# FVCOM (Hydrodynamics) Linkage to CE-QUAL-ICM (Water Quality)

Linkage of the Finite Volume Coastal Ocean Model (FVCOM) hydrodynamics with the CE-QUAL-ICM kinetics was accomplished by developing a modified code, herein referred to as the Unstructured Biological Model (UBM) or simply FVCOM-ICM. In this code, the transport calculations are conducted through the FVCOM framework and biogeochemical calculations are conducted using CE-QUAL-ICM kinetics over the same finite volume mesh used in hydrodynamic calculations using triangular elements. The scalar quantities, such as water-surface elevation, temperature, salinity, and the water-quality state variable concentrations, are computed at the cell nodes, and vector quantities, such as lateral velocities, are computed at the cell centroid.

When FVCOM-ICM is executed, it reads in all of the FVCOM information including computed solution and uses it to conduct transport and biogeochemical calculations. The FVCOM mesh information is read first, followed by the hydrodynamic information, including velocity, diffusivities, open-boundary fluxes, and water levels. Scalars computed in the hydrodynamic step required for the biogeochemical computations, including salinity and temperature, are also read into FVCOM-ICM. The model then reads in the initial conditions for the model domain and the external loads from the open boundaries, river boundaries, and point and nonpoint sources of nutrients. This information includes loadings for each of the 19 biogeochemical model state variables as either masses or fluxes. Once these data are read in to the model, biogeochemical calculations are conducted. A schematic flow diagram of the FVCOM-ICM model is provided below. The technical details describing the development of the offline coupling of FVCOM and CE-QUAL-ICM are provided in detail by Kim and Khangaonkar (2012).