From dysfunction to function.
This article describes a piece of land in Volax, Tinos. Tinos is a rather arid island in the Mediterranean country of Greece. It receives around 350mm of rain (13.7 inches). The land is heavily eroded due to a variety of factors. In this article we will first describe the history and then share some pictures. We will then end with an overall analysis from our point of view and ask for the input of other professionals in the field of streambed restoration. Using this feedback and our own research we hope to come to the best solutions for repairing the damage, which we will use to make a design that sets this site up for a return to abundance in the long term.
Description and History
The land is shaped like an amphitheater and has a relatively flat valley bottom. To some degree it is the concentration point of a watershed, where several flows of water converge and have created a floodplain. The area is known for its huge granite boulders that were formed eons ago and through erosion are the only things that stand out. The sandstone around them has eroded away and the granite boulders remain, giving the whole area a very distinct and appealing aesthetic. Historically this floodplain or valley bottom was managed for grain production; the sides of the valley were planted with grapes of the local Tinian variety. The first dirt roads were brought in 30 or 40 years ago, along with the arrival of the pickup truck. Until then ‘donkey tracks’ were the only mode of transport, as is usual in the rocky Greek landscape. So to some degree this landscape is relatively unspoiled as compared to other areas. Also because of the difficulty in moving these huge boulders that can sometimes be the size of a bus. The dirt road that is bordering the land was asphalted in 2001.
Then around 2006, the client bought this piece of land and was advised to do some works to ensure proper drainage. This advice was taken way too far by a local contractor and huge boulders were brought in and used to create a channel that would help channel the water away. Sadly in the winter of 2008 there was a huge rain event and a large part of the soil around the rocks washed away downstream. This rain event was a part of two seemingly high rainfall years of rainfall which reached 670mm! The boulders are very rounded and without support or proper placement have started collapsing. This erosion problem has continued to this day and the pictures speak for themselves.
I have marked the pictures with a letter, going from A to M in the landscape. Each spot has one or multiple pictures, usually going from left to right.
C. This is the point through which a large amount of water passes during heavy rain. It has caused some erosion but not nearly as much as expected.
The rushes in this field indicate the presence of water year round. Apparently this was prime soil for growing crops in the past according to oral history.
D. The first view of the rocks that make up the waterfall. Erosion has clearly removed some soil as indicated by the absence of Lichen on the rocks.
E: Two points from where road water enters the floodplain and causes erosion. One source of road water comes from behind the Oleander bushes in the back. The wall where the water enters used to be taller.
Its a bit difficult to see but right in the middle of this picture is a bit of a hollow before it enters the gulley on the right. Small stones can be seen, left behind by the erosion. All of this water is concentrated by the dirt road that was put in.
Remnants of the effort to canalyze the water. In some places the canal can still be seen, but in many places it has fully collapsed.
The soil used to reach all the way to the rocks. This is a difference of about 3 meters here.
Here the water has calmed down quite a bit and the rushes almost reach the original soil levels in quite a few areas.
I: Rushess attempting to stabilize the streamflow. Lots of little pockets of water here, with amphibians living in them.
A fig shading out a hand-dug well. It has year round water and is fenced to keep out the goats. But the goats have destroyed the fence and are able to get it.
The gulley as seen from the well. In the background is a huge stand of Kalamia (reeds). Facing into the dominant wind direction and protecting the grapes behind them.
Here the rushes seem to be untouched and the diggers haven’t fully reached and canalized the water. There is still some erosion visible but much less.
These rushes are HUGE! Sometimes nearly as tall as a person!
Original soil level visible again, due to the absence of lichen.
K: The following picture was taken in the gulley that is forming on the side of the dirt road. The pitch of the road is toward the inside, forming a canal on the side of the mountain. Where the water flows the soil has eroded down almost a whole meter!
A video that shows the erosion happening on the side of the dirt road.
The point people are pointing at is where the water crosses from one side of the road to the other. The pitch of the road stays angled towards the inside, causing erosion.
M: This is the point from which the most erosion occurs. Almost a hundred meters of road catchment is funneled down into the is relatively small culvert, which is polished almost to a shine due to the abrasive force of the water.
A selection of different elements that could help resolve the situation.
[ IN THIS SECTION I WILL LATER ADD SUGGESTIONS ON WHAT TO DO AND HOW TO DO THEM ]
- Mini Floodplanes!
Here the idea would be to create a series of stepped ponds whose walls leak like a beaver pond does. Water enters the pond in a concentrated way but leaves in a way where the energy has dissipated. We build the system overly large so there is space for the water to go, never allowing the water to overflow its boundaries and cause erosion.
- Media Luna
A half-moon shaped structure who’s function it is to take a concentrated flow of water and spread it out over a larger area.
- Zuni Bowl
A bowl shaped structure that functions to take the energy out of already falling water in a way that does not encourage further erosion of the soil.
- Rock Rundown
A method of armoring an area that would otherwise erode. The water is unable to take the soil away and is slowed down by the rough rocky surface.
- One Rock Dam
A structure that is part of a larger process which attempts to bring the level of a gulley upward. From entrenched and degraded to restored and able to reach its floodplain.
- Beaver Dam Analog
A beaver dam is a leaky dam in the landscape maintained by beavers. Historically they would have covered almost all of the streams and rivers of Europe, until humans intervened. In this case the idea would be to create leaky dams out of woody debris that hold back the water long enough to drop out its sediment, but not be so water tight as to cause a lake to form. Its function is to take the erosive energy out of a peak flow event.
When implementing a design it is important to protect the loose soil from erosion during the establishment phase. One technique that can be used is called Faggotting or using Brush Bundles. These are bundles of small sticks and twigs all rolled up into a bundle about 30cm across. These can then be placed along the bank, either in line with the flow or perpendicular to it.