I am based in Brisbane.
My property is almost flat, with very limited fall to the street (discharge point). There are no other stormwater services available to discharge to. It's a 46 meter distance. There is only 420mm fall to the street gutter. This makes it difficult, but I am trying to come up with a design which will work.
My design will be using a combination of stormwater pits and 90mm connecting pipes, to try to pick up the surface water and achieve the fall to the street.
I have attached 3 designs (see sketch attached). Do all of these 3 designs work?
To add to the complexity of my site, the ground level of the Pit 1 (upstream) is about 50mm lower than the ground level at the location of Pit 2 (downstream). This has been depicted in design 3 in the attached sketch. Also Pit 1 had wider which also has a thicker "lip", which means the outlet pipe from Pit 1 is lower than the outlet pipe at Pit 2. However you will notice the top of the grate on Pit 1 is still higher than the downstream outlet in Pit 2, which I am hoping will result in this design functioning property (discharging properly).
Design 1 is not satisfactory because it's only got a 0.5% fall.
Design 2 will work (I think) however this design is not physically possible on my site, due to the varying ground level slope which is a constraint that I cannot change (not depicted in the sketch).
Will design 3 work? I am hoping design 3 will work because this correlates to the constraints I am working with on my site.
Note: I've intentionally omitted actual dimensions and level values on my site. The "grid lines" in my notebook illustrates the relative scale and relative invert levels of the pipes and the levels of the pits and that's what I am trying to highlight in my question.