Influência do uso da terra na incidência de processos de dinâmica superficial na região de Marília (SP)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The study area comprises the western portion of the Marília Plateau, State of São Paulo, southeastern Brazil, whose geological substrate encompasses Cretaceous sedimentary rocks of the Bauru Group and local Cenozoic units like colluvium aprons, fluvial terrace deposits, in situ regoliths, and modern alluvial deposits. In a geomorphologic sense, the study area might be characterized as showing two main pediplanes, viz. P1 Surface (upper) and P2 Surface (lower). The latter, a pediment surface, is sculptured in the Marília Plateau remains. Both surfaces are presently under dissecation processes. After the 1920s the expansion of the railroad system fostered the removal of the natural vegetation, which in turn was followed by the introduction of coffee, peanut and cotton crops. This intense exploitation was conducted without respect to the soil carrying capacity and its natural susceptibility to erosional processes. This kind of occupation resulted in one of the most serious cases of erosion in the State of São Paulo, which resulted in a large number of scars, gullies and voçorocas, a local term for aggressive forms of erosional gullies. The consequent intense silting of the fluvial channels affected both aquatic and riparian ecosystems and the future use of the local hydric resources.The present dissertation aims to analyse the environmental impact of this type of occupation that rapidly transformed the regional landscape into a technogenic scenario. These changes were analyzed by means of aerial photographs and satellite imagery encompassing the past 45 years in addition to field studies. This wide photographic record made possible to quantify and to assess both the erosional and the silting processes as well as to identify sediments and soils most susceptible to erosion by surface waters. As a result, the study shows that the most susceptible material includes colluvium aprons, in situ regoliths, and colluvium-alluvium or alluvium deposits. The most critical situation is in the P2 Surface context, near the bottom of the Marília Plateau scarpment, where surface runoff can be very strong. Another point of active erosion is represented by the exposed walls of gullies and voçorocas, mainly in fluvial reaches subjected to talweg lowering. In a general sense, this study shows current evidence of erosional stability due to the ìntroduction of pastures as a predominant type of land occupation and to a series of erosion control procedures. Among these actions are terrace implantation, construction of small pits for runoff control, natural or induced reforestation by land owners. Despite these efforts, some erosion points remain chiefly in steeper country roads and trail stretches, in areas of concentration of cattle tracks (e.g., near cattle ponds), gullies or voçorocas exposed walls, and badly planned urbanization. The permanence of these erosion points demonstrates the necessity of a continuous monitoring of surface dynamics as well as a rapid and effective intervining measures of erosion and/or silting control. Negligence will give room for a return of erosive processes and their costly environmental and social damages

ASSUNTO(S)

planalto de marília análise geoambiental geociencias marília plateau planalto ocidental paulista dinâmica externa assoreamento silting process erosão surface dynamics western são paulo state plateau erosion geoenvironmental analysis

ACESSO AO ARTIGO

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