Browsing by Author "Santos, Fernando Monteiro"
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- 2-D joint inversion of VES and gravity data: application to the Chaves grabenPublication . Represas, Patricia; Santos, Fernando Monteiro
- 3D electrical structure definition of aquifer systems in the Kalahari basin in Southern Angola based on legacy data reprocessingPublication . Ramalho, Elsa; Francés, Alain Pascal; Santos, Fernando Monteiro; Victorino, Américo da MataABSTRACT: The Kalahari-Ohangwena transboundary aquifer system, recently identified in Northern Namibia, comprises 3 major aquifers with very different characteristics. The shallowest is discontinuous and with limited reserves, but it has local importance in water supply for the population, since it is easy to reach, and often presents good hydrochemical quality. An intermediate deeper aquifer is characterized by high salinity while the deepest aquifer, also mostly saline, can present zones with fresh water. However, the latter is located at considerable depths and is shaped by the bottom of the basin basement. There hasn't been a systematic hydrogeological data acquisition for decades in this area of Angola, but legacy electrical resistivity data reprocessing from geophysical surveys conducted >50 years ago in the Cunene Province allowed the construction of a quasi-3D geoelectrical model for the Angolan side of KOH aquifer system in the Cuvelai-Etosha basin. This model is based on 482 vertical electrical soundings carried out in 1966-67, using the Schlumberger array, that contribute to confirming the presence of the Kalahari-Ohangwena aquifer system in Angola. The obtained quasi-3D model highlights the geoelectrical features of hard bedrock and is validated with other hydrogeological and geophysical information. The quasi-3D electrical resistivity data is interpreted using selected boreholes and two time-domain electro-magnetics transects carried out in Namibia, in the 2000s. Although both geophysical data acquisitions were >40 years apart, the results show a very good correlation between the deeper aquifer and the aquitard separating the intermediate aquifer from the deeper aquifer either with the results from Namibia or the borehole data. This is a direct result of the lack of alteration in the hydraulic conditions over these decades, without significant anthropogenic activity and negligible extraction from deep wells. Based on this analysis, the original dataset was considered a reliable source and this quasi-3D model was validated. Furthermore, the model can be considered in the future as an important tool for groundwater resources management, as well as a good starting point for further hydrogeological research in the province of Cunene.
- Aplicação de uma metodologia multidisciplinar para a caracterização da contaminação das águas subterrâneas por contaminantes orgânicos : resultados preliminares e análise comparativa de dois casos de estudo (Estarreja e Seixal) no âmbito do projecto CRUDE (FCT)Publication . Melo, Maria Teresa Condesso de; Neves, Célia; Ordens, Carlos Miraldo; Barreiras, Nuno; Fernandes, Judite; Amaral, Helena; Ramalho, Elsa; Batista, Maria Joao; Gonçalves, Cláudia; Almeida, José António; Quental, Paulo; Brito, Graça; Viana, Paula; Gama, Ana Cláudia; André, Sandra; Silva, Eduardo; Granjeia, Carlos; Inácio, Manuela; Silva, Manuel Marques da; Patinha, Carla; Matias, Manuel João Senos; Khalil, Mohamed; Santos, Fernando Monteiro; Danko, António; Pereira, Paula Sá
- Contribuição do método geofísico eletromagnético no domínio de tempo para o estudo dos sistemas aquíferos multicamada transfronteiriços da bacia do Kalahari, Cunene, AngolaPublication . Francés, Alain Pascal; Ramalho, Elsa; Santos, Fernando Monteiro; Llorente, J.; Mateus, T.; Cuervo, I.; Lobón, Jose Luis Garcia; Dala, V.; Ditutala, M.; Victorino, Américo da MataSUMMARY: Under the scope of project PLANAGEO, a geophysical survey using the time domain electromagnetic (TDEM) method was planned and conducted. This survey aimed to contribute to the hydrogeological conceptual model of the KOS and KOH aquifer systems, to validate the 1960 data electrical resistivity reprocessing and to define the future location of deep boreholes. The TDEM survey allowed identifying different layers with different geoelectric characteristics and assigning electrical resistivity characteristics to each hydrogeological feature of the aquifer systems. These assumptions were found adequate, and the results were used to define the drilling locations of 5 wells.
- Contribution of the time domain electromagnetic method to the study of the Kalahari transboundary multilayered aquifer systems in Southern AngolaPublication . Francés, Alain Pascal; Ramalho, Elsa; Santos, Fernando Monteiro; Llorente, J.; Mateus, T.; Martín-Banda, Raquel; Cuervo, I.; Lobón, Jose Luis Garcia; Dala, V.; Ditutala, M.; Famorosa, A.; Victorino, Américo da MataABSTRACT: The Cunene Province (Southern Angola) is facing recurrent and pluriannual droughts. Surface water supply could be reinforced using the groundwater resources of the multilayered aquifer systems (MAS) hosted in the siliciclastic sediments of the Kalahari Group. The MAS were first identified in the early 2000s in Northern Namibia and recently in the Cunene Province, by studies of the PLANAGEO project based on modern processing and reinterpretation of legacy data from the 1960s and 1970s (electrical resistivity data and deep boreholes). This article presents the results of a time domain electromagnetic (TDEM) survey conducted in the Cunene Province to: (i) contribute to the design of the hydrogeological conceptual model of the transboundary MAS, namely their geometry and extension; (ii) validate the reprocessing of the legacy data; and (iii) guide the future location of boreholes. Results depict the geometry of the sedimentary basin and the characterization of the MAS, with particular emphasis on the intermediate and deep aquifers. The borehole siting, based on the interpretation of the new TDEM data and the legacy data (clay markers in borehole logs), was successful, with a good agreement between estimated and observed horizons of the deep aquifers. However, the presence of clayey layers, a clay-rich matrix in the detrital deposits and saline/brackish groundwater led to uncertainties in the interpretation of the electrical transects. As such, recommendations are made to improve future data collection and mapping of the MAS.
- Hydrogeophysics and remote sensing for the design of hydrogeological conceptual models in hard rocks - Sardón catchment (Spain)Publication . Francés, Alain Pascal; Lubczynski, Maciek W.; Roy, Jean; Santos, Fernando Monteiro; Ardekani, Mohammad R. MahmoudzadehHard rock aquifers are highly heterogeneous and hydrogeologically complex. To contribute to the design of hydrogeological conceptual models of hard rock aquifers, we propose a multi-techniques methodology based on a downward approach that combines remote sensing (RS), non-invasive hydrogeophysics and hydrogeological field data acquisition. The proposed methodology is particularly suitable for data scarce areas. It was applied in the pilot research area of Sardón catchment (80 km2) located west of Salamanca (Spain). The area was selected because of hard-rock hydrogeology, semi-arid climate and scarcity of groundwater resources. The proposed methodology consisted of three main steps. First, we detected the main hydrogeological features at the catchment scale by processing: (i) a high resolution digital terrain model to map lineaments and to outline fault zones; and (ii) high-resolution, multispectral satellite QuickBird and WorldView-2 images to map the outcropping granite. Second, we characterized at the local scale the hydrogeological features identified at step one with: i) ground penetrating radar (GPR) to assess groundwater table depth complementing the available monitoring network data; ii) 2D electric resistivity tomography (ERT) and frequency domain electromagnetic (FDEM) to retrieve the hydrostratigraphy along selected survey transects; iii) magnetic resonance soundings (MRS) to retrieve the hydrostratigraphy and aquifer parameters at the selected survey sites. In the third step, we drilled 5 boreholes (25 to 48 m deep) and performed slug tests to verify the hydrogeophysical interpretation and to calibrate the MRS parameters. Finally, we compiled and integrated all acquired data to define the geometry and parameters of the Sardón aquifer at the catchment scale. In line with a general conceptual model of hard rock aquifers, we identified two main hydrostratigraphic layers: a saprolite layer and a fissured layer. Both layers were intersected and drained by fault zones that control the hydrogeology of the catchment. The spatial discontinuities of the saprolite layer were well defined by RS techniques while subsurface geometry and aquifer parameters by hydrogeophysics. The GPR method was able to detect shallow water table at depth between 1 and 3 m b.g.s. The hydrostratigraphy and parameterization of the fissured layer remained uncertain because ERT and FDEM geophysical methods were quantitatively not conclusive while MRS detectability was restricted by low volumetric water content. The proposed multi-technique methodology integrating cost efficient RS, hydrogeophysics and hydrogeological field investigations allowed us to characterize geometrically and parametrically the Sardón hard rock aquifer system, facilitating the design of hydrogeological conceptual model of the area.
- Hydrogeophysics contribution to the development of hydrogeological conceptual model of coastal aquifers - Albufeira-Ribeira de Quarteira aquifer case studyPublication . Francés, Alain Pascal; Ramalho, Elsa; Fernandes, Judite; Groen, Michel; De Plaen, Joel; Hugman, Rui; Khalil, Mohamed Ahmed; Santos, Fernando Monteiro
- Interpretação hidrogeológica da modelação 3D das sondagens eléctricas verticais (SEV) da década de 1960 na bacia do Cunene, AngolaPublication . Ramalho, Elsa; Francés, Alain Pascal; Santos, Fernando MonteiroRESUMO: Secas severas periódicas e plurianuais constituem um dos grandes problemas da província do Cunene, em Angola, afectando significativamente a vida de perto de um milhão de pessoas. O abastecimento de água às populações rurais dispersas tem por isso que ser feita com o recurso a "chanas", que secam totalmente na estação seca, ou a furos pouco profundos, geralmente de mineralização elevada. Este problema foi identificado já há várias décadas e para o tentar mitigar, na década de 1960, foi levado a cabo pelas autoridades um programa que compreendeu a realização de prospecção geoeléctrica numa área de grande dimensão e perfuração de sondagens. Assim, em 1966/67 foram realizadas 482 sondagens eléctricas verticais (SEV) na região do Cunene. A partir do reprocessamento destas SEVs, foi recentemente possível realizar um modelo 3D de resistividade elétrica com o intuito de melhorar o conhecimento acerca da hidrogeologia da zona do Cunene e relacioná-lo com a nova informação entretanto obtida a partir de trabalhos realizados no âmbito do projecto Planageo e de estudos na Namíbia. A validação deste modelo irá ajudar a planear futuras ações, visando o abastecimento de água para um desenvolvimento sustentável das populações da região.
- New evidence of Late Cretaceous magmatism on the offshore central West Iberian Margin (Estremadura Spur) from potential field dataPublication . Escada, Cláudia; Represas, Patricia; Santos, Fernando Monteiro; Pereira, Ricardo; Mata, João; Rosas, Filipe M.ABSTRACT: The West Iberian Margin (WIM) is a key example of a magma-poor passive margin, punctuated by several postrift magmatic manifestations that are part of the Late Cretaceous Atlantic Alkaline Province. In this work, potential field (gravity and magnetics) data, constrained by 3D multichannel seismic reflection data, are used to describe and characterise the geometry and nature of magmatic features located offshore the central segment of the margin, the Estremadura Spur. The estimated geometry and nature of the magmatic features was achieved through the integration of 3D gravity and magnetic inversion and 2D magnetic forward modelling. The results provide an insightful 3D subsurface model revealing that: 1) the Estremadura Spur Intrusion represents a 28 x 15 km wide laccolith with an overall granitic nature and an estimated density of 2490-2640 kg/m3 and 0.01-0.05 SI magnetic susceptibility, 2) the 26 x 17 km Fontanelas buried volcano is dominantly basaltic, with density values of 2500-2821 kg/m3 and magnetic susceptibility of 0.01 to 0.0875 SI, and 3) multiple sill complexes intruded the region, thus producing a higher magnetic background on otherwise inconspicuous anomalies The models allowed achieving a confident fit suggesting that both the ESI and the Fontanelas volcano are coeval with the outcropping magmatic features from this same magmatic event. Additionally, the results support that Late Cretaceous alkaline magmatism on the West Iberian Margin is more significant than anticipated and provide further evidence to clarify unclear geometrical aspects of similar intrusions observed onshore. Acknowledging the geometry and nature of these magmatic entities allows to better understand the role of postrift intra-plate magmatism on continental hyper-extended rifted margins by clarifying how shallow plumbing systems evolve in these settings.
- Unraveling the Paleozoic "Basement" structure and its impact on the petroleum system in the Western Gulf of Cadiz (Southwest Iberia)Publication . Matias, Hugo; Carvalho, João; Menezes, Paulo; Matias, Luís; Santos, Fernando Monteiro; Barbosa, Valéria C. F.