CONSTRAINING HURRICANE WIND SPEED AT LANDFALL USING STORM SURGE OVERWASH DEPOSITS FROM A SINKHOLE IN ST MARKS, FL
Grain size analyses are performed on each event-deposit to help constrain flow conditions required for erosion and transport. Age constraints on the deposits are developed by using carbon-14, cesium-137, and lead-210 radiometric dating. A series of 2-D coastal inundation simulations of 152 synthetic storms using the Regional Ocean Modeling System (ROMS) establishes the relationship between hurricane wind speed and maximum grain size mobilized by the storm surge. This relationship is used to assess the most likely Saffir-Simpson category which produced each event-deposit.
It was found that 1) simulated wind speeds for modern deposits are consistent with the intensities for historical hurricanes affecting the site, 2) all deposits throughout the 2500 yr record are capable of being produced by hurricanes, 3) a period of increased numbers of intense hurricanes was observed between ~1700 and ~700 yrs ago which is consistent with past reconstructions from nearby sites, and 4) no major (> category 3) hurricanes have struck the site in the past ~500 years, suggesting that the current reoccurrence rate of 1 every 46 years for this area is high.