Types Of Floods

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE MORRISTOWN TN 
500 AM EDT TUE MAR 19 2013 

THE NATIONAL WEATHER SERVICE HAS DECLARED MARCH 18 THROUGH MARCH 22 
AS FLOOD SAFETY AWARENESS WEEK. THE NATIONAL WEATHER SERVICE IN 
MORRISTOWN WILL FEATURE A DIFFERENT EDUCATIONAL TOPIC EACH DAY 
DURING THE AWARENESS WEEK. 

TODAY'S TOPIC: TYPES OF FLOODS. 

IT FLOODS SOMEWHERE IN THE UNITED STATES OR ITS TERRITORIES NEARLY 
EVERY DAY OF THE YEAR. FLOODING CAUSES MORE DAMAGE IN THE UNITED 
STATES THAN ANY OTHER WEATHER RELATED EVENT... WITH AN AVERAGE OF 
EIGHT BILLION DOLLARS A YEAR AND AN AVERAGE OF NINETY FIVE 
FATALITIES PER YEAR IN THE PAST THIRTY YEARS. FLOODING CAN OCCUR IN 
ANY OF THE FIFTY STATES OR U.S. TERRITORIES AT ANYTIME OF THE 
YEAR... SOMETIMES VERY QUICKLY. BEING PREPARED IN ADVANCE AND 
KNOWING A FEW FLOOD SAFETY TIPS WILL HELP YOU AND YOUR FAMILY 
SURVIVE A FLOOD IF IT HAPPENS IN YOUR AREA. 

A FLOOD IS DEFINED AS ANY HIGH FLOW…OVERFLOW…OR INUNDATION BY WATER 
WHICH CAUSES OR THREATENS DAMAGE. THIS USUALLY OCCURS WITH PROLONGED 
RAINFALL OVER SEVERAL DAYS…INTENSE RAINFALL OVER A SHORT PERIOD OF 
TIME…OR WHEN AN ICE OR DEBRIS JAM CAUSES A RIVER OR STREAM TO 
OVERFLOW AND FLOOD THE SURROUNDING AREA. OTHER FACTORS THAT CAN 
CAUSE OR WORSEN FLOODING ARE MELTING SNOW IN THE WINTER AND EARLY 
SPRING…THUNDERSTORMS IN THE SPRING AND SUMMER…AND TROPICAL CYCLONES 
IN THE SUMMER AND FALL. 

FLASH FLOODING… A FLASH FLOOD IS DEFINED AS A RAPID AND EXTREME FLOW 
OF HIGH WATER INTO A NORMALLY DRY AREA…OR A RAPID WATER LEVEL RISE 
IN A STREAM OR CREEK ABOVE A PREDETERMINED FLOOD LEVEL. ONGOING 
FLOODING CAN INTENSIFY TO FLASH FLOODING IN CASES WHERE INTENSE 
RAINFALL RESULTS IN A RAPID SURGE OF RISING FLOOD WATERS. COMMONLY 
IT OCCURS WITHIN SIX HOURS OF A HEAVY RAIN EVENT. HOWEVER FLASH 
FLOODS CAN ALSO OCCUR WITHIN HOURS OR EVEN MINUTES IF A DAM OR LEVEE 
FAILS…FOLLOWING A SUDDEN RELEASE OF WATER HELD BY AN ICE OR DEBRIS 
JAM…OR RAPID PONDING OF WATER CAUSED BY TORRENTIAL RAINFALL. FLASH 
FLOODS CAN EVEN OCCUR IN AREAS AWAY FROM THE CAUSATIVE EVENT. FOR 
EXAMPLE…AN OTHERWISE DRY ARROYO OR CANYON CAN FILL QUICKLY FROM AN 
UPSTREAM RAIN EVENT. FLASH FLOODS CAN CATCH PEOPLE OFF GUARD AND 
UNPREPARED. YOU MAY ONLY HAVE A FEW MINUTES WARNING THAT THESE 
DEADLY…SUDDEN FLOODS ARE COMING. IF YOU LIVE IN AREAS PRONE TO FLASH 
FLOODS PLAN NOW TO PROTECT YOUR FAMILY AND PROPERTY. 

RIVER FLOODING… WITH RIVER FLOODING…THE NWS USES DIFFERENT 
CATEGORIES TO CONVEY THE EXPECTED FLOOD SEVERITY. THESE CATEGORIES 
ARE: MINOR FLOODING... MODERATE FLOODING... AND MAJOR FLOODING. EACH 
CATEGORY HAS A DEFINITION BASED ON PROPERTY DAMAGE AND PUBLIC THREAT 
AND ARE CLOSELY COORDINATED BY THE LOCAL NWS OFFICE…THE SERVICING 
RIVER FORECAST CENTER…OR RFC…AND OTHER EMERGENCY AND PUBLIC 
OFFICIALS. HERE ARE THE OFFICIAL DEFINITIONS OF THE NWS FLOOD 
CATEGORIES… 

MINOR FLOODING USUALLY HAS MINIMAL OR NO PROPERTY DAMAGE... BUT 
THERE COULD BE SOME LEVEL OF PUBLIC THREAT OR INCONVENIENCE. MANY 
TIMES YOU WILL HEAR THIS REFERED TO AS NUISANCE FLOODING. 

MODERATE FLOODING GENERALLY HAS SOME INUNDATION OF STRUCTURES AND 
ROADS NEAR STREAMS AND RIVERS. SOME EVACUATIONS OF PEOPLE AND 
TRANSFER OF PROPERTY TO HIGHER ELEVATIONS CAN BECOME NECESSARY WITH 
MODERATE FLOODING. 

MAJOR FLOODING OCCURS WITH EXTENSIVE INUNDATION OF STRUCTURES AND 
ROADS. SIGNIFICANT EVACUATIONS OF PEOPLE AND TRANSFER OF PROPERTY TO 
HIGHER ELEVATIONS MAY BECOME NECESSARY. 

AN ADDITIONAL CATEGORY OF FLOODING IS RECORD FLOODING. THIS IS 
FLOODING WHICH EQUALS OR EXCEEDS THE HIGHEST STAGE OR DISCHARGE 
OBSERVED AT A GIVEN SITE DURING THE PERIOD OF RECORD. THE HIGHEST 
STAGE ON RECORD IS NOT NECESSARILY ABOVE THE OTHER THREE FLOOD 
CATEGORIES…ESPECIALLY IF THE PERIOD OF RECORD IS SHORT. 

ONE THING TO NOTE: FLOOD CATEGORIES DO NOT EXIST FOR ALL FORECAST 
POINTS OR FLOOD LOCATIONS. THAT DOESN’T MEAN THEY DON/T FLOOD! 
CONTACT YOUR LOCAL NWS OFFICE MORE INFORMATION ON FLOOD CATEGORIES. 

COASTAL FLOODING… COASTAL FLOODING IS ANOTHER TYPE OF FLOOD. WHEN IT 
COMES TO TROPICAL CYCLONES…THE GENERIC TERM FOR A 
HURRICANE…TYPHOON…OR TROPICAL STORM…WIND SPEEDS DO NOT TELL THE 
WHOLE STORY. ALONG THE COAST…STORM SURGE IS OFTEN THE GREATEST 
THREAT TO LIFE AND PROPERTY FROM A TROPICAL CYCLONE. IN THE PAST, 
LARGE DEATH TOLLS HAVE RESULTED FROM THE RISE OF THE OCEAN 
ASSOCIATED WITH MANY OF THE MAJOR HURRICANES THAT HAVE MADE 
LANDFALL. HURRICANE KATRINA IN 2005 IS A PRIME EXAMPLE OF THE DAMAGE 
AND DEVASTATION THAT CAN BE CAUSED BY STORM SURGE. AT LEAST 1500 
PEOPLE LOST THEIR LIVES DURING HURRICANE KATRINA AND MANY OF THOSE 
DEATHS OCCURRED DIRECTLY…OR INDIRECTLY…AS A RESULT OF STORM SURGE. 
BY KNOWING YOUR VULNERABILITY AND WHAT ACTIONS YOU SHOULD TAKE…YOU 
CAN REDUCE THE EFFECTS OF A COASTAL FLOODING DISASTER. 

INLAND FLOODING… SINCE THE 1970/S…INLAND FLOODING HAS BEEN 
RESPONSIBLE FOR MORE THAN HALF OF THE DEATHS ASSOCIATED WITH 
TROPICAL CYCLONES IN THE UNITED STATES. TYPICALLY GREATER RAINFALL 
AMOUNTS AND FLOODING ARE ASSOCIATED WITH TROPICAL CYCLONES THAT HAVE 
A SLOW FORWARD SPEED OR STALL OVER AN AREA. THESE AREAS CAN BE RIGHT 
ALONG THE COAST BUT THEY MAY BE EVEN HUNDREDS OF MILES AWAY FROM 
WHERE THE STORM MADE LANDFALL. TROPICAL STORM LEE IS A RECENT 
EXAMPLE OF INLAND FLOODING SEVERAL HUNDREDS OF MILES AWAY FROM WHERE 
THE EYE OF THE STORM ULTIMATELY LANDED. IN 2011…TROPICAL STORM LEE 
MADE LANDFALL ALONG THE LOUISIANA COAST. BUT THE REMNANTS FROM THE 
STORM CAUSED HEAVY RAINFALL AND HISTORIC FLOODING IN WASHINGTON 
DC…PENNSYLVANIA…AND AS FAR AWAY AS NEW YORK. TEN FATALITIES…ALL IN 
PENNSYLVANIA…WERE CONFIRMED AS FLOOD RELATED DURING THE FLOODING 
ASSOCIATED WITH TROPICAL STORM LEE. 

RAINFALL FROM TROPICAL CYCLONE REMNANTS CAN CAUSE FLOODING IF 
CONDITIONS ARE RIGHT. FLASH FLOODING CAN OCCUR IN CREEKS…STREAMS…AND 
URBAN AREAS WITHIN A FEW MINUTES OR HOURS OF EXCESSIVE RAINFALL. 
STREETS CAN BECOME SWIFT MOVING RIVERS AND UNDERPASSES CAN BECOME 
DEATH TRAPS. RIVER FLOODING CAN OCCUR FROM HEAVY RAINS ASSOCIATED 
WITH DECAYING TROPICAL CYCLONES…AND IN EXTREME CASES… RIVER FLOODS 
CAN LAST A WEEK OR MORE. JUST BECAUSE YOU DON/T LIVE NEAR THE COAST 
DOESN/T MEAN YOU WON/T BE IMPACTED BY TROPICAL CYCLONE FLOODING. 

KNOWING THE DIFFERENT TYPES OF FLOODS…HOW TO PREPARE FOR THEM…AND 
KNOWING THE ACTIONS TO TAKE DURING…AND AFTERWARDS CAN SAVE YOU 
TIME…MONEY…AND EVEN YOUR LIFE. PREPARE NOW…AND BE A FORCE OF NATURE! 

JOIN US TOMORROW FOR INFORMATION ON TURN AROUND DON/T DROWN. 

&& IMPORTANT FLOOD WEBSITES NWS AHPS: HTTP://WATER.WEATHER.GOV/AHPS/ 

NATIONAL HURRICANE CENTER: HTTP://WWW.NHC.NOAA.GOV/ 

NWS MARINE AND COASTAL SERVICES: 
HTTP://WWW.NWS.NOAA.GOV/OM/MARINE/MARINE.SHTML 

NWS FLOOD SAFETY AWARENESS: HTTP://WWW.FLOODSAFETY.NOAA.GOV/ 

NWS: HTTP://WWW.WEATHER.GOV/ 

NWS WRN: HTTP://WWW.NWS.NOAA.GOV/COM/WEATHERREADYNATION/ 

BE A FORCE OF NATURE: 
HTTP://WWW.NWS.NOAA.GOV/COM/WEATHERREADYNATION/FORCE.HTML 

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