Sediment Transport and Morphodynamics at an Estuary Mouth: a Study using Coupled Remote Sensing and Numerical Modelling

Merged with duplicate record 10026.1/712 on 10.04.2017 by CS (TIS)The balance of the physical processes that drive the morphodynamics of a complex inlet system is investigated in this work. For this purpose, an innovative technique using coupled video imaging and numerical modelling has been used to study the relative importance of the driving forces that control the sandbar dynamics at the Teignmouth inlet system. The sandbars that form the ebb tidal delta are highly dynamic, leading to a cyclic morphological behaviour. Application of the numerical model (MIKE21 HD, NSW, ST) served two separate functions. The hydrodynamic model has been used for the image processing and, combined with the sediment transport module, the full model has been used to understand the relative importance of the driving forces at the region. The iterative application of the hydrodynamic model and the video images, with the modelled water levels used as input to the image processing, provides the video-based intertidal morphology that is used in further modelling experiments. This loop is repeated several times during the three-year study period that covered a complete morphological cycle. This results in a quantitative assessment of the relative influence of the key processes that control the environment and in initial steps towards the prediction of its evolution. In order to assess the relative importance of the driving forces a series of modelling experiments were designed to include a variety of forcing conditions. These include the tidal range, wave conditions and river discharge values. The relative importance of each of the physical processes on the sediment transport and consequent morphodynamics varies across the region. The main inlet channel is dominated by tidal action that directs the sediment transport as a consequence of the varying tidal flow asymmetry, resulting in net offshore transport. Sediment transport over the shoals and secondary channels at both sides of the main channel is dominated by wave related processes, displacing sediment onshore. The interaction between waves and tide generated currents controls the transport over the submerged sandbar that defines the channel's seaward extent. High river discharge events are also proven to be important in this region as they can change sediment transport patterns across the area. Waves play a major role in the sandbar morphodynamics. Despite the relative low frequency of high wave energy events that reach the region they are responsible for large amounts of sediment displacement, catalysing some dramatic morphological changes. Therefore, the temporal distribution of storms defines the cyclic behaviour of such environments, making the system more dynamically active over the winter months. It is also during this period that river discharge values reach high peaks, increasing the capacity of the ebbing tidal flows and interacting with the opposing waves. The opposite occurs during summer periods, when less energetic conditions lead to slower morphological changes. The application of an initial sedimentation/erosion model proved to be useful in giving qualitative predictions of the morphological evolution of such a complex sandbar system, reflecting the initial morphological changes for different forcing conditions. Qualitative comparisons between the modelled sedimentation/erosion patterns and the video based observations of the changes at the dynamic offshore sandbar show that the model is able to reproduce its overall evolutionary tendency. The morphological adjustment of the system to the forcing conditions shows the progression towards the next morphological stage, allowing the initial steps towards predicting the evolution to be taken. The technique applied, coupling the numerical model with the video images, has been shown to be of great value in providing a better understanding of the processes that control the dynamics of inlet systems. At short time-scales, quantitative information about the acting processes and how they interact has been gained by the modelling experiments, and at medium time scales, the combined application resulted in qualitative predictions of the evolution of most regions of the system

High-energy events and short-term changes in superficial beach sediments

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Tidal inlet migration and formation: the case of the Ararapira inlet – Brazil

The aim of this study is to assess the morphological evolution of the Ararapira (Brazil) barrier-inlet system, at different time scales. Based on satellite imagery, elevation data, and in-situ observations, we quantify the morphological evolution of the region. Results show that the Ararapira inlet migrated continuously southwards, moving updrift, with erosion at its southern margin and intercalated erosion and accretion at the northern margin. At approximately 5.5 km north of the old inlet, the gradual narrowing of the sandy barrier due to channel meandering and coastal erosion resulted in its breaching, in August 2018. We document the initial stages of the new inlet, which after opening, presents intense erosion at its southern margin, resulting in the channel widening to ~1 km. After the barrier breaches, the system begins to adjust to a new equilibrium condition, with the widening of the new inlet being balanced by the gradual closure of the old inlet. These drastic environmental changes control the functioning of such systems, and our results provide important background information for their use and management

Wave climate and power distribution around a rocky island: Alcatrazes, Brazil

We investigate the distribution of the wave power around the Alcatrazes island, a protected marine reserve in southeastern Brazil, located at 20 nautical miles from the coast of São Sebastião/SP. A 14-year wave time series (2005-2018) extracted from the global WaveWatch III model, was used to obtain the offshore wave climate. Based on the wave climate, a wave propagation model (Delft3D) was applied in order to obtain nearshore information. The most frequent waves are from the east, southeast and south, with heights between 1.0 and 2.0 m and periods of 7 to 10 s. Due to dominant wave direction incidence, the wave power is higher at the more exposed eastern side of the island, with its lee side becoming shadowed from the main wave trains. Magnitudes vary seasonally, with winter and autumn presenting more energetic southerly waves and consequent higher wave power along the rocky island. The wave power distribution is a consequence of the incident wave characteristics and the geomorphology of the island. Our findings are the first assessment of the local wave climate and wave power distribution along the rocky shores of Alcatrazes island, providing important background information for understanding different aspects of its functioning and management

Morphodynamics of a wave dominated embayed beach on an irregular rocky coastline

Praias dominadas por ondas ao longo de litorais rochosos recortados são consideradas de grande potencial turístico, devido a beleza de seus recursos naturais. A compreensão das interações entre os processos oceanográficos, geomorfológicos e a herança geológica dominante neste tipo de praias ainda requer maiores investigações que permitam qualificar nossa compreensão e ajudar a preservar o equilíbrio dinâmico natural destes ambientes. Através da abordagem morfodinâmica clássica, descrevemos pela primeira vez as variações morfológicas da praia de Boiçucanga, localizada em uma baía entre promontórios rochosos no município de São Sebastião, SP; região conhecida por belas praias arenosas incrustadas nos vales da Serra do Mar. Foram realizados levantamentos morfológicos ao longo de 15 meses, entre abril de 2008 e setembro de 2009, buscando avaliar as relações entre a morfologia e as características hidrodinâmicas e sedimentares da praia de Boiçucanga. Os dados de campo permitiram a aplicação de modelos da literatura clássica de morfodinâmica praial, como: classificação de estágios morfológicos; número de bancos; altura relativa da maré; grau de exposição da praia; e o grau de embaiamento da praia. A combinação dos resultados dos levantamentos de campo, em especial dos perfis morfológicos da praia e das caracteríscas dos sedimentos na zona de espraiamento, bem como a aplicação dos modelos morfodinâmicos clássicos, permitiram uma melhor compreensão do papel da herança geológica - posição e alcance dos promontórios mar adentro - sobre as assinaturas morfodinâmicas encontradas ao longo do arco praial de Boiçucanga; sendo uma assinatura mais energética com tendências refletivas, favorecendo o desenvolvimento de feições praiais rítmicas (e.g. cúspides praiais) e correntes de retorno controladas pela topografia, e outra menos energética com tendências dissipativas.Wave-dominated embayed beaches on irregular rocky coastlines are highly appreciated for their landscapes and tourism potential. Yet our understanding about the interaction of the oceanographic processes with the geological inheritance in this type of beaches still needs further investigation to better understand their natural balance. In this study, we apply the classical approach of morphodynamics to describe for the first time the variations in the Boiçucanga beach morphology, an embayed beach located in São Sebastião City on an irregular rocky coastline that is well known for its beautiful beaches embedded in the valleys of Serra do Mar. Field surveys were performed over 15 months, between April 2008 and September 2009, seeking to evaluate the interactions among the morphology, sediments and hydrodynamic characteristics at Boiçucanga. All data generated during the field surveys have supported the application of the following morphodynamic models: Classification of morphological beach stages [O]; Number of nearshore sandbars [B*]; Relative tide range [RTR]; Beach exposure on embayed coasts [Ro/a and ß]; and Embayment beach scaling parameter [d] to determine the geomorphological behavior of the beach on monthly and annual time scales. From these models, Boiçucanga is classified as a deep embayed beach exposed to highenergy waves, with a predominant reflective profile, which favors the development of beach cusps and topographically controlled rip currents. The combined results of the field observations and applied models allowed us to better understand the role of geological heritage in the two morphodynamic signatures found at the same beach arch. For future studies, we will focus on numerical models to increase the understanding of the hydrodynamic processes that govern the sediment transport in Boiçucanga

Mobility of meso-scale morphology on a microtidal ebb delta measured using remote sensing

Argus video-images Ebb tidal deltas usually consist of several large lobes of sediment separated by channels in which the bulk of the tidal exchange takes place. The purpose of this paper is to describe and quantify the migration pattern of bedform features associated with an ebb-tidal delta using a new remote video sensing method during a 23 day experiment at New River Inlet (North Carolina). To quantify the migration rates, a Lagged Least Squares Algorithm(LLSA)was developed that found the vector rate for which the suite of lagged images were most similar, computed on a tile by-tile basis. Our observations revealed a complex set of bedform features that migrated in a circular pattern with movement in offshore regions being away from the inlet mouth and toward the shore while nearshore migration was back toward the inlet. 60% of the wavelength variability of these features is at scales that are smaller than the coherent channel and swash bar structures but much longer than megaripples, i.e., between 10 and 100 m. We\ud have chosen to call these bed form features of meso-scale morphologies. The mean migration rate of these features was found to be 1.53 m/day ± 0.76 m/day. 72% of estimated rates were greater than 1.0 m/day, 31% were larger than 2.0 m/day, and the maximum rate was around 3.5 m/day, averaged over 23 days. Alongshore\ud averages of cross-shore migration rates showed a node at 110 m from the shoreline that separates migration away from the inlet from migration toward the inlet (near the shore). The circular pattern of migration appeared to be consistent with expected residual flow of an ebb-tidal delta system

Hydrodynamics and suspended sediment transport in the Camboriú estuary - Brazil: pre jetty conditions

Estuarine hydrodynamics is a key factor in the definition of the filtering capacity of an estuary and results from the interaction of the processes that control the inlet morphodynamics and those that are acting in the mixing of the water in the estuary. The hydrodynamics and suspended sediment transport in the Camboriú estuary were assessed by two field campaigns conducted in 1998 that covered both neap and spring tide conditions. The period measured represents the estuarine hydrodynamics and sediment transport prior to the construction of the jetty in 2003 and provides important background information for the Camboriú estuary. Each field campaign covered two complete tidal cycles with hourly measurements of currents, salinity, suspended sediment concentration and water level. Results show that the Camboriú estuary is partially mixed with the vertical structure varying as a function of the tidal range and tidal phase. The dynamic estuarine structure can be balanced between the stabilizing effects generated by the vertical density gradient, which produces buoyancy and stratification flows, and the turbulent effects generated by the vertical velocity gradient that generates vertical mixing. The main sediment source for the water column are the bottom sediments, periodically resuspended by the tidal currents. The advective salt and suspended sediment transport was different between neap and spring tides, being more complex at spring tide. The river discharge term was important under both tidal conditions. The tidal correlation term was also important, being dominant in the suspended sediment transport during the spring tide. The gravitational circulation and Stokes drift played a secondary role in the estuarine transport processes.As trocas de água e materiais através das desembocaduras de estuários são de difícil quantificação e são de fundamental importância para o entendimento do funcionamento de estuários e da zona costeira. A hidrodinâmica e transporte de sedimentos em suspensão no estuário do rio Camboriú foram estudados através da realização de duas campanhas de campo em 1998 cobrindo as condições de quadratura e sizígia. O período do levantamento foi anterior à obra de construção do molhe em 2003 que alterou a morfologia da desembocadura, fornecendo assim importantes informações base sobre o sistema. Cada experimento cobriu dois ciclos de maré com medições horárias de correntes, salinidade, concentrações de sedimentos em suspensão e nível de água. Os resultados mostram que o estuário é parcialmente misturado com estrutura vertical variando em função da amplitude e fase da maré. A estrutura dinâmica do estuário é balanceada entre os efeitos estabilizadores gerados pelo gradiente vertical de densidade, que permite produzir fluxo de empuxo e estratificação, e os efeitos turbulentos gerados pelo gradiente vertical de velocidade, que gera mistura vertical. A principal fonte de sedimentos para a coluna de água são os sedimentos de fundo, periodicamente resuspendidos pelas correntes de maré. O transporte advectivo de sal e sedimentos em suspensão foi diferente entre condições de quadratura e sizígia, sendo mais complexo durante a sizígia. A circulação gravitacional e a deriva de Stokes apresentam um papel secundário nos processos de transporte estuarinos.CNP

Hydrodynamics and suspended sediment transport in the Camboriú estuary - Brazil: pre jetty conditions

As trocas de água e materiais através das desembocaduras de estuários são de difícil quantificação e são de fundamental importância para o entendimento do funcionamento de estuários e da zona costeira. A hidrodinâmica e transporte de sedimentos em suspensão no estuário do rio Camboriú foram estudados através da realização de duas campanhas de campo em 1998 cobrindo as condições de quadratura e sizígia. O período do levantamento foi anterior à obra de construção do molhe em 2003 que alterou a morfologia da desembocadura, fornecendo assim importantes informações base sobre o sistema. Cada experimento cobriu dois ciclos de maré com medições horárias de correntes, salinidade, concentrações de sedimentos em suspensão e nível de água. Os resultados mostram que o estuário é parcialmente misturado com estrutura vertical variando em função da amplitude e fase da maré. A estrutura dinâmica do estuário é balanceada entre os efeitos estabilizadores gerados pelo gradiente vertical de densidade, que permite produzir fluxo de empuxo e estratificação, e os efeitos turbulentos gerados pelo gradiente vertical de velocidade, que gera mistura vertical. A principal fonte de sedimentos para a coluna de água são os sedimentos de fundo, periodicamente resuspendidos pelas correntes de maré. O transporte advectivo de sal e sedimentos em suspensão foi diferente entre condições de quadratura e sizígia, sendo mais complexo durante a sizígia. A circulação gravitacional e a deriva de Stokes apresentam um papel secundário nos processos de transporte estuarinos.Estuarine hydrodynamics is a key factor in the definition of the filtering capacity of an estuary and results from the interaction of the processes that control the inlet morphodynamics and those that are acting in the mixing of the water in the estuary. The hydrodynamics and suspended sediment transport in the Camboriú estuary were assessed by two field campaigns conducted in 1998 that covered both neap and spring tide conditions. The period measured represents the estuarine hydrodynamics and sediment transport prior to the construction of the jetty in 2003 and provides important background information for the Camboriú estuary. Each field campaign covered two complete tidal cycles with hourly measurements of currents, salinity, suspended sediment concentration and water level. Results show that the Camboriú estuary is partially mixed with the vertical structure varying as a function of the tidal range and tidal phase. The dynamic estuarine structure can be balanced between the stabilizing effects generated by the vertical density gradient, which produces buoyancy and stratification flows, and the turbulent effects generated by the vertical velocity gradient that generates vertical mixing. The main sediment source for the water column are the bottom sediments, periodically resuspended by the tidal currents. The advective salt and suspended sediment transport was different between neap and spring tides, being more complex at spring tide. The river discharge term was important under both tidal conditions. The tidal correlation term was also important, being dominant in the suspended sediment transport during the spring tide. The gravitational circulation and Stokes drift played a secondary role in the estuarine transport processes

Vulnerability assessment of Massaguaçú Beach (SE Brazil)

With the aim of summarizing several coastal indicators in one index, this paper proposes a vulnerability index to coastal erosion. This index synthesizes coastal and inland indicators quantitatively, becominga useful tool for coastal planning and better management of coastal resources. The index is composed of coastal variables: beach morphology, shoreline position, dune field configuration, wave exposure and presence of rivers and/or inlets; and inland variables: terrain elevation, vegetation, coastal engineeringstructures, occupation percentile and soil permeability. In order to validate the proposed method, it was\ud applied to Massaguaçú Beach (SP) in the Southeast of Brazil. According to its characteristics, the beach was divided into three sectors from south to north. Sectors 1 and 3 are classified as being of moderate vulnerability, both with index 5, while sector 2 is classified as high vulnerability, with index 7.5

Geology and hypsometry of river basins at central-northern Santa Catarina (Brazil): implications for the coastal zone

The central-northern region of the Santa Catarina State (Brazil) is composed basically by the Itapocu, Itajaí-Açu and Tijucas river basins, draining directly to the South Atlantic. The present study uses the hypsometric analysis of those three basins to improve the understanding of the Holocene evolution and dynamics of the respective estuaries and coastal plains. Data on the lithological coverage, topography, hydrography, climate and dimensions were considered, analyzed and interpreted in the geomorphologic context. Information regarding hydrodynamics and sedimentology of the estuaries and stratigraphy of the coastal plains were also considered. The results have shown important differences in the geology, topography, thalweg profile and hypsometry between the studied drainage basins. In the corresponding estuaries and coastal plains substantial differences in the morphology, dynamic and stratigraphy were observed, which could be largely explained by the differences in the drainage basin characteristics.A região centro-norte do Estado de Santa Catarina/Brasil é composta basicamente pelas bacias hidrográficas dos rios Itajaí-Açu, Itapocu e Tijucas, drenando diretamente para o Atlântico Sul. O objetivo do presente trabalho é analisar e correlacionar a hipsometria dessas bacias para melhor entender a evolução holocênica e a dinâmica dos estuários e planícies costeiras associadas àqueles rios. Foram compilados dados gerais da cobertura geológico-sedimentar, topografia, dimensões e clima de cada bacia hidrográfica. Esses dados foram analisados e interpretados no contexto geomorfológico. Dados de hidrodinâmica e sedimentologia dos estuários e estratigrafia das planícies costeiras foram também considerados. Os resultados apontam diferenças importantes na geologia, topografia, perfis de talvegue e hipsometria das bacias estudadas. Foram também identificadas diferenças significativas na morfologia, dinâmica e estratigrafia das respectivas regiões estuarinas e planícies costeiras, que foram diretamente correlacionadas com as características das bacias de drenagem