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glossary
 
DESCRIPTION & DAMAGE OCCURANCES

A hurricane is a type of tropical cyclone that forms over warm tropical waters (80æF or higher) where the winds are light and the humidity is high. It begins as a tropical disturbance and can grow to become a hurricane as long as the above conditions are maintained.

Heavy thunderstorms and tremendously strong winds are generated from hurricanes. While hurricanes lose energy and fuel as they travel inland, they still bring torrential rains that lead to heavy flooding.

 

(Ahrens, 1996)

  • 1996. Four hurricanes passed through or within 210 km of North Carolina's coast.
    • July 12-13. Hurricane Bertha
    • August 31-September 1. Hurricane Edourdo
    • September 5-6. Hurricane Fran
    • September 13-14. Hurricane Hortense
  • 1999. Three hurricanes passed through NC, or near the coast.
    • September 4-5. Hurricane Dennis
    • September 16. Hurricane Floyd
    • October 17. Hurricane Irene

(www.nhc.noaa.gov/pastall.shtml; Paerl et al, 2001; Etherington & Eggleston, 2000).
Figure 1. Path of four major hurricanes passing through or near North Carolina in 1996.
Figure 2. Path of three major hurricanes passing through or near North Carolina in 1999.
Table 1. Freshwater inflow to Pamlico Sound (PS) during September and October 1999.
Freshwater input to PS
at 10^9 m^3
% of PS volume
Basin Drainage area, km^2 Sep-Oct Normal Sep-Oct Normal
Roanoke 25,400 2.49 0.93 9.6 3.6
Chowan 12,820 3.32 0.33 12.8 1.3
Neuse 14,560 5.58 0.54 21.4 2.1
Tar-Pamlico 11,190 4.61 0.31 17.7 5.0
All others 16,320 5.63 1.30 21.6 5.0
Total 80,290 21.63 3.41 83.1 13.2
taken from Paerl et al, 2001

This table compares normal volume of freshwater inflow to Pamlico Sound with inflow during September and October, 1999. The three hurricanes in 1999 occured within a six-week time span. This caused heavy flooding throughout most of the eastern part of the state, and increased freshwater input into Pamlico Sound.

The river basins received more than half of their annual rainfall in just two months. The floodwaters that resulted displaced three-fourths of the volume of the Sound in just six weeks. Normal displacement time is approximately 11 months!

  1. How do you think this flooding of freshwater impacted the estuarine ecosystem, and the blue crab population in particular?

(Paerl et al, 2001)

Table 2 compares the chemical and biological composition of the estuary's water during normal conditions with water composition between September and October 1999. The data shows that the chemistry of the water in the estuary was significantly altered during these six weeks.

  1. What effect would repeated hurricane and flooding events have on the water chemistry in the estuary?
  2. How do you think this change in water chemistry affected the inhabitants of the estuary, and the blue crab in particular?

 

(Paerl et al, 2001)
Table 2. Water chemistry in Pamlico Sound during September and October 1999 compared to normal.
  Normal Sep-Oct
Salinity 15 to 20 psu 7 to 9 psu
Dissolved Organic Carbon (DOC) 500 to 700 mM C 1,200 mM C
Dissolved Inorganic Nitrogen (DIN) 1 mM 10 mM
Suspended particulate carbon 80 mM C 200 mM C
Finfish & shellfish many mobile species moved out of estuary as freshwater flooded in; sessile, benthic invertebrates were killed or stressed.
Chlorophyll a increased 3- to 5-fold relative to normal
 
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This web site was created by Lynn Tran at the North Carolina State University, Department of Mathematics, Science, and Technology Education on 7/12/03. Faculty advisor Dr. David Eggleston, NCSU, Department of Marine, Earth, & Atmospheric Sciences. Last updated December 29, 2003 .