A gabion is a small permeable dam. It is used to control erosion and rehydrate the landscape. It is usually made of rocks that are often held in place with wire. It is used to slow water down, not stop it. This has a number of uses.
Gabions can be engineered, like these sandbags at the bottom of the waterway.
The principles of a gabion check dam, which slows water and prevents erosion rather than stopping and storing it, can even be accomplished with “living dams” like willow trees.
This photo and the previous one with willows illustrates what a gabion does.
It prevents further erosion and eating away of the banks by fortifying those and channeling the water in the middle.
It slows water down, thus allowing silt to drop, which in turn builds up the stream bed. You can see the upper bed has been built up in this case, and banks are not so steep. In a highly eroded, steep channel, it’s hard for trees - which prevent erosion once established - to gain a foothold.
It allows water to seep into the landscape, providing moisture to plants that can now establish more easily on the banks, such as trees or bushes.
We are basically reversing erosion damage and creating the conditions for healthy riparian ecosystems with trees and other deep rooted plants to re-establish. These in turn will protect the water, allow more of it to soak in, and rehydrate the landscape further.
A well done gabion system can cause water to flow again in a dry streambed.
At Quail Springs, a fully off grid permaculture demonstration site north of Los Angeles and one of the places I trained, their entire community of several homes, gardens and food forests is dependent on the water from a single spring that ran dry part of the year when they arrived, and only traveled for a few hundred feet before disappearing into the rock. In other words, not very much water.
The spring is located at the top of the valley straight ahead.
By building gabions, they were able to allow any rainwater they received to sink into the land and replenish the spring. Within a few months, the spring was running much further downhill, to the point where they were able to fill tanks with water catchment, a pond, and an irrigation earthworks.
This is one example of how gabions can rehydrate a landscape.
My first permaculture teacher, Larry Santoyo, tells a story of his gabion. He had a client who had a stream running by his house, and wanted to utilize the water better. Larry was happy to place a gabion in several key spots on the stream.
What could go wrong? In this case, he didn’t think about what would happen in a major flood event, and placed a gabion near the house, slowing raging flood waters, which, needing a place to go, decided to eat away at the bank that led under the house. And yes, the house fell into the stream.
What a way to start your career! He has the courage to tell this story, and I repeat it, because it impinges. And hopefully, you won’t make that same mistake now!
Quail Springs also had a 1000 year flood that blew out their gabion system and destroyed part of the food forest in the above photo. They had designed wisely and all of their housing was above the floodplain. They had built part of their food forest higher on the land as well, using other water catchment methods like swales to hydrate the land, to increase their resilience. Thus they didn't lose everything.
They have now rebuilt their food and earthworks systems in ways that can distribute water even more broadly, with less flood risk.
The pond at Quail Springs, and Warren Brush, founder and exceptional designer and human being.
Quail Springs is located in a series of canyons that had originally been a pine forest. Each canyon had a spring feeding it, that ran to a large river in the central valley that in turn ran to the ocean.
The entire set of canyons had been clear cut to mine for gold and for the lumber. Without trees to help it meander and hold it in the landscape, the water started rushing out of the canyons, cutting deeper and straighter ravines in the process. Many of the canyons had completely dried up and didn’t run at all. The river had become a long, dry river bed that never ran with water.
One goal that Warren Brush has is to get the spring to run all the way to the river again and feed it. He felt that by doing so, every landowner in the region would want to understand what he was doing, so they too could have water again.
His dream is to again get the river running. HIs goal was to inch by inch, fill the canyon with trees, using the techniques outlined here. He knows this is a multiple generation project, and believes that permaculture designs should be designed for not just now, but for the next seven generations hence.
Only then could one achieve “permanent culture.” Warren is no longer at Quail Springs; he’s designing broadscale systems around the world and has a 50 acre drylands farm elsewhere, but the project lives on and is quite a demonstration of permaculture. If you get a chance, visit it! (https://quailsprings.org)