O Controle da Deriva Litorânea no Desenvolvimento do Campo de Dunas e da Antepraia no Litoral Médio do Rio Grande do Sul

Zones of erosion and accretion were delimited by comparing a DGPS shoreline mapping in 1997 and the beach line reproduced from the army chart collection of 1975. The results show extensive shore retreat along of Rio Grande do Sul central coast, while accretion was observed in Mostardas and Dunas Altas beach. Mathematical estimative of the regional longshore transport potential along the Rio Grande do Sul coast, a 630-km long holocenic fine sand barrier, resulted in a large net northward annual sand volume. Additionally, the estimated potential of sediment transport based on the CERC formula predicts a substantial variation of the energy flux into the surf zone, due to little changes in shoreline alignments and in the potential alongshore sediment transport. The reduction in the sediment flux due to changes in the shoreline alignment produce a jam in the longshore transport, meaning that part of the sediment arriving from the upstream stretch may be deposited or diverted offshore by coastal jet. Based on that, it is possible that changes in the net longshore sand transport are responsible for the increase in the shoreface width from less than 1 km to more than 3 km in Mostardas beach and Dunas Altas beach. Interesting to note that wider dune fields are associated to those beaches where shoreface is also wider. In this way, the volume of longshore sand transport and the sediment jam provide by changes on shoreline alignment in Mostardas and Dunas Altas beaches are important for both coastal dune fields and shoreface width.Zones of erosion and accretion were delimited by comparing a DGPS shoreline mapping in 1997 and the beach line reproduced from the army chart collection of 1975. The results show extensive shore retreat along of Rio Grande do Sul central coast, while accretion was observed in Mostardas and Dunas Altas beach. Mathematical estimative of the regional longshore transport potential along the Rio Grande do Sul coast, a 630-km long holocenic fine sand barrier, resulted in a large net northward annual sand volume. Additionally, the estimated potential of sediment transport based on the CERC formula predicts a substantial variation of the energy flux into the surf zone, due to little changes in shoreline alignments and in the potential alongshore sediment transport. The reduction in the sediment flux due to changes in the shoreline alignment produce a jam in the longshore transport, meaning that part of the sediment arriving from the upstream stretch may be deposited or diverted offshore by coastal jet. Based on that, it is possible that changes in the net longshore sand transport are responsible for the increase in the shoreface width from less than 1 km to more than 3 km in Mostardas beach and Dunas Altas beach. Interesting to note that wider dune fields are associated to those beaches where shoreface is also wider. In this way, the volume of longshore sand transport and the sediment jam provide by changes on shoreline alignment in Mostardas and Dunas Altas beaches are important for both coastal dune fields and shoreface width

Recent shifts in coastline change and shoreline stabilization linked to storm climate change

Because cuspate coastlines are especially sensitive to changes in wave climate, they serve as potential indicators of initial responses to changing wave conditions. Previous work demonstrates that Cape Hatteras and Cape Lookout, NC, which are largely unaffected by shoreline stabilization efforts, have become increasingly asymmetric over the past 30 years, consistent with model predictions for coastline response to increases in Atlantic Ocean summer wave heights and resulting changes in the distribution of wave-approach angles. Historic and recent shoreline change observations for Cape Fear, North Carolina, and model simulations of coastline response to an increasingly asymmetric wave climate in the presence of beach nourishment, produce comparable differences in shoreline change rates in response to changes in wave climate. Results suggest that the effect of beach nourishment is to compensate for—and therefore to mask—natural responses to wave climate change that might otherwise be discernible in patterns of shoreline change alone. Therefore, this case study suggests that the effects of wave climate change on human-modified coastlines may be detectable in the spatial and temporal patterns of shoreline stabilization activities. Similar analyses of cuspate features in areas where the change in wave climate is less pronounced (i.e., Fishing Point, Maryland/Virginia) and where local geology appears to exert control on coastline shape (i.e., Cape Canaveral, Florida), suggest that changes in shoreline configuration that may be arising from shifting wave climate are currently limited to sandy wave-dominated coastlines where the change in wave climate has been most pronounced. However, if hurricane-generated wave heights continue to increase, large-scale shifts in patterns of erosion and accretion will likely extend beyond sensitive cuspate features as the larger-scale coastline shape comes into equilibrium with changing wave conditions

A Influência da inflexão costeira na praia de Mostardas-RS sobre as variações da linha de praia

A praia de Mostardas com aproximadamente 36 km de extensão está localizada no litoral médio do Rio Grande do Sul, sendo o balneário de São Simão e o farol de Mostardas os limite norte e sul, respectivamente. Na metade norte da praia de Mostardas verifica-se um comportamento deposicional anômalo a maioria das praias do litoral do estado. O comportamento anômalo deste trecho do litoral é influenciado pela diferença na orientação da linha de costa de aproximadamente 11° presente nesta praia. Esta inflexão faz com que a energia das ondas atue de maneira diferente nos trechos ao norte e ao sul desta inflexão, quando analisadas tanto em escala sazonal quanto em escala anual. Dentro de um mesmo ano, escala sazonal, a morfologia foi moldada de acordo com os eventos à que a praia foi submetida, deixando superfície da praia plana, baixa e regular com a passagem de tempestades e adquirindo um maior estoque de sedimentos em sua porção subaérea em condições de mar com ondulações, marcando a sazonalidade desta praia. As variações anuais, verificadas em um intervalo de 8 anos entre os monitoramentos realizados em 1997 e 2005, notou-se que a metade sul da praia apresenta em quase sua totalidade áreas de erosão. O comportamento da metade norte é bastante distinto, com um aumento significativo das áreas de estabilidade e progradação, com 36,1 e 28,1 % dos 17 km deste trecho da praia e uma média de avanço de 1,1 m/ano em direção ao mar. A metade norte mostra também áreas de progradação superiores às encontradas em estudos anteriores na costa do Rio Grande do Sul, de 7 e 8 % (Toldo et al., 1999; Esteves et al., 2002). Este comportamento confirma que a inflexão costeira encontrada neste local influência de maneira significativa as variações da linha de costa na praia de Mostardas.Mostardas beach, with an approximate extension of 36 km, is located along the intermediate section of Rio Grande do Sul state’s coastline, its North and South limits being São Simão beach and Mostardas lighthouse, respectively. At the northern portion of the beach, an anomalous depositional behavior is found, relative to most beaches along the state coast. The anomalous behavior found at this beach strip is influenced by a nearly 11º change in beach orientation. Such inflexion makes the wave energy act differently in beach strips located north and south from the inflexion, as examined in both seasonal and annual scales. Within a given seasonal scale, the morphology will have been shaped according to events the beach was subjected to, leaving the beach surface even, low, and regular with the passage of storm events, and acquiring a greater sediment stock at its subaerial portion in low-sea conditions, thus marking this beach’s seasonality. Yearly variability, verified at an 8-year interval between monitoring conducted in 1997 and 2005, demonstrated that the southern half of this beach shows erosion in almost its totality. The behavior of the 17 km of the northern half is quite different, with a significant enhance of stability and accretion areas, 36.1 and 28.1 %, respectively, and a seaward progradation mean of 1.1 m/year. The northern half also shows progradation areas between 3 and 4 times longer than those found in previous researches made on the Rio Grande do Sul coast (Toldo et al., 1999; Esteves et al., 2002). Such behavior confirms that the coastal inflexion found at the place significantly contributes with the shoreline variability in Mostardas beach

A Influência da inflexão costeira na praia de Mostardas-RS sobre as variações da linha de praia

A praia de Mostardas com aproximadamente 36 km de extensão está localizada no litoral médio do Rio Grande do Sul, sendo o balneário de São Simão e o farol de Mostardas os limite norte e sul, respectivamente. Na metade norte da praia de Mostardas verifica-se um comportamento deposicional anômalo a maioria das praias do litoral do estado. O comportamento anômalo deste trecho do litoral é influenciado pela diferença na orientação da linha de costa de aproximadamente 11° presente nesta praia. Esta inflexão faz com que a energia das ondas atue de maneira diferente nos trechos ao norte e ao sul desta inflexão, quando analisadas tanto em escala sazonal quanto em escala anual. Dentro de um mesmo ano, escala sazonal, a morfologia foi moldada de acordo com os eventos à que a praia foi submetida, deixando superfície da praia plana, baixa e regular com a passagem de tempestades e adquirindo um maior estoque de sedimentos em sua porção subaérea em condições de mar com ondulações, marcando a sazonalidade desta praia. As variações anuais, verificadas em um intervalo de 8 anos entre os monitoramentos realizados em 1997 e 2005, notou-se que a metade sul da praia apresenta em quase sua totalidade áreas de erosão. O comportamento da metade norte é bastante distinto, com um aumento significativo das áreas de estabilidade e progradação, com 36,1 e 28,1 % dos 17 km deste trecho da praia e uma média de avanço de 1,1 m/ano em direção ao mar. A metade norte mostra também áreas de progradação superiores às encontradas em estudos anteriores na costa do Rio Grande do Sul, de 7 e 8 % (Toldo et al., 1999; Esteves et al., 2002). Este comportamento confirma que a inflexão costeira encontrada neste local influência de maneira significativa as variações da linha de costa na praia de Mostardas.Mostardas beach, with an approximate extension of 36 km, is located along the intermediate section of Rio Grande do Sul state’s coastline, its North and South limits being São Simão beach and Mostardas lighthouse, respectively. At the northern portion of the beach, an anomalous depositional behavior is found, relative to most beaches along the state coast. The anomalous behavior found at this beach strip is influenced by a nearly 11º change in beach orientation. Such inflexion makes the wave energy act differently in beach strips located north and south from the inflexion, as examined in both seasonal and annual scales. Within a given seasonal scale, the morphology will have been shaped according to events the beach was subjected to, leaving the beach surface even, low, and regular with the passage of storm events, and acquiring a greater sediment stock at its subaerial portion in low-sea conditions, thus marking this beach’s seasonality. Yearly variability, verified at an 8-year interval between monitoring conducted in 1997 and 2005, demonstrated that the southern half of this beach shows erosion in almost its totality. The behavior of the 17 km of the northern half is quite different, with a significant enhance of stability and accretion areas, 36.1 and 28.1 %, respectively, and a seaward progradation mean of 1.1 m/year. The northern half also shows progradation areas between 3 and 4 times longer than those found in previous researches made on the Rio Grande do Sul coast (Toldo et al., 1999; Esteves et al., 2002). Such behavior confirms that the coastal inflexion found at the place significantly contributes with the shoreline variability in Mostardas beach

Influence of the coastal inflection in the shoreline variability of the Mostardas beach, southern Brazil

Mostardas beach, with an approximate extension of 36 km, is located along the intermediate section of Rio Grande do Sul state's coastline; its north and south limits are São Simão beach and Mostardas lighthouse, respectively. At the northern portion of the beach, an anomalous depositional behavior is found, relative to most beaches along the state coast. The anomalous behavior observed at this beach strip is influenced by a nearly 11º change in beach orientation. Such inflexion makes the wave energy act differently in beach strips located north and south from the inflexion, as examined in both seasonal and annual scales. Within a given seasonal scale, the morphology will be shaped according to events that the beach was subjected to, leaving the beach surface even, low, and regular with the passage of storm events, and acquiring a greater sediment stock at its subaerial portion in low-sea conditions, thus marking this beach seasonality. Yearly variability, verified at an 8-year interval between monitoring conducted in 1997 and 2005, demonstrated that the southern half of this beach shows erosion in almost its totality. The pattern in the 17 km of the northern half is quite different, with a significant enhance of stability and depositional areas, 36.1 and 28.1 %, respectively, and a seaward progradation mean of 1.1 m/year. The northern half also shows progradation areas between 3 and 4 times longer than those found in previous researches made on the Rio Grande do Sul coast (Toldo et al., 1999; Esteves et al., 2002). Such behavior confirms that the coastal inflexion found at the place significantly contributes with the shoreline variability in Mostardas beach.Mostardas beach, with an approximate extension of 36 km, is located along the intermediate section of Rio Grande do Sul state's coastline; its north and south limits are São Simão beach and Mostardas lighthouse, respectively. At the northern portion of the beach, an anomalous depositional behavior is found, relative to most beaches along the state coast. The anomalous behavior observed at this beach strip is influenced by a nearly 11º change in beach orientation. Such inflexion makes the wave energy act differently in beach strips located north and south from the inflexion, as examined in both seasonal and annual scales. Within a given seasonal scale, the morphology will be shaped according to events that the beach was subjected to, leaving the beach surface even, low, and regular with the passage of storm events, and acquiring a greater sediment stock at its subaerial portion in low-sea conditions, thus marking this beach seasonality. Yearly variability, verified at an 8-year interval between monitoring conducted in 1997 and 2005, demonstrated that the southern half of this beach shows erosion in almost its totality. The pattern in the 17 km of the northern half is quite different, with a significant enhance of stability and depositional areas, 36.1 and 28.1 %, respectively, and a seaward progradation mean of 1.1 m/year. The northern half also shows progradation areas between 3 and 4 times longer than those found in previous researches made on the Rio Grande do Sul coast (Toldo et al., 1999; Esteves et al., 2002). Such behavior confirms that the coastal inflexion found at the place significantly contributes with the shoreline variability in Mostardas beach

A Influência da Inflexão Costeira na Variabilidade da Linha de Praia em Mostardas – RS

Mostardas beach, with an approximate extension of 36 km, is located along the intermediate section of Rio Grande do Sul state's coastline; its north and south limits are São Simão beach and Mostardas lighthouse, respectively. At the northern portion of the beach, an anomalous depositional behavior is found, relative to most beaches along the state coast. The anomalous behavior observed at this beach strip is influenced by a nearly 11º change in beach orientation. Such inflexion makes the wave energy act differently in beach strips located north and south from the inflexion, as examined in both seasonal and annual scales. Within a given seasonal scale, the morphology will be shaped according to events that the beach was subjected to, leaving the beach surface even, low, and regular with the passage of storm events, and acquiring a greater sediment stock at its subaerial portion in low-sea conditions, thus marking this beach seasonality. Yearly variability, verified at an 8-year interval between monitoring conducted in 1997 and 2005, demonstrated that the southern half of this beach shows erosion in almost its totality. The pattern in the 17 km of the northern half is quite different, with a significant enhance of stability and depositional areas, 36.1 and 28.1 %, respectively, and a seaward progradation mean of 1.1 m/year. The northern half also shows progradation areas between 3 and 4 times longer than those found in previous researches made on the Rio Grande do Sul coast (Toldo et al., 1999; Esteves et al., 2002). Such behavior confirms that the coastal inflexion found at the place significantly contributes with the shoreline variability in Mostardas beach.Mostardas beach, with an approximate extension of 36 km, is located along the intermediate section of Rio Grande do Sul state's coastline; its north and south limits are São Simão beach and Mostardas lighthouse, respectively. At the northern portion of the beach, an anomalous depositional behavior is found, relative to most beaches along the state coast. The anomalous behavior observed at this beach strip is influenced by a nearly 11º change in beach orientation. Such inflexion makes the wave energy act differently in beach strips located north and south from the inflexion, as examined in both seasonal and annual scales. Within a given seasonal scale, the morphology will be shaped according to events that the beach was subjected to, leaving the beach surface even, low, and regular with the passage of storm events, and acquiring a greater sediment stock at its subaerial portion in low-sea conditions, thus marking this beach seasonality. Yearly variability, verified at an 8-year interval between monitoring conducted in 1997 and 2005, demonstrated that the southern half of this beach shows erosion in almost its totality. The pattern in the 17 km of the northern half is quite different, with a significant enhance of stability and depositional areas, 36.1 and 28.1 %, respectively, and a seaward progradation mean of 1.1 m/year. The northern half also shows progradation areas between 3 and 4 times longer than those found in previous researches made on the Rio Grande do Sul coast (Toldo et al., 1999; Esteves et al., 2002). Such behavior confirms that the coastal inflexion found at the place significantly contributes with the shoreline variability in Mostardas beach

A influência da inflexão costeira na variabilidade da Linha de Praia em Mostardas-RS

Mostardas beach, with an approximate extension of 36 km, is located along the intermediate section of Rio Grande do Sul state’s coastline; its north and south limits are São Simão beach and Mostardas lighthouse, respectively. At the northern portion of the beach, an anomalous depositional behavior is found, relative to most beaches along the state coast. The anomalous behavior observed at this beach strip is influenced by a nearly 11º change in beach orientation. Such inflexion makes the wave energy act differently in beach strips located north and south from the inflexion, as examined in both seasonal and annual scales. Within a given seasonal scale, the morphology will be shaped according to events that the beach was subjected to, leaving the beach surface even, low, and regular with the passage of storm events, and acquiring a greater sediment stock at its subaerial portion in low-sea conditions, thus marking this beach seasonality. Yearly variability, verified at an 8-year interval between monitoring conducted in 1997 and 2005, demonstrated that the southern half of this beach shows erosion in almost its totality. The pattern in the 17 km of the northern half is quite different, with a significant enhance of stability and depositional areas, 36.1 and 28.1 %, respectively, and a seaward progradation mean of 1.1 m/year. The northern half also shows progradation areas between 3 and 4 times longer than those found in previous researches made on the Rio Grande do Sul coast (Toldo et al., 1999; Esteves et al., 2002). Such behavior confirms that the coastal inflexion found at the place significantly contributes with the shoreline variability in Mostardas beach