Pit Dimensions

[Maxi Eng]

Hello fellow engineers,

I was wondering if anyone could shed some light on minimum stormwater pit dimensions for certain outlet depths as per Australian Standard AS3500 (screenshot below).

For example, why is a 450x450 pit limited to an outlet depth of 600mm? What are the consequences of exceeding this depth?

Thankyou in advance!

 

[HTURKAK]

For example, why is a 450x450 pit limited to an outlet depth of 600mm? What are the consequences of exceeding this depth?

If the invert level of the outlet is LT 600mm, cleaning and maintenance can be made with insertion of a hand (as for lifting) or of a hand and arm . These could be called handhole also , which is a type of small manhole, too small for access but useful for inspection and washing out the mechanism.

If the invert level of the outlet GT 1200mm, acess could be necessary for inspection and maintenance , so could be called MANHOLE .

 

[swazimatt]

I think that is confusing wording. I believe that dimension is the sump dimension ie from the base of the pit to the outlet pipe invert. (highlighted dimension below - not from AS/NZS 3500

If you look at Table 6.2.5 minimum pipe cover you would battle to meet some of the cover requirements on the small pits. especially under trafficked situations

My reasoning is that a larger pit would be selected because of larger flows/outlet pipes and you would want a larger sump to reduce chance of resuspending solids