Análise por métodos hidrológicos e hidroquímicos de fatores condicionantes do potencial hídrico de bacias hidrográficas - Estudo de casos no Quadrilátero Ferrífero (MG)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

As surface water and groundwater are continuously interacting, any external influence is able to affect them in the long or short term. Because of this interconnection, aquifer information can be obtained by the analysis of drainage flow pattern (hydrological approach). This approach is based on the analysis of baseflow recession, i.e., the study of the aquifer ability to yield water and to maintain the stream flow. This approach can be used to analyze the variables that affect the hydrological potential of a basin. It should be stressed that there are many variables which can act together in the flow pattern, sometimes with superimposed effects. In this work the following variables were analyzed: geology, geomorphology, and land degradation, especially by gullies. Nine small catchments were selected, with similar characteristics, but with some pre-defined differences. This research aims to analyze the role of the above mentioned variables in the catchment hydrological potential through indirect (hydrological and hydrogeochemical) methods. The catchments are located in the Quadrilátero Ferrífero region, two of them in rocks of Minas supergroup and the other ones in the Bação Metamorphic Complex. Some alternative monitoring equipments (pluviometers and portable steel weirs, USGS type) were used and they showed very goods results at low operating costs. Some larger hydrographic basins of the region were simultaneously analyzed, in order to compare the results. The recession coefficient was determined through some methods that are very useful to treat small fluviometric series: the correlation method and the matching strip method. The last one showed the best results for the available data. The smoothed minima technique was used to determine the ratio of base flow to total flow (base flow index) and other indices and the results were equally very good. The graphical method of Barnes was applied simultaneously, especially with the data of the larger basins. The diffusivity (transmissivity/storage coefficient) was calculated thorough the assumptions established by Maillet and Rorabaugh, allowing the estimation of an average transmissivity for the study catchments. The results showed that those catchments on granite-gneissic terrains tend to have bigger hydrological potential than the ones on schists and phillites. The catchments placed in high relief areas present lower hydrological potential. In fact, the regolith tends to be thicker over gently sloping areas in basement rocks, which contributes to their higher hydrological potential. Land degradation usually affects the water resources, but in this study these effects were not properly detected. However, it was noted that gullies tend to decrease the baseflow, causing a great impact in the hydrological regime of streams. This study proved that the adopted methodology is very useful to analyze the hydrological potential, even when there is not a great amount of hydrological and hydrogeological data.

ASSUNTO(S)

fluxo de base potencial hídrico hidroquímica bacia hidrográfica geologia ambiental coeficiente de recessão hidrogeologia hidrologia

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