FLOOD10133

• County: Statewide
• Community: State of North Carolina
• Basin: Statewide
• Title: Two Months of Flooding in Eastern North Carolina, September-October 1999: Hydrologic, Water-Quality, and Geologic Effects of Hurricanes Dennis, Floyd and Irene
• Date: 1/1/2000
• Prepared By: USGS
• Floodplain - Doc Type: Flood Documentation Report

September inflow equivalent to 55-60
percent of annual inflow (table 5;
Robbins and Bales, 1995). Estimated
mean water residence time was about
7 days for the Pamlico and Neuse
River estuaries during September,
compared to a long-ternl annual aver-
age 01'72 and 68 days for these estuar-
ies, respectively (Bales and Robbins,
1995; Robbins and Bales, 1995).
During September-October 1999,
the total freshwater inflow volume to
Pamlico Sound was equivalent to
about 83 percent of the total volume
of the Sound, whereas under nonnal
conditions inflow volume during these
2 months is equivalent to about 13 percent
of the volume of the Sound (table 5; Giese
and others, 1985). This means that by the
end of October much of the water that was
in the Sound at the beginning of September
could have been displaced by floodwaters.
In September alone, the freshwater
inflow to Pamlico Sound was about an
order of magnitude greater than nonnal
(table 5). Although the Roanoke River
Basin comprises almost one-third of the
total Pamlico Sound drainage area, fresh-
water inflow from this basin accounted for
only about 10 percent of the total inflow to
the Sound because of (1) the presence of a
large flood-control reservoir near the
downstream end of the basin and (2) the
paths of the hurricanes, whieh avoided
much of the basin (fig. 2). On the other
hand, the Neuse and Tar-Pamlico River
Basins, which together compose about

USGS staff making a discharge measurement using an acoustic Doppler current
profiler on the Tar River

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Results of ADCP measurement at Tar River at Tarboru, :\J.C, showing CTOSS-
sectional distribution of velocity_ Negative velocities in the center of the channel
are about 5 feet per second and are oriented do\'.mstream. Kate upstream eddies
along the left edge. Total measured discharge was 33,600 ft3/s, and the width of
the measured cross section was 1,120 feet.

Tar River at Greenville, N.C.

31 percent of the Pamlico Sound drainage area,
eontributed about 44 percent ofthe inflow to the
Sound in September, and more than half of the
inflow to the Sound in October. This is particu-
larly important because both of these rivers
drain directly to Pamlico Sound and because
these rivers are known to carry relatively high
loads of nutrients and other contaminants (North
Carolina Department of Environment, Health,
and Natural Resources, 1993, 1994; Hamed and
others, 1995).

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Two rvlonths. of Flooding in Eastern :'\orth Carolina. September-Dctober 1999