Basics of Sewer Manholes
What are manholes?
Sewer manholes or also called maintenance holes are formal access points within the sewer pipe network that provide maintenance teams a chance to get access to maintain the sewer pipe network. They can come in many different shapes and sizes depending on how deep they go into the ground and what the surrounding ground conditions are like.
Why do you need manholes?
Once a blockage or a break in the sewer pipe is confirmed through a CCTV inspection, maintenance teams need to get access to remedy the issue. Without the presence of manholes, any remediation would be complicated and expensive.
Where can you find manholes?
The spacing of the manholes depends on a couple of factors. If a sewer pipe is running in a straight line in an area where access is not an issue, then they are usually placed every 80-100 metres (260-330 feet) along a sewer pipe. This spacing is determined by the practical length of water jetting equipment to reach the full length of pipe, regardless of whether the water jetting was done from the upstream manhole, or the downstream manhole.
That being said, manholes can also be built at shorter or longer lengths. For example, if the pipe needs to have bends in it, the design engineer might want to install extra manholes to account for the risk of blockage at the change point in the flow of sewage.
Manholes can also be placed within the network at irregular locations when the pipe network runs under a highly urbanised area. Placing manholes in the middle of roads, or in the middle of someone’s property is not advisable.
There are serious safety issues with placing manholes too close to live roads and having a manhole under a concrete floor slab doesn’t really serve anyone either. For this reason, the configuration of the network and the spacing of manholes might vary to account for the above ground infrastructure.
Drain spotting
You can identify the presence of manholes by the manhole covers on roads, footpaths and even in parks. The manhole covers themselves can come in many different shapes and sizes also, although most are round. They are usually made of metal to withstand the weight of heavy vehicles.
There is a great #drainspotting hashtag that you can browse to see what others have contributed from all over the world. Perhaps on your travels, you might feel compelled to contribute some interesting manhole designs and locations and help educate others on the weird and wonderful world of our underground sewer networks.
