Sediment dynamics and tidal inlet relocation in mixed-energy settings: the case of Ancão inlet (Algarve - Portugal)

Tese de dout., Ciências do Mar, Faculdade de Ciências do Mar e do Ambiente, Univ. do Algarve, 2003The main aim of this thesis is to study the sedimentary dynamics of mixed energy tidal inlets on different time scales (from hours to decades) as well as to analyse inlet relocation as a coastal management tool. The field studies were carried out in the Ria Formosa, a multi-inlet barrier island system located in southern Portugal. Long Term Studies: The four natural inlets of the Ria Formosa were studied for the period between the 1940’s and 1996. Inlet width and position of the inlet channel were determined using a series of vertical aerial photos and charts. The objective was to determine the association between inlet migration patterns and different hydrodynamic conditions, major storms and engineering interventions. Results indicate that natural inlet opening and evolution were mainly affected by three factors: (a) the existence of sub-embayments (western and eastern) inside the system, (b) exposure to wave energy, and (c) inlet efficiency. Two distinctive eastward migration patterns were found by analysing the correlation coefficient (r) between inlet width evolution and inlet migration and by the comparison of the shape of the curves fitted to the inlet migration behaviour. Typical migration of the high-energy flank is characterised by an initial stage of readjustment, with low migration rates, followed by a stage of high eastward migration rates, up to a limiting position. Inlet width remains reasonably constant during the entire migration cycle, thus the correlation between inlet width and position is very low. Typical inlets on the low-energy flank are formed by barrier breaching during major storms and produce, initially, very wide inlets. Eastward inlet migration on the low-energy flank follows a natural logarithmic curve where channel migration is accompanied by strong constructional processes on the updrift barrier. Due to subsequent inlet width reductions, the correlation between inlet width and position is significant. Medium Term Studies: A monitoring program, including the acquisition of a series of topo-bathymetric surveys and oblique aerial photos, has been carried out at Anc˜ao Inlet since its artificial opening in June 1997. The results (morphologic and volumetric) were analysed with relation to the prevailing oceanographic conditions. This allowed the development of a conceptual evolutionary model for the natural evolution of artificially opened inlets with 4 stages: Stage 1 is the artificially opened inlet; Stage 2 represents the inlet after reaching dynamic equilibrium for the channel and while it is developing the deltas; Stage 3 is the mature migrating inlet; and Stage PS (Post-Storm) is the inlet situation after high-energy conditions. Transition between stages 1 to 3 is a continuous process with intermediate sub-stages. Transition to Stage PS is a discrete phenomenon, caused by high-energy events, after which the inlet continuously changes back to the previous stage. Short Term Studies: Three sediment transport studies using tracers were performed at Anc˜ao Inlet. The objectives of the experiments were to determine and understand the sediment transport pathways and magnitudes on the updrift margin of an inlet. In order to apply the traditionally used Space Integration Methodology to the tracer experiments, some adaptations had to be made. The division of the study area into morphologically defined sectors was found to be a key factor for the applicability of tracers in such a complex area. Therefore, 4 sectors were defined: Sector A representing the straight part of the updrift beach; Sector B being the upper area of the swash platform; Sector C being the lower area of the swash platform; and Sector D representing the inner parts of the inlet margin. The integrated study of all data (wind, waves, currents, tracer distribution and topographic evolution) led to the determination of the sediment pathways. Three tidal stages (TS), associated with distinctive sediment transport patterns, were found to occur at the inlet margin during each tidal cycle: TS1 implies flooding currents, and thus, transport towards the inside of the inlet area, both on the swash platform and the inner parts of the inlet area; during TS2 flooding currents transporting sediments towards the inlet occur on the swash platform whilst the interaction of the flooding currents with the flood delta produces the development of an anticlockwise internal gyre (IG) that results in ebbing currents occurring in the inner inlet margin; TS3 implies ebbing transport both in the inner margin and the swash platform. Evidence of the existence of a clockwise external gyre (EG) on the swash platform was found. A semi-quantitative conceptual model was developed in order to explain the sediment transport pathways and magnitudes that a known mass of sediment would follow after arriving at the swash platform. It was found that the areas with the largest sediment accumulation were Sector B and C, whilst almost no sediment was retained in Sector D which underwent strong erosive processes. According to the model only 48% of the initial mass of sediments are still in the system after two tidal cycles. It is hypothesised that sediment losses are due to sediment transport towards the ebb delta and to sediment by-passing occurring from the ebb delta to the downdrift beach through swash bar processes. The herein defined conceptual model represents a useful tool that could be applied to other tidal inlets under similar conditions, facilitating sediment budget studies around tidal inlets. Inlet Relocation Assessment: Two inlets were relocated in the Ria Formosa and were the subject of a monitoring program that included the acquisition of quantitative (topo-bathymetric surveys) data. The data obtained from the monitoring program were analysed together with the wave climate and then compared with historical information on the natural inlets, in order to assess the degree of success of the relocation actions. One of the relocations studied, Anc˜ao Inlet, was considered to be successful even though an initial unexpected behaviour produced some material damage to property. On the contrary, the relocation of Fuzeta Inlet, did not have the expected results and the new inlet was effected by the same problems as the old one. It was found that the most important factor for a relocation action to succeed is the correct choice of the location of the opening. A theoretical procedure to enhance the possibilities of relocation success is suggested: (1) Hydrodynamic studies are needed in order to determine if the present conditions are similar to the historical ones. (2) The position for the inlet opening is chosen according to the hydrodynamic conditions but there are other factors to be taken into account, i.e., the historical migration paths and typical inlet width of the natural inlet; the hydrodynamics of the backbarrier; the morphology of the backbarrier and, for multi-inlet barrier island systems, the proximity to adjacent inlets. (3) Once the position is chosen, environmental impact studies should be made in order to assess the risk of the relocation for the ecosystems of the area. Only if the environmental impact studies are favourable, should a relocation action be performed.European Marine Sicience and Technology ProgramFundação para a Ciência e Tecnologi

Nested Radar Systems for Remote Coastal Observations

Advances in radar technology now allow the observation of sea surface features at multiple scales, from kilometers, down to metres. In the same manner that nested models are used at different resolutions, nested radars of different frequencies can be used to provide data on sea surface features at various resolutions. A new radar system in the millimeter wave-band has now been demonstrated with a resolution of <1m. This MMW-radar was deployed in a nested configuration with an X-band marine radar from a beach near Faro in Portugal. The results from the two systems show how the MMW-radar can image fine detail surf zone and swash processes to a range of O(200m), while the marine radar provides lower resolution images of O(10m) to longer ranges of O(2km). Data from the two nested radars are shown from a recent deployment on a barrier beach in the Ria Formosa region of the Algarve, Portugal. The data from these nested radars are analysed to map wavelengths in 2-D and a non-linear bathymetric inversion is used on both sets of data to estimate the bathymetry of the imaged area. Comparisons with in-situ surveys demonstrate the accuracy of this technique

Variability of depth-limited waves in coral reef surf zones

Wave breaking and transformation on coral reef flats is an important process protecting tropical coastlines and regulating the energy regimes of coral reefs. However, the high hydraulic roughness, shallow water, and steep bathymetries of coral reefs may confound common surf zone assumptions, such as a depth-limited and saturated surf zone with a constant wave height to water depth ratio (γ). Here, we examine wave transformation across a coral reef flat, during three separate swell events, on both a time-averaged and a wave-by-wave basis. We use the relationship between significant wave height and water depth (γ) to examine the change in surf saturation across the reef flat and compare the measured wave height decay to results of modelled wave energy dissipation in the surf zone. Our results show that γ was not cross-reef constant and varied according to location on the reef flat and local water depth. On average, γ was greatest at the outer reef flat, near the reef crest, and progressively reduced towards the inner reef flat, near the reef lagoon. This was most pronounced in shallow water with large γ values (γ > 0.85) at the outer reef flat and small γ values (γ < 0.1) at the inner reef flat. This indicates that there is an increase in wave energy dissipation in shallow water, most likely due to increased breaker and bed frictional dissipation. The measured wave energy dissipation across the entire reef flat could, on average, be modelled accurately; however, this required location specific calibration of the free parameters, the wave friction factor (f) and γ, and further suggests that there is no value for either parameter that is universally applicable to coral reef flats. Despite model calibration inaccuracies were still observed, primarily at the outer reef flat. These inaccuracies reflected the observed cross-reef variation of γ on the reef flat and potentially the limitations of random wave breaker dissipation models in complex surf zones. Our results have implications for the use of wave energy dissipation models in predicting breaker dissipation and subsequent benthic community change on coral reef flats, and suggest that careful consideration of the free parameters in such models (such as f and γ) is required

Morphodynamic controls for growth and evolution of a rubble coral island

Rubble islands are dynamic sedimentary features present on reef platforms that evolve under a variety of morphodynamic processes and controlling mechanisms. They provide valuable inhabitable land for small island nations, critical habitat for numerous species, and are threatened by climate change. Aiming to investigate the controlling mechanisms dictating the evolution of One Tree Island (OTI), a rubble island in the Southern Great Barrier Reef, we combined different remotely-sensed data across varying timescales with wave data extracted from satellite altimetry and cyclone activity. Our findings show that (1) OTI had expanded by 7% between 1978 and 2019, (2) significant gross planform decadal adjustments were governed by the amount, intensity, proximity, and relative position of cyclones as well as El Niño Southern Oscillation (ENSO) phases, and (3) the mechanisms of island growth involve rubble spits delivering and redistributing rubble to the island through alongshore sediment transport and wave overtopping. Frequent short-term monitoring of the island and further research coupling variations in the different factors driving island change (i.e., sediment availability, reef-wave interactions, and extreme events) are needed to shed light on the future trajectory of OTI and other rubble islands under a climate change scenario

Lavoro totale

Le componenti culturali, creative e relazionali investono in modo crescente gli ambiti dell’innovazione sociale e dell’auto-imprenditorialità e come tali vengono ampiamente studiate, ma è solo spostando l’attenzione dalle varietà del lavoro cognitivo alle forze che lo determinano che possiamo tentare di cogliere e interpretare la dinamica del cambiamento in atto. Apprendimento continuo, autonomia, responsabilità, flessibilità, individualizzazione, svalorizzazione e cooperazione diventano così traiettorie di sviluppo del lavoro e non contingenze di alcuni settori o fenomeni. Analizzare le strutture che fondano l’attuale condizione del lavoro cognitivo nei campi dell’innovazione sociale e dell’auto-imprenditorialità può allora aiutarci a comprendere le forze sottostanti ai processi di riorganizzazione del lavoro in atto. L’urgenza e l’originalità di questo libro di Maurizio Busacca consistono nell’analisi di queste strutture, cercando di rintracciare ed evidenziare contraddizioni e distorsioni prima di accettare acriticamente e astoricamente le retoriche più diffuse e dirompenti, e indagando la struttura di fondo del lavoro cognitivo, nella sua dinamica storica e esistenziale, attraverso il concetto di Lavorototale-Improduttivitàmalata. Il lavoro totale si profila come una delle forme di vita economica e sociale, ma anche di patologia individuale, che già contraddistingue nel presente il lavoro cognitivo e minaccia di estendersi a settori sempre più ampi nell’immediato futuro. L’improduttività malata è il suo risvolto, o il fratello gemello. Questo libro di Maurizio Busacca ne indaga i meccanismi, anche alla luce del magistero di Franco Basaglia, e mentre ne denuncia i pericoli cerca di individuare possibili alternative o vie d’uscita

A deep dive into the ecology of Gamay (Botany Bay, Australia): current knowledge and future priorities for this highly modified coastal waterway

Context: Gamay is a coastal waterway of immense social, cultural and ecological value. Since European settlement, it has become a hub for industrialisation and human modification. There is growing desire for ecosystem-level management of urban waterways, but such efforts are often challenged by a lack of integrated knowledge. Aim and methods: We systematically reviewed published literature and traditional ecological knowledge (TEK), and consulted scientists to produce a review of Gamay that synthesises published knowledge of Gamay’s aquatic ecosystem to identify knowledge gaps and future research opportunities. Key results: We found 577 published resources on Gamay, of which over 70% focused on ecology. Intertidal rocky shores were the most studied habitat, focusing on invertebrate communities. Few studies considered multiple habitats or taxa. Studies investigating cumulative human impacts, long-term trends and habitat connectivity are lacking, and the broader ecological role of artificial substrate as habitat in Gamay is poorly understood. TEK of Gamay remains a significant knowledge gap. Habitat restoration has shown promising results and could provide opportunities to improve affected habitats in the future. Conclusion and implications: This review highlights the extensive amount of knowledge that exists for Gamay, but also identifies key gaps that need to be filled for effective management

Wave transformation on a coral reef rubble platform

Wave transformation across coral reef platforms is the primary process affecting changes in coral reef geomorphology. Transformation regulates the amount of wave energy entering reef systems, however there have been relatively few hydrodynamic assessments conducted on coral reefs when compared to siliciclastic environments with the effects of common geomorphic features like rubble platforms on wave transformation never specifically examined. This study focuses on the changes in wave characteristics across a rubble platform in a high energy environment (One Tree Reef, southern Great Barrier Reef). Wave conditions were measured at five locations over two days along a cross-reef transect from the reef rim to lagoon. Most of the wave energy was dissipated during wave breaking with energy attenuation due to bottom friction a secondary process. Wave energy attenuation was between 60-99% of the offshore wave conditions only during high tide would wave propagation across the reef platform be capable of affecting reef geomorphology. The wave spectrum also changed with the shorter period gravity wave energy (3-20 s) almost completely expending during transformation while longer period infragravity waves (20-300 s) were capable of propagating across the reef platform. Wave heights were depth limited and primarily controlled by water depth which suggests that water depth over the reef platform and subsequently elevation of the reef platform above mean sea level govern the amount of wave energy transferred across into reef systems, with most of the gravity wave energy removed during propagation over coral rubble platforms

Supplemental Material: Lagoon infilling by coral reef sand aprons as a proxy for carbonate sediment productivity

Details on the contours of reefs and lagoons, and depths of the Pleistocene base. </p

Geomorphology and sediment transport on a submerged back-reef sand apron: One Tree Reef, Great Barrier Reef

Back-reef sand aprons are conspicuous and dynamic sedimentary features in coral reef systems. The development of these features influences the evolution and defines the maturity of coral reefs. However, the hydrodynamic processes that drive changes on sand aprons are poorly understood with only a few studies directly assessing sediment entrainment and transport. Current and wave conditions on a back-reef sand apron were measured during this study and a digital elevation model was developed through topographic and bathymetric surveying of the sand apron, reef flats and lagoon. The current and wave processes that may entrain and transport sediment were assessed using second order small amplitude (Stokes) wave theory and Shields equations. The morphodynamic interactions between current flow and geomorphology were also examined. The results showed that sediment transport occurs under modal hydrodynamic conditions with waves the main force entraining sediment rather than average currents. A morphodynamic relationship between current flow and geomorphology was also observed with current flow primarily towards the lagoon in shallow areas of the sand apron and deeper channel-like areas directing current off the sand apron towards the lagoon or the reef crest. These results show that the short-term mutual interaction of hydrodynamics and geomorphology in coral reefs can result in morphodynamic equilibrium