Historically flow restricted tidal marshes creek: flooding risks with potential tidal flow restoration and long-term impacts on salt marsh vegetation species
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Byrne, Bertrand.
Historically flow restricted tidal marshes creek: flooding risks with potential tidal flow restoration and long-term impacts on salt marsh vegetation species. Retrieved from
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TitleHistorically flow restricted tidal marshes creek: flooding risks with potential tidal flow restoration and long-term impacts on salt marsh vegetation species
Date Created2023
Other Date2023-01 (degree)
Extent98 pages : illustrations
DescriptionSalt marshes are important ecosystems that contribute economic and ecological services value to society by providing habitat for seafood gestation, storm surge attenuation, carbon sequestration, water quality enhancement, etc. Notwithstanding these societal benefits, many salt marshes today are under anthropological threat from pollution, encroaching human development activities, reduced access to tidal sources of required nutrient and sediment replenishment, etc. Salt marsh impacting tidal flow restrictions are common in parts of the United States, for example according to the United States Environmental Protection Agency (EPA), there were an estimated 1764 or 1.5 tidal flow restrictions per kilometer along the Atlantic Coast States between Virginia and Maine, impacting approximately 70,450 59 or 59 acres per kilometer of salt marsh in 2017.
Removal of tidal flow restrictions with resulting restoration of tidal flow may increase flooding risk to developments located within the pre-flow-restriction waterways’ floodplains. Further, the ecological impact of flow restrictions on salt marsh vegetation should also be determined when flow restoration is contemplated since salt marshes can potentially adapt to the changed conditions imposed by flow restrictions over time.
This dissertation investigates the impact on salt marshes vegetation species when access to tidal nutrient, sediment replenishment, etc. is reduced due to tidal flow restrictions and the flooding risk impact associated with the removal of tidal flow restrictions and the restoration of tidal flow. Specifically, the flooding risk on the Tremley Community in Linden, New Jersey was investigated, for the hypothetical scenario of fully restored tidal flow at adjacent Marshes Creek.
Hydrologic/hydraulic modeling of Marshes Creek was used to simulate the peak water surface elevations (WSELs) generated under existing restricted and proposed fully unrestricted conveyance conditions for the dry weather scenario [spring tide only] and several increasingly wet weather scenarios each combined with spring tide. Modeling results indicated that simulated peak WSELs generated by the fully unrestricted proposed conveyance option versus the existing restricted option were (1) higher under spring tide-only, dry weather conditions (2) increased at a slower rate under spring tide plus increasingly wet conditions (3) equal under spring tide plus wet conditions at a threshold rainfall depth (4) lower under spring tide plus increasingly wet conditions for rainfall exceeding the threshold depth.
It is intuitive to conclude that if the simulated common WSEL generated by both existing restricted and proposed full unrestricted conveyance options is lower than the adjacent minimum grade elevation, then full tidal flow restoration reduces flooding risk. Alternatively, if the simulated common WSEL was higher than the adjacent minimum grade elevation, then full tidal flow restoration will increase flooding risk. A simple procedure based on this conclusion is provided, that identifies the optimal level of flow restoration and threshold rainfall depth combined with spring tide, allowed at a tidal flow restricted waterway without increased flooding risk to adjacent communities.
Severe tidal flow restrictions often diminish the tidal range upstream of flow restrictions with potential impacts on upstream inundation and vegetation species compositions. Accordingly, the relationship between tidal inundation duration, peak and salt marsh vegetation species presence, richness and average coverage was also studies in the Marshes Creek’s salt marsh. hydraulic/hydrologic modeling was used to quantify salt marsh surface inundation durations at two hundred and sixty-four vegetation sampling transects and a vegetation survey was performed to determine species richness, presence, and average coverage. The results of the tidal inundation and vegetation species analyses indicated that for the tidal-flow unrestricted transects: (1) Vegetation characteristics were similar at transects with similar inundation, (2) Native species presence is highest in the 1-130 hours/year inundation range, (3) Many more transects were present 58-130 hours/year inundation range[42.3% to 5.9%], (3) The non-native species Phragmites australis is present in all inundation ranges, and (5) In inundation ranges that favor native species, non-native species presence is limited. Since the optimal local inundation range for native high/mid marsh species is 1-130 hours/year, restoration of the subsided upstream marsh to elevations related to the optimal inundation is recommended.
Given the current and imminent social, cultural, and economic challenges facing coastal communities, it is important not only to understand how anthropogenic action in the past has contributed to these challenges today, but also to ensure planned mitigation to reverse the impacts of these actions are successful. Accordingly, this research focused on both the flooding impact of restoring tidal flow combined with rainfall runoff and on the long-term ecological impact of flow restriction on salt marsh vegetation. This study seeks to add to the body of work aimed at restoring the economic and social service value that is rendered to society by viable, functioning salt marshes in locations where that value has been diminished or lost due to anthropogenic actions.
NotePh.D.
NoteIncludes bibliographical references
Genretheses
LanguageEnglish
CollectionSchool of Graduate Studies Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.
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