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

Hurricane Floyd floodwaters during
this 36-day period (fig. 16). At Tar-
boro (site 14) almost 80 percent of
the mean annual load (2,200 tons;

2.000

~ 1,500
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6
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9
z
~ 1,000
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z
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highest nitrogen load was estimated
to have occurred during flooding
(fig. 15). The sample, collected in
advance of the peak streamflow on

Nause AiveratKinston
IHurricaneFranl
I

Neuse River at Kinston
IHurricaneFtoydl ..'
>

.'

I
Neuse River near
Goldsboro
(Hurricane Fran)
-NeuseRivernearGoldsboro
(Hurricane Roydl
Nause RiveratSmrthfield
lHurricaneFloydl
I

i'
Nause River at Smithfield
lHurricaneFranl

3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
ELAPSED DAYS

Figure 16. Cumulative total nitrogen load at selected Neuse River sites in
floodwaters from Hurricanes Floyd (1999) and Fran (1996),

Hamed and others, 1995) was
transported in Hurricane Floyd
floodwaters (fig. 17).
One flood sample (table 6) was
collected in the Neuse River near
Fort Barnwell (site 32), where the

2,500

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z
o
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6
g 1,500

z
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~ 1,000
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u 500

Tar River atTarboro
IHurricaneFloyd)
I

September 22, had a total nitrogen
concentration of 1. 77 mg/L as N.
Two previous measurements of total
nitrogen at this site in April and July
1999 under low-flow conditions had
concentrations that were similar to

Cape Fear River
atlockl
(Hurricane Franl
1//
,'~

-CapeFearAiveratlockl
IHurricanefloyd)
Tar Aiver atTarboro
IHurricane Franl
...1....

3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35
ELAPSED DAYS

Figure 17. Cumulative total nitrogen load at selected Tar and Cape Fear
River sites in floodwaters from Hurricanes Floyd (1999) and Fran (1996).

the concentration measurcd in Sep-
tember 1999. The median (1.23 mg/L
as N) of these three analyses (April,
July, and September) was used as an
estimate of concentrations before and
after the peak streamflow. This
resulted in an estimate of 3,900 tons
for the floodwater nitrogen load and a
total nitrogen yield of 1.0 tons per
square mile (tons/mi2). To detenninc
a max imum load and yield, the con-
centration measured during the flood-
ing (1.77 mg/L) was used as an
estimatc of concentration for the
entire period, and resulted in an esti-
mated load of 5,400 tons and a yield
of 1.4 tons/mi2 A conservative esti-
mate of nitrogen concentration is
based on the minimum concentration
(1.11 mglL as N on April 21, 1999)
previously measured at Fort Barn-
well, and results in a load of about
3,500 tons and a yield of 0.9 tons/mi2.
The total load of nitrogcn
carried in Hurricane Floyd flood-
waters was quite similar to the total
load carried by Hurricane Fran flood-
waters in the Neuse River (fig. 16)
and the Tar and Capc Fear Rivers
(fig, 17)-despite the greater total
streamflow resulting from Hurricane
Floyd. Nitrogen concentrations
generally were less in Hurricane
Floyd floodwaters than following
Hurricane Fran (Bales and Childress,
1996). In the Tar River Basin, where
the Hurricane Floyd peak dischargc
was more than three times that from
Hurricane Fran, nitrogen load at site
14 was 1,800 tons in Hurricane Floyd
floodwaters compared to 590 tons in
Hurricane Fran floodwaters.
For the period September 15
to October 20, total nitrogen yield
in basins upstream from the sampled
sites ranged from 0.34 to 1.1 tons/mi2
(fig. 18A). Although the total
nitrogen load was much smaller for
the Northeast Cape Fear River
(site 43) than for the Neuse River

Two rv10nths of Flooding in Eastern North Carolina, September-October 1999