The DREN-URBA’S 2.0 Sewer Pipes Tab

Now that we have made the surface system calculations, as we saw in the previous tutorial of this series, it is time to perform the storm sewer network’s design, which will allow the collection and conveyance of the drainage inlet´s intercepted rainfall flow to the network’s outflow point.

In the new version of DREN-URBA, the 2.0, we have incorporated the same creation features of the storm sewer network’s objects: Manholes and pipes as well as the automatic design features that we had included in our software for sanitary sewers network design: CLOACAS.

These built-in features and tools can be found at the SEWER PIPES tab of the new version, which will be introduced to you in the next video.

Since the properties and functionality of the tools on this tab are shared with CLOACAS software, you will see, in the transcript below the video, links to tutorials that will explain in detail how to use them.


The Sewer Pipes tab has, essentially, the same characteristics as the Surface Drainage.

In the new version of our storm sewer design software, you may have one or more storm sewer networks, each having a single discharge point.

The original idea of the software is that the stormwater flow that is conveyed by this pipe sewers system, is strictly provided only by the surface system’s drainage inlets.

That is, the Inlet´s intercepted flow, calculated in the surface drainage system’s design, will be discharged into the nearest sewer network’s manhole so as to be able to establish the stormwater design flow corresponding to each pipe section, according to the network topology.

In this new version, in addition to the above, it is also possible to omit the surface system’s design or definition and perform the analysis, assigning affluent areas or sub basins to the sewer network’s manholes.

This is as to assume that, close to each manhole with one or more assigned sub basins, there is a drainage inlets that intercept one hundred percent of the surface flow that could generate such sub basins.

Under this analysis mode, you can certainly ignore the whole thing related to streets, channels, and drainage inlets, as we saw in the last video of this series, and limit yourself to assigning each sub basin, in the urban area under study, to the nearest manhole.

To do so, you must select the automatically assign areas to Manholes in the General Project´s Settings, so that the software does most of the work, searching for the closest manhole to the centroid of each polygon or sub basin.

Of course, when you perform the calculation of the current sewer network, you will see that assignment lines are now focused to the manholes, instead of to the street sections. And, when you review the properties of any of them, you will also see that the sub basins have been automatically assigned.

Of course, as we saw in the previous video, you can manually create your own user defined sub basins, that is, they will not be drawn in the drawing area.

And, in case you want to override the automatic assignment and manually assign some of those drawn sub basins to one of the manholes, you can select it and, from its Properties dialog, activate the manual assignment check box in order to select any manhole in the Project.

Thus, let’s know the tools we have provided in this tab.

The options for creating one or more stormwater collection systems are in the Sewer Networks panel, each made up of a series of manholes and sewer pipe sections and, as we said, a single discharge point.

This dialog is the same as the surface system’s one; you must specify its unique name, and a prefix used to labels’ automatic creation as well as a number or initial counter for them.

Remember that, for creating, editing, calculation, and design purposes, everything you do will be effective only on the sewer network you have here as current, showing data and results for it at the tables in the respective tab.

The Manholes and Sewer Pipes panels offer options to create them in the drawing area, and, in the case of the buttons here at the right of each panel, will allow you to move the position of each manhole or pipe section in the respective table.

Like all objects in the stormwater urban drainage system that you create in the software, you will see that it is possible, once you select a manhole or pipe section in the drawing area and click the right mouse button, to show its respective properties dialog.

For manholes, note that the known option for automatic elevation assigning from elevations points is available, and clicking the sub basins button gives you access to the list of areas that have been assigned to the manhole, if needed.

Additionally, in case you want to include external flows whose origin is different to the hydrological one in the sewer network, you have the inflow field to enter the respective value in correspondent manholes.

In the case of stormwater sewer pipe sections, you will see that the properties dialog is rather a design dialog, where you can modify the geometric parameters to establish the hydraulic values required in your design.

This sewer pipes editor, with slight differences, is the same that has been already incorporated in the first version of our program for the calculation and design of sanitary sewer systems, CLOACAS.

Click here to See the Tutorial

On the other hand, a very important aspect, not only in terms of the generation of longitudinal profiles as part of the design results but also for the purposes of the automatic design features the software offers, is that, for each sewer network you create, defining the sub networks that make it up is required.

And for that, the option is on the left button at the panel Sub Networks.

As you can see, in this stormwater sewer network, we have defined five sub networks.

A main sewer, which is directly affluent to the manhole selected as the network’s discharge point.

And four sewer lines or secondary sub networks that are tributaries to the main sewer.

Note that the definition of each of these sub networks starts by placing on the list of assigned pipe sections, the one that is the most upstream within that sub network.

This is what we call the sub network starting sewer pipe. From here you go to assigning pipe sections along the flow path to finish specifying the lower one, that is, the section whose downstream manhole is the point at which the sub network discharges, either the manhole defined as the network’s discharge point for the main collector or any other manhole, in a different sub network, in the case of secondary and higher order sewers.

Once more, this feature is similar to the one that already exists in our CLOACAS Software

Click Here to See the Tutorial

As previously noted, this will be used in the sewer network’s automatic design, but it also serves so that, when you go to Results tab and ask for longitudinal profiles, you have all the components of each network separated according to their order in the whole system.

The button at the right of Sub networks panel allows you to automatically sort data in the Sewer Pipes tab’s tables, depending on the division into sub networks that has previously established.

And finally, there are the options of calculation and design for the current stormwater sewers network.

When we speak about the Calculation button, we must be clear that it is the option that allows you to calculate the hydraulic parameters of the current sewer pipes network.

That is, the software will not perform for you any geometrical data modification.

So, in cases where sewer pipe sections exist with null or negative longitudinal slopes, or any other data that invalidates or turns the calculation impossible, the software will warn you that it is not possible to continue to perform the calculation.

The idea behind this button is, to say, the sewer network’s revision.

Now, if your intention is precisely to make the design of the storm sewer system, you have three options within the Design button:

  • The first option is focused on calculating, for each sewer pipe section and depending on conveyed stormwater flows, the required longitudinal slope, and with it, the invert elevations necessary to fulfill conditions such as minimum pipe coverage or minimum slope of the pipe you have specified in the project’s general settings.

In this design option, it is assumed that the pipe sections’ diameters are adequate and  therefore will not be changed.

  • The second design option focuses on determining not only the required diameter for each sewer pipe section, always depending on the design parameters you have specified, but also seeks to determine, if applicable, the minimum longitudinal slope possible to minimize excavation costs.

Where possible, as a first choice, the software will try to assign to each pipe section the same longitudinal slope that the ground has in its alignment.

In cases where the ground’s longitudinal slope is not favorable or does not meet the design requirements, the minimum slope you have specified in the project’s settings will be assigned, and if it still does not fulfill the design’s constraints, the software will start to increase its value until compliance is achieved.

  • Finally, you have the option which unconditionally respects existing pipe sections’ longitudinal slopes and, from them, determines the diameter of each section.

Regarding the latter two automatic design options, and reviewing the pipes libraries we have defined in this project, keep in mind that the diameters to be used in the design are those you have specified in the pipe section’s assigned pipes library.

So, for example, the pipe sections that have this pipes library assigned, may only have a diameter between 45 and 150 centimeters as a result of the automatic design.

In case of considering that, in the automatic design, resulting diameters should be of greater or lesser magnitude,  is a must to add more rows to the pipes library in question, in order to increase, so to speak, the search range of automatic design.

As you can see, DREN-URBA is now a comprehensive program, with which it is practically unnecessary to devote too much time to completing the stormwater drainage system design.