Computer Simulation of Wind-Driven Circulation in a Coastal Lagoon

Abstract

Recording current meter data, together with ancillary wind data from a 43-day study period in the spring of 1980, are used to characterize nontidal motion in general, and the wind-driven current in particular, along the axis of Indian River Lagoon on South Florida’s Atlantic coast. Tidal co-oscillations are quantified, then removed from the time series to reveal better the response to diurnal bursts in windstress. A cumulative net displacement diagram shows low-frequency variations in the current data superimposed onto a long-term net flow to the south. Cumulative histograms of net displacements over time intervals of from one to 20 days quantify both extreme values and the distribution of values between the extremes. Two numerical models are used to simulate wind-driven, one-dimensional motion along the axis of the lagoon. Simulated currents from both models are verified using subsurface currents measured 1.6 m above the bottom in 3.8 m of water. A one-layer model indicates substantially stronger net flow to the north than does a 38-layer model. Results from both models, suggesting flow to the north, are in conflict with in situ current measurements, which reveal southerly flow during the study period. Freshwater outflow appears to be of primary importance in controlling the long-term net displacement through the lagoon.