Contents lists available at ScienceDirect Journal of Sea Research journal homepage: www.elsevier.com/locate/seares Morphodynamic evolution of Laida beach (Oka estuary, Urdaibai Biosphere Reserve, southeastern Bay of Biscay) in response to supratidal beach nourishment actions M. Monge-Ganuzas a,⁎ , J. Gainza b , P. Liria c , I. Epelde c , A. Uriarte c , R. Garnier b , M. González b , P. Nuñez b , C. Jaramillo b , R. Medina b a Urdaibai Biosphere Reserve Service, Environment and Territorial Policy Department, Basque Government, Madariaga tower, San Bartolome auzoa, 48350 Busturia, Bizkaia, Spain b Environmental Hydraulics Institute (IHCantabria), Universidad de Cantabria, Isabel Torres 15, 39011 Santander, Spain c AZTI-Tecnalia, Marine Research Unit. Herrera Kaia, Portualdea z/g. 20110, Pasaia, (Gipuzkoa), Spain. ARTICLE INFO Keywords: Morphodynamics Nourishment Urdaibai Biosphere Reserve Bay of Biscay Beach erosion ABSTRACT Laida beach, located at the Oka estuary mouth (Urdaibai Biosphere Reserve) in the southeastern region of the Bay of Biscay, suffered the impact of a severe succession of storms during the first months of 2014. As a result of the erosion induced by these events, the beach lost its supratidal zone almost completely. The absence of a supratidal beach generated an impact on the recreational use of the beach during the summer 2014, and represented a potential impact for the coming summer 2015. Furthermore, it resulted in an overexposure and damage of adjacent infrastructures due to impinging strong waves. Therefore, the competent authorities, in coordination, decided to take action in order to nourish the supratidal zone of this beach. The solution adopted combined two different actions. The first one accomplished in spring of 2015, consisted in the mobilization of 44,800 m 3 of sand from an area of 35,200 m 2 equal to the 7% of the intertidal zone of Laida beach interpreted as the existing surface between the average low and high tidal limits, to the zone next to the eastern rocky beach contour. This action successfully resulted in an increase of the supratidal beach for the entire summer 2015 without negatively perturbing the morphological system. The second action was somewhat experimental and consisted in the mechanical plough of the previously existing intertidal low-amplitude ridges with the aim of increasing the sand transport toward the supratidal beach. Although this action did not lead to the increase of the supratidal beach, it seems to have resulted in an acceleration of the natural onshore migration of the bars. The objective of this contribution is to describe the morphodynamical response of the estuarine mouth after the performed actions with special emphasis on the evolution of extracted sites and the supratidal Laida beach area. The information here presented represents an innovative step in the understanding of the complex me- chanisms driving the supratidal beach formation at the mouth of Oka estuary and by extension of the majority of the estuaries of the southeastern Bay of Biscay. 1. Introduction The southeastern Bay of Biscay is bounded by a rugged coastline of steep rocky cliffs, breached by narrow inlets and cut by small north- ward flowing rivers (Pascual et al., 2004)(Fig. 1). Changes in sea level during the Holocene have produced a series of isolated estuarine inlets (Leorri et al., 2013). After the drowning of the previous fluvial valleys, sand from the adjacent platform which chokes the mouths of the es- tuaries has been driven landwards by waves and tidal currents to produce at the lower estuary a sandy wedge of coastal and estuarine sediments (Cearreta and Monge-Ganuzas, 2013). The Oka estuary was declared, in 1984, an UNESCO Biosphere Reserve. Nonetheless, it is influenced strongly by human activities. As such, the balance between industrial, recreational and natural con- servation activities is not always easy to establish. For example, the last artificial movements of sand (dredging and dumping) within the es- tuary, carried out in 2003, altered the natural sedimentary equilibrium at the ebb tidal delta and the associated sandbar (Monge-Ganuzas et al., http://dx.doi.org/10.1016/j.seares.2017.06.003 Received 4 November 2016; Received in revised form 7 April 2017; Accepted 6 June 2017 ⁎ *Corresponding author. E-mail address: manu-monge@euskadi.eus (M. Monge-Ganuzas). Journal of Sea Research xxx (xxxx) xxx–xxx 1385-1101/ © 2017 Elsevier B.V. All rights reserved. Please cite this article as: Monge-Ganuzas, M., Journal of Sea Research (2017), http://dx.doi.org/10.1016/j.seares.2017.06.003