Analysis and Extent of Santa Fe River Flooding in North Florida Attributed to Rainfall and Wind Damage Associated with Hurricane Irma

Abstract

The Santa Fe River (SFR) is within the north Florida area of the regional Floridan aquifer system. The extent of recent flood damage in the SFR and tributaries in Bradford County has been attributed to rainfall and wind damage to trees associated with Hurricane Irma, September 2017. Implications of the determined cause of a disaster can include the allocation of disaster relief funds. Bradford County, Florida obtained approximately $2.5 million from the United States Department of Agriculture’s (USDA) Natural Resources Conservation Service (NRCS) for emergency flood abatement assistance and $255,875 from the Suwannee River Water Management District (SRWMD), combined with $13,750 in-kind match provided by the county, based on the attributed cause of that damage to rainfall and winds from Hurricane Irma. On January 2, 2018, Bradford County commissioners also approved grant applications to the SRWMD for $2.2 million for Alligator Creek Flood Mitigation and for $90,250 for Hampton Lake Canal to Santa Fe River Flood Mitigation, requiring in-kind matches from the county of $110,000 and $4750, respectively. Our study analyzed historical precipitation data for the SFR Basin and headwaters from 1895 through 2017 and recorded discharge and gage heights from the United States Geological Survey (USGS) to evaluate that presumed cause of flood damage in that basin and to provide a better understanding of historical relationships between precipitation, gage data and flooding in that basin. Recorded USGS peak gage height and Digital Elevation Models (DEMs) also were used to illustrate the lateral extent and relative depth of flooding associated with an extreme precipitation event in the lower SFR vicinity of O’Leno State Park. Finally, we evaluated the condition of the trees in the SFR Basin as an indicator of long-term anthropogenic groundwater alterations. Those data and analyses did not support the conclusion that Hurricane Irma was the only cause of the magnitude and extent of SFR flooding and tree damage in Bradford County and adjacent counties. Other contributors to stream flow in the SFR basin include heavy mineral mining wastewater discharges that have exceeded the maximum discharge volume of “40 million gallons a day” (MGD) under the National Pollutant Discharge Elimination System (NPDES) permit issued by the Florida Department of Environmental Protection (FDEP) to the Chemours Company TT LLC (Chemours, formerly DuPont) for Trail Ridge mining operations. The magnitude of those discharges suggests that those discharges and extensive Trail Ridge mining in Baker, Bradford, Clay, and Duval Counties contributed to the flooding and were a factor in the tree destruction in the SFR Basin.