4 Factors that Make an Efficient Gravity Sewer

plumber leichhardt - slope of the sewer

Gravity sewers are defined as huge networks of underground pipes that transport greywater, blackwater and most of the time, stormwater from different households. Then, the water will flow to a centralised treatment plant with the use of gravity. In additional, conventional gravity sewers is designed with various branches. Usually, its network is divided into primary, secondary and tertiary networks. This type of sewer doesn’t require any pumps at all. However, upon installation, there are things that must be followed in order to create an efficient gravity sewer.

Listed below are the 4 things that should be followed in the installation procedure:

Slope of the sewer

In the making a gravity sewer system, there are things that must be done in order for the system to operate efficiently. For instance, the sewer pipes used must be laid gently. In addition, the pipe must have a specific grade and downward slope. With this, the gravity will pull the sewages straight to the treatment plant. If the contractors failed to provide a specific slope to the pipe, chances are it’ll have problems in carrying the sewage from domestic establishments to its designated treatment plant. On the other hand, velocity plays a role in the system’s efficiency. There’s also a specific velocity for the sewer system to conduct its own self-cleaning activities. However, sewer obstructions start to gather up if there’s a problem with velocity.

Design flow

The gravity sewer system must be organised. In addition, there must be an accurate computation that the system will conform to the required sewage flow of a particular area. On the other hand, experts suggest to use the “peaking factor”. With this, sewers and treatment plants can manage the rapid run of the system for the whole day. Trying to analyse the flow capacity of the system is important. Moreover, there should also be allowances since it’s possible that the amount of sewage increases due to unexpected events.


Apparently, this type of system depends on gravity when it comes to carrying the sewage. This is the reason why gravity sewers are laid in a downward slope. On the other hand, the velocity must be enough to avoid sewage buildup or sewage disposition. The sole purpose of accurate velocity is to prevent obstructions that will decrease the efficiency of the sewer system and damage it. The worse part of this is when the problem can no longer be saved and users are forced to invest in another sewer system. The velocity required must reach at least 2fps.

Size of the pipe

Experts suggest that the diameter of the pipe must be large enough that cleaning and maintenance equipment can fit inside. Since it’s expected that the system will become half full during the day, it’s recommended to have an allowance in the size of the pipe. In addition, the top part of the sewage flow must be unoccupied so that maintenance tool can get in. With this, the efficiency and the aerobic activities of the sewer system will be maintained.