There are definitely solutions here, some are more resource-intensive than others.
Create a reservoir and pump the water to the storm drain up the hill by going around behind the pergola and along the back fence uphill to the storm drain.
Running pipe under that concrete path and install another sump this side of the shed before connecting to the storm drain. Requires a reservoir container, and a pump.
I tried installing solid pipe to slotted pipe, well that doesn't work, of course. And water doesn't like running uphill by itself either especially when the pipe behind it is slotted, it leaks lol.
The key issues are the quantity of water and the dispersal of the water. Ok, so the quantity is a constant flow pretty much because when watering the front yard, most is collected as run-off because of the high clay content across the property. Despite us adding a layer of soil, it simply isn't enough to absorb the water, nor is adding gypsum as we have done throughout.
In one area under a heavy-duty vertical screen, I dug out 11/2 ft or 45cm down and filled it with compost soil, to create a garden bed. Damn hard work actually as the clay is lovely and sticky and filled with rocks, overflow concrete, scoria, etc. Nasty job. Got an Air-tasker to help But this is now a proper garden bed that will absorb water.
Back in the back yard, we dug holes for the citrus, again using good soil and gypsum before planting. But the rest of the backyard is hardened clay with weeds. We took off the weed layer and simply covered it with mulch.
The directions of fall in the backyard are from front to back fence, and from left to right. approx half a meter fall towards the back right corner. There is no easement and the storm drain is located behind that shed, as said earlier.
Imagine saying 'well John, in that backyard, you are going to have to remove the mulch. Then dig one foot of clay and remove it. Then you can fill it by adding 1/1/2 ft of soil, to create a proper growing surface. And drainage will be better as the new area created will absorb water readily.
I am still thinking that the pattern that you have drawn is the way to channel the water for max spread, the question is how to bring the water around like that. Agi slotted sock pipe collects water it doesn't disperse it. And the clay will not drain the water, it will pond. Hence.... here I am.
Oh, and the water pond I've dug there is attracting wasps... to the muddy water that smells...
Thanks everyone for your suggestions and time to help me with this, I am very grateful.
Yes Red, this is why I ran that river away from the fence.
Before this re-routing, the water simply spilled out towards the fence and down the slope for a few months. I tried digging a delta pattern on the reserve side of the fence to disperse the water. Weeds started to grow and I'd basically constructed a creek! Up that creek...
If water is directed into a slotted ag-line, it will then leak out of it through the slots along the length. It's not just a one-way system where it only collects, hence my suggestion of using it to distribute. However, it sounds as if you're not confident that even if the water was distributed evenly that it would be absorbed in at all.
I think your best option is a large soak pit that potentially is deeper than the clay layer. You might like to check out our post hole diggers as they would help get you past that clay.
Good morning Mitch
Did you see the 1/2m post hole photo I posted above.
it’s my basic understanding that the clay goes down to the bedrock.
I can try agi drain as a dispersal pipe
and yes I’m not convinced that sitting agi pipe into clay soil will achieve anything
looks like a civil engineering problem 🧐