Discussion Application of the parabolic bay shape equation to sand and gravel beaches on Mediterranean coasts: Reply to the comments of D.E. Reeve Chiara F. Schiaffino a, ⁎, Massimo Brignone b , Marco Ferrari a a DipTeRis, University of Genoa, Corso Europa 26, 16132 Genoa, Italy b DIMA, University of Genoa, via Dodecaneso 35, 16146 Genoa, Italy abstract article info Article history: Received 23 February 2012 Accepted 1 March 2012 Available online 24 March 2012 The authors wish to focus on certain aspects which had not been discussed previously in Schiaffino et al. (2012). These aspects cover the methodology adopted to obtain the coefficients proposed for the parabolic bay shape equation and the approach adopted for the evaluation of their applicability and reliability for sand and gravel beaches. In particular, results concerning shoreline variability as regards control point and wave direction are submitted. © 2012 Elsevier B.V. All rights reserved. Discussion We would like to thank Reeve (2012) for his interest in Schiaffino et al. (2012) since his comments provided the authors with the op- portunity to highlight some interesting aspects which had not been covered in the paper. Schiaffino et al. (2012) wants to provide relevant information to extend the applicability of the parabolic bay shape equation (Hsu and Evans, 1989) to gravel beaches. The paper started from the basic premise that the parabolic bay shape equation (Hsu and Evans, 1989) yields the most reliable results for embayed beaches shoreline prediction. In particular, the object of the research was to propose equation coefficients concerning beach sediment grain size and not only wave direction. The statistic computation of sand and gravel beach coefficients showed different values and a different trend compared to those pro- posed by Hsu and Evans (1989). Furthermore, the use of the coeffi- cients proposed in Schiaffino et al. (2012) for sand and gravel beaches improved the accuracy of shoreline predictions. It was therefore assumed that embayed beaches morphology de- pends on sediment grain size, similarly to the relation between grain size itself and beach morhpodynamics and hydrodynamics pointed out in literature (Horn, 2002). This conclusion was based with the assumption that a different sediment permeability primarily influences longshore and cross-shore transport (Horn and Walton, 2007). Therefore, it was demonstrated that on sand beaches sedi- ments mostly move cross-shore, while on gravel beaches sediments are mainly moved by littoral drift (Osborne, 2005). In particular, Reeve (2012) focused his attention on uncertainties related to the definition of wave direction and control points. More- over he [1] questioned if differences in sand and gravel beaches shorelines in static equilibrium obtained with the proposed coeffi- cients are statistically significant or if they are simply due to uncer- tainty in control points identification and position; furthermore he stated that Hsu and Evans coefficients (1989) are the best available coefficients for shoreline computation on embayed beaches; [2] asked if the authors are aware of differences in submerged beach characteristics and if they have considered this aspect in the work. The authors draw on the issues raised by Reeve (2012) to clarify and to take a deeper look into some parts of the paper. [1] Shoreline detection by field survey or by image detection is sub- ject to factors of uncertainty due to subjective visual interpretation (Alesheikh et al., 2007; Boak and Turner, 2005; Liu et al., 2007). A possi- ble strategy for the abatement of computational errors for real shoreline is to calculate mean shoreline, if more images of the same beach for an adequate time interval are available (Holland et al., 1997; Holman et al., 1993). In the specific case of the application of Hsu and Evans (1989) predictive equation, the variability of control points selection can change the predicted shoreline (González and Medina, 2001; Lausman et al., 2010; Moreno and Kraus, 1999; Reeve and Li, 2009). Sim- ilarly, wave direction variability influences shoreline position according to the equation proposed for beaches with predominant waves coming from a single direction (Tan and Chiew, 1994). In Silvester and Hsu (1997) the case of beaches with swell arriving from different directions was tackled. If wave direction is different from that considered (and therefore less frequent), the active contours of a pocked beach respond by rotating. The planform variation is limited in time and the static equi- librium planform is reached again thanks to more persistent predomi- nant waves. In Schiaffino et al. (2012) the persistence of waves was considered and the beach static equilibrium planform was documented by analyzing a selection of previously archived images. Coastal Engineering 65 (2012) 11–15 ⁎ Corresponding author. Tel.: + 39 0103538224; fax: + 39 010353. E-mail address: chiara.schiaffino@unige.it (C.F. Schiaffino). Contents lists available at SciVerse ScienceDirect Coastal Engineering journal homepage: www.elsevier.com/locate/coastaleng 0378-3839/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.coastaleng.2012.03.001