The USF College of Marine Science Integrated Model of Tampa Bay

Transcription

1 The USF College of Marine Science Integrated Model of Tampa Bay Mark E. Luther and Steven D. Meyers Ocean Modeling and Prediction Laboratory USF College of Marine Science 140 Seventh Avenue South St. Petersburg, FL Telephone: Fax: The USF College of Marine Science is developing an integrated circulation, wave, sediment transport, and water quality model. The model system ingests real-time observations of the physical forcing functions for Tampa Bay to produce three-dimensional fields of circulation, temperature, salinity, wave spectra, sediment resuspension and transport, turbidity, primary production, chlorophyll, nutrients, dissolved oxygen, and other biogeochemical quantities. The need for a detailed three-dimensional integrated water quality model has become apparent in Tampa Bay management issues. The integrated model development is well underway. The hydrodynamic model is fully operational in either a nowcast-forecast mode or a hindcast mode and is described on our web site ( The wave and sediment transport component of the model has been implemented (Shi et al., 2002) and is being tested against observations made in December 2001 and January 2002 and in May through August The water quality model code has been obtained and is being adapted to the other components of the Tampa Bay model system. The integrated model has been and will continue to be calibrated and validated against extensive observational data available for Tampa Bay collected by the Tampa Bay Estuary Program (TBEP), the Environmental Protection Commission of Hillsborough County (EPCHC), the US Geological Survey, and others. The integrated model provides a management tool that can be used to evaluate the bay ecosystem response to severe storms or to seasonal and interannual changes in fresh water input, as well as to changes due to human impacts, such as river withdrawals, nutrient loading, changing land use patterns, or alterations in bay bathymetry. The model system has been used to support management decisions in several environmental issues affecting the bay. For example, the model was used to simulate the trajectory of the discharge from the Piney Point phosphate plant that occurred in October and November of 2001 for the Florida Department of Environmental Protection (see Fig. 1) and to evaluate changes in salinity and estuarine residence time in the Palm River and McKay Bay for the Southwest Florida Water Management District (see Fig. 2). Circulation Model The circulation model has been under development at USF since It is a threedimensional time-dependent model of the hydrodynamics of circulation in Tampa Bay (Galperin et al., 1992a,b; Vincent, et al., 1997, 2000), based upon an advanced version of the Princeton Ocean Model (Blumberg and Mellor, 1987). The governing equations consist of conservation of mass and momentum and conservation equations for thermal energy and salt. Equations are also solved for the turbulence kinetic energy and turbulence macroscale. Salient features include a curvilinear orthogonal grid in the horizontal plane and a bed and free surface following sigma

2 coordinate system in the vertical axis. Turbulence closure is provided by an embedded Mellor- Yamada 2.5 level closure submodel (Mellor and Yamada, 1982) as modified by Galperin. Time splitting allows for the fast external or barotropic waves to be solved for explicitly, and the slower internal baroclinic waves implicitly. Specified forcing boundary conditions include the free surface elevation and temperature/salinity profiles at the open water boundary; the flow rate, temperature, salinity and level of inflows or outflows; surface heat flux; surface wind stress, precipitation, and evaporation. Among the important parameters computed are free surface height, magnitude and direction of current velocity fields, and temperature and salinity fields. Various model versions have been deployed and tested at numerous sites such as the Hudson- Raritan Estuary, Chesapeake Bay, Delaware Bay, Apalachicola Bay, Florida Bay, the lower Mississippi River and adjacent continental shelf, the west Florida shelf, and the New York Bight. The present version of the Tampa Bay model uses a 70-by-100 horizontal curvilinear grid (Figure 3) with 11 sigma levels in the vertical (Figure 4). Boundary conditions for the Tampa Bay model are provided by the PORTS data stream. The model is automatically updated every 12 minutes to provide a nowcast of present conditions in the bay. Every 4 hours, a 25 hour forecast is performed using winds from the National Weather Service ETA model and water levels at the mouth of the bay extrapolated from present observations and forecasts of offshore conditions. Model nowcast and forecast fields are presented in graphical format and can be viewed on the OMPL Web site ( and can be obtained via a DODS (Distributed Ocean Data System) server. The DODS interface to the model fields was designed in collaboration with the NOAA HAZMAT office to assist in hazardous material spill response and contingency planning. Trajectory Model The hydrodynamic model output velocity fields drive a trajectory model to predict the movement of hazardous material spills or persons or objects in the water in Tampa Bay. Trajectories are treated as a cloud of a large number of Lagrangian particles, each modeled by a first order Markov process using instantaneous velocities from the hydrodynamic model and a dispersion coefficient calibrated using observed drifter tracks. Trajectory predictions have been verified by a limited number of GPS and radio-tracked drifters. The information on contaminant distribution from the trajectory model can be ingested into the Florida Marine Research Institute s Marine Spill Assessment and Response System (FMSAS), a GIS-based spill mitigation tool. The predicted distribution of contaminant from the spill model forms a layer in the FMSAS database and can be used as a template to cut through the resources-at-risk data layers to arrive at an inventory of resources exposed. Predicted trajectories can be generated in real-time via a web-based form that is linked to the USCG Area Contingency Plan for emergency response or for search and rescue. Residence Time Estuarine residence time is estimated by seeding each model grid cell with large numbers of particles or with a passive tracer, as described above for the trajectory module (Burwell et al., 2000). The e-folding time for particle concentration is computed in each grid cell under a variety of boundary conditions observed in the bay (Figure 5). The resulting residence times vary

3 widely in space and time. Residence time is most sensitive to variations in wind forcing and to variations in fresh water input. Wireless Data Delivery Information from the real-time observations or model output and on the predicted distribution of passive particles (for hazardous material spills or search and rescue efforts) can be delivered in real-time to harbor pilots, shipping agents, resource managers, or others in the field using wireless internet technology. At present, we utilize Cellular Digital Packet Data (CDPD) or Wireless IP that uses the commercial cellular network to connect to the Internet from a notebook computer wherever the local cellular provider supports this service (usually the wireline cellular provider; see for more information). The CDPD network is being replaced with the GSM/GPRS network, which is a much faster and more versatile system. GSM/GPRS is a global standard serving twothirds of the world's population. The second is via a dedicated 900 Mhz spread spectrum radio modem link using Point-to-Point Protocol (PPP) between the USF St. Petersburg campus and a remote notebook computer. This radio link has a radius of approximately 30 miles, depending on antenna height. The advantage to the spread-spectrum radio link over the CDPD link is that the cellular frequencies often become crowded and throughput is hindered. The spread-spectrum radio link has much faster throughput even under optimal conditions for CDPD. The disadvantage to the spread-spectrum radio is its range limitation, although multiple radios can be used as repeaters to easily set up a local network. Because they work in the 900 Mhz frequency band, no special licensing is required. Using either wireless communications link, the remote computer can access the predicted spill trajectory or other model or observational products using standard web browsers. In addition, the wireless delivery technology can be implemented through our collaboration with L-3 Communications, the developer of the Tampa Bay Vessel Information and Positioning System (see L-3 provides a wireless wide area network in the Tampa Bay region and has the capability to transmit real-time data from Tampa Bay PORTS to the harbor pilots and other maritime interests via carry-on units in use in Tampa Bay (Husick, 1999). Wave Model The SWAN wave model is coupled to the circulation model and computes wave spectra at each model grid cell under observed wind conditions and modeled water velocity (Shi et al., 2002). Wind stress forcing and bathymetry for the wave model are the same as that used for the hydrodynamic model. Bed stresses are computed as a superposition of stresses due to wave orbital velocity and those computed by the hydrodynamic model. The information on bed stresses are combined with data on sediment type, compiled by USGS, to compute sediment resuspension. The velocity field from the hydrodynamic model is combined with the information on sediment resuspension and settling velocity to compute sediment transport. Turbidity and nutrient flux due to sediment resuspension will provide input to the water quality model component. During December 2001 and January 2002, four Sea Bird Electronics SeaGauge wave and tide recorders were deployed in Tampa Bay in each major bay segment. Since May 2002, a

4 SeaGauge has been continuously deployed at a site in middle Tampa Bay as a component of the Bay Regional Atmospheric Chemistry Experiment (BRACE; see Preliminary analyses of these wave data show good agreement with modeled wave spectra at each site. Water Quality Model Development is underway of the water quality component of the model system that will take information from the circulation and wave components to compute primary production, chlorophyll, turbidity, nutrients, dissolved oxygen, and other biogeochemical quantities. The water quality model code has been obtained and is being integrated with the other model components. A new, higher resolution model grid is being developed to better resolve the main channels and important sub-basins of the bay, like the McKay Bay-Palm River system. In the integrated model, waves, sediment resuspension and transport, and water quality variables are computed on the same grid as used by the three-dimensional hydrodynamic circulation model. The water quality component will utilize the EFDC code developed by John Hamrick, formerly of Virginia Institute of Marine Science and now of Tetra-Tech. Much of this model was developed with EPA funding and is considered the state-of-the-art in water quality modeling. The EFDC model is now being adapted to the other model components. Data from EPCHC, TBEP, BRACE, and the US Geological Survey are being used for model calibration/validation and to set the boundary conditions for nutrient loading of the bay. The wave and sediment resuspension model component combined with data collected by Prof. Florence Thomas of the USF Dept. of Biology provide input to the water quality model component on water column turbidity and on benthic nutrient flux. The integrated model should be operational within the next few months. Continued model development, calibration/validation, and application to specific problems of concern will take place during the next year. References: Blumberg, A. and G. L. Mellor, A description of a three-dimensional coastal ocean circulation model. In: Three-Dimensional Coastal Ocean Models, N. S. Heaps, Ed., American Geopgys. Union, Washington, DC, pp Burwell, D., Vincent, M., Luther, M., Galperin, B., Modeling Residence Times: Eulerian vs Lagrangian. In: Estuarine and Coastal Modeling, M. L. Spaulding and H. L. Butler, eds., ASCE, Reston, VA, pp Galperin, B., A. Blumberg, and R. Weisberg. 1992a. A time-dependent three dimensional model of circulation in Tampa Bay. Pages in S. Treat and P. Clark, eds., Proceedings of the Tampa Bay Area Scientific Information Symposium 2, Tampa, FL, February 27-March 1, Galperin, B., A. Blumberg, and R. Weisberg. 1992b. The importance of density-driven circulation in well-mixed estuaries: The Tampa Bay experience. Pages in the Proceedings of the 2nd International Conference on Estuarine and Coastal Modeling, Tampa, FL, November 13-15, Husick, C., 1999: Tampa Bay setting the pace with Automatic Identification System. Professional Mariner, 38,

5 Shi, Z., S. Meyers, and M. E. Luther, Modeling of wind wave-induced bottom currents and fine sand transport in Tampa Bay, Florida. Estuaries, Submitted. Vincent, M., D. Burwell, M. Luther, and B. Galperin, Real-time data acquisition and modeling in Tampa Bay. in Estuarine and Coastal Modeling, M. Spaulding and A. Blumberg, eds., ASCE, Reston, VA, pp Vincent, M., D. Burwell, and M. Luther, The Tampa Bay Nowcast-Forecast system. in Estuarine and Coastal Modeling, M. Spaulding and H. Butler, eds., ASCE, Reston, VA, pp Figure 1. Simulated trajectory of the discharge plume from the Piney Point phosphate plant into Bishops Harbor. Color is time in hours past 0 UTC on November 15, 2001 (color scale to right). The centroid of all particles is indicated by the black symbols and the position

6 is given in latitude and longitude in the columns to the far right. No particles exit Bishops Harbor for the first 75 hours. After this time, two groups of particles exit Bishops Harbor and are transported toward the southwest. The first group of particles quickly leaves Tampa Bay through Southwest Passage within 90 hours. The second group recirculates within the bay and are trapped to the south of the Skyway Bridge and just north of Anna Maria Island.

7 Figure 2. Salinity in McKay Bay and Palm River for the baseline case (top), the Tampa Bay Water permitted withdrawal (middle), and an intermediate withdrawal case (bottom). The vertical axis is depth in meters and the horizontal axis is distance along the section. Structure 160 is at the far right of the figure and the 22 nd St. Causway is at the far left

8 edge. Both withdrawal cases show salinities elevated by 0.5 to 1 psu (or part per thousand) throughout the water column. Figure 3: 70 x 100 horizontal curvilinear orthogonal grid with Tampa Bay PORTS observing sites Figure 4: typical cross section of 11 sigma layers in the vertical dimension

9 Figure 5. Residence time based on the Lagrangian particle trajectory method for boundary conditions observed during the fall and winter of Color represents e-folding time in days, or the time required for the number of particles in a grid cell to decrease by 65%. Residence times in Lower Tampa Bay and in areas adjacent to the main channels are 10 to 20 days or less, while on shoals and in areas restricted by causways, they exceed 140 days.