Apr 29, 2021 10:35 am
I'm stuck in a difficult situation and hope I can get valuable advice from forum members here.
As seen in the diagram below (sorry I don't know why it's rotated after uploading, you can "imagine" rotating it 90 degree counter clockwise), the storm water pit (900x900mm) is the lowest point in the land, and it's about 500-600mm below my backyard level, which can be a falling hazard (despite council insists it's not!!!). I wanna rise the pit so that it's level to the backyard but that's where the headache begins. I can think of 2 options for me, both with its own problem:
Option 1: I can buy a precast concrete pit riser readily available from Everhard or Civilcast and put in on top of the current pit before backfilling to level it with the rest of the yard. There are 2 problems with this approach:
a. Council argues that doing so will reduce the hydraulic flow from adjoining properties and if flood occurs in adjoining properties, I'll be responsible. It makes absolutely no sense to me.
b. If I ignore council's comment and do it, I still face the issue of drainage for the yard. The water flow according to the original base ground level is sloping towards the pit and if the pit is risen, I need to find another way for the water to flow to the pit. I have a junction box near the house slab but it's on the high side and I don't know if it's possible to collect and direct the water there.
Option 2: This is what I currently have (albeit temporary). I'm having a temp timber retaining wall around the pit. If I choose to go ahead with this approach, I might upgrade it to concrete sleepers instead of timbers. This approach will solve the issue of drainage as the agi pipe still can pour the water to the pit (which sits lower at the sleepers' bottom). But again there are issues with this approach:
a. By right I cannot have retaining wall within 1m of the boundary.
b. By right the retaining wall should not be across the storm water easement (which runs West to East to the pit)
Is there any brilliant idea I can do to solve these issues? I'm in Sydney Southwest if that matters
Re: Rising Storm Water Pit2
May 09, 2021 6:45 am
If you built the house, do you have a drainage design? It could be that the pit was placed too low.
Can you add some photos? It does sound like raising the pit is all that is required. But maybe you could just add a second lid up higher that allows water entry.
https://*.com.au/article/who_is_r ... ter_drains
Your neighbor is responsible for their own drainage.
Re: Rising Storm Water Pit3
May 09, 2021 9:36 am
"Your neighbor is responsible for their own drainage."
that is not correct, neighbour is responsible for run off, not drains
drain is part of easement and op's garden may not be the lowest on that section of pipe
sounds like op's garden may have been raised, before or after construction
Re: Rising Storm Water Pit4
May 12, 2021 12:36 am
Is the pit a surcharge pit? If there is a shared stormwater easement you need a surcharge pit to allow overflow overland in extreme rain events.
These pits are normally above the surrounding ground level at the last point before leaving your site.
You might be able to raise the pit if you install a new pit connected to it at a lower level to allow surcharge. If you raise it without a surcharge point your stormwater will flow upstream out of their surcharge pit flooding their property.
best to listen to the council, or get a hydraulic engineer to help you or download AS3500 and read the section on stormwater drainage.
Re: Rising Storm Water Pit5
May 13, 2021 2:10 pm
"But maybe you could just add a second lid up higher that allows water entry"
Yes I'm going to have a lid on top of the riser but I don't see it's possible for the flood water to rise that high
"sounds like op's garden may have been raised, before or after construction"
Yes. the garden has been raised so that it's level. Originally, it slopes from the slab to the pit (600mm for 4.5m)
"Is the pit a surcharge pit?"
It looks like a surcharge pit with a grate on top.
"If you raise it without a surcharge point your stormwater will flow upstream out of their surcharge pit flooding their property."
I don't understand this part. Can you elaborate? The whole street is pretty much has the same issue. Most of my neighbours choose option 2.
To help you easily imagine, the ground level (which is also the pit level) of all slots in the street is sloping. Let say my ground level (and pit level) is x, then the whole street looks like this:
[x+50] [x+40] [x+30] [x+20] [x+10] [x (mine)] [x-10] [x-20] [x-30] [x-40] [x-50]
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