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Tropical Storm Irma storm surge pushes brackish water from Doboy Sound to GCE11, over 30km up the Altamaha River

Tropical Storm Irma may not have hit Sapelo Island directly, but the strong sustained northeasterly winds with gusts to 70mph hit the island near spring tide, piling up water in the sounds and resulting in water levels 0.5-1m above those during Hurricane Matthew in October 2016. Many UGAMI buildings and field sites experienced significant flooding for the first time in many decades, and the dunes at Nannygoat beach were decimated (see the dramatic YouTube video by Rachel Guy at SINERR, and GCE flux tower damage observed by the field crew).

In addition to impacts on Sapelo, the storm surge also pushed estuarine water far up the Altamaha River into normally freshwater reaches. The GCE MicroCAT sonde at Lewis Creek (GCE11), over 30km upriver, recorded estuarine salinities for an entire day during the storm peaking at 22 PSU on 9/11. The GCE7 sonde at Hammersmith Creek recorded significant salinities for 2 days, peaking at 26 PSU (nearly full Doboy Sound salinity). For comparison, during Hurricane Matthew Lewis Creek only experienced a short peak of 10 PSU salinity even though Doboy Sound high tide salinity was much higher in October 2016 than September 2017 (32 PSU vs 27 PSU).

This significant disturbance event has already produced very visible changes to Sapelo Island and the entire Georgia coast, and will certainly be the focus of much GCE research moving forward. Water level and salinity plots are included below for reference. Data and additional plots are available on the GCE Data Portal and Provisional Sonde Data pages (but note that the latest GCE sonde data are still being downloaded and processed for distribution).


(Contact Wade Sheldon for additional information)

submitted Sep 24, 2017


This material is based upon work supported by the National Science Foundation under grants OCE-9982133, OCE-0620959 and OCE-1237140. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.