The effects of dredging operations on the hydrodynamics of an ebb tidal delta: Oka Estuary,northern Spain |
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| Authors: | P Liria E Garel A Uriarte |
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| Institution: | 1. Urdaibai Biosphere Reserve Service, Environment and Territorial Policy Department, Basque Government, Madariaga tower, San Bartolome auzoa, 48350 Busturia, Bizkaia, Spain;2. Environmental Hydraulics Institute (IHCantabria), Universidad de Cantabria, Isabel Torres 15, 39011 Santander, Spain;3. AZTI-Tecnalia, Marine Research Unit. Herrera Kaia, Portualdea z/g. 20110, Pasaia, (Gipuzkoa), Spain.;1. State Key Lab of Estuarine and Coastal Research, East China Normal University, Dongchuang Road 500, Shanghai 200241, China;2. State Key Lab of Marine Geology, Tongji University, Siping Road 1239, Shanghai 200090, China;3. School of Ocean and Earth Sciences, University of Southampton, Southampton, UK;4. Department of Hydraulic Engineering, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft 2600GA, the Netherlands;5. Marine and Coastal Systems Department, Deltares, Delft 2629HV, the Netherlands |
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| Abstract: | The hydrodynamics associated with the Mundaka Sandbar are described. The sandbar (ebb tidal delta) is responsible for the formation and the quality of a “world famous” surfing wave, at the mouth of the Oka Estuary in the Urdaibai Biosphere Reserve. The primary factor controlling the shape of the sandbar is the shoreline configuration. In turn the size of the sandbar is controlled by the volume of the tidal outflow and the wave energy. Periods of tidal dominance occur during summer (associated with sandbar accretion); with mixed energy conditions during winter and wave dominance under storms (sandbar erosion).The surfing wave lost its characteristics following, intensive dredging along the estuary, combined with beach nourishment, in May 2003. Between May 2005 and April 2006, the outer part of the estuary was monitored, to understand the processes controlling recent morphological changes over the area.Recent studies undertaken in the mouths of estuaries, together with the results of the monitoring are described; these are complemented by the numerical modelling of wave hydrodynamics under medium and extreme sea states. Analyses of the wave and current survey data, combined with the modelling outputs, have demonstrated that the changes were not irreversible. As such, the natural shape of the sandbar has recovered gradually, as has the quality of the Mundaka surfing wave. |
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