Biotic and abiotic factors governing dune response to storm events

Garzon, Juan L.; Costas, Susana; Ferreira, Oscar

http://hdl.handle.net/10400.1/17614

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Authors

Garzon, Juan L.

Costas, Susana

Ferreira, Oscar

Abstract(s)

The alongshore response of dunes to storm events can be extremely variable and,consequently, their capacity to maintain their services, including the protection ofhinterland communities. In this study, the role of biotic and abiotic factors determin-ing the magnitude of dune retreat driven by a severe storm along a 60 km barrierisland system was investigated. Data from high-resolution satellite imagery, digitalterrain models, and wave propagation models were used in this assessment. Theassessed abiotic factors included the backshore volume, dune height, downdrift inletdistance, and incident wave power. The evaluated biotic factor was the vegetationcover, characterized by a vegetation index retrieved from the multispectral imagery.The results revealed large alongshore variability on dune retreat, ranging from negli-gible impact to ca. 40 m of retreat. All combined factors allowed us to explain up to70% of the dune retreat variability through a multi-regression analysis. Among allinvestigated factors, the major contributor controlling the magnitude of dune retreatwas the backshore volume (more robust berms reduced the retreat) followed by thewave power (normal and longitudinal components). Moreover, the removal of localsalient features in the dune line caused the straightening of the coastline, highly con-tributing to the development of dune retreat hotspots. The other evaluated factorshad a smaller influence on reducing coastal retreat, including the vegetation, whosecontribution to dune protection was around one order of magnitude lower than thatprovided by the backshore volume. The results highlight the importance of regionalassessments to understand the causes behind the large alongshore variability ofstorm impacts at dunes. They also state the relatively low influence of the vegetationfrom this climatic region to enhance dune resistance to storms.