Modelling Nature-based Solutions: an application to mitigate coastal erosion

<p>Nature based solutions (NBSs) address key societal challenges through the protection, sustainable management and restoration of both natural and modified ecosystems. In this work we present a modeling application of this innovative approach, inspired by nature, with the goal of mitigating coastal erosion. Within the framework of the OPEn-air laboRAtories for Nature baseD solUtions to Manage environmental risks (OPERANDUM) project, the natural reserve of Bellocchio in Lido di Spina (Italy) faces frequent marine floods and intense erosive phenomena, hence being chosen as Open-Air Laboratory for the NBS implementation. The project aims to mitigate coastal erosion through the realization of an artificial sand dune made of natural materials, such as sand, wood, geotextiles and geomembranes and covered by native herbaceous and shrubby vegetation. We present the modeling activities carried out in the context of the project, aiming on the performance and efficiency evaluation  of the designed NBS, with a specific focus on the coastal morphological modelling. Thus, a numerical modeling chain has been set-up to simulate a long-term current scenario with and without the NBS. The chain is composed of the wave model WAVEWATCH III, the oceanographic model SHYFEM and the morphodynamic model XBeach for the coastal area.</p><p>XBeach was validated with available and specific (for the project) topo-bathymetric surveys of the area of interest as means to define the more accurate set-up of the model parameters. The 10 years period 2010-2019 was defined as the time range for modelling simulations. Sea level outputs from SHYFEM and wave outputs from WAVEWATCH III for the 10 years simulations are used to force the coastal model XBeach. Given the huge computational costs related to long-term simulations, an input-schematization was applied (so called “input reduction”). The approach followed for the long-term morphodynamic modelling of the NBS-XBeach setting will be shown. Moreover, the chosen coastal model domain, the model set-up and the input reduction applied will be presented.</p>

Intertidal floodplain controls on centennial-scale morphological channel development

<p>Intertidal areas disappear in deltas worldwide because of land reclamations. This greatly impacts delta morphology because the presence and physiological characteristics of intertidal areas determine the tidal regime and, as a result, residual sediment transport patterns in tidal basins. Understanding how the interaction between intertidal areas and channels in tidal basins influence morphodynamics is therefore important to predict morphological development and to assess the resilience of delta’s to changing boundary conditions.</p><p>In the Ems estuary (The Netherlands), the gradual embankment of a large intertidal embayment altered the planform and cross-sectional geometry of the estuary, leading to changes in the tidal regime and associated residual sediment transport patterns. As early as 1952, it was already suggested that these changes eventually caused a shift towards an alternative historical development of the geometric configuration of the channels; from a multiple to a single channel system.</p><p>This study shows through centennial-scale morphological modelling that the observed system shift can be hind-casted, while conserving model validity by comparison to the observed gross morphodynamics trends. The results indicate that the system shift is indeed driven by land reclamations. This provides a unique case to study the processes leading to the observed developments and evaluate the value of tidal-asymmetry based stability relationships to predict regime shifts in estuarine development.</p>

Communicating Simulation Outputs of Mesoscale Coastal Evolution to Specialist and Non-Specialist Audiences

Coastal geomorphologists and engineers worldwide are increasingly facing the non-trivial challenge of visualising and communicating mesoscale modelling assumptions, uncertainties and outcomes to both coastal specialists and decision-makers. Visualisation of simulation outcomes is a non-trivial problem because the more abstract scientific visualisation techniques favoured by specialists for data exploration and hypothesis-testing are not always as successful at engaging decision-makers and planners. In this paper, we show how the risk of simulation model outcomes becoming disconnected from more realistic visualisations of model outcomes can be minimised by using the Coastal Modelling Environment (CoastalME). CoastalME is a modelling framework for coastal mesoscale morphological modelling that can achieve close linkages between the scientific model abstractions, in the form of lines, areas and volumes, and the 3D representation of topographic and bathymetric surfaces and shallow sub-surface sediment composition. We propose and illustrate through the study case of Happisburgh (eastern England, UK), a transparent methodology to merge the required variety of data types and formats into a 3D-thickness model that is used to initialise a simulation. We conclude by highlighting some of the barriers to the adoption of the methodology proposed.

Effects of Wave Orbital Velocity Parameterization on Nearshore Sediment Transport and Decadal Morphodynamics

Nearshore morphological modelling is challenging due to complex feedback betweenhydrodynamics, sediment transport and morphology bridging scales from seconds to years.Such modelling is, however, needed to assess long-term effects of changing climates on coastalenvironments, for example. Due to computational efficiency, the sediment transport driven bycurrents and waves often requires a parameterization of wave orbital velocities. A frequently usedparameterization of skewness-only was found to overfeed the coast unrealistically on a timescale ofyears—decades. To improve this, we implemented a recently developed parameterization accountingfor skewness and asymmetry in a morphodynamic model (Delft3D). The objective was to compare theeffects of parameterizations on long-term coastal morphodynamics. We performed simulations withdefault and calibrated sediment transport settings, for idealized coastlines, and compared the resultswith measured data from analogue natural systems. The skewness-asymmetry parameterization wasfound to predict overall stable coastlines within the measured envelope with wave-related calibrationfactors within a factor of 2. In contrast, the original parameterization required stronger calibration,which further affected the alongshore transport rates, and yet predicted erosion in deeper areas andunrealistic accretion near the shoreline. The skewness-asymmetry parameterization opens up thepossibility of more realistic long-term morphological modelling of complex coastal systems.

A Biscriptual Morphological Transducer for Crimean Tatar

This paper describes a weighted finite-state morphological transducer for Crimean Tatar able to analyse and generate in both Latin and Cyrillic orthographies. This transducer was developed by a team including a community member and language expert, a field linguist who works with the community, a Turkologist with computational linguistics expertise, and an experienced computational linguist with Turkic expertise. Dealing with two orthographic systems in the same transducer is challenging as they employ different strategies to deal with the spelling of loan words and encode the full range of the language's phonemes and their interaction. We develop the core transducer using the Latin orthography and then design a separate transliteration transducer to map the surface forms to Cyrillic. To help control the non-determinism in the orthographic mapping, we use weights to prioritise forms seen in the corpus. We perform an evaluation of all components of the system, finding an accuracy above 90% for morphological analysis and near 90% for orthographic conversion. This comprises the state of the art for Crimean Tatar morphological modelling, and, to our knowledge, is the first biscriptual single morphological transducer for any language.