Study of shelly shore ridge formation using wave flume experiments: Morphological evolution and depositional patterns

• Published in: Geomorphology (Amsterdam, Netherlands) Netherlands), 2021-11, Vol.392, p.107926, Article 107926
• Main Authors: Fick, Cristiano, Puhl, Eduardo, Toldo-Junior, Elírio E., Pereira, Leonardo M., Oliveira, Vinicius C.B., Cruz, Francisco E.G.
• Format: Article
• Language: English
• Subjects: Beach processes; Bioclastic beach; Equilibrium beach profile; Laboratory experiments; Shell organization
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2021.107926

Coarse shore/berm ridges comprising mollusk shells are peculiar morphological features occurring in some beaches globally, generally wave-built, generated during storms and high tides. Studies regarding the formation of these shelly shore ridges using wave flume experiments (physical modeling) do not provide a detailed analysis of their morphological evolution and depositional features. A bioclastic beach profile with a constant dip, formed by mollusk shells (whole and fragmented ones, DSV-50 = 4.5 mm) of bivalves and gastropods, was subjected to a storm wave condition simulated in a two-dimensional flume with a scale reduction factor of 1/20. A decimeter-scale shelly shore ridge was successfully formed by swash bar emergence. The seaward surface was steeper than the landward slope. The bar was progressively built by swash currents that accumulated shells along the shoreline. According to Dean's function, the equilibrium beach profile displays a good fit for coefficient A, as related to the settling velocity of the bioclasts. The power of m is lesser in the equilibrium beach than that in beaches composed of siliciclastic sand. Three patterns of shell organization and pore framework represent the back, top, and frontal sectors of the ridge. The ridge front includes poorly organized shell particles of dense packing. The crest comprises bioclast beds of uniformly obliquely oriented, densely packed particles. Back ridge sediments exhibit loosely packed moderate shell organization. The morphological evolution of the bioclastic ridge formed in the flume closely resembled bioclastic beach sediments. The depositional pattern in the flume ridge was directly related to the energy of breaking waves and associated swash-current energy. •Shelly shore ridge formation from the swash bar accretion under action of storm waves•Parameters of the equilibrium profile for a bioclastic beach•Shell organization is controlled by the intensity of the swash and wave breaking processes.