Rafael M. Oliveira

Vulnerabilidade natural e perigo de contaminação do Sistema Aquífero Dunas na região norte do Município de Aquiraz, Ceará

This paper examines the natural vulnerability and contamination hazard of the Dunas Aquifer System in the northern region of the municipality of Aquiraz (CE), using the GOD (G - groundwater hydraulic confinement, O - overlying strata/lithology, D - depth to water table) method and taking into account potential contamination by the in situ sanitation system, which uses pits as a means of depositing domestic effluents. Geological and hydrogeological data were analyzed from tubular wells obtained through the SIAGAS database and during the field work. The Dunas Aquifer System in the study area consists of eolian sands and presents static levels between 2.0 and 61.0 m depth, with a predominance of values less than 20.0 m. The GOD vulnerability varied from medium to high, with average vulnerability in most of the area (76%). The potential contamination by the anthropic activities in the area was estimated by means of the analysis of the density of cesspools, given that these static systems have a high contamination potential because of the constant application of contaminant load in the subsoil. Assessment of the contamination hazard of the Dunas Aquifer System was based on the comparison of the natural conditions and the anthropic activities. It was found that the areas with the highest risk of contamination are those with the highest density of cesspools, associated with the highest GOD vulnerability indexes. These results will be useful for managment of groundwater resources in the region.

Saffman-Taylor Instability and the Inner Splitting Mechanism

For viscously unstable, miscible Hele-Shaw displacements, we investigate the origin of the streamwise vorticity shown to be responsible for the inner splitting mechanism by Oliveira and Meiburg [J. Fluid Mech. 687 431 (2011)JFLSA70022-112010.1017/jfm.2011.367]. Towards this end, we compare 3D Navier-Stokes simulation results for neutrally buoyant, viscously unstable displacements and gravitationally unstable, constant viscosity ones. Only the former exhibit the generation of streamwise vorticity. The simulation results show that it is caused by the lateral displacement of the more viscous fluid by the less viscous one, with the variable viscosity terms playing a dominant role.