Publication Date

11-1-1994

Degree Program

Department of Geography and Geology

Degree Type

Master of Science

Abstract

The Matozinhos-Pedro Leopoldo limestone area is a tropical karst located near the metropolis of Belo Horizonte, East Central Brazil, in an area undergoing rapid urbanization and land degradation. Qualitative dye tracing experiments have determined the groundwater routes and catchment areas in the two major drainage basins in the area, Samambaia Basin and Palmeiras-Mocambo Basin. Other drainage basins were identified, but not traced due to the absence of related swallets. Fluorescein and optical brightener had a poor performance as tracers under tropical climate. Dilution due to the existance of lakes at some swallets prevented some dye traces. The water that flows through this karst area is almost entirely autogenic, having a small external contribution from some phyllite areas. About 88% of the total water discharge of identified springs drains directly toward Velhas River, the regional base level. The remaining 12% drains toward Mata Creek, a tributary of the Velhas River. Hydrochemical monitoring in four of the major springs showed that groundwater quality for the measured parameters in the discharge zone is generally good, despite the heavy industrialization and occupation in some of the recharge areas. Conduit flow predominates in Samambaia and Palmeiras- Mocambo Basins. The outlets for these basins show a marked seasonal variation in the physical and chemical parameters monitored. Some of the other springs such as Moinho Velho Spring and Jaguara Spring show little variation in temperature, suggesting a diffuse flow component. All springs are characterized by hardness dilution during the wet season, suggesting a small residence time during the wet season, not allowing the water to achieve saturation. Seasonal variation in runoff is the most important control on the hydrochemical pattern of the area. It determines the marked dilution of major ions in both conduit-flow and diffuse-flow springs. Variation in soil C02 due to the rainfall pattern may also play an important role in the water chemistry. Observation of paleoflow indicators made in several dry caves showed that the past flow pattern at Palmeiras-Mocambo Basin agrees with the present groundwater routes. At Samambaia Basin, however, the lower reaches of the basin show paleoflow directions pointing toward other active base levels such as Mocambeiro Depression or Velhas River, suggesting that Samambaia Basin may have developed its present morphology in a later stage.

Disciplines

Geography | Hydrology

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