This PhD thesis combines geomorphological and sedimentological analysis (i.e. drone surveys, sediment traps, sediment coring, historical orthophotos) with a multi-disciplinary approach to study the evolution of young tidal flats located worldwide, which origin was caused by human intervention, specifically due to the breach of a dyke or a channel excavation that has connected the sediment supplier with an intertidal area that was not a tidal flat. Three study sites were chosen based on their environmental characteristics and the tidal range: i) the tidal flat of the Barbamarco lagoon, located in the Po River Delta (microtidal) in Italy, ii) the artificial tidal flat of Perkpolder (macrotidal) located in the Scheldt Estuary in The Netherland, and iii) the management realignment of Converse (ultratidal) located in the Bay of Fundy in Canada. The analyses were improved by fieldwork carried out in the accidental marsh of Halfway River, and the marsh of Eldriken, which are other tidal flats located in the Bay of Fundy. The study aims to define the sedimentological evolution of different human-induced tidal flats, to discuss the processes that have led to their present conditions, and to understand whether and how the transition from flat to marsh will occur, defining which factors should be considered for future restorations. The first part of the PhD focused on fieldwork activities carried out on the tidal flat of the Barbamarco lagoon in the Po Delta (Italy). Several UAV (Unmanned Aerial Vehicle) surveys were performed between October 2018 and October 2020 and a collection of DSMs (Digital Surface Model) were processed. The granulometric distribution was achieved through core sampling and the rates of deposition were obtained using an innovative structure for Petri dish sediment traps that were built with a 3D printer. A historical review was accomplished using orthophotos acquired from the IGM (Istituto Geografico Militare Italiano) and the Veneto Region archives, from the 1950s until nowadays. Between fieldwork and data processing, the tidal flat of Perkpolder (The Netherland) was investigated using a dataset of Lidar provided by Rijkswaterstaat (Dutch Ministry of Infrastructure and the Environment) and rates of deposition that were obtained by the author during the master thesis (2017-2018). General knowledge regarding salt marshes and data processing were improved during a short period at the University of Cadice (Spain) (second year of the PhD). During the last year of the PhD, a period of three months at Saint Mary’s University in Halifax (Nova Scotia, Canada) allowed investigating the evolution of the restoration site of Converse (Bay of Fundy). However, in this thesis, the results concern sediment deposition, particle size analysis, and water level variations. In addition, further analyses of sediment deposition were carried out in two different sites from the southern basin of the Bay of Fundy between 12 – 13 August 2021: Halfway River and Eldriken. The combination of the results from all study sites, which is discussed in the final part of the thesis, enhanced how artificial morphologies led to morphodynamic instability that alter the rates of deposition and, consequently, future insights. The strong erosion of the inlets and the strong accretion inside the tidal flats suggest that a cannibalization process might be ongoing, causing an increase in the rates of vertical variations for the short-term evolution. The analysis showed how vegetation growth is strongly linked to elevation with respect to the MHT (Mean High Tide) and the sediment supplier. Salt marsh restoration can be a quick process (i.e. few years) but it can take longer periods (i.e. decades). Future management realignments of coastal wetlands should consider how the design affects the future evolution of the morphology of artificial tidal flats with respect to the MHT as a preliminary evaluation to predict the waiting time for salt marsh development.

Negli ultimi decenni, la concezione di difesa costiera è profondamente cambiata e, come risultato, lo è anche il nostro approccio all’ambiente costiero. Nuove strategie di “riallineamento” si stanno esplorando e soluzioni “natural-based” sono preferibili alle tradizionali opere rigide, come argini, difese parallele e pennelli. La presente tesi di dottorato fonde analisi geomorfologiche e sedimentologiche (ad es. rilievo con drone, trappole per sedimento, carotaggi e studio di ortofoto storiche) con approcci multidisciplinari per studiare l’evoluzione di giovani piane tidali, localizzate in diverse parti del mondo, la cui origine è legata ad interventi umani, nello specifico, a causa della rottura di un argine o dello scavo di un canale che ha connesso il meccanismo di trasporto sedimentario principale con una zona intertidale che non era una piana tidale. Sono stati scelti tre casi studio in base alle loro caratteristiche ambientali e l’intervallo tidale: i) la piana tidale della laguna di Barbamarco, situata nel Delta del Po (microtidale), in Italia; ii) il progetto Perkpolder (macrotidale), localizzato nell’estuario dello Scheldt nei Paesi Bassi; e iii) a Converse (ultratidale), situato nella baia di Fundy in Canada. Le analisi sono state implementate da attività di campo effettuate nelle paludi salate (o barene) di Halfway River e Eldriken (Baia di Fundy, Canada). Lo scopo di questo studio è di comprendere l’evoluzione sedimentaria delle giovani piane tidali nate da interventi umani, discutere dei processi che hanno portato alle condizioni attuali, e comprendere se e come avverrà la transizione da piana tidale a palude salata, identificando i fattori che dovrebbero essere considerati nei progetti futuri. I risultati ottenuti da tutti i casi studio, discussi nella parte finale della tesi, hanno messo in evidenza come morfologie artificiali portano ad una instabilità morfologica che altera i tassi di deposizione e conseguentemente future previsioni. La forte erosione localizzata nelle bocche e i forti tassi di accrezione riscontrati nella piana tidale suggeriscono che potrebbe essere in corso un processo di cannibalizzazione che aumenta i tassi di variazione verticale nell’evoluzione a breve termine. Le analisi hanno messo in evidenza come la crescita della vegetazione è fortemente legata all’ elevazione della superficie rispetto al MHT (Mean High Tide) e il fornitore di sedimento. La restaurazione di paludi salate può essere un processo veloce (ad es. pochi anni) ma può necessitare di periodo più lungo (ad es. decenni). Future strategie di “riallineamento” relative alle zone umide dovrebbero considerare come il design influenza l’evoluzione della morfologia per poter dare una valutazione preliminare e predire i tempi di attesa prima dello sviluppo della palude salata.

Evolution of restoration projects of coastal wetlands: from tidal flat to salt marsh

BRUNETTA, RICCARDO
2022

Abstract

This PhD thesis combines geomorphological and sedimentological analysis (i.e. drone surveys, sediment traps, sediment coring, historical orthophotos) with a multi-disciplinary approach to study the evolution of young tidal flats located worldwide, which origin was caused by human intervention, specifically due to the breach of a dyke or a channel excavation that has connected the sediment supplier with an intertidal area that was not a tidal flat. Three study sites were chosen based on their environmental characteristics and the tidal range: i) the tidal flat of the Barbamarco lagoon, located in the Po River Delta (microtidal) in Italy, ii) the artificial tidal flat of Perkpolder (macrotidal) located in the Scheldt Estuary in The Netherland, and iii) the management realignment of Converse (ultratidal) located in the Bay of Fundy in Canada. The analyses were improved by fieldwork carried out in the accidental marsh of Halfway River, and the marsh of Eldriken, which are other tidal flats located in the Bay of Fundy. The study aims to define the sedimentological evolution of different human-induced tidal flats, to discuss the processes that have led to their present conditions, and to understand whether and how the transition from flat to marsh will occur, defining which factors should be considered for future restorations. The first part of the PhD focused on fieldwork activities carried out on the tidal flat of the Barbamarco lagoon in the Po Delta (Italy). Several UAV (Unmanned Aerial Vehicle) surveys were performed between October 2018 and October 2020 and a collection of DSMs (Digital Surface Model) were processed. The granulometric distribution was achieved through core sampling and the rates of deposition were obtained using an innovative structure for Petri dish sediment traps that were built with a 3D printer. A historical review was accomplished using orthophotos acquired from the IGM (Istituto Geografico Militare Italiano) and the Veneto Region archives, from the 1950s until nowadays. Between fieldwork and data processing, the tidal flat of Perkpolder (The Netherland) was investigated using a dataset of Lidar provided by Rijkswaterstaat (Dutch Ministry of Infrastructure and the Environment) and rates of deposition that were obtained by the author during the master thesis (2017-2018). General knowledge regarding salt marshes and data processing were improved during a short period at the University of Cadice (Spain) (second year of the PhD). During the last year of the PhD, a period of three months at Saint Mary’s University in Halifax (Nova Scotia, Canada) allowed investigating the evolution of the restoration site of Converse (Bay of Fundy). However, in this thesis, the results concern sediment deposition, particle size analysis, and water level variations. In addition, further analyses of sediment deposition were carried out in two different sites from the southern basin of the Bay of Fundy between 12 – 13 August 2021: Halfway River and Eldriken. The combination of the results from all study sites, which is discussed in the final part of the thesis, enhanced how artificial morphologies led to morphodynamic instability that alter the rates of deposition and, consequently, future insights. The strong erosion of the inlets and the strong accretion inside the tidal flats suggest that a cannibalization process might be ongoing, causing an increase in the rates of vertical variations for the short-term evolution. The analysis showed how vegetation growth is strongly linked to elevation with respect to the MHT (Mean High Tide) and the sediment supplier. Salt marsh restoration can be a quick process (i.e. few years) but it can take longer periods (i.e. decades). Future management realignments of coastal wetlands should consider how the design affects the future evolution of the morphology of artificial tidal flats with respect to the MHT as a preliminary evaluation to predict the waiting time for salt marsh development.
CIAVOLA, Paolo
File in questo prodotto:
File Dimensione Formato  
Riccardo_Brunetta_PhD_Thesis.pdf

Open Access dal 01/07/2023

Descrizione: Riccardo_Brunetta_PhD_Thesis
Tipologia: Tesi di dottorato
Dimensione 22.89 MB
Formato Adobe PDF
22.89 MB Adobe PDF Visualizza/Apri

I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2496485
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact