Tech Tips

Sewer Erf Connections

This tech tip explains how to insert erf connections onto a sewer network.


Setting the defaults:

Erf Connections Menu Erf Connection Defaults

Erf Length

This is the length of an erf. The engineer must decide whether this length is enough to drain the whole erf and if necessary, adjust it upwards.

Distance of Connection from Sewer Line

The distance the erf connection point on the erf is located from the municipal sewer line for the sewer position Inside Erf.

Distance of Sewer from Erf Boundary

The distance a municipal sewer is located from the erf boundary.

Sewer Position

The method that the Erf connection distance from the sewer main is used in the calculations depends on the Sewer position.
Outside Erf - The municipal sewer is located outside the erf boundary.
In Road Reserve - The municipal sewer is located inside the road reserve.
Inside Erf - The municipal sewer is located in a servitude inside the erf boundary.

Minimum Cover on erf connection

The minimum values of cover to the outside of the pipe barrel for connecting sewers. Recommended values are:
Inside Erf - 600mm
Outside Erf / In Road Reserves - 1000mm

Minimum Cover on house connection

The minimum value of cover at the head of the house drain. The recommended value is 300mm.

Erf Connection Diameter

The external diameter for the erf connection sewer link.

Erf Connection Slope

The slope of the erf connection sewer link.

Number of Unit Flow units

The number of inflow units that the erf connection represents. The unit name will change according to the selected Inflow Calculation method. The units will be used when the Dynamic Inflow Update option is selected in the Design Parameters.

Unit Flow Inflow Class

The Unit Flow Inflow class or Inflow Hydrograph that the erf connection represents for the Dynamic Inflow Update function.

Calculate Minimum Ground Level on erf

If this option is selected the minimum ground level on the erf will be calculated when the erf is indicated while the erf connection is added. Else the position for the minimum ground level point must be indicated by the user self.

Erf Connections Menu Erf Connection Types

The erf connection types allow the designer to define up to 6 different erf connection types according to the height difference between the invert level of the sewer at the Y-piece and the invert level of the erf connection at the end of the connection.

To change one of the displayed items enter the required value in one of the white cells. The value in the associated grey cell will be updated as soon as the focus is removed from the edited cell by clicking on another cell. Click on OK once all the required parameters have been set.

Once the defaults have been defined and the connection types, the erf connections can be graphically added to the network

Erf Connections Menu Add Erf Connection

The program will prompt:

Indicate the position of the new erf connection. You may use any of the drawing snap modes to do so. As the mouse cursor is moved the elevations are interpolated from the dtm surface and displayed in the prompt area.

Click with the mouse to indicate the correct side.

The program will prompt:

Type in the new erf connection name e.g. Connection 1

If the Calculate Minimum Ground Level on Erf option is selected in the Erf Connection Defaults dialog the program will prompt:

Click in the middle of the polygon that indicates the erf for which you are adding the erf connection.

The program will trace the drawing lines that form the erf boundary and the search for the lowest point inside the erf.

The minimum ground level will be extracted from the dtm and the erf connection data dialog will open.

Once the erf connections have been added you can view them on the project.

Settings Menu Display Settings

Make sure Show erf connection layout is selected, click on Erf Connections to make further changes to the display settings.

Right clicking in the Erf Connection text box, will show test that can be displayed for the connection.

Sewer network showing erf connections and the minimum ground level on the erf.

Once the erf connections have been added, the erf connections have to be analyzed to see if flows are possible.

Erf Connections Menu Analyze Erf Connections

You can analyze all the erf connections or only a selection, click OK to continue.

The results of the erf connection analysis showing the type of connection, if no connection is possible this will be noted in the type column.

For the erf connections that are not possible, the sewer line will have to be lowered. This can be done by changing the minimum cover for the section of pipe that needs to be lowered.

Finding all the "not possible" erf connections can be made easier by changing the colour schemed used to show the connections.

Settings Menu Display Settings Sewer Colour Scheme

Under Colour Scheme select Type. You can then modify the colours individually for the various type (click on the colour button to change the colour), or define a Colour Ramp.

The erf connections shown using the new colours, any erf connections drawn in red will indicate issues.

Viewing the erf connections on the graphical long section.

Tools Menu Vertical Alignment

Click on Display Settings

The Display Settings dialog will open. Select Show Connections.

In the Crossings dialog, click Erf Connections and then on the Select button. Erf connections will be added to the Plot Crossings For section.

The long section now showing the erf connections.

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