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This is an update to the stormwater rectification I started in 2021-2022. After last Fridays downpour I thought I would show how the landscaping, Berms and Culverts held up during the storm.
Good news is that it really held up, It does look like they almost failed in two sections but the quantity of water that fell in a short period of time was imense, 200mm over night I think it was.
I will have some links to the actually builds of sections of the overall project as it did take a year to put it into place. Worth it but 3 weeks ago I almost removed the berms from my front yard as they hadnt really done anything... I am glad I left them in place.
Materials
Clay
Soil
Pavers
1m Gutter lengths of concrete
Old Branches chopped into lengths.
Bessa Blocks
Tools
Shovel
Mattock,
Mallet
Steps
Step 1
We have had a fair few inundation events that dumped a large quantity of water where I live over the last 4 years. There was no way I could imagine directing it into the stormwater pipes as it was mostly surface water from my block and the surrounding neighbours blocks funneling towards me. At first I started with the idea of fixing the gutters and replacing the old stormwater pipe that had been compressed in multiple places but that soon enlarged to having to re-landscape my front yard.
Once I started sketching out ideas the thought crept in to reuse the excess water as much as possible. We are in drought a fair amount of time and the ground drys out like crazy. While I was in the process of replacing the stormwater pipes I saw how much surface water ran accros my yard and how it would eat away at the underlying soil very easily.
The stormwater pipes had been back filled but rain was eating it away.
After a heavy batch of rain a lot of the gravel and clay had washed down the hill.
The surface runoff from my neighbours was impacting my path plus water from my backyard and the houses behind me up the hill.
The gravel I had used under the pavers was easily being washed downwards. (I used gravel instead of sand for drainage and also because I had a lot left over from the stormwater project)
The stormwater showed how strong it could be and how far it moved the debris.
Step 2
This was where the slowing and diverting the water idea began, It was all straight runs for the water and the longer it ran in a straight line the more destructive it was. My solution was to slow it with holding ponds and berms. I wanted my front path to go through the area so I had to somehow accomodate it also.
The solution to the path beaing eaten away by runoff
On scale of last weeks downpour across Sydney and South of Sydney this one 2 years back was maybe half the quantity.
The solution being implemented
I just reveresed the garden edging and it works a dream, Its still working after 2 years.
Installed
Tested and passed with another rain event
You can see the water flowing. This was all water from the neighbours. Not delibrate but just happens when it rains.
Step 3
The Next section came about as I really needed a solid path through the clay that was there. We had a lot of rain in 2022.
You can see the slope of the yard from the pile of rocks in the background. The idea was for a culvert under the path and a holding pond before it
Putting down the base of bessa block cap stones
I used the light in weight sawable concrete slabs that Bunnings dont stock anymore for the sides.
Then covered it with a clay base
And just kept up sloping the path.
At the end of the "gutter" is where the holding pond will be, it will then empty under the path and around the trees via a berm yet to be built.
The paths base is taking shape.
After some rain it still held up. Clay can be useful sometimes.
Step 4
The two landscaping stages are the next steps in controling the stormwater.
Stormwater rectification stage 1 and
Stormwater rectification stage 2
These will show you the steps I followed throughout the builds.
After the landscaping the path the holding pond and berms started to take shape.
The wheelbarrow is sitting where the holding pond will be. You can also see the trimmed branches of the crepe myrtle being prepped for the berms.
Sketches always help...
They really do. The final version came out very close to this. Orange is for paths and blue is for stormwater run off path
The culvert is just where the dry dirt ends.
You can see the holding pond taking shape.
More sketches of the path and the associated gabion walls. Note the figtree in the corner of the paths
Actual layout of the path matches the drawing. Fig tree is next to the large daisy bush.
Crepe myrtle prunings then repurposed and trimmed down to go into the base of the berms to give body and long term nutriants to it.
After a large rain even washe dall the loose and compacted soil down the hill and washed under the windbreak. The Large gabion retaining wall build held solidly throughout all the major rain events.
More branches for the berms.
The path I want the watercourse to follow to maximise the soaking into the ground and slow the path of stormwater runoff.
Green is the berm edge, blue water and orange the major trees that I dont want to move.
Before for the first holding pond area.
Holding pond area being filled out.
This is where the winding berms will be moved to. There was a big half moon to help soak in the water for the liquid amber tree. That has worked well during drought times.
Where a berm will also go to give an outer edge to the yard. I intend to plant the berms out one day.
Step 5
This was the final fittout of the landscaping and berms. I had used all my poor soil in the base of the berms and the topsoil was running out fast.
So starting from the front of the house and working your way down the yard the excess stormwater will go down the straight gutter edge of the path, for ground water running under the pavers and through the 8mm gravel it will exit next to the gabion walls and the clay ground has all been slopped towards the dip where the fig tree is to maximise the water for the plant.
The beginins of the berms you can see being put in on the other side of the path. The path also has a dip in it purposely to feed the water through the path and into the valley of the berm. You can see it if you look at the figs branch.
The valley for the runoff between the berms.
Berm to the left to stop water and to give it the right direction for runoff.
Better view of the berms and the way they will sit.
There was a lot of earth moving involved but the soil had to used somewhere.
Holding pond to the left and then under via the culvert to the swirls of the berms.
Hard edge to keep the excess water in the yard.
Pretty much how it ended up. Intention to plant flowers along the berms.
To show the slope of the hill. It wasnt intense but definently sloped
Looking down at the earthworks.
Hard edge to the path.
Coffee tree to take advantage of whatever water flows down the yard.
Holding pond
Starting to green up.
Month-ish later and weeds were loving the area.
Time to put mulch down and I used ex coffee heshian bags for weedmat. So far they are the best thing I have found especially above the bought weedmat.
Berms covered.
Garden tidied for awhile until the weeds grow again 
The yard is now tied together.
The slope of the yard shot.
Step 6
This next batch of photos show the aftermath of the rain from the 05-04-24 night into 06-04-2024 early morning where 200mm of rain fell.
The straight gutter exiting into the first holding pond, The grass was pushed over due to the amount of water travel and the ground eaten
Small retaining pond area for the figtree, all soaked in nicely with some flow lines leading to it.
First holding pond, note the grass and soil erosion.
Under the culvert. I have two large bessa facing blocks lying flat to stop animals running under it, Think it stopped the gravel being swept into it as well. The gravel came from the side path and has traveled at least 10m but probarly 15m or more.
Low side of the culvert, grass is well and trully washed over due to the quantity of water. The white snow flowers are what you can see overgrown on the sides.
Flow lines of the exit from the berms, this whole area is a shallow dish type deal to capture and hold a large quantity of water if it ever came to it. I dont think it filled as I had my topography levels wrong on the corners of the berms.
The low side of the major holding pond, the water overtopped it and started eroding the soil. It came close to failing I would say. The depth of the pond is 25 to 30cm at least.
Surprise at seeing that the berm had been overtopped here. It exits onto a terrace garden but means the water would have been at least 20cms deep at this point.
Two points of almost failure on a structure I had built a year and a half ago with only a small amount of maintence other then mowing. I think this was pretty good going.
Step 7
Overall the stormwater mitigation worked well.
2 points of almost failure.
Topography of the land was out (yeah messed that part up lol)
Almost removed these berms in the last three pics as I hadnt needed them in two years and they hadnt looked like they did anything.
December last year I brought the berm back up to spec a little.
This was the overflow point six months later
I bpought some plants on the "special" table so put them in here just to see if they would surrvive. They didnt but for $5 it was worth a try.
Hi @Dave-1
Thanks for the update. I can only imagine what the damage would have been like if you didn't make any preparations or alterations to your landscape. I'm guessing a large amount of your topsoil would have been carried away and water damage would probably have been severe. Overall, I think your modifications worked very well.
Eric
Evening @EricL
The update was mainly for a question that was asked about stormwater I do find it interesting and kicking myself I didnt go out in the middle of the night to see how it was all working. If I hadnt had anything in place then a new pathway and repairing retaining walls would definently be on the list. Now all that is on the list is how to smooth some areas I thought were higher then they are and what to grow that looks like a garden but allows me to maintain the area as tidy.
I still have a plan for a creek bed in the in between the berms but not sure about how to seal it so the water wont soak and not cost a bomb in the rubber/pool liner amount of plastic for a watercourse. But now you have me thinking about it again as I put it into words lol
Dave
