. Open Yarra31.xp. This is the model that was completed in Tutorial 3 - Surface Water Hydraulics.
    2. Save As Yarra40.xp
    3. Adjust the display of Yarra_Area.dwg by right-clicking the layer name and selecting Properties from the menu. 

    4. On CAD File Properties dialog, clear the LinksNodes and Node ID layers and then click OK.

  2. Remove the outfall at node 3/375:
    1. In the Hydraulics mode, double-click Node 3/375 to open the Node Data dialog. 
    2. Clear the Outfall button and then click OK.

  3. Add downstream network objects:
    1. Select the link drawing icon. 
    2. Click and hold on Node 3/375. A vertical pipe will appear next to the cursor. Drag to draw a link. Click once to draw a node. Drag towards Alexandrina Drive and double-click to complete drawing. 
    3. Add two links and two nodes as indicated in figure below.

  4. Rename the objects:
    1. Select each of the new objects and right-click. 
    2. Select Properties and edit the names to those indicated in the following figure.

  5. The grass lined constructed channel will be modeled as a trapezoidal cross section. Double-click the link Channel. Select the Trapezoidal radio button. Enter the parameters according to the figure below. Click OK.

  6. Enter pond data. The node labeled Pond will be converted to a storage node in the next section. 
    1. Double-click the node Pond.
    2. In the Node Data dialog, enter Spill Crest = 1276.3 and Invert = 1274.8.
      Note: Do not select Ponding or Storage

    3. Click OK.

  7. Add vertices to stream:
    1. Select the link Stream. Right-click and choose Edit Vertices from the menu. The cursor will assume the pulsating crosses shape. 
    2. Add vertices at locations ¼, ½, and ¾ the distance downstream from the pond. 
    3. Move the cursor away from the link. The cursor will have a red dot next to it. Grab each vertex and drag until the stream assumes the 'zigzag' appearance as shown below.

  8. Define natural channel shape:

    1. Double-click the Stream to open the Conduit Data dialog. 

    2. Select the Natural cross section. 

    3. Enter the Upstream Elev and Downstream Elev and the channel len values as shown in the figure below.

    4. Click the button next to Shape to open the Select dialog for natural section shapes. 

      Make sure that the invert levels are aligned with the Link Elevation so that there would be no error.

  9. Define the Natural Section Shape:

    1. In the Select dialog, type in Stream shape and click Add, then Edit

    2. Enter the data as shown in the figure below.

    3. Click the Insert button to insert rows and Delete button to delete rows. Click OK to close the Natural Section Shape dialog.

    4. Click OK twice to return to the network view.

    5. Click Select to choose the Stream Shape record. 

    6. Click OK twice.

  10. Add Outfall data:
    1. Double-click the node Outfall
    2. Enter the Invert and Spillcrest values as 1274.6 and 1276 respectively. 
    3. Click the Outfall button. 

    4. Select Type 1, Free Outfall and then Use minimum of Yc-Yn

    5. Click OK three times.

  11. Save your file as Yarra41.xp
  12. Solve the model. Specify Yarra41.out as the output file.
  13. Select links Channel and Stream and click the Review Results tool. The maximum flows are 1.4295 and 1.4156 cms, respectively. To determine if either of these links flooded open the Output file.

    Table E16 is used to determine maximum depths. For the Channel:

    Max upstream depth1275.77 – 1275.000.77
    Max upstream depth1275.47 – 1274.800.67

    Review Table E14 for information on flow in natural channel sections. Note that the flows are described here for the left over bank and the right over bank in addition to the center. The maximum depth is also shown by using the maximum in the upstream or downstream end.


Review the output file (Yarr41.out) to answer the following questions.

  1. What is the total volume of flow at the outfall?_____ m3
  2. What is the maximum depth in the channel?____ m.

Part 2 – Detention Basins and Node Storage

A common practice is to use detention basins or ponds to temporarily store stormwater and release it downstream using passive control structures. The program has tools to model the depth to volume characteristics of any natural or man-made storage facility and a combination of weirs, orifices, or other devices that are used to control the discharge.

In this exercise, the flow in the network developed in Part 1 is reduced with a dry detention pond.


Introduce the steps required to:

  • Define a storage node
  • Simulate an outlet structure consisting of weirs and orifices
Time1 hour
Data files

Yarra41.xp (from Part 1)



  1. Open Yarra41.xp. This is the model completed in Part 1.

  2. Convert a node to pond:

    1. Double-click node Pond to open the Node Data dialog. 

    2. Click the Storage button to open the Storage Node Data dialog. 

    3. Set the Measure Depth from to Node Invert

    4. Click Stepwise Linear to open the next dialog.

    5. Click Insert six times to add blank data rows. 

    6. Fill in the Stepwise - Depth and Stepwise - Surface Area table as shown in the following figure. The relationship is displayed graphically as the values are entered. 

    7. Click OK three times to return to the network view.

  3. Add a new upstream node:
    1. Select the node drawing tool and add a new node adjacent to the pond. Rename the node StrmInlet to indicate that it will represent the upstream node of the stream.
    2. Select the stream at a point near the pond. Holding left button down, drag the end to the StrmInlet node and release connecting the link Stream to the new node.

  4. Enter node data:
    1. Double-click StrmInlet to open the Node Data dialog.
    2. Set the Invert Elevation to 1274.8 and the Spill Crest to 1276.3.

  5. Add Outlet structure. The pond structure consists of three controls. An orifice drain, a primary sharp crested weir, and an emergency broad crested weir. 

    1. Select the link drawing tool and add a link from Pond to StrmInlet. Rename the link Outlet

    2. Right-click the link and select Multi Link from the menu.

    3. Double-click Outlet to open the Multiple Link dialog. Clear the conduit button in row 1. Click the Orifice button in row 1 to open the orifice dialog.


    4. The pond is drained with a 6-inch diameter (0.2 ft2), Side Outlet located at the bottom (invert = 1269.5). Set the orifice invert elevation to 1274.8. Click OK.

    5. Click the Weir 1 button in the Multiple Link dialog. Stormwater discharge is controlled with a 2-foot long sharp crested weir with a crest at 0.5 ft above the pond invert. Enter the data as shown in the figure below. Click OK.

    6. Click the Weir 2 button in the Multiple Link dialog. Emergency overflow is provided with a gravel spillway at elevation 1273.5. Enter the data as shown in the figure below. Click OK twice to return to the network view.

  6. Save your file as Yarra42.xp. Solve the model. 

  7. Assess the performance of the detention pond. Open the hydrographs for link Stream. Note that the peak flow is 18.82 cfs. The peak flow entering the pond is 29.43 cfs. Thus the pond reduced peak flow by approximately 36 % for the design.


Review the output file (Yarr42.out) to answer the following questions.

  1. Did the pond eliminate flow in the left and right overbanks of the stream?

  2. What was the maximum and volume of runoff stormed in the pond?

Part 3 – Street Flooding and Dual Drainage

Up to this point, it has been assumed that the hydraulic capacity is controlled only by the conduits in the network. In some cases, the capacity of grated and curb inlets restrict the amount of flow entering the collection system. The program provides a variety of options for defining an Inlet Rating Curve (IRC). 

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 water divided by the time step. The maximum total diverted flow 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 three 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 on 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].

In Part 3, the inlet capacity feature will be used to control flow in conduits and excess flow will be routed in surface streets.

Level Novice 
ObjectivesIntroduce the steps required to:
  • Define an inlet rating curve
  • Route excess flow along a street modeled as a multilink
Time 1 hour
Data files




  1. Define shape for streets:

    1. Open the file Yarra 42.xp

    2. In the Configuration menu, select Global Data, then Natural Section Shapes in the left panel. 

    3. Type Stream shape for the record name. Click Add Record and then click Edit.

    4. The Stream shape section is defined as 20 ft wide with a 0.3 ft crown and 1 ft curbs. A value of 0.016 is used form Manning’s n in the center channel (from the Left Overbank at = 0 to the Right Overbank at = 20). Add data for the Stream shape as shown in the figure below. 

    5. Click OK twice to exit Global Database dialog.

  2. Convert links to multilinks:

    1. Select link Pipe07

    2. Right-click and select Multi Link from the menu. 

    3. Double-click Pipe07 to open the Multi Link dialog. Add a second conduit, Street 07 in the 2nd row of the conduit column and double-clicking the 2 box.

    4. Street 07 is defined with the Stream shape record. Select Natural and then click the button next to Shape and select Stream shape. This section is 1 ft deep. Set the upstream and downstream elevations 1 ft below the ground elevations of the respective nodes as shown in the dialog below. Enter 110 in the length box. Click OK three times to return to the network view.

    5. Repeat the above steps for Pipe06. Select the same Stream shape. Set the upstream elevation to 1292.28, downstream elevation to 1283.95 and the length to 178

    6. Click OK three times to return to the network view. 

  3. Double-click Node 3/2 and then click the Inlet Capacity button to open the Inlet Capacity dialog. Set the Maximum Capacity to 2 cfs and select the Maximum Capacity Only radio button. Click OK twice to return to the network view.

  4. Save the file as Yarra43.xp. Solve the model. Select Pipe07 and open Review Results. Note that graphs are displayed for each conduit in the multi link. A new node 3/2 was created as the upstream end of the underground conduit. The flow in Pipe07 reaches a maximum 2 cfs. The remaining is conveyed by the street.

    The cross section of flow in the street may be obtained by selecting Node 3/2, holding the shift key down and selecting node Junction. Click the Dynamic Section View tool. The panel in the lower left shows the cross section of the Street07. Start the video to display. At the maximum flow the cross section will appear as shown in the figure below.


Review the output file (Yarr43.out) to answer the following questions.

  1. What proportion of the total flow was conveyed in the street between nodes 3/2 to Junction?

  2. Is this level in the street appropriate? Why?

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