Renaturalization of watercourses

Hydrogeological instability and the renaturalization of watercourses

Il hydrogeological instability includes all those processes that can cause soil degradation. Usually these actions are caused by both meteorological phenomena and human activities, such as cementing.

THEhydrogeology deals with the study of underground water, also in relation to surface water.

The phenomena that comprise hydrogeological instability are water erosion (landslides), floods, avalanches, deforestation,illegal building, the abandonment of high-altitude lands, the continuous excavations, the extraction of hydrocarbons and water from the subsoil, invasive interventions and not eco-sustainable on the waterways.

In Italy it is a fairly significant problem, it varies from area to area and the consequences of the process are different. The problem is widespread throughout the country especially due to the geological conformation, determined by a complex orographic surface and limited-sized hydrographic basins.

Weather conditions can sometimes take on a dangerous character, especially if they manifest themselves with particular intensity; it is in fact possible that they can cause significant damage to things and people. However, a distinction must be made between risks caused directly and indirectly. The former can be caused by storms, winds, fog, snow and frost, therefore by atmospheric phenomena. Indirect risks are caused by the union of meteorological processes with aspects of the territory, linked to human activities: for example, they concern heavy or abundant rain, combined with particular conditions of a territory, which can cause landslides or floods (hydrogeological or hydraulic risk). High temperatures, low humidity and strong winds, combined with the characteristics of the soil, can determine the risk of fires. Or heavy snowfall in the mountains, combined with winds and significant slopes can generate avalanches.

Naturalistic engineering

With the deadline of Environmental Engineering refers to those techniques that are used to reduce the risk of erosion of a land during consolidation works. The techniques of Naturalistic Engineering represent an excellent solution, especially for the creation or restoration of a degraded natural environment, through the use of native vegetation and the hydrogeological arrangement of the territory, the recovery of the natural habitat and the landscape insertion of artifacts and infrastructures.

- renaturalization interventions are increasingly widespread in our country, especially in those environments where the state of alteration related to river courses is a problem. These works are usually addressed to secure nearby urban areas. 

All Naturalistic Engineering works are carried out with natural materials Which:

• plant materials such as seeds, plants and shrub species, roots and plant parts of woody plants, turf;
• inert organic materials, such as wood, jute nets, straw, hay and biodegradable organic materials;
• synthetic materials, which best protect the soil by giving it greater stability, such as grids, nets and fabrics together with nylon, polyethylene and chemical glues;
• generic inert materials, such as stones, wire, iron, galvanized nets.

When dealing with a Naturalistic Engineering operation, there are some recurring elements that are used, which differ from more traditional interventions.

It begins with the analysis of the topographic and climatic characteristics of each surface subject to intervention, then the soil is examined in relation to the chemical, physical, hydrological and geomorphological characteristics; a phase of floristic and vegetative study follows, paying attention to the possible presence of botanical species and rare seeds, and also evaluating the biotechnical characteristics of the species themselves, their capacity and speed of growth, of adaptation to the environment, and also to their possible availability on the market.

We then move on to evaluating the possible presence of existing infrastructures. After this first analysis, we arrive at the study of the use of the new materials that will be used, with the relative selection of the plant species to be used and possible transplants of turf. Then we evaluate the type of environmental and naturalistic reinsertion, trying to improve the area by masking the artificial elements of the work.

Among the advantages of the methods used by Bioengineering are the reduced costs for construction and maintenance, the creation of natural habitats, the conservation and improvement of the landscape.

Among the disadvantages are the periodic and continuous maintenance, the limits on the size of the interventions and the times that are not always immediate and fast.

All the operations and processes studied by Naturalistic Engineering have the objective of protecting watercourses: rivers are not simple river channels; since the past rivers have been the birthplace of countries, civilizations and cities, since they are natural axes of supply of water resources but also function as means of navigation and transport. Watercourses are resources to be exploited.

Hydraulic system interventionsPlanning hydraulic system interventions along the course of a river must be the result of a study of the places where one should not intervene, since one wants to give naturalness to the river. 
The hydrogeological arrangement operations must guarantee the storage of continuity of watercourses, of maintaining the diversification of microenvironments, of the natural morphology of riverbeds and banks, of the biological productivity of watercourses, of the landscape value, of the use of the watercourses themselves.

Naturalization of the banks and bank defenses (see dwg drawings). One of the most important hydraulic system operations concerns the naturalization of the banks.
The paths of river courses are hindered both by the shape and the surface of the section of the riverbed itself (bends, curves, irregularities of the riverbed, etc.).

The transformation of a watercourse involves the redefinition of the riverbed, and this change is carried out by trying to straighten the watercourse (which will therefore increase its speed), making the surfaces of the seabed and banks smooth, but also by shaping the flow sections.
Interventions in the riverbed cause a significant impact on the life of macro organisms since they cannot avoid the alteration of the habitat. The main damages are caused by construction vehicles and by the deposits of materials on the seabed (damage to fish fauna).
The processes of reshaping of the riverbed of the river must allow for adequate flow; any widening of the riverbed leads to a dispersion of water over a naturally larger surface area, causing a consequent slowing of the current; during periods of low water in the river this can be harmful to the activity of fish fauna, since the riverbed is poor and sparse, with the presence of medium-sized granular boulders. On the contrary, during periods of high water and in the absence of adequate shelters, the transport of solid granulometry can be fatal for organisms that live in rivers.
Therefore, in order to avoid these disasters, but at the same time widening the river section, the riverbed leveling should be avoided, trying to differentiate between the low and high water periods. In the first case, the original and natural riverbed should be maintained, while in the second case the high water bed should be obtained at a higher level, since it receives significant flow rates. The banks should be renaturalized by native vegetation.

To implement the transformations of naturalization of the banks are made bank defenses: this is a sort of covering of the external banks, made with materials such as boulders, concrete prisms, walls, gabions, etc.

Among the bank defense works we find the ballast and prisms, made with rocks of different sizes; the spaces between the rocks can be free or closed with different cements; however, dry reefs are preferable, without cement material, in fact the spaces allow a greater continuity between the river and the aquifer, since they reduce the development of the roots of the plants and also favor the diversification of the ichthyofauna.

Also the cliff It is a bank defense work that is used to protect inhabited areas or important buildings and roads.

I gabbioni They are usually used in association with boulders and cement prisms. They are made of metal mesh cages filled with coarse gravel and offer shelter for small organisms. They also allow easy growth of vegetation.

I wall They allow the protection of artefacts and function as artificial banks for waterways.
They are made of stones, bricks and cement. The construction of walls is not advisable, since they limit the growth of plants and cause a negative impact on fish fauna, except for artificial canals, which must avoid continuous water losses.

Le double-walled palisades They are bank defense structures, and they fit in well with the landscape also from a landscape point of view, because they are made using natural materials and local vegetation. This type of structure is mainly used in waterways where the speed of the current is limited. The drawback is the degradation of the wood, and to delay this problem it is advisable to place the piling on a cliff, thus avoiding that the wood is always submerged under water. Another disadvantage is the obstacle that this method causes to the fish fauna, since it is separated into many isolated nuclei. When installing structures of this type, attention must be paid to some considerations: the speed of the flow must be low, the fish must be allowed to overcome the barriers, it is advisable to proceed with the renaturalization of the bank to recreate a suitable natural habitat.

Studies, interventions and guidelines for the renaturalization of watercourses (PDF):

• Naturalistic engineering and slope consolidation
• Naturalistic management manual for irrigation canals
• Ichthyocompatible hydraulic interventions guidelines
• Regulation for the implementation of naturalistic engineering interventions of the Campania Region
• Dynamic Glossary for Environment and Landscape – ISPRA
• Atlas of river management works
• General study for the implementation of hydrogeological reorganization interventions with Naturalistic Engineering techniques of the Sardinia Region