Tidal and nontidal flushing of Florida’s Indian River Lagoon |
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| Authors: | Ned P Smith |
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| Institution: | 1. Harbor Branch Oceanographic Institution, 5600 Old Dixie Highway, 34946, Fort Pierce, Florida
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| Abstract: | The flushing of Florida’s Indian River Lagoon is investigated as a response to tidal and low-frequency lagoon-shelf exchanges in the presence of freshwater gains and losses. A one-dimensional computer model uses the continuity equation to convert water-level variations into both advective transport within the lagoon and lagoon-shelf exchanges. The model also incorporates transport by longitudinal diffusion. Flushing is quantified by calculating the 50% renewal time, R50, for each of 16 segments. R50 is calculated for tidal exchanges enhanced by 0–30 cm nontidal fluctuations in coastal sea level, then for a range of rainfall rates. In both series of simulations, results suggest that in the northern sub-basin, R50 increases dramatically with distance from the inlet due to relatively weak tidal and nontidal exchanges. A 50% renewal occurs in about one tidal cycle just inside Sebastian Inlet; at the northern end of the northern sub-basin, R50 is over 230 d, and only coastal sea-level variations on the order of 30 cm and/or dry season rainfall rates decrease R50 to less than 1 yr. R50 is 1 wk or less throughout the central and southern sub-basins, where lagoon-shelf exchanges occur through two inlets. Simulations involving seasonal variations in precipitation and evaporation indicate that maximum and minimum rates of freshwater input lead minimum and maximum salinities by time periods on the order of 2–3 wk for the lagoon as a whole and in the northern sub-basin. The central and southern sub-basins respond in 1–2 wk. |
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