Monday, January 12, 2009

Water Security

We all need a reliable source of water, but this is especially critical for farmers and those who are growing food. When we developed our permaculture design for Tenderbreak PF, there were two issues that had the highest priority, and influenced all our decision making - these were water supply and fire defence.

The dam was the first thing we built. It was sited where it would have a good catchment area- at the junction of two natural shallow gullies. During periods of heavy rain we had seen these carry water runoff and knew they would help our dam fill rapidly. The critical words here are “periods of heavy rain”. Unfortunately there can be long gaps between these periods, but when the rain does come, it is a real joy to see small streams flowing into the dam.

We sited our house, outbuildings and drive so that runoff from these is directed to the “house gully” adding to the natural runoff. Of course roof run-off initially goes into our water tanks, but once these are full, the overflow runs into the gully. Another advantage of this design is that moisture levels in the “house gully” are kept higher, improving the microclimate in the vicinity of the house.

The house and other structures are also positioned so that the dam is to the north, forming a static 50m firebreak between our “house envelope” and the thousands of acres of state forest in that direction. The dam is also a reliable water supply for fighting fires if the need should ever arise. Even in the worst of the drought it only dropped around 1m out of its total depth of 7m.The thought of wildfire is not very pleasant, but having a reliable water supply helps.

Having the dam to our north, and all runoff from our developed area flowing to the dam works really well. To make use of that water though, it has to be pumped, and relying on a pump for irrigation and especially for firefighting leaves one vulnerable to mechanical failure. Our solution was to build a small (.5 megalitre) header dam 200m up the hill behind the house. This is the dam we use for day to day watering and with a 30m head is suitable for fire fighting.

This dam has a much smaller catchment and will only fill naturally during good rainfall years. To overcome this we have connected both dams with a 50mm pipe. When the main dam is overflowing in the winter, we can pump up to the header dam to top it up. This system enables us to start each summer with a good supply of water, capable of being fed by gravity to any of our developed areas.

Even though we have a good catchment, the dam still took over 12 months to fill with water. We reckon it was us bulding a dam that caused the drought. Anyway this gave us plenty of time to build a jetty. (Much easier building it in an empty dam than a full one.) The jetty allows access to the water (for watering, boating, fishing or going for a refreshing dip) without stirring up the mud. More on our main dam in the next post.

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