An effective tool
Soil bioengineering is the technical discipline which allows for the application of scientific knowledge in the use of matter and energy sources, through useful inventions and constructions based on living matter. Although we need moisture for the development of living materials, good results may also be obtained on dry slopes.
The most sophisticated technique is the Krainer wall, developed in the north of Italy, which is built using wood trunks stitched to other added materials. Therefore, it represents an improvement on more traditional techniques, obtaining higher resilience, but it still needs a climate with constant humidity.
In the 1980s in Germany, new techniques appeared which combined inert materials, such as coir fibre, with living materials. These living materials are usually herbaceous plants, and their great variety allows for many possibilities. They are riparian herbaceous species adapted to stress conditions, such as a lack of water, water impact, poor soil, etc.
In some stretches of a river, the decline in a section makes it impossible to plant trees, which can have an impact on the hydraulic capacity. In these stretches, which are mainly urban, the use of herbaceous plants, specifically helophytes, can prove very suitable. Many of these species are specifically adapted to floods. When water flows, they fold on the ground and are very elastic, so that they have a minimal hydraulic resistance and protect the soil.
As in previous examples, the technique is based on using native species and the preparation of a suitable substrate. At the same time, this must have some physical characteristics allowing for good hydraulic resistance.
One of the most commonly used techniques is pre-vegetated fiber-structured roll. It is a coir fiber cylinder of 30cm in diameter, packed in non-biodegradable netting. This inert material, coir fibre, is one of the slowest-degrading natural fibre materials and is totally harmless. In fact, coir fibre is obtained from the fruit shell, which is widely used in food and the pharmaceutical industry, and is known as copra, a by-product which until now was difficult to sell. This material, which has a uniform structure inside the fiber roll, is appropriately pressed so that there is a balance between the degradation of the fiber and the use of this space by plant roots. In this manner, its structure does not experience damage over time despite being entirely overfilled by vegetation. To accelerate the process as much as possible and promote resistance to drying and to other environmental variables, they are pre-vegetated at the nursery.
It is recommended to collect plant materials from the area of intervention: planting it, inserting it into the structure, growing it at the nursery and finally placing it in the environment.
There is, in fact, a wide range of products and techniques that aim to obtain more mature plants while ensuring their structural role. They are also based on coir fibre: structured-fiber plant units, different formats of pre-vegetated mats…
In the early 1990s, a type of flexible gabion was developed which, through a high-resistance network structure, allowed us to use a smaller filling stone with the same resistance while allowing plant colonisation. Recently, many new products have also been developed, such as geonets and organic blankets, which are highly-resistant plant materials.
Today, the integrated management of river basins, the recovery of river areas and the use of soil and water bioengineering techniques, have enabled a new relationship with rivers in which they are no longer a problem but an advantage. This has allowed us to restore the enormous natural heritage they represent.