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Improved method for calibration of exchange flows for a physical transport box model of Tampa Bay, FL USA
Citation:
Rogers, Johne, M. Russell, AND M. Harwell. Improved method for calibration of exchange flows for a physical transport box model of Tampa Bay, FL USA. JOURNAL OF COASTAL RESEARCH. Coastal Education Research Foundation Incorporated, West Palm Beach, FL, 33(4):972-988, (2017).
Impact/Purpose:
Historical nutrient cycling models have not correctly incorporated evaporation in the mixing of flow of water within an estuary. This paper address this concern through a box model, which can be run on laptop computers in seconds for rapid assessment of potential effects of watershed management on nutrient levels in estuaries. A new approach based on conservation of mass and sound mathematics is described herein for calibrating the exchange flows in Tampa Bay, an estuarine system under management actions of large scale nutrient abatement programs. This approach provides the basis for developing nutrient cycling models for the estuary to better inform area managers regarding the potential water quality consequences of nutrient load reduction scenarios.
Description:
Results for both sequential and simultaneous calibration of exchange flows between segments of a 10-box, one-dimensional, well-mixed, bifurcated tidal mixing model for Tampa Bay are reported. Calibrations were conducted for three model options with different mathematical expressions for evaporative loss. Evaporation was subtracted from freshwater inputs in the first option. Evaporative losses were replaced by water from the adjacent down-bay segment in the second option. Evaporative losses in the third option described a complete water balance. For example, when starting at the head of the bay, water drawn from Segment II to replace evaporative losses from Segment I must be replaced by water from Segment III, and so on. Three questions were asked in approaching this project: does simultaneous calibration or sequential calibration yield better box model performance, which evaporation option best predicts observed salinities, and how well does model performance compare to more complex hydrodynamic models? Sequential calibration followed the classical salt balance and steady-state approach. A nonlinear parameter estimator was used for simultaneous calibration. The sequential approach proved useful in evaluating the three evaporation options. However, simultaneous calibration proved superior in predicting observed salinities but was ineffective in discerning differences between evaporation options. Simultaneously calibrated model option 3 produced residence times that fell within the range of more complex hydrodynamic models of Tampa Bay.
