Coastal Sensitivity/Vulnerability Characterization and Adaptation Strategies: A Review

Coastal area constitutes a vulnerable environment and requires special attention to preserve ecosystems and human activities therein. To this aim, many studies have been devoted both in past and recent years to analyzing the main factors affecting coastal vulnerability and susceptibility. Among the most used approaches, the Coastal Vulnerability Index (CVI) accounts for all relevant variables that characterize the coastal environment dealing with: (i) forcing actions (waves, tidal range, sea-level rise, etc.), (ii) morphological characteristics (geomorphology, foreshore slope, dune features, etc.), (iii) socio-economic, ecological and cultural aspects (tourism activities, natural habitats, etc.). Each variable is evaluated at each portion of the investigated coast, and associated with a vulnerability level which usually ranges from 1 (very low vulnerability), to 5 (very high vulnerability). Following a susceptibility/vulnerability analysis of a coastal stretch, specific strategies must be chosen and implemented to favor coastal resilience and adaptation, spanning from hard solutions (e.g., groins, breakwaters, etc.) to soft solutions (e.g., beach and dune nourishment projects), to the relocation option and the establishment of accommodation strategies (e.g., emergency preparedness)

Interaction between breaking-induced vortices and near-bed structures. Part 1. Experimental and theoretical investigation

The present work describes the vortex–vortex interactions observed during laboratory experiments, where a single regular water wave is allowed to travel over a discontinuous rigid bed promoting the generation of both near-bed and surface vortices. While near-bed vortices are generated by the flow separation occurring at the bed discontinuity, surface vortices are induced by the wave breaking in conjunction with a breaking-induced jet. A ‘backward breaking’ (previously observed in the case of solitary waves) occurs at the air–water interface downstream of the discontinuity and generates a surface anticlockwise vortex that interacts with the near-bed clockwise vortex. With the vortex–vortex interaction influenced by many physical mechanisms, a point-vortex model, by which vortices evolve under both self-advection (in relation to both free surface and seabed) and mutual interaction, has been implemented to separately investigate the vortex- and wave-induced dynamics. The available data indicate that both self-advection and mutual interaction are the governing mechanisms for the downward motion of the surface vortex, with the effect of the breaking-induced jet being negligible. The same two mechanisms, combined with the mean flow, are responsible for the almost horizontal and oscillating path of the near-bed vortex. The investigation of the vortex paths allow us to group the performed tests into three distinct classes, each characterized by a specific range of wave nonlinearity. The time evolution of the main variables characterizing the vortices (e.g. circulation, kinetic energy, enstrophy, radius) and their maximum values increase with the wave nonlinearity, such dependences being described by synthetic best-fit formulas

Wave-Forced Dynamics at Microtidal River Mouths

Microtidal river mouths are dynamic environments that evolve as a consequence of many forcing actions. Under the hydrodynamic viewpoint, river currents, sea waves and tides strongly interact, and their interplay determines specific sediment transport and morphological patterns. Beyond literature evidence, information comes from field observations made at the Misa River study site, a microtidal river along the Adriatic Sea (Italy), object of a long-going monitoring. The river runs for 48 km in a watershed of 383 km2, providing a discharge of about 400 m3/s for return periods of 100 years. The overall hydrodynamics, sediment transport and morphological evolution at the estuary are analyzed with particular attention to specific issues like: the generation of vortical flows at the river mouth, the influence of various wave modes (infragravity to tidal) propagating upriver, the role of sediment flocculation, the generation and evolution of bed features (river-mouth bars and longitudinal nearshore bars). Numerical simulations are also used to clarify specific mechanisms of interest

Numerical Hydro-morphodinamic 2DH model for the shallow waters

Nella presente tesi viene descritto un solutore numerico idro-morfodinamico, quale contributo innovativo nello studio e previsione dei flussi sotto-costa e delle variazioni di fondale indotte da onde e correnti. Il modello include un robusto solutore idrodinamico per l'integrazione delle Non-Linear Shallow Water Equations (NSWE) ed un solutore piuttosto flessibile per la risoluzione dell'equazione di Exner (utilizzato per valutare l'evoluzione morfologica del fondale marino). L’accoppiamento delle NSWE con l’equazione di Exner e l'aggiornamento della soluzione vengono effettuati mediante uno schema di splitting sequenziale. Il modello è stato validato mediante la riproduzione sia di test numerici/analitici, presenti nella letteratura degli ultimi anni, sia delle esperienze di laboratorio eseguite nel Laboratorio di Idraulica dell’Università Politecnica delle Marche (AN). La simulazione delle soluzioni teoriche esistenti ha portato a risultati coerenti sia per quanto riguarda l'idrodinamica sia la morfodinamica, soprattutto nella previsione dell’evoluzione dei fondali marini dovuta al trasporto solido al fondo o a quello in sospensione, in seguito a eventi di dam-break e di swash. Il confronto tra risultati numerici del solutore e dati sperimentali è parzialmente soddisfacente. Infatti, il solutore riproduce abbastanza bene le caratteristiche principali del fondo in presenza di onde spettrali, ma fallisce quando vengono riprodotte onde regolari, a causa di “effetti di laboratorio”, verificatisi in canaletta

L’influenza delle opere sommerse nella morfodinamica costiera: uno studio numerico

Negli ultimi anni, le mareggiate risultano avere un impatto sempre più importante sull’economia dei litorali, incidendo pesantemente anche sul mantenimento delle strutture ricettive/turistiche, specialmente se hanno luogo nel periodo estivo. La progettazione delle tradizionali opere di difesa della costa risulta determinante nella protezione di tali strutture. Per questo motivo sono state effettuate alcune simulazioni mediante un solutore numerico idro-morfodinamico che risolve le equazioni delle acque basse e l’equazione di Exner. Sono stati realizzati test numerici con lo scopo di valutare i) l’effetto di mareggiate reali con diverse caratteristiche spettrali e ii) l’influenza della distanza da riva di una coppia di scogliere sommerse sulla morfologia della spiaggia. I risultati delle simulazioni hanno evidenziato una variazione minima nelle forme di erosione/accrescimento al variare delle caratteristiche spettrali delle mareggiate. La morfodinamica che si realizza intorno alle scogliere e nel varco è invece fortemente influenzata dalla posizione delle opere: le variazioni del fondale sono tanto maggiori, quanto più lontane sono le opere da terra. La zona di battigia, invece, è poco influenzata dalla distanza da riva delle scogliere

A wave-by-wave analysis for the evaluation of the breaking-wave celerity

none2noThe paper gives an overall description of the breaking-wave celerity on the basis of a wave-by-wave analysis that has been performed by using field data collected during the ECORS Project (Truc Vert Beach, France, 2008). Data coming from two pressure sensors have been analyzed with the aim to correlate, after a zero-crossing analysis, each wave of both signals. The method is based on a first correlation between 10 ' time windows of both signals and, then, on the individuation of the correct time lag for each wave. Such data, which reveals a quasi-gaussian behavior of the breaking wave celerity, have also been used to relate the wave celerity with suitable wave characteristics, and comparisons are made with the most common formulas that can be found in the literature. The wave-by-wave method, validated by means of suitable laboratory test data, gives good results in the evaluation of the celerity, especially when it is made to depend on both a velocity scale and the wave non-linearity parameter. Further, a comparison with literature models used for the prediction of breaking wave celerity suggests good performances of both solitary-wave (correlation coefficient R-2 = 0.79) and shock-wave (R-2 = 0.71) theories, that give results well matched to the field data.Postacchini M.; Brocchini M.Postacchini, Matteo; Brocchini, Maurizi

Scour depth under pipelines placed on weakly cohesive soils

We here study the scouring processes that evolve around a submarine pipeline placed on a weakly cohesive seabed. We first analyze some laboratory tests carried out by Vijaya Kumar et al. [21], Xu et al. [25] and Zhou et al. [28] that focused on the scouring around a horizontal cylinder lying on a cohesive bed, subject to waves and currents. The specific purpose is that of finding a new formula for the prediction of the equilibrium scour depth under submarine pipelines. After a theoretical analysis of the main parameters, the sought formula has been found to be a function of: (i) the hydrodynamic forces acting on the cylinder (through the Keulegan-Carpenter parameter KC), (ii) the clay content of the soil C-c, and (iii) the burial depth eo ID. In the presence of small amounts of clay (C-c< 5%), the scour depth depends directly on KC (as confirmed by many literature works for pipelines lying on sandy soils, e.g.[18]) and inversely on C-c (as already seen for bridge abutments on cohesive soils, e.g. [1]), the best-fit law being characterized by a coefficient of determination R-2 = 0.62. If some burial depth is accounted for, this being a novelty of the present work, a more general formulation can be used, valid in the presence of weakly-cohesive soils and with burial depths of the pipe smaller than 0.5 (R-2 = 0.79). For large clay-content ranges (2% <C-c < 75 %), the scour depth depends directly on both KC and C-c, this giving R-2 = 0.79 (no burial depth) and 0.91 (some burial depth). However, this finding is at odds with the main literature, because, for large amounts of clay, it is fundamental to consider the liquidity index LI, which accounts for some important clay properties, like the plasticity. We argue that the absence of LI is balanced by the direct dependence of the scour depth on C-c. Notwithstanding the small number of available data, a formula for the prediction of the scour depth under pipelines lying on cohesive soils is fundamental for several engineering applications. The present contribution represents the first attempt to build such a formula, when the pipeline is subject to the wave-current forcing and the seabed is characterized by a relatively small clay content. (C) 2015 Elsevier Ltd. All rights reserved

Dynamics of the Coastal Zone

The coastal zone hosts many human activities and interests, which have significantly increased in the last few decades [...

Fluid-Structure Interaction of a Partially Submerged Body: an Analytical Model for the Human Stability in Floodwaters

Climate change is increasing the number of extreme events, like floods or long-lasting rainfalls, in densely inhabited area, this focusing the attention on the safety of human being in flooded urban areas. The stability of people subjected to floodwaters is an important aspect to evaluate people’s safety. To this aim, many theoretical and experimental works analyze human stability using simplified and conservative approaches, although the role of body articulation and posture on human stability in floodwaters is relevant. We here propose simple analytical models to evaluate the effect of flood impact on a human body with different postures, composed by a two-dimensional frame of three beams, which represent different parts of the human body with variable orientation. The body stability is described by means of a dynamic equilibrium of the system, which accounts for a tilting moment generated by the toppling mechanism induced by floodwater conditions, and a resisting moment that changes with the body posture and the inertial characteristics of each beam. The model results are compared with recent laboratory experiments, where a human body at a quasi-natural scale was reproduced and subjected to several floodwater scenarios. Results show how the posture of the human body can provide a significant contribution to the stabilizing moment in the case of backward toppling