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Relative sea-level (RSL) rise associated with decreased fluvial sediment discharge and increased hurricane activity have contributed to the high rate of shoreline retreat and threatened coastal ecosystems in Port Fourchon, Louisiana, USA. This study, based on QuickBird/drone images (2004–2019) and LIDAR data (1998–2013), analyzed the impacts of shoreline dynamics on mangroves (Avicennia germinans) and marshes before and after the initiation of a beach nourishment project in 2013. The coastal barrier and dune crest migrated landward between 1998 and 2013. Meanwhile, the dune crest height increased between 1998 and 2001, then decreased in 2013, probably due to hurricane impacts. The total sediment volume along this sandy coastal barrier presented an overall trend of decline in the 1998–2013 period, resulting in a wetlands loss of ~15.6 ha along 4 km of coastline. This has led to a landward sand migration onto muddy tidal flats occupied by Avicennia germinans (1.08 ha) and Spartina (14.52 ha). However, the beach nourishment project resulted in the advancement of the beach barrier from Nov/2012 to Jan/2015, followed by a relatively stable period between Jan/2015 and Mar/2019. Additionally, both the dune crest height and sediment volume increased between 2013 and 2019. This set of factors favored the establishment and expansion of mangroves (3.2 ha) and saltmarshes (25.4 ha) along the backbarrier environments after 2013, allowing the tidal flats to keep pace with the RSL rise. However, waves and currents caused shoreline erosion following the beach nourishment project between Oct/2017 and Nov/2019, threatening wetlands by resuming the long-term process of shoreline retreat.
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SHORELINE DYNAMICS ON A HIGH ENERGY BEACH ASSOCIATED WITH RELATIVE SEA-LEVEL FALL ON THE PACIFIC COAST, USA
In this study progradation of the dune toe on the sandy, dune-backed beaches of Makah Bay, on the Pacific Ocean shorelines of the reservation lands of the Makah Tribe, were documented for the first time. A shoreline assessment was implemented that included repeat beach profile surveys using RTK-DGPS and aerial lidar, and historical change analysis using aerial photos. Analysis of GNSS and aerial lidar suggest patterns of dune toe progradation over the last decade at average rates of ~0.8 m/yr between 2010 and 2022 over almost all the 5.5 km length of beach in Makah Bay, excepting the ~250m long erosional area that prompted the study. A beach vegetation line delineated in aerial photos collected between 1952 and 2019 moved seaward at average rates of ~0.7 m/yr across the entire length of Makah Bay, suggesting that the pattern of progradation is long-lived. We assess evidence to evaluate whether this pattern of dune progradation can be explained by sediment supplies from watersheds draining to Makah Bay and conclude that local sediment supply cannot explain observed patterns. A variety of shoreline processes associated with relative sea-level fall are discussed and may explain the observed rates of shoreline progradation.
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- Award ID(s):
- 2103713
- PAR ID:
- 10579288
- Publisher / Repository:
- WORLD SCIENTIFIC
- Date Published:
- ISBN:
- 978-981-12-7989-8
- Page Range / eLocation ID:
- 364 to 378
- Format(s):
- Medium: X
- Location:
- New Orleans, LA, USA
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1142/9789811275135_0034
