Decadal wave attenuating capacity of foreshores under extreme wave conditions

    Research output: Contribution to conferenceAbstract

    Abstract

    Living near estuaries comes with flood risks from riverine and coastal sources, nevertheless the population density is high and still growing. The population and assets are generally protected by conventional coastal measures, which are challenged by increased storm intensity and sea level rise (SLR). However, those solutions are static and do not adapt to a changing climate. Foreshores, consisting of a tidal flat and salt marsh can serve as add-on to conventional coastal protection. Such a hybrid solution is more sustainable, in that the salt marsh part can cope, to a certain extent, with SLR. Previous studies proved the wave attenuating capacity of foreshores. However, all studies focused on the relative small scale only; i.e. some isolated foreshores in space and at most up to several years in time. The key question addressed in this study is: to what extent can foreshores safely act as additional coastal protection over a decadal time scale?

    A unique bathymetrical dataset was analyzed, covering the whole of the Westerschelde estuary (The Netherlands) over a period of 65 years. A total of 36 transects (aligned with the dominant wind direction) were constructed over a selection of six foreshores. The wave attenuating capacity of the foreshores was assessed under daily conditions both with and without vegetation and under extreme conditions (i.e. events statistically occurring once every 10.000 years), using the numerical model SWAN (Simulating WAves Nearshore).
    By assessing the wave attenuating capacity over the evolving bathymetry over a period of 65 years, it was found that foreshores always contribute to wave attenuation. Under extreme conditions, foreshores sheltered from the prevailing wind direction were more efficient in wave attenuation (i.e. decrease of wave height per meter foreshore), than foreshores located at the exposed shores. Moreover, at all foreshores, the bare tidal flat caused a baseline wave attenuation, while a linear relation was observed between the width of the salt marsh and the wave attenuation; The longer the vegetated marsh, the larger the wave attenuation. Nevertheless, the relation was different per foreshore. The relation found, provides the knowledge needed to calculate the minimum width of the salt marsh to provide the desired wave attenuation under extreme conditions.
    Original languageEnglish
    Publication statusPublished - 2019
    EventAGU Fall Meeting 2019 - San Francisco, United States
    Duration: 9 Dec 201913 Dec 2019
    https://www.agu.org/fall-meeting

    Conference

    ConferenceAGU Fall Meeting 2019
    CountryUnited States
    CitySan Francisco
    Period9/12/1913/12/19
    Internet address

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    wave attenuation
    saltmarsh
    coastal protection
    tidal flat
    wind direction
    estuary
    wave height
    bathymetry
    marsh
    population density
    transect
    timescale
    vegetation
    climate

    Cite this

    Willemsen, P. W. J. M., Borsje, B. W., Vuik, V., Bouma, T. J., & Hulscher, S. J. M. H. (2019). Decadal wave attenuating capacity of foreshores under extreme wave conditions. Abstract from AGU Fall Meeting 2019, San Francisco, United States.
    @conference{a35af58c7ed54f77b4bf97f62153809b,
    title = "Decadal wave attenuating capacity of foreshores under extreme wave conditions",
    abstract = "Living near estuaries comes with flood risks from riverine and coastal sources, nevertheless the population density is high and still growing. The population and assets are generally protected by conventional coastal measures, which are challenged by increased storm intensity and sea level rise (SLR). However, those solutions are static and do not adapt to a changing climate. Foreshores, consisting of a tidal flat and salt marsh can serve as add-on to conventional coastal protection. Such a hybrid solution is more sustainable, in that the salt marsh part can cope, to a certain extent, with SLR. Previous studies proved the wave attenuating capacity of foreshores. However, all studies focused on the relative small scale only; i.e. some isolated foreshores in space and at most up to several years in time. The key question addressed in this study is: to what extent can foreshores safely act as additional coastal protection over a decadal time scale?A unique bathymetrical dataset was analyzed, covering the whole of the Westerschelde estuary (The Netherlands) over a period of 65 years. A total of 36 transects (aligned with the dominant wind direction) were constructed over a selection of six foreshores. The wave attenuating capacity of the foreshores was assessed under daily conditions both with and without vegetation and under extreme conditions (i.e. events statistically occurring once every 10.000 years), using the numerical model SWAN (Simulating WAves Nearshore). By assessing the wave attenuating capacity over the evolving bathymetry over a period of 65 years, it was found that foreshores always contribute to wave attenuation. Under extreme conditions, foreshores sheltered from the prevailing wind direction were more efficient in wave attenuation (i.e. decrease of wave height per meter foreshore), than foreshores located at the exposed shores. Moreover, at all foreshores, the bare tidal flat caused a baseline wave attenuation, while a linear relation was observed between the width of the salt marsh and the wave attenuation; The longer the vegetated marsh, the larger the wave attenuation. Nevertheless, the relation was different per foreshore. The relation found, provides the knowledge needed to calculate the minimum width of the salt marsh to provide the desired wave attenuation under extreme conditions.",
    author = "Willemsen, {Pim Wilhelmus Johannes Maria} and Borsje, {Bastiaan Wijnand} and Vincent Vuik and Bouma, {Tjeerd J.} and Hulscher, {Suzanne J.M.H.}",
    year = "2019",
    language = "English",
    note = "AGU Fall Meeting 2019 ; Conference date: 09-12-2019 Through 13-12-2019",
    url = "https://www.agu.org/fall-meeting",

    }

    Willemsen, PWJM, Borsje, BW, Vuik, V, Bouma, TJ & Hulscher, SJMH 2019, 'Decadal wave attenuating capacity of foreshores under extreme wave conditions' AGU Fall Meeting 2019, San Francisco, United States, 9/12/19 - 13/12/19, .

    Decadal wave attenuating capacity of foreshores under extreme wave conditions. / Willemsen, Pim Wilhelmus Johannes Maria; Borsje, Bastiaan Wijnand; Vuik, Vincent; Bouma, Tjeerd J.; Hulscher, Suzanne J.M.H.

    2019. Abstract from AGU Fall Meeting 2019, San Francisco, United States.

    Research output: Contribution to conferenceAbstract

    TY - CONF

    T1 - Decadal wave attenuating capacity of foreshores under extreme wave conditions

    AU - Willemsen, Pim Wilhelmus Johannes Maria

    AU - Borsje, Bastiaan Wijnand

    AU - Vuik, Vincent

    AU - Bouma, Tjeerd J.

    AU - Hulscher, Suzanne J.M.H.

    PY - 2019

    Y1 - 2019

    N2 - Living near estuaries comes with flood risks from riverine and coastal sources, nevertheless the population density is high and still growing. The population and assets are generally protected by conventional coastal measures, which are challenged by increased storm intensity and sea level rise (SLR). However, those solutions are static and do not adapt to a changing climate. Foreshores, consisting of a tidal flat and salt marsh can serve as add-on to conventional coastal protection. Such a hybrid solution is more sustainable, in that the salt marsh part can cope, to a certain extent, with SLR. Previous studies proved the wave attenuating capacity of foreshores. However, all studies focused on the relative small scale only; i.e. some isolated foreshores in space and at most up to several years in time. The key question addressed in this study is: to what extent can foreshores safely act as additional coastal protection over a decadal time scale?A unique bathymetrical dataset was analyzed, covering the whole of the Westerschelde estuary (The Netherlands) over a period of 65 years. A total of 36 transects (aligned with the dominant wind direction) were constructed over a selection of six foreshores. The wave attenuating capacity of the foreshores was assessed under daily conditions both with and without vegetation and under extreme conditions (i.e. events statistically occurring once every 10.000 years), using the numerical model SWAN (Simulating WAves Nearshore). By assessing the wave attenuating capacity over the evolving bathymetry over a period of 65 years, it was found that foreshores always contribute to wave attenuation. Under extreme conditions, foreshores sheltered from the prevailing wind direction were more efficient in wave attenuation (i.e. decrease of wave height per meter foreshore), than foreshores located at the exposed shores. Moreover, at all foreshores, the bare tidal flat caused a baseline wave attenuation, while a linear relation was observed between the width of the salt marsh and the wave attenuation; The longer the vegetated marsh, the larger the wave attenuation. Nevertheless, the relation was different per foreshore. The relation found, provides the knowledge needed to calculate the minimum width of the salt marsh to provide the desired wave attenuation under extreme conditions.

    AB - Living near estuaries comes with flood risks from riverine and coastal sources, nevertheless the population density is high and still growing. The population and assets are generally protected by conventional coastal measures, which are challenged by increased storm intensity and sea level rise (SLR). However, those solutions are static and do not adapt to a changing climate. Foreshores, consisting of a tidal flat and salt marsh can serve as add-on to conventional coastal protection. Such a hybrid solution is more sustainable, in that the salt marsh part can cope, to a certain extent, with SLR. Previous studies proved the wave attenuating capacity of foreshores. However, all studies focused on the relative small scale only; i.e. some isolated foreshores in space and at most up to several years in time. The key question addressed in this study is: to what extent can foreshores safely act as additional coastal protection over a decadal time scale?A unique bathymetrical dataset was analyzed, covering the whole of the Westerschelde estuary (The Netherlands) over a period of 65 years. A total of 36 transects (aligned with the dominant wind direction) were constructed over a selection of six foreshores. The wave attenuating capacity of the foreshores was assessed under daily conditions both with and without vegetation and under extreme conditions (i.e. events statistically occurring once every 10.000 years), using the numerical model SWAN (Simulating WAves Nearshore). By assessing the wave attenuating capacity over the evolving bathymetry over a period of 65 years, it was found that foreshores always contribute to wave attenuation. Under extreme conditions, foreshores sheltered from the prevailing wind direction were more efficient in wave attenuation (i.e. decrease of wave height per meter foreshore), than foreshores located at the exposed shores. Moreover, at all foreshores, the bare tidal flat caused a baseline wave attenuation, while a linear relation was observed between the width of the salt marsh and the wave attenuation; The longer the vegetated marsh, the larger the wave attenuation. Nevertheless, the relation was different per foreshore. The relation found, provides the knowledge needed to calculate the minimum width of the salt marsh to provide the desired wave attenuation under extreme conditions.

    M3 - Abstract

    ER -

    Willemsen PWJM, Borsje BW, Vuik V, Bouma TJ, Hulscher SJMH. Decadal wave attenuating capacity of foreshores under extreme wave conditions. 2019. Abstract from AGU Fall Meeting 2019, San Francisco, United States.