Development and Evaluation of a Coupled Hydrodynamic (FVCOM) and Water Quality Model (CE-QUAL-ICM)

Recent and frequent fish-kills in waters otherwise known for their pristine high quality, created increased awareness and urgent concern regarding potential for degradation of water quality in Puget Sound through coastal eutrophication caused by increased nutrient loading. Following a detailed review of leading models and tools available in public domain, FVCOM and CE-QUAL-ICM models were selected to conduct hydrodynamic and water quality simulations for the fjordal waters of Puget Sound. A high resolution hydrodynamic model of Puget Sound has already been developed and tested. The objective of this effort was to develop an associated sophisticated water quality model of Puget Sound to help nearshore restoration managers and planners in the management of nutrient loading to Puget Sound. In this study we present a one-way coupling of FVCOM hydrodynamic solution to CE-QUAL-ICM water quality kinetics. The coupled model uses FVCOM model grid and transport solution scheme to conduct water quality kinetic calculations in CE-QUAL-ICM. Through this approach, it is possible to construct the linked model with sufficient resolution in the nearshore region to address dynamics of water quality state variables in the complex coastline, multiple tidal channels, tidal flats, and a deep fjord such as Puget Sound. In this paper, we demonstrate the scalar transport and water quality module tests (a propagated pulse, diffused plumes, a BOD/oxygen sag, and phytoplankton/nutrients reactions) and compare model results with their analytical solutions as part of model validation.