Geography Reference
In-Depth Information
2. Location and classification of geo-forms in the Ria Formosa estuary
2.1. Introduction
The study of the risk of soil degradation is the starting point for development and
sustainable land management. The global warming and the land use changes expected in
the XXI Century predict loss of quality and reduction of soil's productivity (Cerdan
et al.
,
2010). In the Mediterranean area the natural and semi-natural vegetation is sclerophyllous,
which is well suited for the local climatic conditions, however, extreme weather and human
activity can cause imbalances in the ecosystem (Kosmas
et al.
, 2000). The southern Portugal
is a region where the balance between the natural environment and human activity is very
sensitive to erosion and desertification (Gonçalves
et al.
, 2010). Thus, it is necessary to
employ control, prevention and correction measures to preserve the soil and prevent the
emergence and intensification of desertification processes, which can become irreversible, as
has happened in other Mediterranean areas (Kosmas
et al.
, 2000).
This study emphasizes geomorphologic processes, because they describe the natural space,
the dynamics of occupations and the anthropogenic changes. According to Hammond (1954,
1964), geomorphologic studies of the earth's surface can be carried out over large areas
(small scale) and based on the analysis of the land features, topographic maps or directly
through field measurements. The variables considered should be quantitative, been used for
a hierarchical classification.
Later, with the appearance of the GIS, Dikau (1989) and Dikau
et al.
(1991), the Hammond
procedures were rectified and automated in some regions in the United States. The DEM
becomes the most important tool in the process of identifying landforms. Using the
"moving-window" process and through algorithms based on local operators (spatial filters)
it is possible to create models (such as slope, local relief and relative position). This allows a
more detailed study, with a large number of variables in a large scale. The landforms
hierarchy is made in terms of size, order and geometric complexity.
Many researchers have used this methodology, although with some modifications as
explained by Martínez-Zavala
et al.
(2004) and Jordan
et al.
(2005), in studies conducted in
Spain and Mexico in a detailed scale. Drãgut and Blaschke (2006), and Gerçek
et al.
(2011)
classified the landforms in regions of Transylvania (Romania), Germany and Turkey,
respectively based in decision rules of fuzzy logic. Another technique widely used was the
non-supervised classification based on levels of information. For example, Sallun
et al.
(2007)
in the catchment of Alto Rio Paraná in Brazil extracted information by applying the
Principal Component Analysis (PCA) in multispectral satellite images. Oliveira and Santos
(2009), applied spatial filters of high pass and low pass in DEM in Feira de Santana (state of
Bahia, Brazil). Teng
et al.
(2009) extracted the landforms in Shaanxi Province (China) with
hillslope units from DEM.
In the present study we intend to carry out the mapping of landforms in the catchment of the
Ria Formosa located in the south of Portugal (Algarve), using the methodology followed by
Jordán
et al.
(2005), modified in order to take in consideration the specific features of this region.
