RAPID: The Impact of the 2009 Suwannee River Surge on the Gulf of Mexico

University Of Florida, Gainesville FL

Investigators

Abstract

The response of estuaries to extreme freshwater pulses has been mostly studied theoretically through numerical model approaches. Few observations are available to test the theories proposed by the models. This dearth of observations happens because extreme freshwater fluxes are typically associated with storms whose paths and regions of impact are uncertain until only a few hours in advance. However, extreme freshwater pulses may also develop from large precipitation pulses occurring far upstream in a river that ultimately feeds onto an estuary. This is the case developing at the Georgia-Florida border. Intense rains in Georgia have caused flood levels in the rivers that flow through Florida into the Gulf of Mexico. Such a pulse represents a unique opportunity to collect observations on the impact that it may have on an estuary and the adjacent continental shelf. In particular, this pulse will impact a relatively shallow estuary and continental shelf (mostly <5 m). New findings will likely be generated on the influence of a freshwater pulse onto a shallow shelf. Intellectual Merit: The rivers of North Florida (Santa Fe and Suwannee), according to U.S. Geological Survey forecasts, are expected to attain record flood levels in their path toward the Gulf of Mexico. The Suwannee River is expected to crest at its lower reaches, at some time between April 21 and 23, 2009. This means that there will be record freshwater pulses that will affect the estuarine area of the lower Suwannee River and dramatic buoyancy inputs to the shallow, coastal region of the northeastern continental shelf of the Gulf of Mexico. This represents a unique opportunity to address three scientific questions that can only be addressed with the influence of extreme freshwater pulses: 1) does the river pulse enhance or hinders estuarine circulation? 2) what is the transverse structure of the exchange flow at the estuary/ocean transition before, during and after the freshwater pulse? 3) what is the shape and extent of the outflow plume? These three objectives will advance basic understanding of estuarine processes, of processes of water exchange between ocean and estuary and of plume hydrodynamics. Data will be collected in two modes: with hydrographic surveys and with moored instrumentation. Surveys will examine the plume characteristics on the inner continental shelf and will include towing an acoustic Doppler current profiler and a surface temperature-salinity sensor. Surveys will also include profiles of temperature and salinity and will be targeted to characterize the extent and shape of the plume, as well as the stratification and flow characteristics associated with it. Also to determine the temporal reach of the plume influence, current profilers will be deployed (moored) in the estuary, at the ocean/estuary transition and over the inner shelf. These instruments are expected to address questions 1) and 2). They will be deployed before the river pulse arrives at the lower estuary and will remain moored for a month. These instruments are expected to record the horizontal and vertical characteristics of the plume and how those characteristics change over time. Broader Impacts: This project will support and train one graduate student at the University of Florida and will involve the participation of at least 5 others in the field work. They will all become well versed in the operation of state-of-the-art oceanographic equipment. The results should be innovative enough to produce publishable manuscripts.