Abstract

(Received: 2013/09/03 - Accepted: 2013/11/20)The present work compares the rate of transpiration and its effect in the runoff of watershed covered with evergreen (Bonifacio) and deciduous (Las Palmas) native forests, during the spring-summer season change. We used as variables the precipitation, runoff, leaf area index, transpiration of the species, and the distribution of water in the soil. The results show a greater consumption of water in the deciduous forest, by a greater evotranspiration of 2273.6 mm compared to the evergreen forest of 1740 mm, which generates a greater runoff than the last one. The comparison between leaf area indexes of the two forests shows a significant difference, especially during spring for the deciduous forest, since the increase of the transpiration rate due to the increase of biomass, generates fewer runoffs even though in this location there were more precipitations. Moreover, the species of the evergreen forest consumed the water of the first centimeters (10-20) of the soil profile; in contrast, in the deciduous forest we observed a greater decrease in the deep soil water content (40 cm). Regarding water yield, we show that the evergreen forest is more efficient than deciduous forest, during the period spring-summer.

Abstract

The study examines the drying and wetting cycles of tailings dams (TDs) and their impact on physical, mechanical and hydraulic properties. TDs are divided in four zones: the dike, the discharge zone, the transition zone and the distal zone (also known as the decantation pond). The filling process of the tailings dam involves five phases: 1) dumping and wetting, (2) segregation, (3) sedimentation, (4) consolidation, and (5) drying. The occurrence of drying and wetting cycles depends on the water balance, which can be expressed as Inflow = Outflow ± Storage Coefficient. These cycles are influenced by factors such as changes in the discharge point within TD dike and reservoir, weather conditions, and other external factors. The analysis of drying and wetting cycles in TDs reveals several trends: (a) grain size, density, internal friction angle, and permeability decrease from the discharge zone toward the decantation pond and (b) porosity, fine particle content (particle less than 75 microns), plasticity, cohesion, and capillarity height increase as we move toward the decanting lagoon. Despite these findings, there is currently no established methodology for managing the filling process or controlling wetting and drying cycles of TDs.