Basic charged stormwater system

Hi all
Long time reader here, first time poster.



My Mum bought a house a few years back and the downpipes off the bullnose verandah basically just went about a meter away
from the house which isn't ideal. The downpipe went down the post to an elbow, then underground for about 1 meter then
turned back up with another elbow that finished at ground level, so it was basically a charged system. These pipes have been
removed as it wasn't far enough away from the concrete verandah. There is very little fall where these pipes are located
which I am thinking why maybe they didn't bother getting something a bit better happening.
Since there is virtually no fall to get the water away I'll have to put in a charged system again I think.
The verandah is approx 2.4x15.0m and is serviced by a downpipe on either end.
The block is approx 2 acres so there is no kerb to go to- the downpipe will just be draining to a point in the yard.
One end will be approx 5m away from the house, 2m from the neighbours boundary and approx 30 meters from the neighbours house.
The other end will be a 12m run approx and is located well inside the property boundary and no where near other houses.

I have a design in mind.

Basically I come out of the gutter to a 45 degree junction so this give an overflow if the system is blocked up somewhere. Even if they system totally blocks up, it's a verandah with slotted gutter, and even then it's a verandah with no eaves etc for water to flow back in to.

From that junction I continue with 90mm pipe but once underground I'm going to go to 100mm. There isn't likely to be any vehicles on the shorter 5m run but you never know, so I'm going to use it anyway. On the longer run for the other side of the gutter there may be the occasional car and the septic guy might drive over it so I'm going to go with 100mm there too. Ground is hard as so I think I'll dig 300mm and hope 200mm cover will suffice.

Coming back up to the ground again I was told by a plumber they normally just use a finishing collar and grate in this
situation but I thought I could use a small Reln vortex pit. I know they are normally used for water going in to them,
but I see no reason I cannot use it as an outlet. Being a charged system it will be full of water to the top of whatever I
put at ground level- I was thinking of drilling a few 10mm weep holes in the last 500mm of 100mm pipe and one in the
100mm elbow and wrapping some geofab around it and placing come coarse aggregate under this pipe and the elbow so
water doesn't stagnate in the pipe and seeps away through the holes in to the aggregate.
I will lastly concrete around the Reln pit to give it decent support.

Is there anything I'm missing in this system? I realise I could put in a small pit too, but i think with the small amount of
water these pipes are collecting I don't need one. Also the ground is very hard, I don't really fancy digging in a pit....
I think I'll be right with getting access if it blocks up. I have the mozzie cap access on the post if required and also 100mm
pipe underground to the pit so should get something up there if needed. I do realise silt will probably build up in the
end elbow, but you can just pull the pit lid off and take some of it out when you see it needs it.

Please point out any potential problems and advise anything i should change.

Thank You

Schmo
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