Feedback Frenzy

Stay on the designated walkway

 

As I've been mulling over what to share about the garden, on Friday night, we received a downpour. Perhaps the biggest rainfall we've seen since January 2011, when the infamous Queensland floods destroyed the Lockyer Valley. That's nine years of increasingly, smaller amounts of rainfall, and my garden had to cope all that time. Much to my surprise, there are successes when plants survive. However, the soil takes a beating when fast water is on the move again. Especially after drought conditions. This latest event has revealed problems I still need to address. 

Until this recent downpour, I couldn't tell if improvements I made since 2011, has made a difference. The above photo shows a deepening sinkhole. This is where the swale around the house, drops it's water down the slope. We have a plank of wood for crossing, and a large rock to hold back silt. The job is being done successfully behind it (catching silt) but as the fast moving water goes over it, soil gets chewed out.

Thankfully, I have another swale just bellow this drop-off point, to slow the water again and catch silt. But it's feedback I need to pay attention to. So I've decided this area is a candidate for a Zuni blow. Or a specially designed, rock pool, which allows water levels to drop without causing further erosion.

Mine won't be as large as the one in the video, but it shares the principles behind proper construction of a Zuni bowl, and why you might need one. I especially liked the idea, it becomes a moisture magnet in the landscape - growing vegetation on the edges. It's a design feature, arid landscapes like mine, need, when struggling to grow vegetation on a slope. 

Formerly, I explored the idea of a pond in that location. However, evaporation would be the major issue, in the dry years. That location is limited in space and close to the house, so I cannot grow large shading shrubs to prevent evaporation. Plus I've always had problems growing plants in that particular area. So a Zuni bowl, is probably the best solution here.  

Feedback in the system

We're now going higher up the slope, in front of the house. This is where water uses our access paths to migrate downhill. We do have swales at the top, to prevent too much water travelling down. This recent event however, caused the swales to spill over slightly. There's a reason it happened, and I'll explain soon. But you can see where the fast moving water, beat down a track - exposing the red clay.

Years ago we mulched this footpath with chunky bark, and it looks like it needs another dressing. It was a brilliant area for feedback though. As just a few days prior to the downpour, I saw an ant spout being being built, between the top, two lines. They formed a dirt spout around their nest, which scaled about 2 inches high. I had a sudden urge the day prior, to start chopping and dropping, what mulch I could. Seeing that spout, just confirmed the ants sensed (like me) a LOT of rain was coming.

Mulching this walkway again will help break up the water, as it migrates downhill. Where we can make the most difference though, is probably higher up the slope.

JULY ~ 2012

Eighteen months, after the 2011 floods

Before I show where we get fast water, entering from the street, I want to share what we did improve at the top of the walkway, roughly eight years ago. The walkway slopes down towards the house. Our berm is on flat ground, just before it drops off down the slope. We mulched it with bark and grew cana lilies into it for stability. In theory, water can get a foot high, before spilling over, into the garden. 

The susceptible point, is where the two colours of my lines, meet. It's where the walkway starts to drop off. Water will spill over that, before it reaches a foot in height. So the berm is doing it's job for the most part, protecting the garden. But I need to address that susceptible point, at the top of the walkway. I can do that by tweaking the contour on this slope more. 

It will also help to top-dress the berm with woody material again, It's been a while. We actually stopped doing it, when the brush turkeys would rake it away religiously, to build their nesting mound. We'll just have to bight the bullet though and put some more down.  

Street level, at the very top of the slope

This is where all the problems are originating. Our neighbours driveway is on the other side of the street, and runs down their hill. So gets plenty of momentum from water rushing down their slope. The problem is the silt, the water carries. It's deposited in The Council spoon drains, filling them up. So instead of the water being carried away in the Council spoon drains, which are now blocked with silt, water shoots across the road, over to our side. Where we get a torrent of water down the slope.

This doesn't happen all the time, just when there's particularly heavy rainfall. As the water rushes down our front slope though, it takes silt with it too. I'd love to do a series of swales down this particular slope, however it's too steep. So the swale at the very bottom of this slope (near the berm and walkway) is where the silt gets deposited.

Water mitigation works

This is the main swale that disperses water down the walkway, if the neighbours driveway floods. The swale is designed to hold a lot of water, before dispersing it gently, at both ends. This is not the swale, on the same level as the house. It's above it, on a slope, to hold back as much water and silt as possible. What I need to address in this area, is dispersing the two main channels of water, coming down the slope. On the actual slope. With no room to do much.

By dispersing the water higher up the slope, it will prevent silt from blocking this main swale. It will also prevent erosion of the slope, itself.

Erosion

This is small chunk out of the slope, just before the silt deposits. The hard part about only being able to observe this fast water event, some nine years after the flood, is that in between, we experienced a prolonged drought. So there was absolutely no way, I could establish plants to hold this back. Not without additional water, which is challenging to find in a drought.

Okay, that's not entirely true. There is a way I can work this slope better - and hopefully to establish some plants also. It won't depend on reliable rainfall either. But I'm going to have to share that strategy in another post. Not sure if it will be before, or after Christmas. I'm in a feedback frenzy, workathon, in the garden at the moment. Doing my best to implement better strategies, before the next storm. Still with Christmas presents waiting to be finished and wrapped too. 

Basically though, it's a strategy I've tested successfully in other parts of the garden. Only, on a smaller scale. I look forward to sharing that with you, when I can. I hope your garden is receiving the rain it needs, or snow, if that's part of your water cycle too. It all counts towards more hydrated land, and happier plants.