ABSTRACT

Rollnic, M. and Medeiros, C., 2016. Equilibrium Beach Profile in the Presence of Beachrocks In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 452–456. Coconut Creek (Florida), ISSN 0749-0208.

Equilibrium Beach Profile (EBP) models are used to estimate sandy beach profiles, they assume the existence of a shoreface shape that represents an equilibrium condition between wave climate and sediments, making it possible to identify erosion/accretion trends. EBP models suit beaches with near homogeneous grain size sediments. However, in subtropical and tropical areas, beachrocks are often found underlying the beach face, such that EBP models may not be suitable as shadowing areas may favour settling of variable grain size sediments. Our goal was to evaluate the Bruun-Dean EBP model for a beach along which beachrocks were at times absent and at times present as onshore or submerged reefs. Eight 1km-long bathymetric profiles were performed from the surf zone to the 10m isobath and sediment samples obtained at 50, 100, 200, 500 and 1000 m from the surf zone. EBP was computed for distinct coefficient (m) values and evaluated as a function of resulting summed square error. A closure depth of 3.97 m was computed using wave characteristics were derived from 1 year radar records. Along the study area the 3.97 m isobath is positioned 140 to 400m offshore, disregarding the quotas of the beachrocks. At the control areas where beachrocks were absent, m=0.67 yielded the best fit. At areas where beachrocks were present, profiles tended to be steeper and m=0.77 results in a better adjustment near the shore. For the more seaward portion of the profiles, the incorporation of a parameter related to the reef high could improve fitting.

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