A nearshore wave and current operational forecasting system.(Report)

ABSTRACT

An operational forecasting system for nearshore waves and wave-induced currents is presented. The forecasting system (FS) has been built to provide real time information about nearshore conditions for beach safety purposes. The system has been built in a modular way with four different autonomous submodels providing, twice a day, a 36-hour wave and current forecast, with a temporal resolution of 1 hour. Making use of a mild slope parabolic model, the system propagates hourly deep water wave spectra to the shore. The resulting radiation stresses are introduced in a depth-integrated Navier-Stokes model to derive the resulting current fields. The system has been implemented in a beach located in the northeastern part of Mallorca Island (western Mediterranean), characterized by its high touristic pressure during summer season. The FS has been running for 3 years and is a valuable tool for local authorities for beach safety management.

ADITIONAL INDEX WORDS: Rip currents, wave propagation, surf zone currents generation, beach hazards.

RESUMEN

En este trabajo se presenta un sistema operacional para la prediccion de las corrientes generadas por la rotura del oleaje en aguas someras. El sistema se ha desarrollado con el proposito de proporcionar las condiciones de oleaje y corrientes para la seguridad en playas. El sistema esta construido en forma modular con cuatro submodelos funcionando de forma autonoma para proporcionar el oleaje y las corrientes dos veces al dia con un horizonte predictivo de 36 horas. Las condiciones de oleaje en aguas profundas, se propagan hasta la costa mediante un modelo parabolico de pendiente suave y los tensores de radiacion resultantes se introducen como forzamiento en un modelo de Navier Stokes verticalmente integrado. El sistema se ha aplicado en una zona piloto en la Isla de Malloca (Mediterrfineo occidental). El sistema ha estado funcionando ininterrumpidamente durante tres anos habiendose mostrado como una herramienta muy valida para la gestion de la seguridad en la playa por parte de las Autoridades. La extension del sistema a otras areas del litoral es inmediata una vez se disponga de las batimetrias detalladas de las zonas de interes.

INTRODUCTION

Coastal areas are among the most complex and variable marine systems because their dynamics are subjected to the effects derived from a complex geometry, where the bathymetry plays a crucial role in wave propagation. Moreover, the wide range of processes affecting coastal hydromorphodynamics such as waves, currents, and tides, among others, interact at different spatial and temporal scales, making these zones highly variable environments.

Despite the socioeconomical relevance of coastal areas, modeling, observation, and continuous monitoring of coastal variability is to date scarce because of the intrinsic complexity of these systems. Besides the morphological importance of coastal areas, they are a major recreational resource around the world, and human activities have been constantly growing in the last three decades. Coastal management has increasingly relied on the scientific results obtained from different research fields that have been transferred to new engineering methodologies and applications to environmental systems in search of new, more integrated, and sustainable solutions to coastal problems. Although beach erosion and coastal evolution are, in a global change context, top scientific issues, accurate information, in an operational sense, of short term variability is still required by governments and end users.

Continuous observation of coastal variability is expensive and sometimes impossible to obtain. Comprehensive information in coastal areas is nowadays required to establish efficient coastal zone monitoring as well as to develop management policies to effectively study these marine systems (Smit et al., 2007). The scarcity, and in most cases the lack, of information becomes a problem when scientists need to assess the current state (diagnostic) of specific coastal systems as well as to build predictive models (prognostic) of their evolution. The spatial and temporal evolution of different physical systems …