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It's the rainy season here in Australia, so I decided to put in some proper swales.

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Comment by Andrew Cumberland on November 22, 2019 at 0:26

Cheers Cres.  I did get the vetiver planted all around the bottom end.  It's been so dry though that it really hasn't gotten going properly yet. I hadn't thought about a proper overflow but yeah, I'll need to put one in.  

Comment by Cres on November 21, 2019 at 9:53

Andrew : Your water retention setup looks good. In one of my newly built swales I hadn't completed my overflow and the following day a downpour broke the berm (A backyard is small scale so wasn't a major flooding issue) but it reinforced what I'd learned and seen implemented on dams and swales on a much larger scale (50tonne excavator style!) on my friend's permaculture farm.

A recommendation for your overflow channel. Either put a lot of rocks/old pavers in and around it or something like an overflow pipe. I use a short bit of 90mm stormwater pipe and cover with rocks and dirt, as well as pavers and rocks on others. What happens in a massive downpour is that the narrow egress point erodes very quickly both downwards and sideways as the water velocity increases through the narrow gap.

Dave touched on vetiver to stabilise the banks which is a great idea. I plan on planting vetiver on the berm, the deep roots will hold it together, access the swale water but keep the swale free for maintenance. I still think you ideally need a 'non erodable' type exit point.
Personally I put the exit point on the end of the swale that's on higher ground. Given the swale is obviously on contour  it is the end where the height of  the berm is shortest. It maximises the time water is spent on my land.

I put wood chip and prunings in my swales. Some washes away but mostly it soaks up water and keeps the swale wet for much longer allowing the water to seep deeper into what would normally be hard clay. It also means I can go a little bit deeper with the dig and still walk across the channel without rolling my ankle.

Comment by Andrew Cumberland on November 20, 2019 at 19:37

They certainly slow down the water which is what I wanted.  Of course, we've had so little rain that I can't really say if it will have an impact on the plants.  

Comment by Sophie on November 20, 2019 at 12:41

How did you go with these a few months on? Happy with them? Do you think they are working?

Comment by Andrew Cumberland on April 24, 2019 at 19:28

I put some pretty substantial rocks on the corners where the water would undermine banks.  I'm not so worried about banks.  My biggest worry is that I'm worried a big downpour will move the mulch.  I'm wondering if I could plant a few vetiver inside the swales to slow the flow.  I could also then use it to increase the height of the banks and maybe chuck a few more big rocks into the low points.   

Comment by Dave Riley on April 24, 2019 at 18:50

True -- Christa is right: Vetiver is a good option --and you'll save on your sugarcane mulch bill as you'd have a domestic harvest of mulch.

'Swale' is very much a Permaculture term that presumes physical digging and heaping. Whereas Vetiver 'grows' a swale if you lay it out according to your contour preferences -- your sculpting to a plan.

Watching the video you'd have two options, I reckon:

  1. Planting Vetiver to consolidate the banks of your  drain (as you've shaped it) -- especially where the force of the water during a  storm could undermine the bank. your bank is also only so deep/high when Vetiver may give your more hold back without erosion
  2. Planting Vetiver across the flow to create pooling to slow the water rate and encourage the water to seep into the soil behind the hedge so less is lost to the street without domestic flooding.

I'm not qualified to 'consult' on bio-enginneering challenges   -- but yours is a small scale problem that a few plants -- later divided into greater numbers -- could readily solve.

Christa's drainage problem --that she applied Vetiver to -- seems similar to yours.

My guess is that many rising blocks on smallish lots in the Brisbane foothills could utilize Vetiver plantings for drainage management...with the added advantage of a ready mulch harvest.

And Vetiver, as grasses go, looks good.

Comment by Christa on April 24, 2019 at 14:52

Have you thought about using some vetiver around the edges to hold the banks of soil.  It looks much better than the last time we saw it, Andrew.

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