Watermasses, currents and tides at the Sofala Bank, November 1987

The southern part of the Sofala Bank (in Mozambique) was investigated. A net of closely spaced hydrographic stations were obtained and a current meter mooring consisting of two current meters and a bottom pressure recorder was deployed. High salinity shelf water was observed near shore with a maximum salinity above 36.6 ppt. Both average and tidal currents are discussed. The mean currents are steered by the continental slop and seem to be influenced by the wind. The tides have strong semidiurnal components, with a major axis of 53 cm/s perpendicular to the coast at 60m depth. The possibility that the tides may transport passive drifters with a diurnal vertical migration pattern up to a few kilometers a day is considered

Elementos basicos de teledetecção. Possibilidades da sua aplicação na investigação pesqueira em Moçambique

Mozambique has a large Exclusive Economic Zone (EEZ). Satellite remote sensing combined with ground observation would help in the research undertaken for fisheries purposes. NOAA could be applied for sea surface temperature mapping of the open sea water as the thermal gradient is high enough here. Coastal zone dynamics would be remotely sensed by visible passive radiance, since colour contrast is here the relevant pattern. Landsat/MSS seems to be economically advantageous for this purpose. This knowledge would contribute to locate the areas adequate for the concentration of fisheries resources

Convergência intermediática para a disseminação e preservação de bens culturais: o caso das timbila de Moçambique

O interesse na preservação e sustentabilidade dos patrimónios culturais, veículos de transmissão das marcas culturais entre gerações e de construção de suas identidades, vem ganhando cada vez mais destaque, quer no âmbito académico, quer no político. Este estudo interessou-se na preservação das timbila, numa altura em que uma combinação de fatores adversos leva ao risco de desaparecimento desta marca cultural, parte da memória coletiva das comunidades Copi, no sul de Moçambique. O estudo alicerçou-se na tese de que a combinação de tecnologias gera convergência intermediática que contribui para disseminar a narrativa do bem cultural e conduzir à reflexão e consciencialização dos sujeitos em torno da preservação e produção sustentáveis, corroborando as recomendações da Agenda 2030 da ONU. Assente em bases teóricas em torno do património cultural, tradições, identidades, tecnologias digitais e preservação cultural, o estudo desenvolveu-se tendo como suportes o paradigma interpretativista e o modelo de pesquisa baseada na prática artística. Nele foram desenvolvidos uma Plataforma Digital e um artefacto/instalação que passaram pelas etapas de conceção, experimentação, reverberação, implementação e reflexão, envolvendo o pesquisador e sujeitos de diversas faixas etárias, sexos, níveis académicos e origens geográficas. Houve ainda o contacto com entidades locais bem como a imersão do pesquisador na Comunidade Copi, junto de praticantes e mestres das timbila. Os resultados da intervenção realizada mostram que a convergência intermediática permitiu uma boa disseminação de conhecimentos comummente transmitidos pela oralidade; levou os sujeitos a uma compreensão mais substancial da gravidade do problema que é a ameaça de desaparecimento das práticas culturais associadas às timbila; ajudou a criar consciência e sensibilidade sobre a necessidade de se pensar em soluções para a sua preservação e produção sustentáveis. Por ter-se verificado que os meios explorados foram eficientes e promissores para a preservação cultural, o estudo sugere que numa altura em que cultura e tecnologia coabitam fortemente os mesmos espaços, haja continuidade da exploração das possibilidades oferecidas pela media digital e de sua apetência aos nativos digitais e não só, para consciencializa-los da importância da preservação dos bens culturais, sobretudo os que estejam em risco de desaparecimento. Paralelamente, sugere-se a combinação de diferentes atores e ações para a preservação ambiental nas comunidades.The interest in cultural heritage preservation and sustainability, vehicles for cultural marks transmitting between generations and their identities building, has been gaining more and more prominence, both in the academic and political spheres. This study was interested in the timbila preservation, at a time when adverse factors combination leads to the risk of this cultural mark disappearance, part of Copi communities’ collective memory, southern Mozambique. The study was based on the thesis that technologies combination generates intermedia convergence that contributes to disseminate the cultural asset narrative and leads fellows’ reflection and awareness around sustainable preservation and production, inline with the UN 2030 Agenda recommendations. Based on theoretical foundations around cultural heritage, traditions, identities, digital technologies and cultural preservation, the study was developed grounded on the interpretive paradigm and the research model based on artistic practice. Within it, a Digital Platform and an artifact/installation were developed that went through conception, experimentation, reverberation, implementation and reflection stages involving the researcher and fellows of different age groups, genders, academic levels and geographical origins. There was also contact with local entities as well as the researcher immersion in the Copi Community with timbila practitioners and masters. The results of the intervention carried out show that the intermediary convergence allowed good dissemination of knowledge commonly transmitted orally; led fellows to a more substantial understanding the seriousness of the problem; helped to create awareness and sensitivity about the need to think about solutions for preservation and sustainable production. As it was verified that the means explored were efficient and promising for cultural preservation, the study suggests that at a time when culture and technology strongly cohabit the same spaces, should have continuity of exploration possibilities offered by digital media and its appeal to digital natives. It is also necessary to make them aware of the importance of preserving cultural assets, especially those that are at risk of disappearing. At the same time, this study suggests different actors and actions to be combined for environmental preservation in communities

Estudo da Influência do Ângulo das pás na Potência e Eficiência Mecânicas de uma Turbina Eólica Híbrida de Eixo Vertical do Tipo Savonius-Darrieus

Turbinas eólicas do tipo Savonius operam a baixas velocidades de vento, mas tem baixa velocidade de rotação o que faz com que não sejam adequadas para a geração de altas quantidades de energia elétrica. As turbinas eólicas do tipo Darrieus, diferentemente, são mais adequadas para a geração de energia elétrica mas necessitam de altas velocidades de vento para que possam operar. Necessitam-se de turbinas híbridas para combinar as vantagens das duas. O presente estudo, dedicou-se a avaliação da influência do ângulo das pás da turbina em relação ao braço na velocidade necessária para iniciar o movimento da turbina, potência e eficiência mecânica de uma turbina eólica de eixo vertical tipo Savonius-Darrieus de três pás e testados nos seguintes ângulo das pás: 45, 54, 63, 72, 81 e 90°. As experiências consistiram na medição da velocidade do vento que incidiu no sistema utilizando um anemómetro e no registro do número de rotações da turbina utilizando uma camera digital. Deste estudo, concluiu-se que ângulos menores podem desenvolvem maior eficiência a baixas velocidades de vento, mas geram baixas potências mecânicas; enquanto ângulos maiores necessitam de velocidades de ventos mais altas para desenvolverem altas eficiências e potencias mecânicas. A faixa ótima para o funcionamento deste sistema está entre 63 e 72°, uma vez que estes ângulos possuem uma combinação ideal entre a intensidade mínima de vento necessária para iniciar a turbina, a potência e eficiência mecânica

Secchi disk measurements in turbid water

In the classical theory of the Secchi disk depth, diffuse sunlight falling on the disk is reflected back to the observer’s eye along the most direct route, as a beam. The disappearance depth, ZSD, of the disk is then expected to vary inversely with the sum of the beam and diffuse attenuation coefficients: c+KD. Observations presented here show that, in the most turbid waters sampled, the Secchi disk is visible at greater depths (by a factor of up to 4) than predicted by this theory. In these conditions, the disk appears blurry and it seems likely that some of the light reflected by the disk returns to the eye as diffuse light, photons being scattered one or more times on their journey from the disk surface to the observer. We have modified the theory of the Secchi disk in turbid water to allow for a mixture of beamed and diffuse light contributing to disk visibility. The modified theory corrects the under-estimate of Secchi depths in turbid waters and gives good agreement with observations over a wide range of turbidity. The insight gained allows a more informed interpretation of Secchi disk measurements in turbid water. Supplemental data files: https://doi.org/10.25773/z8qm-c77

Estuarine Management and Technologies: A way forward for estuarine research

Editoria

Referenciais de Intersubjectividade de José Castiano: Um paradigma libertário do pensamento Africano

Numa época e num mundo em que povo procura se reconhecer como um povo autónomo, livre e independente. A África não se distancia desta realidade, por isso, muitos dos pensadores africanos procuram a todo custo mostrar e incutir a ideia de que a África é continente livre e autónomo. E outros pensadores como é o caso de Castiano – um pensador moçambicano, historiador, filósofo e sociólogo – procuram dar directrizes para que este continente os habitantes do mesmo optem pela intersubjectividade como forma de contribuir para a edificação de uma África livre não só politicamente, mas sim, socialmente, economicamente e intelectualmente. Esta intersubjectividade deve ser vista como processo do reconhecimento do Outro como uma parte integrante do Eu. Por isso, no presente artigo procurar-se-á reflectir em torno das referenciais de intersubjectividade de José Castiano um paradigma libertário do pensamento africano. No entanto, a investigação sob o ponto de vista metodológico serve-se do método hipotético-dedutivo, para tal, a hermenêutica e a comparação são técnicas indispensáveis

Detecting the Zambezi River plume using observed optical properties

In April 1998 a research cruise was carried out in the Mozambique Channel taking detailed optical, water quality and salinity measurements; the Zambezi plume waters were apparent through strong colour fronts with green waters in the plume and clear blue waters offshore. A good (r2=0.76) negative empirical relationship was found between the salinity (S) and yellow substance, represented by the absorption of filtered samples at 440 nm (g440). An empirical relationship was found between the salinity and a reflectance ratio: An optical model in which light absorption is dominated by yellow substance and light scattering by inorganic particles confirms this empirical relationship. This has been applied to a SeaWIFS image to map salinity on the Sofala Bank, demonstrating the potential to remotely determine the distribution of the Zambezi River plume. It is thought that any significant level of chlorophyll would reduce the effectiveness of the above algorithm

Modelling alongshore flow in a semi-enclosed lagoon strongly forced by tides and waves

Alongshore flows strongly driven by tides and waves is studied in the context of a one-dimensional numerical model. Observations from field surveys performed in a semi-enclosed lagoon (1.7 km×0.2 km) outside Xai-Xai, Mozambique, are used to validate the model results. The model is able to capture most of the observed temporal variability of the current, but sea surface height tends to be overestimated at high tide, especially during high wave events. Inside the lagoon we observed a mainly uni-directional alongshore current, with speeds up to 1 ms−1. The current varies primarily with the tide, being close to zero near low tide, generally increasing during flood and decreasing during ebb. The observations revealed a local minimum in the alongshore flow at high tide, which the model was successful in reproducing. Residence times in the lagoon were calculated to be less than one hour with wave forcing dominating the flushing. At this beach a high number of drowning casualties have occurred, but no connection was found between them and strong current events in a simulation covering the period 2011–2012

The ocean as a source of renewable energy in sub-Saharan Africa: sources, potential, sustainability and challenges

The present paper examines, based on literature review and data from Africa Energy Outlook 2019, the feasibility of adoption of renewable energy from the ocean for socioeconomic development in sub-Saharan Africa, given the enormous potential the region has for ocean-based sources of energy. The study concludes that mini tidal power plants and salt gradient power are the ocean energy sources most suitable for coastal development. It recommends a gradual reduction in subsidies of fossil fuel-based energy sources in favour of support to renewable energy, building human resources and technical capacity, the establishment of smart partnerships and mobilisation of resources for an effective promotion of ocean renewable energy. It recommends further, that community engagement is needed to assure ownership and acceptance