How to Design Sanitary Drainage Systems with CLOACAS (SEWERS)

In the fourth video in this series of 5, we show you how to perform the sanitary sewer network design of the urban sector that we have been using as an example to show the capabilities of our CLOACAS (SEWERS) software.


Once we have defined the sanitary sewer system’s geometry as well as the wastewater design flows to be used in the design, it is time to calculate the longitudinal slopes, diameters, and inverts of each sewer pipe within each conforming network.

In our sanitary sewer design software, you can define two types of criteria to be used in the automatic design.

Design Parameters Settings

When you open the General Settings dialog in any sanitary sewer project, you will find in the Calculation and Design tab the aforementioned two criteria.

The first one allows you to set that the pipe sections’ longitudinal slope or diameter to be determined by the software, seeks to satisfy the requirement of a minimum full flow velocity, in which case the value you enter here in the left box will be used as reference.

In the second criteria, the design approach focuses in that each sewer pipe section in the sanitary drainage system fulfills a specific design flow between full flow relationship, and which must be entered in this field in the Sewer Pipes Automatic Design group.

Also, as a control parameter in the automatic design, you must set a minimum longitudinal slope here and, in order to serve as the design’s results review element, it is necessary to specify in this field to the left the minimum acceptable design flow velocity on your design.

Automatic Design Options

Having selected your preferred design criteria in your sanitary sewers project, you can go to the SEWER PIPES tab to use any of the three available automatic design options:

  • The option that calculates the longitudinal slopes and invert levels in sewer pipes and manholes, keeping the current diameters on each pipe section.
  • The one that seeks to set, if it is favorable, for each sewer pipe section, the same longitudinal slope that the ground has in its alignment and, calculating from this slope and the corresponding wastewater design flow, the required diameter to meet the chosen criteria condition.

In the case that the terrain’s longitudinal slope is not favorable, it is assumed that the slope of the section is equal to the minimum value you entered in the General Settings dialog.

And note that this design option is based on the fact that when the pipe section has the same longitudinal slope as the ground in its alignment, the excavation is usually the minimum.

  • With the last option, the required diameters to fulfill the design criteria will be calculated, but without modifying the current invert levels in sewer pipes and manholes in the sanitary drainage system.

In other words, the actual pipe sections’ longitudinal slopes are accepted as adequate; that is, they have a value consistent with the required flow direction and, of course, that is different from zero.

When it comes to determining diameters in the automatic design options, our software will take as a reference the sewer pipes library that has been assigned to each sewer pipe section.

Note that by editing one of the pipe sections, among other properties, you see the one that shows the selected sewer pipes library to be used as reference in the design. The project’s list of libraries is specified in the SETTINGS tab, through the Libraries Pipes Manager dialog.

In the transcript of this video, we have left the link to a detailed tutorial that helps you to know the characteristics of this dialog better.

Thus, if the library assigned to any sewer pipe section is this, the diameter’s search range in the automatic design will be restricted to these values. That is, the search process would culminate, in this case, when the diameter reaches the 600 mm value.

Keep this in mind in order to properly interpret the results of the sanitary sewer design performed by our software.

Thus, when you choose and click on one of the automatic design options, a message informing you about the results will be shown.

In our case we will use the second option, because at this time all sewer pipe sections have the same diameter and non-adequate longitudinal slopes.

In this case, no errors were detected, although a text is shown stating that there are sewer pipe sections discharging at invert elevations lower than the receiving manhole’s.

Visualizing the Design’s Results: Table and Longitudinal Profiles

Let’s see how this is in its longitudinal profile.

In the RESULTS tab, we will click on the Show Longitudinal Profiles button.

Then we select the main sub network to be displayed and we see here that, indeed, the discharging elevation in the sub network A 5, as well as that of the A 1, are below the invert levels calculated for this main sewer line at the respective manholes.

Later we will see how to solve this situation in our design, but in any case, when I select the link to display all of the project’s longitudinal profiles, the longitudinal slopes and diameters for each sewer pipe section have been adequately defined.

Similarly, when you check the manholes and sewer pipes tables, you will see the components data and results required to understand the hydraulic calculations performed.

Here, highlighted in light red color, are some sewer pipe sections that violate any of the design conditions pre-set in the general Settings of our sanitary sewer project.

To sort the rows in these tables based on the sub networks that we have defined for the sanitary sewer system under study, you can click this button on the SEWER PIPES tab.

This way you will better visualize the results and note that the Starting Sewer pipes labels are shaded in gray color and, in the manholes tables, the sewer network’s discharge manhole label is yellow colored.

Using the Sewer Pipes Editor to Improve the Sanitary Sewer Network’s Design

Of course, in this case, there are several sewer pipe sections where the full flow velocity values are not satisfied because, remember, we have set as the design criteria the capacity ratio in each section.

If, for example, we change this condition in the Project’s General Settings and carry out the design again, we will have these results.

There are improvements in the full flow velocity, but at the cost of increasing diameters, and therefore this does not seem to be the best solution. It is more reasonable to return to the previous design condition and manually make modifications to those sewer pipe sections with problems.

For cases like this, you will see that the Sewer Pipes Editor dialog offers a number of design tools which are explained in detail in the tutorial whose link you will find in the transcript of this video at the bottom of the page.

For example, to resolve the reported situation in the main sewer line, at the manhole receiving the A5 Sub network, we could edit it and use this option, which changes the downstream-located pipe section’s invert elevations by the value you enter here.

In this case, we see that the A5 sub network discharges at this invert elevation, which is about 50 centimeters below the main sewer line, the A0 at the A5 manhole.

Then, let’s go to the A6-A5 pipe section in the A0 sub network and specify an invert’s decrease of 55 centimeters for all those sections located downstream.

Now, when we visualize its longitudinal profile, you will see that the necessary inverts drop to capture the affluent sub network, the A5, is created, and as a result, the A1 sub network discharges at invert levels higher than the receiving one.

The Calculation Tool only calculates, does not design.

Although this change does not involve modifications in the hydraulic calculations, always be careful, when you use automatic design options, that the values you have set will be modified.

That is why you should use the Calculation button in the SEWER PIPES tab in order to update only the hydraulic values. Thus, the specific geometric changes you have made are kept.

Also, with the Sewer Pipes Editor, you could vary the longitudinal slopes of those sewer pipe sections with full velocity issues.

For example, in the A1-A0 sewer pipe section, I will vary the invert elevation at the downstream manhole until the full-flow velocity exceeds the 0,7 meters per second.

You have everything you need to tune up your sanitary sewer designs in our software.

To visualize results with colors

Another helpful design tool incorporated in our sanitary sewer design software is the one that allows you to visualize the results using colors in the sewer pipe sections of the networks within your Project.

For example, I would like to visualize how the capacity ratio is in the pipe sections of this sewers network.

So I go to the DRAWING tab and click this button to display the dialog that allows me to specify colors and ranges of values for several sewer pipes’ properties.

I will keep the default values and close the dialog.

Check this box and select the property to be visualized.

You will see the sewer pipes lines’ color change and, also, the corresponding legend is shown.

This way I can identify the surcharged sewer pipe sections or those with low capacity ratio.

Using the Global Editor for Diameters Modification, among other Properties

Our Sanitary Sewer Design Software also incorporates the Global Editor, which allows you to make changes to one or more objects in the current Project.

For example, we wish to change the diameter of some sewer pipe sections, so let’s select from here, check this box, and select the desired diameter from the list.

When clicking on the OK button we will see, in their properties, that the modifications are done.

The Global Editor is also useful when combined with the Objects Selection tool.

With this tool you can select objects based on some property’s value.

Let’s suppose that we want to select those sewer pipe sections whose diameter is 20 centimeters.

I change the object type to Sewer Pipe, select the Diameter property, the equal operator, and enter the value in the text box.

When clicking the OK button, you can see the corresponding sewer pipe sections selected.

Once selected, and supposing that you want to change their diameter, you only need to open the global Editor.

And you see now that the objects selection is not enabled, because the tool is taking as selected pipes those that have been selected before loading this dialog.

I will modify the diameter and click OK.

The changes are easily performed, as you can see.

This will save you a lot of time in the editing, analysis, and design process of your sanitary sewer project.

The Tool for Searching Sewer Pipes Lines in the drawing area

Finally, also take into account the Search tool on the DRAWING tab.

Sometimes, especially in very large sanitary sewers projects, you will want to locate a manhole or a pipe section from their name in the drawing area.

Clicking this button, you will see that the list of labels or names for each type of object is available.

If I select, for example, this manhole’s label and click OK, the display of the drawing area will change to have the object in question on the screen area.

As you saw in this video, the sanitary sewer systems design options offered by our software are not only multiple but also versatile enough.

It only remains to know the Project’s plans as well as the bill of materials generation options that our software offers.

In the next video, the last of this series, we show these features so do not miss it.