Hydro-metrologic assessment of October 2015 extreme precipitation event on Santee Experimental Forest Watersheds, SC
The extreme precipitation event on October 3-4, 2015, likely resulting from the convergence of a persistent the terrain, and the
circulation associated with Hurricane Joaquin off the eastern Atlantic Coast(http://cms.met.psu.edu/sref/severe/2015/04Oct2015.pdf) resulted in extreme present the precipitation amounts and intensities observed at four gauges on the USDA Forest Service Santee Experimental Forest (SEF) watersheds during this extreme event in conjunction with the antecedent conditions for 5 days prior to the event. All four rain gauges recorded 24-hr maximum rainfall of 340 mm or more during October 3-4, exceeding the Natural Resource Conservation Service (NRCS) 100-yr 24-hr design rainfall data. The 5-day antecedent measured rainfall prior to October 3 already exceeded 170 mm in three of the four gauges resulting in weekly (September 28-October 4) totals exceeding 625 mm in all gauges. Local surface water ponding of as much as 0.46 m above land surface was observed on one of the groundwater wells at an elevation of 10.395 m. The recorded stage heights at one 1st order (WS 80) and one- 2nd order (WS79) watershed gauging stations over topped the compound weir (WS 80) and weir/culvert (WS 79) outlets, with the highest stages coming near the invert of the bridge above the weir gauges and inundating large riparian areas upstream of them. Preliminary calculations yielded peak 3 s-1 (10.9 m3 s-1 km-2 or 996 cfs/mi2) and 33.9 m3 s-1 (6.8 m3 s-1 km-2 or 620 cfs/mi2) for a 1st and 2nd order watersheds, respectively. These values exceeded the previously measured peak discharges within a 25-year record of 3.8 m3 s-1 and 11.2 m3 s-1 for these two watersheds that were recorded on October 24, 2008. When compared discharges on October 4, 2015 exceed the values for a 500-yr provide insights for a need to revisit existing approaches for hydrologic analyses and design of cross drainage and other water management structures as concerns about extreme storm events resulting from global warming continue.