Amaia Ruiz de Alegria-Arzaburu

Post-nourishment beach scarp morphodynamics

ABSTRACT Ruiz de Alegria-Arzaburu, A., Mariño-Tapia, I., Silva, R., Pedrozo-Acuña A., 2013. Post-nourishment beach scarp morphodynamics Large and persistent beach scarps can be safety hazards to beach users and result in serious social and economic implications. In this study the morphological evolution of beach scarps of large dimensions is examined on a nourished microtidal Caribbean Mexican beach. Beach profiles were measured three-to-four monthly along the beach after the nourishment in December 2009 and over 1.5 years. A beach scarp was defined as a feature with a slope larger than the critical angle of repose of 32° and a minimum height of 0.25 m. The top and bottom positions of the scarps were calculated from the minimum and maximum values of the second derivative of the measured beach profiles (slope gradient). The cross-shore morphological evolution of the scarps was related to wave runup (R2) and tides, and also to both with the contribution of the longshore energy flux (Pl). During calm conditions characterised by longshore uniform mean and maximum R2 of 0.73 and 0.83 m, and Pl=180KN/s, the scarps remained present along the beach. Energetic conditions with mean and maximum R2 of 0.83 and 1.2 m and Pl=400KN/s, increased the longshore rythmicity of the beach and induced significant cross-shore erosion (over 20 m) and the disappearance of ~50% of the scarps. The added contribution of the longshore energy flux, wave runup and tidal elevation explain 40% of the morphological evolution of beach scarps over the study period.

Predicting Barrier Beach Breaching due to Extreme Water Levels at San Quntín, Baja California, Mexico

ABSTRACT Vidal-Juárez, T.; Ruiz de Alegría-Arzaburu, A.; Mejía-Trejo, A.; García-Nava, H., and Enriquez, C., 2014. Predicting barrier beach breaching due to extreme water levels at San Quintín, Baja California, México. This study comprises a first approach to numerically determine the hydrodynamic conditions leading to barrier breaching at San Quintín, located in the northwestern coast of the Baja California peninsula in Mexico. The barrier is backed by a large coastal lagoon, fronted by a field of submerged volcanoes located several kilometers off the coast and is exposed to large incoming wave energy dominated by the Pacific swell. The narrowest barrier beach sections are vulnerable to flooding due to overwash events that take place during concurrent high spring tides, energetic storm waves and a range of storm surge levels. Here, the conditions to barrier overwash and breaching occurrence are identified, and the extent of the floods is numerically quantified. For that purpose, the Delft3D hydrodynamic model is applied coupling waves and flows to simulate a series of scenarios, which comprise storm waves of different magnitudes and periods approaching from typical directions, and coupled to spring tides and several storm surge levels. As a consequence of the presence of submerged volcanoes off the coast, the incoming wave energy is mostly concentrated at two specific locations along the barrier beach, which correspond to the lowest and narrowest barrier locations. Due the large distance between both sites, longshore variations are not expected to be as strong as the cross-shore. Numerical results suggest that the barrier is susceptible to flooding during spring tides combined with extreme waves of significant wave heights larger than 3.5 m and a peak period of 7.5 s, and storm surge levels exceeding 0.9 m, which may lead to breaching.

The Effects of Beach Morphology Variations on the Profile of Nearshore Currents on a Gently Sloping Mesotidal Beach

ABSTRACT Ruiz de Alegria-Arzaburu, A.; Arreola-Cortez, M.A.; García-Nava, H.; Hernández-Walls, R., and Mejía-Trejo, A., 2016. The effects of beach morphology variations on the profile of nearshore currents on a gently sloping mesotidal beach. 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. 457–461. Coconut Creek (Florida), ISSN 0749-0208. Concurrent measurements of subtidal beach morphology and profiles of nearshore currents have been collected over a year period on a gently sloping mesotidal beach in the northwestern coast of the Baja California peninsula in Mexico. Data collected in August 2014 and February 2015 during similar tide, wave and wind conditions are compared at different alongshore locations on the beach in order to determine differences on the vertical structure of the nearshore currents in relation to significant morphologic variations. The beach presents a clear seasonal variability, showing the formation of an inner sandbar during the winter as a result of the erosion of a large portion of the subaerial beach. The morphological differences on the inner subtidal beach shows a subsequent effect on the vertical structure of the nearshore currents. Locations with pronounced sandbars have generally associated cross-shore and longshore components of the current of larger magnitude. Generally, the surface and bottom cross-shore currents are the most energetic while the middle layer presents milder magnitudes. With the presence of an inner bar, the shoreward directed upper and bottom layers become wider (deeper) reducing the width of the middle less energetic layer, and after the breaking zone the water column becomes vertically quasi-homogeneous. This study contributes to the understanding of the feedbacks between the hydrodynamic forcing and the beach morphology.

Steps to improve gender diversity in coastal geoscience and engineering

Robust data are the base of effective gender diversity policy. Evidence shows that gender inequality is still pervasive in science, technology, engineering and mathematics (STEM). Coastal geoscience and engineering (CGE) encompasses professionals working on coastal processes, integrating expertise across physics, geomorphology, engineering, planning and management. The article presents novel results of gender inequality and experiences of gender bias in CGE, and proposes practical steps to address it. It analyses the gender representation in 9 societies, 25 journals, and 10 conferences in CGE and establishes that women represent 30% of the international CGE community, yet there is under-representation in prestige roles such as journal editorial board members (15% women) and conference organisers (18% women). The data show that female underrepresentation is less prominent when the path to prestige roles is clearly outlined and candidates can self-nominate or volunteer instead of the traditional invitation-only pathway. By analysing the views of 314 survey respondents (34% male, 65% female, and 1% ‘‘other’’), we show that 81% perceive the lack of female role models as a key hurdle for gender equity, and a significantly larger proportion of females (47%) felt held back in their careers due to their gender in comparison with males (9%). The lack of women in prestige roles and senior positions contributes to 81% of survey respondents perceiving the lack of female role models in CGE as a key hurdle for gender equality. While it is clear that having more women as role models is important, this is not enough to effect change. Here seven practical steps towards achieving gender equity in CGE are presented: (1) Advocate for more women in prestige roles; (2) Promote high-achieving females; (3) Create awareness of gender bias; (4) Speak up; (5) Get better support for return to work; (6) Redefine success; and, (7) Encourage more women to enter the discipline at a young age. Some of these steps can be successfully implemented immediately (steps 1–4), while others need institutional engagement and represent major societal overhauls. In any case, these seven practical steps require actions that can start immediately.

PREDICTING THE RESPONSE OF GRAVEL BARRIERS TO STORMS USING XBEACH

To investigate new ways to improve the prediction of gravel barrier beach erosion, XBeach, a processed-based numerical model capable of computing nearshore circulation and morphodynamics, including overwash and breaching, has been used in 1D mode to simulate: a) prototype-scale laboratory experiments; and b) storm response of a natural gravel barrier. For laboratory tests XBeach predicted beach face erosion well and demonstrated good quantitative skill (Brier skill score, BSS, typically 0.65). At field-scale, XBeach was used to simulate the response to a storm of a steep (average tanβ = 0.12), 4.5km-long and 100m–140m wide macrotidal gravel barrier (D50 = 2mm to 10mm). Although in this case XBeach predicted erosion with moderate accuracy (BSS = 0.60), the development of a berm was not reproduced well by the model. XBeach was also used to improve estimation of threshold conditions for overwash.