Permaculturing in Portugal

I have been thinking for a while now about ways to retain water for longer in its passage through the quinta. Not just for irrigation purposes, but to increase the range of environments we have for growing and to support a greater diversity of wildlife. The extent to which we can emulate strategies like Sepp Holzer’s at the Krameterhof and Tamera is constrained by the vastly smaller amount of land we have to work with, not to mention the topography and difficulty of access, but even on a much smaller scale, the principles ought to be similar.

The quinta has slate-built concrete-lined tanks on each main terrace, designed to collect water from the stream and its springs, which is then released through sluices into irrigation channels along the back of each terrace to flood-irrigate crops grown on the terrace. Slate-lined channels underground beneath the terraces take the water from terrace to terrace. At the moment, the tanks are full of years of accumulated sludge, the irrigation channels are overgrown and the transport channels don’t function in quite the way they were designed to.

But even were we to restore this system to its original working order, it’s a predominantly anthropocentric system: designed for a specific agricultural purpose and not particularly user-friendly for wildlife. The tank sides, for instance, are far too precipitous for frogs to get in and out, and the very containment of the water limits its use to a particular form of irrigation of a particular form of cultivation. It doesn’t work for raised beds, though it would irrigate fruit trees well.

One idea has been to create a series of ponds for the water to flow through from terrace to terrace rather than using the underground channels. Constructing unlined ponds using Sepp Holzer’s techniques will also allow the development of wetlands in which to grow plants that thrive in this environment and encourage more amphibious wildlife which will hopefully enjoy feasting on our plentiful supply of slugs and snails.

First I wanted to experiment on a small scale with the construction technique.

Underneath the bottom terrace is a pouço – a slate-lined underground dome with a collection tank below it, designed to collect water filtering through the ground above it. In order to keep the ground wet enough to supply my neighbours’ drinking water requirements, this area had become a stagnating marsh, breeding mosquitoes and bad smells, not to mention prodigious amounts of vegetation which considerably slowed the rate of water filtration. Turning this area into a shallow pond fed with plentiful clean water seemed a good project both to deal with my neighbours’ water supply issues and to begin my pond-building experiments.

I began digging with Simeon‘s help back in August. Together we created the first of two ponds, with the outfall of the first to feed the second.

Upper pond dug and filling with water. Some of the fine sludge from the bottom terrace tank was put into this pond and, along with the clay-rich soil, was mixed and trod in imitation of pigs creating a wallow so that a natural seal is formed as progressively finer particles settle out and line the pond.

The digging of the second, lower pond. This pond is directly over the neighbours’ pouço and is necessarily very shallow.

The ponds after a month. Water levels maintain themselves very well with only an occasional adjustment required to compensate for sudden changes in flows upstream. The water is kept moving to prevent stagnation and the pond feeding the pouço is full of sweet clear water. I would like to make the top pond larger and deeper though, and plan to do this sometime before Spring. Frogs have already been spotted swimming.

Duckweed (Lemna spp) starting to grow.

The pond digger

Tags: ponds, pouço, water retention landscape, wildlife ponds

This entry was posted on Monday, October 31st, 2011 at 7:25 pm and is filed under Ecology, Groundworks, Growing things, Water supply, Wildlife. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.