Our first dam

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The studio dam, the one halfway up the ridge and in the middle of our system, was the first one we all sunk our teeth into. And boy oh boy…earthworks are something else… it’s like having your skin torn off in large slabs, while someone tells you it’s not skin, it’s just butter. No problem…

Strange analogy, perhaps… but until I had witnessed these earthworks, the landscape of Milkwood to me was a solid and impermeable mass… something that you could get a shovel into if you were lucky, but essentially one big, solid object. And then the bulldozer showed up. And now everything looks like a completely different place.

We were actually really lucky with what is usually a  traumatic time (don’t get me wrong… it was still pretty scary) when setting up a property… hydrology earthworks are something that you want to only do once, if at all possible. Nick and I had chewed over the Permaculture earthworks design for months, and to add excitement to the situation, we invited Geoff Lawton to Milkwood to teach a Permaculture Earthworks course during the first three days of the madness that has been the terra-forming of Milkwood.

So then we had 35 farmers and earthmovers on-site at Milkwood for three days. The course was great, and many of the participants came up to me during or after to express thanks that such a course had been run… you have to understand that there are bugger-all courses or workshops in sustainable hydrology earthworks for farmers and earthmovers around… unless they want to do a PDC, which for most of them might be a bridge too far, for various reasons.

But back to our fabulous dam. The minute it was finished, the rain came down… which was not at all what we wanted (sorry, rain) because we wanted to mulch and plant out the dam wall first. At the final stage of the dam’s construction, our earthmover re-covered the earthworks with the topsoil that he’s scraped off at the start, before he began his digging proper. This meant that our completed dam was covered in topsoil, which meant that we could plant stuff into it, and reasonably expect it to grow. Not trees, mind you… taproots (ie most trees) and dam wall = bad. Hairnet roots (perennial grasses, clumping bamboos) and dam wall = good.

A couple of weeks after this video was made, Nick turned a neighbor’s disaster into our Christmas present, and pumped the contents of a failing dam (‘she’s about to blow, boys!’) across the valley into our dam with a fire-fighters pump and a very long hose. Despite growing up by the ocean and always eschewing muddy water when it came to swimming, I am in love with my dam! And I am proud to say we already have four froggy friends that have moved in, and sing us to sleep all this summer long…

Technical bits:

  • We sowed the dam wall with a 50-50 mix of Lablab and Cowpea seeds, both of which had been inoculated with nitrogen-fixing bacteria, which will help them grow (you just ask for the to be inoculated before you buy the bags of seed). Geoff recommended sowing at between 4-8 times the commercially recommended rate – the idea is to get that dam wall jumping with growth asap, and growing with the species you want.
  • Both these species are nitrogen-fixing legumes, which means they will improve the topsoil quick smart so we can plant some other things in there .
  • Over the top of the broadcast seeds, we did a ‘feather mulch’ of oaten straw, which we got cheap because it was all a bit wet and rotten. A ‘feather mulch’ is where you lightly mulch the ground so that you can only *just* not see the soil. This mulch holds dew, protects the seed from birds and increases the germination rate of the seeds, all without blocking out all the light.
  • We hit good clay in in this dam, which should mean that it doesn’t leak much at all. We also hit a lot of huge rocks.
  • A dam this size when full, will hold just under 1 Megalitre. It took about 3 days (24 hours) to build with one bulldozer and Nick manning the laser level to check heights of various bits. The bulldozer (with a driver in it) cost us $150 p/h. So that’s about $3,600 for this dam. Which is not much at all, really, for the multi-purpose resource that it will be for Milkwood.
  • In terms of dam size on Australian rural properties, this is a very small dam. We wanted it small and deep, in order to minimize surface area (evaporation) and  so that it would be on a complimentary scale to the other elements in the system nearby.
  • By putting in multiple small, deep dams, rather than one big-kahuna dam, we are spreading the many benefits a body of water brings to its immediate environment around the property, hedging our bets in case one dam leaks badly or gives way all together, minimizing evaporation and generally creating diversity in the landscape. Diversity in a productive landscape = good.

Once we had all made it through the first four days of earthworks, things started hotting up with Nick and the Bulldozer… top dam, top swale, middle swale, bottom dam, studio site… it was on for young and old… at an hourly rate of $150 – yikes… and we’ve got approximately 3 weeks of work for the bulldozer.. so… better have a cake stall sometime soon, I think…

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