IMPACTS OF 1999 HURRICANES ON THE DISTRIBUTION OF MUDS IN THE NEUSE RIVER ESTUARY, NC

Three hurricanes came ashore in North Carolina during September and October 1999. Associated record rainfall produced sustained high discharge in Coastal Plain streams, including the Neuse River. Highest discharges followed Hurricane Floyd, during mid-September through early October. During this period peak daily-average discharges in the Neuse River (Kinston, NC, USGS Station No. 02089500) exceeded 1000 m3/s, much higher than any other discharges recorded since March 1930. Satellite imagery from late September 1999 clearly shows highly turbid waters discharging into Pamlico Sound. Given these circumstances, substantial erosion and/or deposition of estuarine muds should be expected.

To test for impacts of 1999 flood discharges on muddy sediments of the Neuse estuary, we have re-occupied five stations where studies of modern sediment chronology (based upon excess 210Pb and weapons-fallout radionuclides) were conducted previously (1982, 1988, 1993). Sediment cores were collected by divers using SCUBA during November 1999 (two stations) and July 2000 (three stations). For convenience we designate the earlier (1982-1993) and later (1999-2000) cores "pre-hurricane" and "post-hurricane," respectively. Sediment porosity profiles are very similar in pre-hurricane and post-hurricane cores, indicating that any sediment redistribution did not substantially change lithologies at our stations. Initial chronological studies of post-hurricane cores, by gamma spectrometry for fallout 137Cs (+ radium isotopes and potassium) are still in progress. Existing data (1999 stations) provide evidence of significant sediment redistribution. At an upper-estuary site, where we have our best chronologic control, upward migration of the buried 137Cs peak implies net erosion of 6-7 cm after 1993. At a lower estuary site (opposite Oriental, NC) field observations (red mud in the top 6 cm) and burial of the 137Cs peak both imply net deposition, possibly exceeding 10 cm.