FLOOD10133 - Laserfiche WebLink

Home Browse Search

occurs during the storm. Dry soil allows more infiltration of rainfall and less run- off, whereas wet soil results in more runoff for the same amount of rainfall. The soaking rains from Hurricane Dennis (table I) that fell over a wide area of eastern North Carolina immedi- ately prior to Hurricane Floyd resulted in wet soils capable of storing little additional water. Another factor that affects the rela- tion of a particular rain event to the potential for flooding is the spatial extent and duration of the rainfall rela- tive to the watershed size. An intense, localized thunderstorm may result in IOO-year rainfall over part ofa basin but little rainfall over the remainder of the watershed, resulting in minimal down- stream flooding. Moreover, a IOO-year, I-hour storm on a l-square-mile (mi2) basin willmore likely result in severe flooding in that basin than the same event on a I ,OOO-mi2 basin; longer dura- tion storms generally are required to produce flooding in large river basins. Consequently, the wet soils caused by Hurricane Dennis, the broad regional coverage of rainfall from Hurricane Floyd (table 1; fig. 4), and the long dura- tion of the rainfall combined with the large rainfall amounts (table 2) ensured that unprecedented regional flooding would occur in eastern North Carolina in response to these storms. Flooded car in Greenville, N.C. Grifton, ~.c. ,:'"- Flooded church near the Black River near Tomahawk, N.C. ~ " ~ ~ I~". a: Q:t~ "eo ""'l!~;',.... ~~" Surf at Pine Knoll Shores, N.C., prior to Hurricane Floyd landfall ~ w a u z Two ~tomhs of Flooding in Eastern North Carolina, September-October 1999