Conservation, Gabions, Irrigation, Land, Rehabilitation, Soil Conservation, Water Harvesting — by Geoff Lawton November 25, 2010
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!