Development and validation of a sediment dynamics model within a coastal operational oceanographic system

The rising interest in environmental and ecosystem dynamics have lead coastal oceanographers to not only investigate the “traditional” physical
parameters describing the ocean state and its dynamics (e.g. temperature, salinity, currents, water levels in coastal areas), but to also account for
the dynamics of parameters describing its biogeochemical components. To that end, MARS3D regional and coastal modelling system has been
coupled to ecosystem modules (ECO-MARS3D, ECO3M) as well as sediment dynamics modules (MARS3D-SEDIM): sediment, nutrient and primary
production contents can be considered as the lower level environment and ecosystem descriptors of the “biogeochemical” ocean. Early investments
into physical and biological analysis at the regional scale have led to the development of several operational configurations within PREVIMER since
2006 for physical and biological parameters, providing 3 to 5-day forecasts as well as hindcasts. The more recent introduction of sediment-related
parameters into the operational chain required validating computed sediment transport at the regional scale. Such validation is mostly accessible
through indirect measurements – namely turbidity measurements in the water column or derived from satellite data.
This paper describes the main features of MARS3D sediment module, the sensitivity analyses and the validation procedures based on dedicated data
acquisition, as well as the assessment of the operational configuration focused on the Bay of Biscay continental shelf. Comparison between in situ
measurements and satellite data shows a fairly systematic overestimation of the satellite-derived SPM in Southern Brittany; this result stresses the
need for further investigation regarding the correct quantitative satellite SPM determination at all times and all places. On the other hand, numerical
results highlight the difficulty to simultaneously predict the correct magnitude of bottom and surface concentrations.