Hydrodynamic Model of Coos Bay
What is a Hydrodynamic Model?
A hydrodynamic or “circulation” model is a three-dimensional computer simulation used to describe the motion of water in a defined body of water (e.g. lake or estuary). The model informs us about water circulation and related water quality attributes such as temperature or salinity. For example, a hydrodynamic model simulating water movement in an estuary will be able to inform us how far up the estuary salt water can be found during different tides and at different times of the year, or what the water current speed and direction is at a given location in the estuary during different tides and at different times of the year.
Hydrodynamic models for estuaries rely on computer simulation techniques to describe water circulation, temperature and salinity in the estuary. A computer model of the estuary consists of a three-dimensional grid made of thousands of individual three-dimensional cells. Each cell is programmed using data collected from instruments deployed in the estuary, including information about water temperature, salinity, current speed and velocity, river discharge, and wind direction and speed (among other data). Computers determine how all these cells act together to create a full three-dimensional simulation of water flow and changes in water temperature and salinity in any given part of the estuary- all based on the values assigned to every grid cell in the model!
The Coos estuary circulation model is being developed by Dave Sutherland, Assistant Professor in Geology at the University of Oregon.
The success of the hydrodynamic model depends on how well validated it is; that is, how well the modeled values compare with real, measured observations, and correcting the model accordingly. Important variables to validate include water level, salinity, temperature, current velocity and direction, and depth.
Validation of the Coos estuary model will be a collaborative effort, with information provided by multiple sources: South Slough National Estuarine Research Reserve (SSNERR) is extending their monitoring work into the Coos estuary in order to supply dataon water level, salinity, temperature, and current velocity and direction. Bathymetry data will be taken from a combination of NOAA charts, Oregon Department of Geology and Mineral Industries data created for inundation modeling of the Oregon coast, and intertidal bathymetry provided by Oregon State University. River discharge data will be provided by the stream gaging efforts of the Coos Watershed Association. Meteorological data will be supplemented by local weather stations to account for influences of winds.
How will the model be used?
Once the Coos estuary hydrodynamic model is developed and validated, it will be a useful tool to examine numerous questions. Shellfish growers will be interested in understanding the fate of secondary wastewater effluent that is released into the bay. Waterfront landowners will be able to look at changes in currents, erosion or wave action that would be caused by the widening or deepening of the shipping channel. It will also be a valuable tool for compensatory mitigation planning for any dredging activities. Recreational shellfish management agencies will be able to answer questions involving larval transport (e.g. what part of the estuary are most important for Dungeness crab larvae?). The Oregon Department of Environmental Quality can look at a multitude of water quality and sediment transport questions. As climate change influences our bay, the model could be used to help predict and understand local effects of heightened storm intensity, or forecast harmful algal blooms. As these and many more questions are answered, it will provide our community with the ability to consider long-term changes during decision-making processes.