Gabions: Water Soaks in the Desert

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nPosted November 25, 2010 by Geoff Lawton & filed under Gabions, Irrigation, Land, Soil Conservation, Soil Rehabilitation, Water Conservation, Water Harvesting.

Gabions are one of the crucial feature elements of dry land nlandscape water harvesting design.
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nA gabion is a leaky rock dam wall nbuilt in a wadi, valley canyon or water flow, at a point where there nwould be a reasonable amount of water caught if there was a dam wall in nthe same position, but the gabion instead leaks through the rocks, nslowly releasing a steady flow of water and retained moisture over time.
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nAs the water is slowed down by a gabion, it drops its sediments, norganic materials, behind the rock wall.
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nDesert catchments are often nlarge and feature very infrequent rainfall events, and are an actively neroding landscape that is continually being blown away, with sediments neither eroded or deposited by the wind if there are wind traps like ndesert tree systems and forests, but also by water flows which are nusually strong and can carry large amounts of organic material and nsediments away with them.
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nnAn gabion traps this material, because, as a principle of aqua dynamics, nthe slowing of the water drops the material volume and quantities that nthe velocity can carry. So this aqua-dynamic deposition system, placed nin a location that forms a large back-up silt field, retains nwater-soaked silt enriched with organic materials, storing it away from nthe sun, and acts as a giant sponge, holding the water for long periods nwhilst slowly leaking it into the landscape.
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nA winter’s rainfall can be nharvested in a set of silt fields in a gabioned, wadi, canyon or a ndesert valley that then release that water over the next few months. nThese silt fields retain more rainfall each year, soaking in quicker nbecause they are already have dampened hydrology, building to a maximum ncapacity on an average of 7 years.
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n In the photos I have included in this post, there is a documentation nof two gabions in a wadi in the Dead Sea valley that comes down to the nDead Sea itself. I witnessed these gabions built in 2002 and have nvisited this site many times since, often after winter rain, and have nseen residual water flows extending through the silt fields and down then wadi for long periods of time — increasing each year.
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nDuring a PDC in nJordan in Oct/Nov this year (2010), the students and I took a field tripn to examine these two wadi gabions and much to our surprise at the end nof an exceptionally hot summer with record temperatures the gabions weren releasing large flows of clean water through the silt traps.
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nGreen nvegetation, although overgrazed by goats, was beginning to proliferate, nand there were even frogs and native freshwater crabs in the water. nThese are exceptional features for regenerating life in the shaded ncanyons and other potential locations in a desert system.
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nnI’ve included one or two other photos from reference points around nthe world where I have witnessed the dramatic effect of gabions that nhave been used traditionally for productive yields. We can reverse ndesertification by the use of these features and others I’ll be nreporting on in future posts.
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nMy advice to you is to study and learn nabout gabions, report in about good gabion systems, have fun installing nthem and seeing the great beneficial results that will be obvious as a ncomparison to the surrounding arid landscape!
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