Implementing Posidonia oceanica effects in ROMS_SED

J. Chiggiato¹, M. Sclavo¹, J. C. Warner², R. P. Signell² and S. Carniel¹

1 CNR-ISMAR, Venice Italy
2 USGS, Woods Hole, MA-USA

Understanding the effect of posidonia oceanica on near-shore dynamics is a challenging area with devoted research basically boosted not before the late 80ies-early 90ies, but even now many processes have not been discerned. Major impacts identified are the reduction of flow speed, the modification of flow and turbulence structure, attenuation of wave energy, thus obviously local modification of sediment transport. The usage of numerical models to simulate such impacts is still at an early stage, and most available parameterizations rely on few laboratory experiments with very few sensitivity analyses, and with very idealized situations, hardly generalizable.

The approaches used up to now are basically two, and both work on tuning the drag coefficient of the bottom friction: Kobayashi-type models (dealing with waves only) and Nepf-type models (dealing with currents only). Very recently, few papers addressed the issue of modelling, in a pretty much realistic way, seagrass meadows impact on flow-wave-sediment dynamics in the near-shore (Chen et al., Estuaries and Coast 2007, US Army CEM, 2006). The approach used is basically Nepf-type, and it is focussed on the estimate of the bottom drag coefficient for current and, with similar formalism, for waves. We have implemented the possibility to activate a modified bottom roughness in the bottom boundary layer of ROMS_SED in order to simulate the presence of posidonia oceanica. Sensitivity analyses based on idealized case study as well as a realistic case study along the western Italian coastline will be presented and discussed.

ROMS Operational in the Adriatic Sea: the AdriaROMS system

J. Chiggiato¹, M. Deserti², S. Tibaldi², T. Paccagnella² and A. Valentini²

1 CNR-ISMAR, Venice Italy
2 ARPA-SIM, Bologna, Italy

AdriaROMS is the operational ocean forecast system for the Adriatic Sea running at the HydroMeteorological service ARPA-SIM in Bologna, Italy.

It is based on ROMS version 2.2 (3.0 now being implemented). The Adriatic configuration has a variable horizontal resolution, ranging from 3 km in the north Adriatic to ~10 Km in the south, with 20 s-coordinates levels. The model (originally AdriaROMS 1.0) has been initialised in September 2004 from MFS (general circulation model for the Mediterranean Sea) fields optimally interpolated onto AdriaROMS grid, then run in preoperational configuration until June 2005 when the first forecast have been published on the web. The current version, AdriaROMS 2.0, has been instead re-initialized in order to reset some biases, with optimal interpolation mapping of CTD casts collected during the August 2006 oceanographic cruise DART06b Dynamics of the Adriatic in Real Time (NR/V Alliance).

Surface forcing are provided by the Limited Area Model Italy (LAMI), non hydrostatic numerical weather prediction model with 7 km horizontal resolution, that provides tri-hourly shortwave radiation, 10 m wind, 2 m temperature, relative humidity, total cloud cover, mean sea level pressure and precipitation. All of them are used to compute momentum and heat fluxes. MFS data are used at the open boundary to the south with relaxation-radiation boundary conditions with superimposed four major tidal harmonics (S2, M2, O1, K1). Forty-eight rivers (and springs) are included as well, using monthly climatological or persistence of NRT available measurements.