Abstract:

The main research aim of this paper is to examine the slope-stream erosional
process in the Korinthos drainage basin located in the north – eastern part of
Peloponnese, Greece, by means of applying the fuzzy set theory on a GIS platform.
The main steps of this procedure are: the definition of the input variables (erodibility
of rocks, slope angle, slope morphology), the construction of a fuzzy inference system based on theoretical and empirical knowledge for transforming the input to output variables (erosion – deposition) and the visualization of the output variables (Spatial distribution of the erosion-deposition processes). The earth’s surface is the result of endogenous (weathering) and exogenous (erosion) processes. Weathering destroys chemically, biologically and mechanically the structure and the cohesion of the rock. The erosional mechanism transports the sediment and depends on many factors such as: frequency and magnitude of precipitation, surface and subsurface waters, slope elements (geometry, length and angle), rocks’ susceptibility to erosion, vegetation cover, human actions and land use. The study of the erosional process demands a series of steps in order to obtain the final output maps. These steps include: 1) field-work, air-photos and satellite images interpretation, map digitization (geological, topographical, drainage), 2) definition of input and output variables, 3) formulation of the proper logical rules (Boolean or fuzzy) for the transformation of input variables to output variables, 4) analysis and visualization of the output results.
The input variables used in this research are: erodibility of rocks, slope angle and
slope morphology. The erodibility of rocks depends on many variables which show
spatial and time variation. Firstly, it depends on physical and chemical characteristics of the rocks and the rocks’ structure and discontinuities. Secondly, it depends on the existence of a protective vegetative cover which contributes in the increase of the infiltration capacity and limits the runoff flow. Thirdly, it depends on the characteristics of the involved processes: the intensity and duration of precipitation and also its spatial and time distribution and its raindrop size.
The input variables are inserted into a fuzzy inference system, constructed in order
to transform them to output variables (erosion-deposition variable). This is achieved
by the formulation of the proper ‘if…then’ rules based on theoretical as well as
empirical knowledge of the erosional processes.
The output variable (erosion) expresses the degree of erosion and deposition of
the various parts of the drainage basin and is presented through erosion risk maps of the area that is studied.