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1_INTRODUCTION
2_ANALYSIS OF PHYSICAL TERRITORIAL TRANSFORMATION PROCESSES
3_ANALYSIS TOOLS AND HYPOTHETICAL COSTS
4_GEMORPHOGRAPHICAL CONTROL
5_GEMORPHOGRAPHICAL CONTROL: THE "FOSSO CUPO" BASIN
6_CONTOUR LINE LENGTH PARAMETER AND RELATED PARAMETERS.
7_HYPOTHESIS OF WORKING METHOD.
8_CLASSIFICATION OF LANDSLIDES ACCORDING TO THE CRUDEN & VARNES 1996 CRITERIA.
1_INTRODUCTION
The morphology of the physical landscape is also described by contour lines through their geometry and lengths, and these geometric characteristics change both over time and space as the landscape shape evolves.
The morphology of the physical landscape, in fact, also changes over time and space, especially as a result of stresses induced by impulses of various origins.
The impulses and stresses can be meteorological, climatic, geomorphological, tectonic, and anthropogenic, each of which produces modifications or variations in the landscape morphology.
2_ANALYSIS OF THE TRANSFORMATION PROCESSES OF THE PHYSICAL TERRITORY
In the proposed model, morphological changes are considered significant or important if they induce changes in the contour line of the surveyed portion of land.
Furthermore, the proposed model hypothesizes that variations in the geometry and lengths of the contour lines describing a given portion of the topographic surface can be analyzed over time and space in order to verify transformations in the shape of the surveyed territory.
3_ANALYSIS TOOLS AND HYPOTHETICAL COSTS
This analysis process can be performed using state-of-the-art technologies that not only deliver high-quality results but also offer affordable costs. This analysis process can also be conducted using highly accurate drone surveys.
It is hypothesized that this method, within certain limits expressed in terms of deformation rate, could replace traditional monitoring methods at a lower cost.
Generally, these changes are analyzed following a generic impulse of any nature that can produce any change to the morphology of the landscape being surveyed.
To achieve the above, a schedule of drone surveys is required, both before and after a given meteorological event. This schedule allows us to verify whether this monitoring method is truly effective by detecting the changes produced by the meteoric impulse.
These changes can be either local, and therefore evaluated in terms of local deformation velocity, or generalized, and therefore evaluated in terms of deformation velocity.
4_GEOMORPHOLOGICAL CONTROL
In the proposed model, the search for the main shaping agent in a given geographic area of the globe also aims to identify which agent, among all the others, absolutely or predominantly controls the morphological evolution of that area.
Therefore, geomorphological control is also understood as the set of geomorphological processes or the single process that controls and directs the morphological evolution of the slopes of a given area of the globe.
4.1_MORPHOZONE OF BELONGING
In morphozones where mechanical disintegration processes prevail and in areas where gravitational phenomena and surface runoff have been recognized as having a predominant shaping effect, the evolution of slopes and, consequently, the evolutionary processes of a generic catchment area are closely linked to the structure of the basin's hydrographic network.
The relationships exist in particular between the hierarchical structure of the hydrographic network, the structure reconstructed according to the Stralher criteria, and the morphology of the territory itself, if the latter is recognized as belonging to the appropriate morphozone.
In this model, it is assumed that, as the order of the hydrographic network's segments increases, they lose direct control over the shaping of slopes and therefore the evolution of the basin's morphology.
Finally, it is assumed that the considerations made remain valid for basins and networks of all sizes or, in general, as long as the water appears to obey the law of gravity alone or as long as the water appears to be gravitational.
4.2_AN APPLICATION CASE
Given the main climatic characteristics of the territorial context within which the surveyed area is located, in particular, the average annual precipitation (1051.48 mm/year, approximately 42 inches/year) and the average annual temperature (14.48°C, approximately 58°F), it is already possible to determine whether the area under study falls within a morphozone characterized by predominantly chemical weathering or mechanical weathering, or by both but in different proportions.
This initial step allows us to identify the dominant morphogenetic agents within the catchment area, and in the case of the territorial area under study, it was found that it falls within a zone characterized by predominantly mechanical weathering and mild chemical weathering.
This area, therefore, is characterized primarily by gravitational movements and erosion processes caused by surface runoff.
The Leopold, Wolman, and Miller diagram from 1950 is helpful for this purpose.
FIG_1:
FIG_2:
FIG_3:
4.3_MASS MOVEMENTS and HYDROLOGICAL PROCESSES
Let us consider a generic, defined and delimited portion of land that falls within the above-mentioned morphozone and in which gravitational phenomena and erosive processes related to surface runoff prevail over other modeling processes.
At time T0, which precedes the stress, the morphology of this portion of land is also described by contour lines characterized by a specific geometric shape and the values of their relative lengths.
Assume the occurrence of a generic meteorological/climatic event of a rainfall type, during which drainage channels ("gullies") form and gravitational movements (landslides and landslides of various sizes) are activated.
At time T1, following the rainfall event, the newly formed channels, landslides, and landslides produce changes in the morphology of the physical land and consequently vary the geometric shape and length values of the contour lines.
In general, it can be stated that: given a generic portion of a slope, which is not subject to significant subsidence or retreat, at a given time T0, its geomorphological structure is also described by the shape/geometry of the contour lines and the trend of their lengths.
If the shaping action is achieved solely by concentrated runoff water, through the formation of furrows, the slope changes shape and consequently both the trend of the contour lines describing it and their lengths vary.
FIG_4:
FIG_5:
A generic, defined and delimited portion of territory whose evolutionary process is to be analyzed, understood as the change in its morphology over time and space, through the analysis of the variations over time and space in the geometry of the contour lines that describe it and of the values of their length appropriately represented.
FIG_6:
The contour line length values are represented within a graphical solution in which the elevations to which they refer are shown along the X-axis, while the values expressed in the most appropriate units of measurement are shown along the Y-axis.
At time T0, before the meteorological stress, the morphology of the surveyed area is therefore also described by the trend of the contour line length values along the elevation.
FIG_7:
At instant T1, which follows the hypothetical meteoric event, a hypothetical mass movement induced by this stress is generated.
FIG_8:
The formation of the detachment niche and the accumulation area produce a more or less evident variation in the morphology of the portion of territory investigated and this variation in morphology is also highlighted by the variation in the geometry of the contour lines and by the values of their lengths.
FIG_9:
FIG_10:
By superimposing the two models, the model preceding (T0) the stress and the model following (T1) the stress, it is possible to highlight the areas of the portion of physical territory investigated within which the variations in the geometry of the contour lines are most evident.
FIG_11:
Once the areas within which the contour line geometry changes are evident along the horizontal plane are defined, the variations in the contour line length values along the elevation are determined.
This analysis process is performed in a graphical solution like the one above, within which the elevations to which the contour lines refer are plotted along the X-axis, while the contour line length values, expressed in the most appropriate unit of measurement, are plotted along the Y-axis.
FIG_12:
In the graphical solution of FIGURE_12, the trend of contour line length values is compared along the elevation at time T0 (in RED) before the rainfall and at time T1 (in BLUE) after it.
Comparing the two series (T0 and T1) in the graphical solution of FIGURE_12, it is noted that, although slight, the differences in contour line length values are evident in an elevation range between 160 meters above sea level and 135 meters above sea level.
In this specific case, the contour line length values in this interval have increased by a ΔL > 0, albeit modest.
Similarly, let's now assume that the rainfall produces a visible furrow along the studied slope section.
Here too, the effects of the modelling action are recorded by the variations in the length values of the contour lines and by the variations in their geometry.
FIG_13:
FIG_14:
FIG_15:
Similarly, the area within the investigated area within which the evidence of the variations in the shape of the physical territory are located is defined by comparing the trend of the contour lines before (T0) the meteorological stress and the trend after (T1) it.
FIG_16:
To integrate the data defined during the previous phase of the analysis process, the graphic solution is created which reports the trend of the values of the lengths of the contour lines with the altitude at instant T1.
FIG_17:
Finally, we compare (FIGURE_17) the trend in contour line length values at time T0 (in BLUE) with the trend at time T1 (in RED).
The analysis and comparison of the two series (T0 and T1) in the graphical solution of FIGURE_17 shows that, in this case too, there is a variation in contour line length values in the altitude range between 170 meters above sea level and 135 meters above sea level, equal to a ΔL > 0, albeit modest.
In both of the cases described above and under the conditions cited, it appears that the processes influence the shape of the contour lines considered, and their lengths also vary by a positive factor ΔL > 0.
From the examples shown in the various figures, a close relationship emerges between the lengths of the contour lines, indicated by Lz, where z stands for elevation, and the processes described. Specifically, Lz depends on the number and size of the processes acting on the slope.
Generally and descriptively, the dependence of Lz on the number and size of watersheds crossing the contour line considered is demonstrated, in the case where the shaping action is performed by concentrated runoff alone.
Furthermore, the dependence of Lz on the number and size of mass movements acting on the slopes is also demonstrated.
5_HIERARCHICAL STRUCTURE OF THE HYDROGRAPHIC NETWORK AND GEOMORPHOLOGICAL CONTROL
THE "FOSSO CUPO" BASIN
The purpose of the following discussion is to propose a model for analyzing the evolution of the slopes of a generic river basin, subject to the predominant shaping action of surface runoff, which highlights the relationship or dependence between the hierarchical structure of the hydrographic network and the morphology of the catchment area, described solely through contour lines.
The following discussion aims to identify this relationship or dependence in appropriate graphical solutions (scatter diagrams) in which the main parameters considered are the length of the contour lines and the number of channels that constitute the corresponding hydrographic network that cross them, distinguished both by elevation and hierarchical order.
For the stated purposes and to introduce the proposed analysis methodologies, a single hydrographic network, relating to the "Fosso Cupo" basin, was examined. Subsequently, drainage networks established in different territorial contexts were examined with the aim of obtaining appropriate statistical data for analysis.
For the basin under study, the main climatic characteristics of the territorial context within which the basin was formed and evolved were initially defined to identify the morphozone to which it belongs and thus determine the prevailing morphogenetic agent or agents.
Subsequently, the hydrographic network and its geometric and hierarchical structure were reconstructed, particularly along the vertical direction or along the elevation.
Furthermore, the main geomorphological aspects were addressed through the analysis of contour lines, and the morphology of the catchment area was described through them, also reporting their lengths, expressed in meters, as a function of elevation.
The comparison between the number of watersheds expressed as a function of elevation and the lengths of the contour lines, also expressed as a function of elevation, in appropriate graphical solutions, produced evidence for the research conducted in this study.
FREQUENCY DISTRIBUTION CURVE "FDC"
In fact, the representation of the data in scatterplots and the application of statistical analysis techniques, particularly the linear regression model, allowed us to deduce that there is a causal relationship between the length of the contour lines (dependent variable) describing the basin under study and the total number of river channels crossing them (independent variable), and that this relationship does not hold as the hierarchical order of the catchments increases.
To construct the network, we proceeded from basic definitions that allowed us to unambiguously and objectively describe the individual channel or segment constituting a generic hydrographic network. In this way, it was possible to reconstruct, with consistent criteria, the integrated hydrographic networks of the 76 analyzed basins.
These definitions considered individual points on the surface of a generic catchment and their role or function in the case of surface flow.
In the proposed model, watershed lines are the geometric locus of points toward which surface runoff converges from at least two directions along the slopes and has a collection surface for precipitation upstream. From the watershed points, water flows away along a line given by the watershed section immediately downstream. Furthermore, runoff also converges toward the considered watershed point from the watershed section, albeit short, immediately upstream.
The watershed represents the geometric locus of points from which water diverges in at least two directions, along the right and left slopes respectively, and converges from a single direction given by the watershed section immediately upstream of the point under consideration. Furthermore, water flows away from a generic watershed point also along the watershed section, albeit short, immediately downstream. Furthermore, watershed points have a dispersion area for surface runoff in the downstream section.
All other points towards which the water converges from a single direction and recedes in a single direction are slope points.
DATA REPRESENTATION
To identify the relationships between morphology and concentrated runoff, the basin morphology is initially analyzed by analyzing the length of the contour lines versus elevation.
These values are then plotted graphically to produce a bar chart showing both absolute and relative minima and maxima.
In this model, the following conditions apply: At the apex of the watershed, the contour line length is assumed to be 0, as this is represented by a single point.
Near the basin outlet, the contour line length is assumed to be equal to 1.
6_LENGTH OF CONCENTRATION LINES, STRAIN RATE AND KINETIC ENERGY OF STRAIN.
The cases above highlight the possibility that the physical landscape may change following a generic meteorological stimulus.
The proposed model hypothesizes that this may occur even in a manner that is imperceptible or undetectable by the instruments designed to measure such changes in shape.
If these "changes," which the author believes occur continuously over time but at varying speeds depending on the intensity of the induced stimulus, are detectable by highly accurate drone surveys, it is possible to define a series of pathometers that also quantitatively describe the phenomenon.
In this sense, if we consider a deformation along a generic slope that materializes over time and is described as a variation in the length of the contour lines, the ratio between the two parameters considered, "L" and "t," defines a velocity called "DEFORMATION RATE," which can be local or generalized, as defined previously.
In this sense, moreover, from the two deformation speeds it would be possible to trace a further parameter which is given by the kinetic energy of deformation.
7_WORKING METHOD HYPOTHESIS
Overall, the method suggested for determining the extent of deformation of a generic portion of land located in an area known to be subject to hydrogeological instability or in other areas is simple in theory.
A first series of surveys should be conducted for that portion of land, prior to the meteorological event, aimed at creating a digital terrain model from which contour lines can then be extracted.
The length of these contour lines should be determined.
The same series of operations should then be repeated after the meteorological event.
The ultimate goal of these activities is to determine the extent of the deformations, the speed with which they occur, and to define other parameters that define the magnitude of the deformation.
The author believes that the most suitable and cost-effective investigation tool, compared to other types of surveys, may be, given the current state of the art, the drone, particularly one that allows for highly accurate surveys.
For this reason, we provide an indicative initial comparison between the costs associated with studying landslide areas using interferometric data and the "typical" costs of high-accuracy surveys using drones, in order to highlight the relative costs.
8_CLASSIFICATION OF LANDSLIDE MOVEMENTS AS A FUNCTION OF DEFORMATION RATE ACCORDING TO CRUDEN & VARNES 1996
EXTREMELY SLOW SPEED: Movements with velocities less than 16 millimeters per year.
VERY SLOW SPEED: Movements with velocities between 16 millimeters per year and 1.6 meters per year.
SLOW SPEED: Movements with velocities between 1.6 meters per year and 13 meters per month.
MODERATE SPEED: Movements with velocities between 13 meters per month and 1.8 meters per hour.
RAPID SPEED: Movements with velocities between 1.8 meters per hour and 3 meters per minute.
VERY RAPID SPEED: Movements with velocities between 3 meters per minute and 5 meters per second.
EXTREMELY RAPID SPEED: Movements at speeds greater than 5 meters per second
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