Institute Dom Luiz

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Publications

Identifying seawater intrusion in coastal areas by means of 1D and quasi-2D joint inversion of TDEM and VES data

Publication . Martínez-Moreno, F.J.; Monteiro Santos, Fernando Acácio; Bernardo, I.; Farzamian, M.; Nascimento, C.; Fernandes, J.; Casal, B.; Ribeiro, J.A.

Seawater intrusion is an increasingly widespread problem in coastal aquifers caused by climate changes –sea-level rise, extreme phenomena like flooding and droughts– and groundwater depletion near to the coastline. To evaluate and mitigate the environmental risks of this phenomenon it is necessary to characterize the coastal aquifer and the salt intrusion. Geophysical methods are the most appropriate tool to address these researches. Among all geophysical techniques, electrical methods are able to detect seawater intrusions due to the high resistivity contrast between saltwater, freshwater and geological layers. The combination of two or more geophysical methods is recommended and they are more efficient when both data are inverted jointly because the final model encompasses the physical properties measured for each methods. In this investigation, joint inversion of vertical electric and time domain soundings has been performed to examine seawater intrusion in an area within the Ferragudo-Albufeira aquifer system (Algarve, South of Portugal). For this purpose two profiles combining electrical resistivity tomography (ERT) and time domain electromagnetic (TDEM) methods were measured and the results were compared with the information obtained from exploration drilling. Three different inversions have been carried out: single inversion of the ERT and TDEM data, 1D joint inversion and quasi-2D joint inversion. Single inversion results identify seawater intrusion, although the sedimentary layers detected in exploration drilling were not well differentiated. The models obtained with 1D joint inversion improve the previous inversion due to better detection of sedimentary layer and the seawater intrusion appear to be better defined. Finally, the quasi-2D joint inversion reveals a more realistic shape of the seawater intrusion and it is able to distinguish more sedimentary layers recognised in the exploration drilling. This study demonstrates that the quasi-2D joint inversion improves the previous inversions methods making it a powerful tool applicable to different research areas.

2017-09Journal article

Open access

Morphological controls and statistical modelling of boulder transport by extreme storms

Publication . Oliveira, Maria Alexandra; Scotto, Manuel; Barbosa, Susana; Andrade, C.; Freitas, Maria Da Conceição

The study of coastal boulder accumulations generated by extreme marine events, and of the energy and frequency involved in boulder transport, is of paramount importance in understanding the risk associated with extreme marine inundations. One of the frequently asked questions is whether the deposits are storm or tsunami-related, both events being characterized by different return periods. Boulder transport by storms was monitored on the west coast of Portugal. Significant changes were detected in boulders' position as a result of extreme inundation by the 2013/2014 winter storms. Results presented in this work indicate that the wave power associated with the “Christina” and “Nadja” storms occur once every three years. However, this interval is not supported by field observations of boulder displacement, which suggests that wave power over-predicts boulder movement in the study area. Furthermore, wave parameters from the “Christina” and “Nadja” storms were very similar, but have generated different impacts in the boulder accumulation described herein. Differences include the magnitude and direction of boulder movement, and are most likely associated with distinct tidal levels during the events. Higher tide levels generated an increase in the sea surface level and thus in the reach of waves, which generated displacement of larger boulders and consequent cross-shore contribution in boulder transport. Regardless, the combination of monitoring campaigns, wave data, and statistical modelling of extreme values indicate that boulder transport by storms is more frequent than initially expected. Based on recorded boulder movements, we present a conceptual model for boulder ridge formation and development and identify significant control of incoming flow by local geomorphological/topographical features. Storm events, not less frequent tsunamis, are identified as the events responsible for modulating this rocky coastline. These results question a direct attribution of coastal boulder deposits to tsunamis in coastal regions with a high risk of tsunami inundation.

2020-08-01Journal article

Open access

Water prospection in volcanic islands by Time Domain Electromagnetic (TDEM) surveying: The case study of the islands of Fogo and Santo Antão in Cape Verde

Publication . Martínez-Moreno, F.J.; Monteiro Santos, Fernando Acácio; Madeira, J.; Bernardo, I.; Soares, A.; Esteves, M.; Adão, F.

Water demand in islands, focused in agriculture, domestic use and tourism, is usually supplied by groundwater. Thus the information about groundwater distribution is an important issue in islands water resources management. Time Domain Electromagnetic (TDEM) provides underground resistivity distribution at greater depths and is of easier application than other methods. In this study TDEM technique was used for groundwater prospection in two volcanic islands with water supply problems, the islands of Fogo and Santo Antão in the Republic of Cape Verde. The 10 islands of Cape Verde Archipelago, located off the coast of Senegal (W Africa), present a semi-arid climate and thus suffer from irregular and scarce precipitation. In the Island of Fogo 26 TDEM soundings, presenting an area distribution, were performed on the SW flank of the volcanic edifice. These allowed obtaining a 3D model composed of 5 layers parallel to the topographic surface separated by 50 m depth down to − 250 m. The results indicate the presence of the water-table at a depth of 150 m in the lower ranges of the W flank of the island, and at > 200 m depth in the area above 250 m above sea level (a.s.l.). In the Island of Santo Antão 32 TDEM soundings, distributed along 5 linear profiles, were obtained on the north-eastern half of the island. The profiles are located in two regions exposed to different humidity conditions to the N and S of the main water divide. The northern flank receives the dominant trade winds first and most of the precipitation and, therefore, the water-table is shallower (~ 50 m depth) than in the S (~ 100 m depth). Our study demonstrates the applicability and usefulness of the TDEM method for groundwater prospection in high resistivity contexts such as in volcanic islands.

2016-11Journal article

Open access

Faulted Middle Pleistocene fluvial terrace deposits at Leiria, central Portugal

Publication . Silveira, António Brum da; Cabral, João; Cunha-Ribeiro, João Pedro; Pinto, Andreia; Cunha, Pedro Proença e

Folded and faulted Middle Pleistocene terrace deposits of the Rio Lis were identified at Capuchos-Quinta de Santa Clara site, located in the city of Leiria (central-western region of mainland Portugal). These deformed sediments present a relevant assemblage of Acheulean lithic industry making them an unequivocal marker of neotectonic deformation. A detailed study of the brittle and ductile structures revealed a strong relationship with two major regional seismogenic faults that cross the site and also with the diapiric structure of Leiria. The age, intensity, and location of this tectonic deformation is particularly relevant because it may potentially increase the seismic hazard for Leiria region.

2018Book part

Open access

Challenges and opportunities for a successful mining industry in the future

Publication . A., Mateus; Martins, Luís

Modern models of sustainable economic growth are metal-intensive and will not be successful in the future unless a continuous supply of mineral-derived products is ensured. Despite this being logical, there is still a significant reluctance regarding mineral exploration and mining activities, often reflected in: (i) unfavourable public opinions; and (ii) absence of political measures or continuity of agendas that actually appreciate the way minerals are produced and the players directly or indirectly involved in this production. To succeed, the mining industry will have to (re)define its strategy and find innovative approaches to old problems and clearly demonstrate that mineral products can be efficiently delivered to support global development and assist suitable paths to welfare and quality of life, thus also providing real value to all concerned. In this study we give a concise review of the main challenges posed to the mining industry, and also indicate the most relevant opportunities and advance some proposals to constructively face the identified weaknesses and threats. The fundamental outcome is that the long-term balance between supply and demand of mineral products requires concerted actions on different fronts aiming: (i) the safeguarding of known resources; (ii) high-quality (scientifically and technologically driven) exploration surveys; (iii) improvements in mining and mineral transformation/ beneficiation; (iv) advances in consistent combinations of primary and secondary sources of raw materials, along with higher concerns on their judicious use; (v) effective and stable mining policies; and (vi) new insights on the role played by the mining industry through fruitful dialogues with society in general.

2019Journal article

Open access