Sewer Lateral Connection to Manholes 1

[StocktonD]

I have seen many city codes and standards say sanitary sewer laterals cannot connect to manholes. Sometimes it will state that you can get the city engineer's permission to do it, but the general rule is that it is not allowed. What is the reasoning behind not allowing this?

 

[cvg]

its a bit messy when you have to enter a manhole with a lateral discharging through the manhole wall

 

[fel3]

Some cities I have worked with allow laterals to connect to manholes, but you have to come in near the bottom, precisely for the reason cvg mentioned.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[GeoEnvGuy]

Along the same lines but the sewer hydraulic grade line must remain below the potable water line. So coming in 2 ft up in the manhole can be the water grade line.

Manhole are also just precast concrete, don't need another penetration, poorly sealed, on the side wall allowing potential seepage of groundwater infiltrating and increasing the erosion rate of the concrete or the steps. The bottom of some manholes also have channels where the pipe enters and exits to allow for a working step.

 

[bimr]

Same reason that one uses a drop manhole:

Drop manholes are used to allow the use of reduced slopes in sewers. Reduced slopes are desirable to minimize the scouring effect of high velocities caused by high slopes. Drop manholes are also used to reduce turbulence in the manhole. Turbulence will cause gases to be released in the manhole.