Gabions: Water Soaks in the Desert

Gabions are one of the crucial feature elements of dry land landscape water harvesting design. A gabion is a leaky rock dam wall built in a wadi, valley canyon or water flow, at a point where there would be a reasonable amount of water caught if there was a dam wall in the same position, but the gabion instead leaks through the rocks, slowly releasing a steady flow of water and retained moisture over time. As the water is slowed down by a gabion, it drops its sediments, organic materials, behind the rock wall. Desert catchments are often large and feature very infrequent rainfall events, and are an actively eroding landscape that is continually being blown away, with sediments either eroded or deposited by the wind if there are wind traps like desert tree systems and forests, but also by water flows which are usually strong and can carry large amounts of organic material and sediments away with them.

A gabion traps this material, because, as a principle of aqua dynamics, the slowing of the water drops the material volume and quantities that the velocity can carry. So this aqua-dynamic deposition system, placed in a location that forms a large back-up silt field, retains water-soaked silt enriched with organic materials, storing it away from the sun, and acts as a giant sponge, holding the water for long periods whilst slowly leaking it into the landscape. A winter’s rainfall can be harvested in a set of silt fields in a gabioned, wadi, canyon or a desert valley that then release that water over the next few months. These silt fields retain more rainfall each year, soaking in quicker because they are already have dampened hydrology, building to a maximum capacity on an average of 7 years.

In the photos I have included in this post, there is a documentation of two gabions in a wadi in the Dead Sea valley that comes down to the Dead Sea itself. I witnessed these gabions built in 2002 and have visited this site many times since, often after winter rain, and have seen residual water flows extending through the silt fields and down the wadi for long periods of time — increasing each year. During a PDC in Jordan in Oct/Nov this year (2010), the students and I took a field trip to examine these two wadi gabions and much to our surprise at the end of an exceptionally hot summer with record temperatures the gabions were releasing large flows of clean water through the silt traps. Green vegetation, although overgrazed by goats, was beginning to proliferate, and there were even frogs and native freshwater crabs in the water. These are exceptional features for regenerating life in the shaded canyons and other potential locations in a desert system.

I’ve included one or two other photos from reference points around the world where I have witnessed the dramatic effect of gabions that have been used traditionally for productive yields. We can reverse desertification by the use of these features and others I’ll be reporting on in future posts. My advice to you is to study and learn about gabions, report in about good gabion systems, have fun installing them and seeing the great beneficial results that will be obvious as a comparison to the surrounding arid landscape!

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11 thoughts on “Gabions: Water Soaks in the Desert

  1. Hey Geoff,
    That’s some serious gabion work in Jordan. Scott Godfredson and I just spent a few hours on a beautiful days in southern NSW at Mulloon Creek with Cam Wilson, looking at Peter Andrews work on the on the 4km of creek running through the farm.
    Cam has been put in charge of the maintenance of the gabion system and doing a great job. What we saw was the life that these systems are becoming so diverse and hydration is slowly returning to the landscape.
    For the humid climate, we discussed the use of more natural ways to achieve the same results but using plants (willows). Slower process, but less impact in the construction, more maintenance and observation of the processes required but hopefully this would lead to seeing how these peak rain events affect the system over time.
    Thanks for the Pic’s Geoff.

  2. Hi Geoff,
    Its incredible how clear the water is. Beyond compare to the Jordan… not to mention my local river the Yarra haha. Looking at the gambions, they seem very effective, but is the use of those very big boulders causing the gambion to be too leaky? would using a greater number of smaller boulders on the down stream side be better to retain water for longer periods?

    *addressed to Nick*
    which type of willow are they using there? weeping or black willow? i am exploring the use of black willows, seems they put on more growth.

  3. Hi Adam

    At Mulloon Creek, mainly Crack Willow (Salix fragilis) were used, partly because there were plenty already on the property to take cuttings from but also because they are considered faster growing. However, there were a number of Weeping willow (Salix babilonica) cuttings planted at the same time and in my opinion they have not been far behind the fragilis in growth rates at all. Since they are less invasive and more beautiful (in my opinion), why not go for the babilonica.

    By the way, although the willows play a very important bio-engineering role holding the rock structures together, we are aiming to manage the system in such a way that the willow crowns are kept at a density that balances the need for a healthy root structure, whilst not shading out the reeds that will take over the system. Coppiced branches from the willows can either provide excess organic material on the upper edge of the structures, or provide valuable fodder for stock during early autumn.

    Having said that, at Tarwyn Park, Peter Andrews originally planted around 3,000 willows 30 years ago. Now, they are only 10% of the vegetation and in many places the Casuarinas have overtaken and shaded the willows out (they are only a pioneer species after all, and once the system’s health was restored from Peter’s efforts, other species have proved more vigorous).

    All the best, Cam

  4. Up in the hills here I live large areas of marshland has been drained to give room for tree planting. The result is that the rivers overflow during heavy rainfall, and in dry periods they dry out too much, giving problems for the fish. The marshland used to function exactly like the silt ground behind these gabions.

    Also the birds Gavia arctica and Gavia stellata have got problems as they nest just down by the water shores, and their nests become overflowed during rainfall because of the draining of the marshlands. Some places they try to make artificial floating islands where these birds can nest.

  5. Hi Cam,
    Thanks for the reply! i’m rather infatuated with broadleaf trees and nitrogen fixers! would love to visit Mulloon and Tarwyn, the perfect pilgrimage. i’ve read both of Peter Andrew’s books while i was on a placement in the country. its changed me ever since and launched me straight into sustainability.that together with greening the desert movement, has motivated me more than ever to own land and transform australia. we’re full of great ideas so we have to show the world!

  6. What can be used in a gabion besides stone? I want to construct some as a silt dam to slow down runoff from a neighbor’s field. I had hoped that the silt collection would raise an area that is prone to flooding. Are gabions a good choice? My other option would be bamboo.

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