Mountainous catchment area as a self-organizing geosystem

Abstract:

Abstract

We discuss the problem of catchment areas of different types as structural elements of landscape being well recognizable objects by Earth surface analysis based on aerospace images. We have indentified the principal factors in formation of the river basin patterns, in mountain regions of Armenia as an example, in the frames of general approach based on universal processes of the 3D-structure crack formation in mountain rock. On the basis we assume a possible impact of the surface-ground water coupling on the catastrophic floods.

1. Catchments: problems, objects and methods

The principal question which has to be answered is the mechanism of formation of such a natural object as catchment being the key structure for whole geo-system. There is no doubt that permanent and temporary water channels as well as an ancient ones (both on surface and in underground) play a leading role in development of dynamic processes on the Earth surface and in Earth crust due to existence of unified 3D-cracknet.

We have chosen the river basin in a mountain massif as an object under consideration. The reason is that, firstly, the unit is not covered with mellow deposits as a rule. Secondly, localization of slope surface allows us to observe the universal phenomena within a compact dislocation area but in comparison with quite a number of different river basins. "Young" fold mountains and fold-blocky mountain ridges of the Small Caucasus is a good candidate for that. Visible catchment areas of different types on mountain surface being a manifestation of 3D-structure of fracturing for rocks, are easily recognized by available space images. We have used the approach under our conception to select the universal structural elements for so called "landscape pattern" to detect the genetic conformity, formations and functioning of different catchments in various conditions. Basic principles of our consideration result in self-organization of dynamic many step processes in river basin functioning.

In fact, formation of the mountain river basin is examined within the frames of analogues with the processes, happening in non-linear dynamic systems, and such formation can be presented as evolutionary stage process of mountain massive failure, accompanied in some periods by the abrupt change - bifurcation. The variation conditions are happened under the changes of managing processes such as fractures formation. Specific form and picture of mountain basin's relief is the result of this. System is self-regulated as a result of action and interaction of energetic streams, the necessary amount of endogene and exogenic energy is formed as a result of natural processes. Under this, all the conditions of development of such self-regulated structures are greeted, and the system is non-linear, open, with a feedback and spatially distributed.

2. Basic principles: energy model for formation of a mountain river basin and river channel

Catchment areas of Small Caucasus ridges have been defined in space images. Pattern composition usually was represented by a system of adjoint contours enclosed between the base line (main water intake) and catchment line, passing along the catchment ridge. Rhythmic alternation of two contour types were observed, i.e. blade (or leaf-like) and also deltoid (triangle), located in the lower part of the slope. Blade-like and leaf-like contours were arranged around the catchment run-off system. We have carried out morphometric research - in particular the determination of river net density for every basin (total amount of basins is about 200 within three major mountain ridges) - which allowed to make an important conclusion. There is no strict dependence for slopes partition degree on exposition nature. Frequently southern exposition basins have higher density index than basins of the northern exposition. Consequently the saturation of the forming river net is not just a function of water streams, as southern slopes differ in considerably lower reserve of solid and liquid sediments and total liquid discharge.

Thus, the mountain river basins are considered, featuring different configuration and pattern on river basin net and water divides. A hypothesis is introduced which explains the mechanism of the mountain river basin formation as a result of endo- and exogenic processes interaction. The leading role is attributed to relaxation processes in the mountain mass when it appears on the day surface. The pressure release results in a fissure system formation which may be considered a prototype of channel network accumulating/concentrating surface water and groundwater. A river channel is regarded as an independent emergent system created by the principal processes interaction.

3. The catchment area structure based on its geometric image

Two principle systems are distinguished in the morphology of the studied basins: run-off and catchment. Slopes serve as a subsystem functionally dependent on riverbeds nature forming a basis for erosion. For further classification let's observe geometric parameters of the image as the latter is clearly expressed result of genetically provided natural processes.

Catchment system. Space-image analysis demonstrates that this unified system consists of 2 interrelated elements (Fig. 1 left): a) lower part represented by specific structures as butt slopes with typical deltoid (triangle) image in plan, and b) upper part represented by isometric contour approximated arch connecting two adjacent deltoid contours.

We believe that such fundamental geomorphologic structures as "funds" (as we call them) - despite their relative independence - are the lower parts of a unified catchment separating adjacent catchment areas. Funds provide stable basin configuration and it life duration (Fig.1-right). That is why catchment is characterized by quite definite spatial evidence as a contour approximated with an arc, connected with funds by its ends.

Determining the basic lines of the river basin we shall directly analyze its origin mechanism.

4. The river basin formation as a process of self-organization

Such origin mechanism will be discussed in the concept of open dissipative systems where exchange of energy, substance and information with environment takes place. With the time autogenic conditioned tensions are accumulated in the mountain massif, their relaxation in terrestrial conditions results, as a rule, in breaking or cracking. The analysis of their formation mechanism relies on mountain massif stability and consequently on river basin formation basis.

So, we consider that controlling process is cracking formation or rather cracking system distribution dynamics in relatively isotropic (simple approximation) mountain massif. This approach is based on very simple fact - cracking releases tension inside mountain rock. Cracking formation process recurrence is well known in physics of solid destruction. It is natural to suppose that destruction (cracking formation) starts in the surface or boundary massif layers along its basement perimeter, where the most "critical situation" from the energy point of view occurs. Firstly vertical cracks and afterwards horizontal cracks appear. Cracking growth and consequently massif destruction occurs, as a rule, stage by stage with successive transition from stability state to growth stage. Each stage is characterized with specific energy state of the crack itself and a massif as well. As destruction takes place "in the open air" along the slopes, this process is accompanied with fractured mineral substance transit resulting in depressed landscape shaping of water-drained basin.

In the case of water-drain basin, a self-organization is the process of cracking growth and evolution. In fact, a mountain massif is discharged from mechanic tension by cracking formation in its bottom contact part. That will be the initial stage of central axis formation in water drain basins. Though there is limit (minimum) of crack length. If the crack is longer the destruction tension depends on its length, if shorter - it doesn't. Considerable role here belongs to physical-mechanical properties of the rock and the slope tilt angle.

Upward (but not downward in contrariwise) crack arises along the slope, like a wedge, forms some heterogeneous energy area, more intensive around final crack border. In this local area plastic deformations are developing. Specific slope structure is formed in the shape of crater, replicating energy zone shape.

The simplest chart of such development finally leads to the formation of the two peak deformation distribution, i.e. one crack at its end splits in two - and the point of deformation bifurcation appears (Fig. 2). Each new crack develops further independently. This stage of crack deformation is very important as it stipulates tributaries formation in riverbed channel.

Comparing to relatively isotropic mountain massif the crack becomes an anisotropic structure (chinked collector), so its water penetrability has tensor nature. Thus rather definite direction is created with the lowest hydrodynamic resistance for water flow, i.e. forming riverbed "draws" groundwater in its sphere.

Mountain water drain basins formation is controlled by the collection of conditions and, in particular, by geologic peculiarities. For instance, dolomite, shale mountain structures cracking will occur according to their physical-mechanic properties.

5. Practical results of proposed approach

Because of the 3D-watershed/river basin is an open system with unified dynamic processes, it should be an interaction between surface water and groundwater in river basin. This can result in catastrophic water events on Earth's surface, in particular floods.

The necessary conditions for such a coupling are the following: (1) the 3D Crack-Net does exist in the frames of unified river shed basin in mountain massif, and the unit is principally a dynamic system under action of many factors (depends on conditions: meteorological, climatic, hydro-geodynamic, Earthquake, anthropogenic activity, etc); (2) the states of the 3D Crack-Net sections are different in respect of both structure/geometry/topology and filling rocks/water/other compositions; (3) the 3D Crack-Net is a natural transportation system for the movement of ground water (including - from the isolated ground reservoirs) in accordance with several factors: the map of hydrostatic and hydrodynamic pressure distribution, the percolation/capillary effects development and also vs the channel status (empty and/or preliminary blocked but becomes active by shower runoff action, geo- thermal stream influence, etc); (4) the output of groundwater on earth surface in localized area, including the flash regime, should be provoked by any reason (both natural and artificial) under some adjustable territory conditions (the pressure in water horizon can sometimes be quite strong, and reach more than tens bars). All these factors must be under study for the catastrophic floods forecast and early warning.

Conclusion

Basin formation in the mountain slop can be considered as a self-organizing staged process of its evolution passing through several non-equilibrium but steady-state conditions. The controlling parameter is the process of the crack spreading out. Crack development up the slope but downward substance transit, stipulates a feedback within the unified 3D-basin system. We believe, the model (and the conception around) should result in more reasonable forecast of the natural water hazard taking into account the groundwater dominant role in river basin dynamics under some adjustable conditions.