Morphosedimentary and ecosystem evolution at Belharucas beach after a sand nourishment (Algarve, south Portugal)

<p>Beach nourishment is an increasingly recommended solution for reversing the erosion process that affects nowadays the coastal zone. Usually, it is used in emergency situations as a local and short-term solution or as a regional and long-term management strategy.</p><p>From April 2017 to November 2019, sediment samples and beach profile data were collected seasonally, before and after a sand nourishment (100.000m<sup>3</sup>) that increased 30m of width in Belharucas beach (south Portugal, Algarve).</p><p>The main objective of the work was to evaluate the nourishment impact in the beach ecosystem, aiming at contributing to seafloor integrity assessment, in the scope of Descriptor 6 of the Marine Strategy Framework Directive. </p><p>Methodology included grain size and macrobenthic fauna analyses in two profiles of the nourished area and another one further away, selected as a control area. Each profile was sampled at three intertidal zones: supralittoral (beach berm), mediolittoral (beach face) and infralittoral (low tide terrace).  Beach profile data were collected with the main objective of measuring the beach width and evaluate nourishment longevity.</p><p>Results show that grain size variability, higher at beach face, is dominated by local energy beach conditions rather than to changes related to the nourishment.</p><p>Morphological data shows that beach nourishment had a relatively low longevity as two years after the nourished beach present roughly the same width as priori to nourishment.</p><p>While supralittoral samples were defaunated, medio and infralittoral ones exhibited extremely low diversity. Assemblages were dominated by small-size polychaetes, bivalves and isopods. No statistically significant differences were found in assemblage composition regarding pre- and post-sand nourishment, year seasons, tidal zones and control stations.</p><p>In conclusion, Belharucas beach exhibited high resilience to the sand nourishment, preserving its morphodynamics and ecosystem conditions.</p><p> </p><p>The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL and through the strategic project UIDB/MAR/04292/2019 - MARE and ECOEXA project (MAR-01.04.02-FEAMP-0016)</p>

GUIDELINES FOR DESIGNING SAND NOURISHMENT ON LOW TO VERY EXPOSED COASTS

Danish law establishes a common right of passage on foot along the Danish shoreline, even though beaches are often privately owned. The law also states that coastal protection must not hinder this. Therefore, sand nourishment should be part of every coastal protection scheme against erosion. Sand nourishments can be designed in numerous ways depending on their objectives. As part of the European Interreg project, Building With Nature (BWN), guidelines will be developed by the Danish Coastal Authority (DCA) in end-2020. This abstract presents these guidelines with special focus on the coasts of Denmark. Special emphasis will be on insight into the natural variation of the coasts, as this is vital both when designing effective coastal protection schemes and when evaluating the impact of the nourishment. In this project, the pathway along which sediment is being transported spans from offshore at the outer bar to the coastal cliff. The aim is to be able to determine the along- and cross-shore paths, along which the nourishment sand is transported, the diffusion velocity of the nourishment and the impact on the surrounding coasts. Based on the results of the multiple analysis, the primary objective is to produce guidelines on how to use sand nourishment to counteract erosion in a sustainable and socioeconomic way.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/nIrFFmH98V8

Beach Nourishment Alternatives for Mitigating Erosion of Ancient Coastal Sites on the Mediterranean Coast of Israel

Since 2011, beach nourishment has become the preferred solution for mitigating coastal erosion along the Mediterranean coast of Israel, as it is considered “soft” and environmentally friendly. However, using fine sand for nourishment in Israel without supporting measures is problematic due to the high wave energy and strong longshore currents in the littoral zone that tend to drift the sand away. This would require ongoing, multiyear, costly, and never-ending maintenance. In the present study, we analyzed sand and pebble alternatives for nourishment of the eroded beach in front of Tel Ashkelon, an important coastal archaeological site in southern Israel that suffers from severe erosion. Based on Pranzini et al. (2018), we analyzed the alternatives, evaluated their cost and efficiency, and assessed their potential environmental impacts. The study concluded that for protecting the southern part of Tel Ashkelon beach, pebble nourishment is the optimal solution, mainly regarding durability and cost. Using this material for nourishment will better absorb the storm wave impact and protect the foot of the archaeological Tel from erosion, and require lower maintenance cost than using finer sand nourishment.

Accommodation space indicates dune development potential along an urbanized and frequently nourished coastline

With densely populated areas well below mean sea level, the Netherlands relies heavily on its dunes to ensure coastal safety. About half of the sandy coastline, however, is subject to structural marine erosion and requires frequent sand nourishment as a counteractive measure. A key component of present-day coastal safety policy is creating favorable conditions for natural dune development. These conditions essentially involve (1) a steady supply of wind-blown sand towards (2) a wide accommodation space where sand can accumulate and dunes are sheltered from frequent storm surge impacts. This paper examines to what extent an experimental mega-scale beach nourishment (termed Zandmotor in Dutch) has contributed to creating accommodation space favorable for dune development. Using publicly available airborne lidar data and Sentinel-2 satellite imagery, favorable accommodation space is identified by comparing recent changes in coastal morphology against dune vegetation-cover dynamics. With a focus on European marram grass (Ammophila arenaria) as the most prominent dune-building species, this paper demonstrates that the Zandmotor supports an especially high potential for incipient (embryo) dunes to develop as most of its favorable accommodation space is located on the beach. However, considering the conditions required for successful marram grass establishment as well as persistent anthropogenic disturbances arising from recreation and nature management practices, it is not likely that dune development along this urbanized coastline reaches its full potential.

A Regional Application of Bayesian Modeling for Coastal Erosion and Sand Nourishment Management

This paper presents an application of the Bayesian belief network for coastal erosion management at the regional scale. A “Bayesian ERosion Management Network” (BERM-N) is developed and trained based on yearly cross-shore profile data available along the Holland coast. Profiles collected for over 50 years and at 604 locations were combined with information on different sand nourishment types (i.e., beach, dune, and shoreface) and volumes implemented during the analyzed time period. The network was used to assess the effectiveness of nourishments in mitigating coastal erosion. The effectiveness of nourishments was verified using two coastal state indicators, namely the momentary coastline position and the dune foot position. The network shows how the current nourishment policy is effective in mitigating the past erosive trends. While the effect of beach nourishment was immediately visible after implementation, the effect of shoreface nourishment reached its maximum only 5–10 years after implementation of the nourishments. The network can also be used as a predictive tool to estimate the required nourishment volume in order to achieve a predefined coastal erosion management objective. The network is interactive and flexible and can be trained with any data type derived from measurements as well as numerical models.

Impact of coastal protection systems on marine ecosystems

Various solutions, which consist of numerous techniques, technologies and planning measures, are testing for reduction shoreline erosion, precisely for protection shore against waves attack. These methods may affect the site's geology and geomorphology, involving changes of the habitats in the site. Coastal defense projects and ideas must take into account the structure and functions of protected natural areas and their conservation objectives in order to avoid threatening the species and/or habitats on the site. The ecological impacts expected from coast protection structures on short-term are mostly negative, may disturbance the birds from their habitat, and destruct the marine coastal habitats with their own flora and fauna. In this study, we are indicating the effects of coastal protection measures on the ecosystem. Therefore, we present a part of methods applied or which will be apply on the Romanian shoreline and the effects that have an impact on the species and/or habitats on the site. The methods referred to “hard” methods so to harder the shore with fixed structure (bulkhead, seawall, revetment, breakwaters, sills or groins) or “soft” methods like beach nourishment that is not a sustainable method in time. The protection structures like breakwaters and groins trap or add sand and will change the beach geometry this means that can introduce new artificial material, which is extensively and rapidly colonized by algae and marine animals. In the cases of beach nourishment, under water sand nourishment and mudflat recharge, there are impacts both at the borrow site (the sediment source) and the target site. In the zone of extraction of borrow, sediments appear a damage and mortality to the benthos. Finally, it can conclude that some of the effects are beneficial for socio-economic aspect, but it is important also, the environment, which can bring bad consequences for earth landscape and make the ecosystem, be unbalanced.

A METHOD TO SYSTEMATICALLY CLASSIFY DESIGN CHARACTERISTICS OF SAND NOURISHMENTS

The decades of collected monitoring data of coastal profiles in combination with the decades of experience with sand nourishments in the Wadden Sea, forms an invaluable basis to study the inter-site efficiency of sand nourishment design. However, a systematic data-driven study of this type needs to be applicable for the inter-site varying (i) nourishment design strategies, (ii) coastal monitoring data sets and (iii) natural morphodynamics of the shorelines, respectively. This study introduces a four-step method able to systematically classify the influence of individual nourishment design parameters on the nourishment lifetime (i.e. the period of influence on the natural dynamics of a coastal profile). With the non-linear and adaptive principle component analysis (PCA) method, nourishment lifetimes of beach- and shoreface nourishments are extracted from data sets that describe different natural morphodynamics. Based on an application of the method to a limited number of nourishments placed in two coastal areas in the Netherlands (Ameland) and Germany (Sylt), increasing nourishment concentration, alongshore nourishment length and absolute nourishment peak elevation seem to increase the lifetime of beach- and shoreface nourishments. Nourishment lifetimes at profile more downstream seem to decrease for beach nourishments, but increase for shoreface nourishments. The method supports inclusion of additional coastal profiles and parameters related to the nourishment design, natural morphodynamics of the coastal profile and hydrodynamic forcing, to quantify nourishment design influences on nourishment lifetimes at different locations.