In this post I want to talk about the incision process and present each action I propose in my Master thesis describing the actions, materials used and a budget for the project. In addition, this week will be presented at the International Symposium on Soil and Water Bioengineering in a Changing Climate to be held at GLASGOW, September 7-8. This symposium will be a meeting within the Life + ECOMED project.
The processes of incision of the channel, form sections deeper and a smaller coefficient width / depth, becoming very unfavorable for the aquatic fauna, reducing the diversity of habitats existing in the channel and the banks.
This change of the section determines a concentration of the flow and an increase of the speed of the waters, gradually lowering the base level, thus lowering the water table of the banks and the frequency of its flood, being disconnected from the operation of the river.
A channel with incision problems indicates a period of vertical instability or imbalance due to degradation. Degradation represents a response to a disturbance. The height of the banks increases until the height or critical angle is reached, at which time the slope fails and the channel begins to widen.
As a degradation process, the discharge capacity is increased and the channel is able to progressively pass larger volumes of water within its section. In a system with incision, the currents are restricted to the section and exert a strong stress to shear, transporting more sediments than the same current before its degradation. The contribution of sediments from channels with incision can reach high numbers of tons per year. The sediment derived from the incision is stored along the courses.
A grade and widening of the channel is often a feature of recovery from incised channels. Bed channel recovery is often incomplete because widenings ratios are significantly lower than those prior to degradation.
There are a large number of causes that cause the incision in the channels but all produce the same result under a similar dynamic. Often it is not possible to determine the causes that produce it because the same incision destroys the geological evidence.
Once the incision process has begun, erosion is unlikely to cease naturally until the channel has progressed to more advanced stages of degradation.
During the last years, there has been a rapid and continuous degradation of the channel and the banks of the Saúca creek that evolves in a process of degradation by incision of the bed of the channel and that is triggering a widening of the channel in some points with the fall of the slopes. The moments in which there has been greater degradation have been periods with peak flows due to strong spring rains coupled to soft temperatures with the consequent thawing of the snows.
The erosion and degradation of the channel is causing the drag of the material excavated downstream where important quantities have already accumulated a few meters before the confluence with the Lozoya River causing a clogging of the channel that has come to produce episodes of small floods in the areas low of the urban helmet with the events of rains and extraordinary flows.
Proposed actions for restoration
The objectives in the proposed actions are to stabilize the form and layout of the different channels, to improve the river ecosystem favoring the revegetation of banks, the formation of shelters, the shading of the water and to protect the margins and the bed of the channel that have suffered erosion or are susceptible to future erosion.
All actions that involve changes in the terrain and fixation and stabilization of slopes would be carried out using bioengineering techniques to avoid, as far as possible, denaturalizing the channels.
The solutions that are proposed to correct these problems comprise the following actions:
- Stabilization of slopes and banks.
- Afforestation of the banks.
- Protect the restorations for the wildlife and the cattle by fences.
Slopes and banks stabilization
The stabilization of slopes detached in this section will be realized through the application of bioengineering techniques for their better integration of the landscape.
At the foot of the slope there will be placed a base of Rockrolls based on stones from the place on which the FiberRolls are mounted and all this is fixed by the installation of treated wood. In this way, a certain protection of the edge and the base of the slope of the erosive processes is obtained.
Therefore, the structure that is proposed to install is formed by a base of Rockrolls on which are mounted the Fiber-Rolls that are fixed by the installation of poles of treated wood in a way that protects the shore and the base of the slope of the erosive processes. To complete the restoration, the geocell system is installed and filled with vegetal soil and subsequently afforestated to improve its colonization.
Since the soil depth is minimal, consisting of large blocks and alluvial ridges, the rest of the slope will be protected by the installation of a framework of geocells.
This geocell system is indicated in places where the natural regeneration of a slope is not viable and a strong and permanent reinforcing structure is required.
Afforestation would be carried out following a broad plantation framework that would not entail future problems with extraordinary episodes and peak flows that may occur along a channel length.
The plantation frame to follow would be of 2.00 x 2.00 meters intercalando the tree species and shrubs distributed of random form trying to form a floristic composition in agreement with the natural sotos and taking into account the difficulties that can entail the planting of some of the species provided.
Protecting the restorations by fences.
In order to preserve the actions carried out during the time necessary for the planting and development of the plant material installed, it is proposed to make a zone limited to livestock where it can not access and put the danger of preserving the works carried out.