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Spring Weather Safety Campaign Kickoff
February 28 - March 5, 2016

FLOODS/FLASH FLOODS

 

 Resource: National Weather Service Flood Safety Page

                      Turn Around, Don't Drown Page and Video

***Fact: Floods and flash floods kill more people across the nation than any other weather hazard***
Terminology:

Flash Flood:
Flash floods involve a rapid rise of water that can develop quickly, within minutes to hours of the onset of heavy rain. It is even possible to experience flash flooding in an area that does not receive rain if heavy rain is occurging upstream.  They can also be caused by the failure of a dam or levee. Flash floods cause most of the fatalities associated with flooding events. Usually, less warning lead time is provided for flash flooding so quick action and decision making may be required.

Urban Flood:
Flooding can occur more quickly in urban areas as more runoff is created in developed urbanized areas with less green space available. . Urbanization increases runoff by 2 to 6 times over what would occur in natural terrain. Flood waters can fill streets, freeway underpasses, and parking lots and can sweep away cars.

River Flood:
Heavy rainfall falling over a widespread area (such as a large portion of a watershed) over a prolonged period (like several days) can cause river flooding. Typically, river flooding begins as a high crest on the upper part of a watershed that takes several days to move downstream. Due to the slow nature of river flooding, ample advanced warning is provided to evacuate people or property in the path of the flooding.

National Weather Service Flood Products:


Flood or Flash Flood Watch
Conditions will be favorable for flooding or flash flooding during the specified period. This usually means heavy rainfall is expected, especially following a period of wet weather when soils are saturated.

 

Flash Flood or Areal Flood Warning
Flash Flood Warning implied flash flooding is reported or is imminent in the areas specified in the warning. Take immediate precautions to protect yourself, most importantly be certain not to drive through flooded areas. Flooding is considered life threatening. If the flooding is more gradual based on a longer period of rain, the areal flood warning may be used.

Flood Warning
Flooding forecast or occurring at and near a forecast point along a river or bayou. This is similar to the Areal Flood Warning described above except the warning applies to a point along a river rather than a general area.


Urban and Small Stream or Areal Flood Advisory
Flooding of streets, low-lying areas like underpasses and storm drains, and small streams is expected. Caution should be taken while traveling.  Flooding may be dangerous and could be life threatening if caution not excersised.




How does flooding impact southeast Texas?

Flooding in Friendswood (Harris County) during Tropical Storm Allison, June 2001. Flash flooding is a relatively common event over Southeast Texas. Tropical systems during the summer and early fall, and strong winter storm systems can cause widespread flooding and flash flooding across the area. Flash flooding can also be produced by strong slow-moving thunderstorms especially during the spring and summer months. Flooding and flash flooding can occur anywhere in southeast Texas, but is usually most severe near major watersheds like the Colorado, Brazos, San Jacinto or Trinity Rivers, and near urban areas like the Houston metropolitan area.



What are some major floods that have impacted Southeast Texas?
August 16, 2007
Tropical Storm Erin made landfall along the middle Texas coast around the Port Aransas area. A southeast to northwest feeder band developed from Katy to the western end of Galveston Island in the morning and moved slowly eastward to a line from Clear Lake to Humble by late in the afternoon. Training of cells along this line combined with rainfall rates upwards of 4 to 5 inches per hour resulting in major street flooding and minor flooding of several bayous in Harris County. Widespread major street flooding occurred throughout the afternoon across the eastern half of Harris county with SH 288 impassable near the 610 south loop, I-10 east closed at Wayside, and numerous secondary roads closed along I-45 S, SH 225, and I-10 E. Flooding of homes and businesses occurred in the La Porte area where some structures were inundated with more than a foot of water. House flooding also occurred in the Pasadena area. There were also at least a dozen schools that received water damage. There were three fatalities from this flood. Two deaths were from a supermarket roof collapse under the weight of the heavy rainfall. The third death was from a vehicle that drove into a flooded detention pond.

June 19, 2006
Some water rescues occured with this flash flood event that brought flood waters from 2 to 8 inches to as high as 18 to 20 inches into homes along area bayous and creeks. Sections of Sims, Halls and Hunting Bayous along with parts of Vogel and White Oak Creeks experienced significant flooding. The Washburn Tunnel was flooded and impassable while Interstate 10 at federal Streets bypass was under water. Approximately 3,370 homes were flooded in the Interstate 10 and Beltway 610 vicinity (Belfort an Telephone Roads).

June 8-9, 2001
Tropical Storm Allison devastated a large portion of Southeast Texas with an incredible amount of rain as she meandered around Southeast Texas for over five days. Between the 5th and the 10th, much of Houston and the surrounding areas to the north, east and south received between 15 and 35 inches of rain which caused devastating flooding and flash flooding. The largest amount fell over a 6 to 12 hour period on the 8th and 9th resulting in 22 deaths in the Houston area. More than 48000 homes were damaged (11000 with major damage and 3600 completely destroyed). More than 70000 automobiles were flooded during the storm. In Harris County alone, an estimated 300 billion gallons of water fell. This amount was enough to fill the Astrodome more than 5600 times! Allison ended up being the costliest tropical storm ever (>$5 billion) for the state of Texas and for the United States.

September 11,1998
Tropical Storm Frances made landfall along the upper Texas coast on September 11th. As the storm moved inland, widespread heavy rainfall occurred in the Houston metropolitan area. Rainfall amounts of up to 16 inches were reported in the downtown Houston area. Frances caused extensive flooding along White Oak Bayou and flooded several major roads and freeways in the Houston area.

October 17-21, 1994
The October 1994 Floods were perhaps the worst floods to impact southeast Texas on record. Lake Livingston recorded a record height on the 17th and a record flow of 110,000 cfs. Liberty recorded 30 inches of rainfall in less than 48 hours, and much of the city went underwater due to a failed levee system. Spring Creek and Lake Houston set new flood crest records. Several major highways into and out of Houston were flooded including I-45 north of Houston and US 59 northeast of Houston. Four fuel pipelines ruptured on the San Jacinto River, causing a massive fuel spill and widespread fires. An estimated 22,000 homes were flooded across southeast Texas during this event, with $900 million in damage reported. Seventeen fatalities resulted from the floods.
The power of moving water (image from New Braunfels flash flood - June 9, 2010). More than half of all flash flood fatalities in 2014 were auto related. Road washout from heavy rainfall at Bastrop State Park Jan. 25, 2012.
What do you do in flash flood situations?
The worst place to be in a flash flood is traveling by car.
TWO FEET of water will carry away most automobiles.
Do not cross water flowing over a roadway if you do not know its depth.
 


Things you can do ahead of time to prepare for major floods:
  1. Know the flood risk at your place of home or business and its elevation above flood stage.
  2. Store drinking water in clean bathtubs or containers. This is very important as flood waters will contaminate the drinking water supply in your area.
  3. Stock non-perishable food items requiring little cooking and no refrigeration.
  4. Keep first aid supplies on hand.
  5. Keep NOAA Weather Radio, battery-powered portable radio, emergency cooking equipment, and flashlights in working order.
  6. Install check valves in sewer traps to prevent flood waters from backing into your home.



Disaster Supply Kit
Flood disaster supply kit:
first aid kit
canned food/can opener
bottled water
rubber boots/gloves
NOAA Weather Radio
battery-powered radio/batteries
flashlight


What city/county officials can do:

Keep updated with the latest warnings, watches, advisories, and statements issued by the National Weather Service and be prepared to take action as necessary. Monitor flood prone areas in your jurisdiction for flooding or rising water.

Assist hospitals and other operations which are critically affected by power failure by arranging for auxiliary power supplies.



What do you do when a Flash Flood Warning is issued or flooding is imminent?
  1. If advised to evacuate, do so immediately. However your best action may be to shelter in place.
  2. Move to a safe area...not cut off by flood waters. If applicable move to higher ground.
  3. Avoid areas you know are subject to flooding.
  4. Do NOT attempt to drive over a flooded roadway. Do not drive into barricaded areas, the barricades are there for a reason!
  5. Children should never play around storm drains, creeks, streams, or rivers, or in flooded streets.

 




What do you do after the flood has passed?
Cape Hatteras area home destroyed by flooding from Hurricane Isabel in 2003.
  1. Boil drinking water before using. Do not use tap water without boiling it!
  2. Seek necessary medical care at the nearest hospital. Clothing, food and shelter are available at the nearest Red Cross.
  3. Do not visit disaster areas. You may hamper rescue and emergency operations.
  4. Electrical equipment should be checked or dried before being returned to service. Make sure to wear rubber gloves and rubber boots when working with electrical equipment.
  5. Report broken utility lines to the proper authorities.


Flood Statistic for Southeast Texas (1992-2015 graphs)
Flood Events (by year)
Flood Events (by county)
Flood Events (by month)
Flood Events (by time)
Remember...if your car stalls in high water, leave it and seek higher ground!

 


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