Top tank overflow: design + implementation

| Permaculture, Permaculture Design, Water Harvesting + Reuse | comments | Author :

On occasion, our two big water tanks at the very top of Milkwood Farm overflow. What to do with the intermittent extra water? It’s too precious to just drain away. Time to design a water catchment and planting plan to make the most of it.

Since solving this problem is both necessary and interesting, we decided to develop an intern project around it. The brief: design, implement and plant a system that makes use of intermittent excess water, shelters the intern camp and shed, and provides a useful yield. Go, you fabulous interns!

Installing the water tanks, January 2011. Rather big, aren’t they?
The water tanks in place, with the western slope below them in a particularly wet year (read: grass) January 2011.

Stepping back a bit, a word about our water tanks. At Milkwood, we’ve chosen to collect all the rainwater we need for our home via a big shed at the top of our ridge. The very big shed roof is connected to two very big stainless steel water tanks, and hence all the drinking water we need for the farm is gravity fed. You can read more about it here.

And so our interns Claire, Adam, Sabina, Jurgen, Olivier and Ashley set to work designing a system to make use of the occasional gift of excess water. The design brief included a short timeframe (4 days from start to end), and the use of what materials and plant stock we already had available on-farm.

It was decided to catch and use the runoff by creating and implementing a series of small swales which spilled one into the other, stepping down the western slope of our ridge.

Intern design for water tank overflow
Interns Jurgen and Claire discussing the design
Design all done, it’s time to dig. Olivier gets into it…
More digging…

These swales have rubble spillways to enable the runoff water to spill gently from one swale down to the next when the first one is full.

The plantings on the swales are firstly hardy pioneer species (mostly acacias), in order to get some biomass and microbiological action happening on this rather barren, exposed and rocky slope. Once these plantings are up and happy, we’ll introduce some other plantings inbetween.

Where the tank overflow meets the beginning of this swale system. The surrounding rockwork will help spread and slow the flow of water.
From this overflow influx, the water runs out along the first swale, before spilling gently into the next, and the next
And on down the hill the water spills, filling each small swale and soaking in quickly…
Ashley, process manager Trevor, and Sabina. Happiness is a rainy day of digging.
The rockwork swale spillways which take the water down to the next swale.

It was great luck that as this project was just being completed, down came the rain, conveniently overflowing the tanks and testing the whole system. It was great to see everything working as it should!

The later plan is to create a sloping guild of useful, extremely hardy tree species, planted along these same swales. Perhaps something like Olives, Chestnuts and Paulonias. We’ll have to do some trials and see what works best, as this slope is west facing and gets a lot of hot summer sun.

All the swales are also planted with lomandra, a very hardy and useful plant whose roots will help hold things together in between the available water. And the end result will hopefully be a beautiful, sloping area, full of the promise of shade and possibilities.

A necessary task that needed to be dealt with to prevent future erosion and a great little design project, all in one. Cheers, all!

Design and implementation all finished and awaiting the next overflow event.

Many thanks to our great interns Ashley, Olivier, Adam, Claire, Jurgen and Sabina for their efforts in implementing this necessary feature of Milkwood. Thanks also to Adam, Olivier and Claire for the pictures.

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5 responses to “Top tank overflow: design + implementation

  1. “and a great little design project” – I’ll have to agree with that. Looking forward to the progression photos.

    Were those swales eye-balled or exactly on contour?

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