Morphologycal variations of the Mundaka Sandbar from the surfing perspective

Supervisors: A. Uriarte, T. Butt (AZTI)
The Mundaka wave, named like that due to the small fishing town that is located next to the breaking point, is one of the most famous globally left-hander plunging surfing spot. This «world-class» wave breaking process is directly dependent on the morphology of the Mundaka Sandbar. Like that, the combination between the marine climate conditions at the area and the morphodynamical characteristics of the environment, result in the surfing conditions of a certain surfing spot. With the main objective of studying the temporal variability of the Mundaka Sandbar, this study is based on the analysis of variations of the surfing conditions, establishing a methodology to study the different marine conditions at Mundaka for a nine year period (2007 to 2015), defining the highest surfing quality days and measuring the different surfability parameters that describe the nature of the Mundaka wave from the surfing viewpoint. This surfability parameters are the surfable distance, defined by the breaking point of the wave to the end of the surfing ride, and the peel angle, which is defined as the the angle between the trail of the broken foam and the crest of the unbroken wave. A Quality Index (Q) has been created, ranging the marine climate conditions from 1 to 4 according to their quality for surfing. Once the highest quality days were recognized, by the application of the KOSTASystem videometric program, monthly images of the highest quality days have been studied, measuring the variations of the surfable distance and the peel angle, getting a continuous dataset of the surfability parameter variations. As a result, 7424 surfable days are observed from where 195 hours are from an optimum surfing quality (Q=4), with the highest number of surfing quality days in the Winter period. Similarly, it can be observed that no significant relationship can be established between the variations of the surfability parameters and the wave breaking height. The study of these surfability parameters will allow the description of the morphological variations of the Mundaka Sandbar during the nine year period. Similarly, two different peel angle parts with different surfable distances can be observed, and in some cases, two different sections, defining if it is partitioned or not. Surfable distance values range between are 567 and 151 metres, defining the length of the Sandbar, and the peel angle from 66 to 12º, with lowest values related to first section of the wave, indicator of a higher surfing quality during the first part of the Sandbar. Similarly, by studying the temporal evolution of both parameters, the objective of analyzing the morphological variations of the Sandbar is achieved, describing that there is no significant seasonal trend for the study period and the bigger changes occur in a multiannual scale, related to the variations of intensity of the storms during the study time-scale, where longest surfable distances and optimum peel angles are related to lower energy years, consequence of a low erosion process in the Sandbar. Contrary, high energetic Winter periods, related to erosion process in the Sandbar, will induce lower surfable distance and peel angles. Finally, the anthropogenic impact that the Mundaka wave suffered has been established, by comparing the impacted Sandbar state due to the dredging activities on 2003, with the optimum conditions along the study period.