Luciana S. Esteves

Beach ridges, foredunes or transgressive dunefields? Definitions and an examination of the Torres to Tramandaí barrier system, Southern Brazil

Many prograded barriers and some dunefields in the world have been termed ‘beach ridge’ plains, but the actual genesis of the ‘ridges’ is often unknown. Use of the terms, berms, beach ridges and foredunes is also confusing in the literature because their definitions are highly variable and are commonly used interchangeably. Thus, the formation and definition of sand berms, beach ridges and foredunes is briefly reviewed. Beach ridges are re-defined as entirely wave formed deposits which are most commonly formed during high wave conditions and/or elevated water levels (e.g. storm surges). Foredunes are formed by aeolian sand deposition in vegetation on the backshore. Some dunefields in Brazil have been called beach ridge plains when they are, in fact, foredune plains, transgressive dunefields, or complex barriers (i.e. barriers comprising two types of dunes). The Holocene barrier extending from Torres to Tramandai in southern Brazil has been regarded as a beach ridge plain. The landforms of this Holocene barrier comprise wide, relatively linear, widely spaced (400–600m), shore parallel ridges on the landward half, and more closely spaced (80–400m), lobate and crescentic, discrete ridges on the seaward half. Low, rolling dunefields, sand sheets, nebkha fields and deflation plains occur between the ridges. The barrier is re-interpreted as a prograded, transgressive dunefield

Long- and Short-Term Coastal Erosion in Southern Brazil

ABSTRACT Rio Grande do Sul is the southernmost state in Brazil. Open sandy beaches dominate the 630-km long shoreline that is 76% still undeveloped. Less than 5% of the states population (totalling 9.7 million people) live in coastal cities. However, the coastal population is growing faster than the states average since 1990. Although intense erosion is widely accepted along the beaches of Conceição lighthouse and Hermenegildo, the extent of erosion along the Rio Grande do Sul shoreline is still a controversial issue. Discussions arise from the contrasting results presented by studies addressing coastal erosion in Rio Grande do Sul. Recent DGPS monitoring indicates that about 80% of the Rio Grande do Sul shoreline is eroding; wave refraction studies indicate that it is mainly stable, and long-term coastal evolution modelling reveals a predominantly prograding shore for the last 5 ka. This work critically evaluates published data on long- and short-term causes of coastal erosion in Rio Grande do Sul, in an attempt to highlight the unanswered questions that could minimize the debate. The analysis includes sea-level rise, concentration of wave energy due to large-scale coastal topography, sand deficit as the long-term causes of erosion, storm surges, concentration of wave energy due to small-scale submerged features, interference in the longshore sediment transport, and human activities as the short-term causes. Discrepancies in shoreline change results are a matter of the temporal scale in question and what are the causes that play a significant role in it. For coastal management purposes short-time events represent a far greater hazard than long-term trends. It is therefore reasonable to state that in order to support decision-making mechanisms in Rio Grande do Sul a better understanding of the relationship of storms, sand budget, and beach erosion is necessary.

Improving integration for integrated coastal zone management: an eight country study.

Integrated coastal zone management (ICZM) is a widely accepted approach for sustainable management of the coastal environment. ICZM emphasizes integration across sectors, levels of government, uses, stakeholders, and spatial and temporal scales. While improving integration is central to progress in ICZM, the role of and the achievement of integration remain understudied. To further study these two points, our research analyzes the performance of specific mechanisms used to support ICZM in eight countries (Belgium, India, Israel, Italy, Portugal, Sweden, UK, and Vietnam). The assessment is based on a qualitative comparative analysis conducted through the use of two surveys. It focuses on five ICZM mechanisms (environmental impact assessment; planning hierarchy; setback lines; marine spatial planning, and regulatory commission) and their role in improving integration. Our findings indicate that certain mechanisms enhance specific types of integration more effectively than others. Environmental impact assessment enhances science-policy integration and can be useful to integrate knowledge across sectors. Planning hierarchy and regulatory commissions are effective mechanisms to integrate policies across government levels, with the latter also promoting public-government integration. Setback lines can be applied to enhance integration across landscape units. Marine spatial planning is a multi-faceted mechanism with the potential to promote all types of integration. Policy-makers should adopt the mechanisms that are suited to the type of integration needed. Results of this study also contribute to evidence-based coastal management by identifying the most common impediments related to the mechanisms of integration in the eight studied countries.

A critical evaluation of coastal erosion in Rio Grande do Sul, Southern Brazil

Evidences of coastal erosion in Rio Grande do Sul have been obtained by three methods: (a) analysis of the long-term morphodynamics and stratigraphy of coastal barriers, (b) annual shoreline mapping using the Differential Global Positioning System (DGPS), and (c) local beach profile measurements. The first method reflects coastal erosion as continuity of the geological evolution in the last 5 ka, taking place mainly along the southern half of gentle coastal projections. The second method represents a shorter temporal scale and indicates that approximately 80% of the coast is eroding. Beach profiling has been measured in very few places that are distant from each other since the early 1990s; consequently, their results reflect local and very short time shoreline behavior. A critical evaluation of published data addressing coastal erosion in Rio Grande do Sul strongly suggests that short and long term negative balance on the sediment budget is the main cause of erosion along this coastline.

Seasonal and Interannual Influences on the Patterns of Shoreline Changes in Rio Grande do Sul, Southern Brazil

Abstract Changes in shoreline positions along the Rio Grande do Sul coast, southern Brazil, are analyzed to determine the spatial and temporal variability of shoreline movements at a regional scale. Using a kinematic Differential Global Positioning System (DGPS) survey method, the 618-km long shoreline of Rio Grande do Sul has been mapped on five occasions between November 1997 and April 2002. These data show that the coastline responds differently to hydrodynamic and meteorological forcing along the three major coastal sectors. The observed differences occur especially in the magnitude of changes, in the time interval in which the shoreline returns to a previous position, and in the length scale of dominant shoreline changes. Here changes in shoreline position are examined with respect to grain size, shoreline orientation, storms, El Nino–Southern Oscillation (ENSO) events, and gradients of longshore sediment transport. Data analyses and modeling indicate that the alongshore variability in the patterns of shoreline change through time is closely related to shoreline orientation and the associated gradients of longshore sediment transport. Results indicate also that variability in wave energy and storminess influence seasonal changes, whereas ENSO events influence interannual changes. This study demonstrates the importance of understanding the drivers of shoreline change at a regional scale and has applications in studies concerned with coastal engineering and shoreline response to climate change.

Managed Realignment : A Viable Long-Term Coastal Management Strategy?

Climate change and environmental and financial concerns have led to a shift from the traditional ‘hold-the-line’ approach of coastal protection towards more flexible soft engineering options. Managed realignment is a coastal management strategy increasingly implemented in Europe and other countries worldwide. It is a relatively new soft engineering alternative aiming to provide sustainable flood risk management with added environmental and socio-economic benefits by creating space for coastal habitats to develop more dynamically. The natural adaptive capacity of coastal habitats and the delivery of ecosystem services underpin the sustainability of managed realignment. However, many definitions of managed realignment exist and the understanding of what the term actually represents in practice has evolved through time and varies regionally. This book clarifies the definitions and terminology used in the literature and proposes that managed realignment is used as a general term that encompasses the many different methods of implementation worldwide, including: removal, breach and realignment of defences; controlled tidal restoration ; and managed retreat. These methods of implementation are explained and illustrated with examples from around the world. In addition to a general overview of emerging policies and current practices, specific chapters discuss approaches adopted in the Netherlands, the UK and Maui (US). The UK experience is presented from the perspectives of three sectors: the National Trust (a charity that owns 10% of England’s coastline), the Environment Agency (a government organisation responsible for implementing flood and erosion risk policy) and a private consultant involved in the design and delivery of managed realignment projects. Recent national and regional strategies worldwide give managed realignment an increasing role in climate change and flood risk management. Gaining stakeholders and public support is fundamental for the success of emerging coastal management strategies. However, public perception and stakeholders engagement are often cited as a factor limiting the wider uptake of managed realignment. Results from a recent survey are used to benchmark the current thinking about the potential, the performance and the limitations of managed realignment in the UK and elsewhere. The views of stakeholders are considerably more negative and notably contrast with the views of practitioners and researchers. The only clear and dominant agreement across all groups of respondents is that better understanding about the long-term evolution of sites is needed. Taking a wider perspective to consider the range of implementation methods, the viability of managed realignment as a long-term coastal management strategy is discussed.

Modelling storm responses on a high-energy coastline with XBeach

The XBeach model has been used to simulate the morphological impacts of storms on sandy and gravel beaches. Taking as a case study Rossbeigh Spit located on the high-energy coast of western Ireland, the study reported here tests the capacity of XBeach to reproduce barrier breaching during a storm in December 2008. It demonstrates that predictions of the breaching event agree reasonably well with observations. However, the main focus of the paper is to establish using the model results, site-specific critical wave and water level conditions giving rise to dune erosion, overwashing and breaching. By deriving simple-to-use expressions to define hydrodynamic thresholds the study advances the ability to predict the impacts of infrequent and rarely observed storm events and is considered to provide useful coastal management tool for assessing the vulnerability of sandy barriers to breaching high-energy during storms.

Using Combined Modelling Approaches to Improve Coastal Defence Design: a case study at Hopton, UK

ABSTRACT Williams, J.J., Esteves, L.S., Conduche, T., Barber, P., Tindle, A., 2014. Using Combined Modelling Approaches to Improve Coastal Defence Design: a case study at Hopton, UK. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 018–022, ISSN 0749-0208. A storm that occurred close to the spring tidal maxima in March 2013 resulted in beach lowering and cliff recession of c. 5 m along a 110 m frontage at Hopton-on-Sea, UK and threatened the static caravan park of Bourne Leisure Ltd. This paper reports a study using XBeach and MIKE21 models to assist with the design of new coastal defences to reduce cliff and beach erosion. Two schemes are examined here: three fishtail rock groynes (Scheme 1); and ten ‘double-head’ curved rock groynes (Scheme 2). The selected design must provide acceptable level of protection and, to be granted consent, no adverse environmental impact must be demonstrated. Current practice using a single numerical model can provide a cost-effective tool for coastal defence assessments. However, the work presented here show that when good agreement between complementary models can be demonstrated, greater confidence can be given to model results. Specifically, refinements to the present scheme design were made possible by the use of the XBeach model, which allowed identification of the cross-shore limits of sediment transport in storm conditions, and by the MIKE21 model which allowed quantification of alongshore scheme impacts. Together, the model results have assisted the development of an improved final scheme design which minimizes potential environmental impacts.

What is Managed Realignment

Many definitions of managed realignment exist. The understanding of what the term actually represents in practice has evolved through time and varies regionally, across sectors and among practitioners. A common understanding of managed realignment is further complicated by the use of other related terms; sometimes synonymous with managed realignment while at other times reflecting different concepts. Terms such as managed retreat, setback, regulated tidal exchange, depoldering have all being used in the literature associated with managed realignment, many times inconsistently. The lack of clarity in the use of terminology has contributed to negative connotations expressed by some stakeholders and the general public. This chapter clarifies the terminology currently in use and proposes a wider definition of managed realignment so it can be applicable to encompass the many forms of implementation adopted worldwide. Within this broader context, managed realignment becomes a general term that can be used to describe collectively the many mechanisms implemented to allow coastlines to evolve more flexibly with the objective of promoting more sustainable flood and erosion risk management.

Current Perceptions About Managed Realignment

Despite the diversity of managed realignment approaches adopted in different countries, there are certain elements of commonality that provide relevant lessons that can be applicable to facilitate and improve the implementation of managed realignment in general. Public perception and stakeholders’ engagement are often cited as a factor limiting the wider implementation of managed realignment. Considering the scale and importance of managed realignment in national and regional strategies in many countries, gaining wider public acceptance is fundamental. To take adequate actions that can improve social uptake of managed realignment, it is first necessary to understand the differences between public perception and the current knowledge of practitioners and researchers. This chapter describes the current thinking of researchers and practitioners about the potential, performance and limitations of managed realignment and contrasts these with the perception of stakeholders. Critical differences are identified and ways to address these with the aim to increase the social acceptance of managed realignment are suggested.