Mapping Rainfall and Flooding

Written By:
Walbert, David

Although Hurricane Floyd was the biggest storm of 1999 and the one most remembered, eastern North Carolina was hit by three hurricanes in a six-week period in September and October that year. All brought large amounts of rain. Hurricane Dennis (September 4...œ5) saturated the ground. Floyd (September 14-16) created the worst of the flooding. Then, a month later, Hurricane Irene (October 17) brought rivers and streams back to the flood stage.

The maps and charts on this page will help you analyze where and when the rain fell and why the flooding was so bad.

Paths of the hurricanes

The image below is a satellite image of eastern North Carolina, with tracks for Hurricanes Dennis, Floyd, and Irene, September...œOctober 1999. The red lines represent boundaries of river basins. If you look closely, you can see flooding along the Tar, Neuse, and Waccamaw rivers, as well as sediment plumes in Albemarle Sound and the Pamlico River.

A slow-moving storm

Hurricane Floyd was a very large storm -- much larger than most hurricanes, even many that were far more powerful. It also moved very slowly across eastern North Carolina, which is why rainfall totals were so high. The following animation shows satellite images of the storm for September 15 and 16; the numbers at the bottom show the date and time of each image.

Rainfall from Hurricanes Dennis and Floyd

The maps in the margins show rainfall in eastern North Carolina during the passage of hurricanes Dennis and Floyd, with the locations of selected rain gauges.

Rainfall amounts

The table below shows rainfall amounts from hurricanes Dennis, Floyd, and Irene at various locations in central and eastern North Carolina, with normal totals for the same period. The locations are divided by river basin (see below).

Rainfall from hurricanes Dennis, Floyd, and Irene, September–October 1999 .

Location Hurricane Dennis (Sept. 3–7) Hurricane Floyd (Sept. 14–17) Hurricane Irene (Oct. 17–18 Sept.–Oct. 1999 total Annual average rainfall
Tar-Pamlico River Basin
Oxford 6.07 5.67 1.94 20.15 43 (est.)
Louisburg 5.59 8.88 2.01 24.34 45.56
Rocky Mount 5.06-7.59 14.07-18.00 5.16 37.72 44.24
Enfield 7.01 11.84 4.30 32.39 44.54
Greenville 7.03 12.63 3.29 30.20 49.00
Washington 7.60 10.73 5.07 31.05 46.96
Neuse River Basin
Durham 3.30 5.98 0.91 18.60 48.10
Raleigh 8.46 6.55 1.50 24.24 41.43
Clayton 5.35 9.80 2.59 20.98 45.11
Goldsboro 7.19-7.94 12.06-12.70 4.36 32.10 49.27
Wilson 7.60 10.73 5.07 31.05 46.96
Kinston 6.07-6.93 13.35-13.98 5.37 29.48 51.20
New Bern 4.00 5.51 6.39 19.82 53.11
Trenton 7.42 14.98 >24.60a 52.22
Cape Fear River Basin
Chapel Hill 12.52 4.67 0.84 26.55 46.02
Dunn 4.50 7.65 4.34 23.81 47.72
Fayetteville 2.12 7.23 4.19 21.83 46.72
Clinton 2.96 11.50 4.33 27.50 49(est.)
Willard 1.30 13.23 >21.01a 53.04
Elizabethtown >1.19b >14.19b >6.69b >28.00b 46.78
Wilmington 0.59 19.06 2.73 27.10 54.27
Waccamaw and Lumber River Basins
Lumberton 1.34 9.82 5.48 24.16 46.54
Whiteville 1.52 16.76 5.97 34.27 48.73
Other sites
Lewiston 3.56 9.73 3.47 19.55 46.82
Williamston 7.20 16.28 5.54 35.55 48.07
Edenton 5.07 6.18 6.12 23.59 48.54
Elizabeth City 7.68 2.64 5.06 17.73 48.48
Plymouth 5.03 7.37 -- >15.15a 51.06
Morehead City 4.29 4.33 >11.21a 55.05
Hoffman Forest 6.49 9.78 >19.58a 55.60
(a) October rainfall records are unavailable.
(b) Partial record; some missing values for period.

River basins

By comparing the maps and data of rainfall totals with this map of river basins, we can see why flooding occurred where it did. A river basin is all the land drained by a given river. All rain that falls in the Cape Fear River basin, for example, runs off into streams and smaller rivers that eventually join the Cape Fear before it ends in the Atlantic Ocean. If there is a great deal of rainfall in a river basin, that river is likely to flood downstream -- even if the locations downstream didn't get much rain.

Based on this map and the data and map above, which rivers would you predict were most likely to flood?

Flood levels

The data below, provided by the U.S. Geological Survey, shows how high the water was at various streamgaging stations (stations where stream or river information is measured) at the peak of flooding. The recurrence interval is how often the river was expected to be that high. Note that in some places, the waters overflowed the 500-year floodplain -- the region where flooding would reasonably be expected an average of once every 500 years! (See this discussion of floodplains.)

Compare these flood levels with your predictions above. Were you right?

Hurricane Floyd flood information for selected streamgaging stations in North Carolina and Virginia

Station name 1999 floods
Date Peak stage (ft) Recurrence interval (years)
Chowan River Basin
Nottoway River near Sebrell, Va. 9/20 27.01 50-100
Blackwater River near Franklin, Va. 9/18 26.27 100-500
Meherrin River near Lawrenceville, Va. 9/18 29.95 10-25
Potecasi Creek near Union 9/16 28.9 >500
Ahoskie Creek at Ahoskie 9/17 17.32 >500
Roanoke River Basin
Cashie River near Windsor 9/16 18.52 >500
Tar-Pamlico River Basin
Tar River near Tar River 9/16 17.59 10
Tar River at Louisburg 9/17 26.05 50-100
Tar River below Tar River Reservoir 9/17 32.89 100-500
Tar River at Rocky Mount 9/17 31.66 100-500
Swift Creek at Hilliardston 9/17 21.30 >500
Little Fishing Creek near White Oak 9/16 30.8 >500
Fishing Creek near Enfield 9/18 21.65 500
Tar River at Tarboro 9/19 41.51 >500
Conetoe Creek near Bethel nd 19.79 nd
Tar River at Greenville 9/21 29.72 nd
Chicod Creek near Simpson 9/18 21.46 nd
Pamlico River at Washington 9/16 8.14 nd
Van Swamp near Hoke 9/16 7.43 25
Neuse River Basin
Neuse River near Falls 10/14 5.95 5-10
Crabtree Creek at U.S. 1 at Raleigh 9/16 16.88 nd
Neuse River near Clayton 9/17 20.67 25-50
Neuse River at Smithfield 9/18 26.72 >50
Swift Creek near McCullars Crossroads 9/16 13.06 10
Middle Creek near Clayton 9/16 13.02 10-25
Little River near Princeton 9/17 16.58 >500
Neuse River near Goldsboro 9/20 28.85 50
Neuse River at Kinston 9/22
 
9/23
27.71 50-100
Contentnea Creek near Lucama 9/16 25.0 100
Nahunta Swamp near Shine 9/17 21.00 >500
Contentnea Creek at Hookerton 9/18 28.28 >500
Neuse River near Fort Barnwell 9/20 22.75 nd
Trent River near Trenton 9/17 22.33 >500
New River Basin
New River near Gum Branch 9/16 25.12 >500
Cape Fear River Basin
Haw River near Bynum 9/16 13.42 <2
Deep River at Moncure 9/6 9.15 2-5
Cape Fear River at Lillington 9/16 14.46 2
Flat Creek near Inverness 9/16 3.84 2-5
Cape Fear River at Lock 3 9/17 21.59 10
Cape Fear River at Lock 1 9/20 23.30 5-10
Hood Creek near Leland 9/16 13.89 100
Black River near Tomahawk 9/18 27.14 100-500
Northeast Cape Fear River near Chinquapin 9/18 23.51 >500
Lumber and Waccamaw River Basins
Waccamaw River at Freeland 9/20 19.30 >500
Lumber River at Boardman 9/19 10.70 25

Source:Two Months of Flooding in Eastern North Carolina, September - October 1999: Hydrologic Water-Quality, and Geologic Effects of Hurricanes Dennis, Floyd, and Irene,” by Jerad D. Bales, Carolyn J. Oblinger, and Asbury H. Sallenger, Jr. USGS report.

Mapping the flood

How far did the floodwaters spread? The floodmap data combines satellite data from three different sources to give you a picture. How far floodwaters spread depends not only on how high the water is but on the local terrain. If the land near a flooded river is quite flat, the floodwaters may spread quite a distance.

 

Artifacts

Rainfall map for Hurricane Dennis. Dense rainfall on the coast.
Rainfall during Hurricane Dennis, September 4 - 5, 1999.

Rainfall during Hurricane Floyd. Dense rainfall on the coast.
Rainfall during Hurricane Floyd, September 14 - 16, 1999.

Map of rivers and basins in North Carolina.
Rivers and river basins of North Carolina, with cities and county outlines shown for reference.

comparisons of the flood data collected by AVHRR, Radarsat, and Landsat 7
This flood map shows a comparison of the flood data collected by AVHRR (pink pixels), Radarsat (red pixels), and Landsat 7 (green pixels). These colors show areas that were flooded in the wake of Hurricane Floyd. Due to interference from clouds and forest canopies, geographers often get the best insight into a flood when they use data from multiple satellite sensors.

A satellite image depicting paths of various hurricanes across North Carolina.

Satellite image of eastern North Carolina with generalized basin outlines and tracks for Hurricanes Dennis, Floyd, and Irene, September-October 1999. (Satellite image from National Aeronautics and Space Administration, 1999.)