Special Report - US: Flooding to Inundate Gulf Coast through Early September, Even as Rainfall Abates

Thursday Aug. 31, 2017

Special Report - US: Flooding to Inundate Gulf Coast through Early September, Even as Rainfall Abates

Executive Summary

Tropical Storm Harvey has made its final landfall and will weaken over the next several days. However, the storm will continue to bring life-threatening weather conditions to southeastern Texas and southern Louisiana over the coming days. As of Aug. 30, officials have linked at least 24 deaths to Harvey's impacts. A long-duration, catastrophic flood event is underway in southeastern Texas and southern Louisiana, particularly in the Greater Houston area. The widespread flooding will likely continue throughout the region into at least early September.

Projected path of Tropical Storm Harvey through Sept. 2. Data obtained from the US National Hurricane Center.

Key Judgments

  • Rainfall will steadily decline over the next several days, but protracted flooding will persist through early September. 
  • Health risks in the area are likely to become more severe due to the threat posed by floodwaters and the increased potential for disease transmission at emergency shelters, which may house more than 32,000 people by the end of the week.
  • The storm and associated flooding have brought business operations and transportation to a halt; disruptions are likely over at least several weeks, as floodwaters recede and recovery efforts begin.

Tropical Storm Harvey came onshore near Cameron, Louisiana, early Aug. 30. As of 1600 CDT, the center of circulation was located approximately 80 km (50 miles) north of Lake Charles, Louisiana. Harvey should continue tracking northeastward over the Mississippi River Valley in the coming days. The system will likely weaken into a tropical depression by Aug. 31, and should dissipate over the Ohio Valley by Sept. 2. 

As of Aug. 30, widespread accumulations of 50-101 cm (20-40 inches) have been reported across much of southeastern Texas. A record-setting 130 cm (51 inches) was recorded at Cedar Bayou near Mont Belvieu, Texas. The threat of torrential rainfall has subsided in the Greater Houston and Galveston areas; however, life-threatening flooding will be a protracted issue. Heavy rain continues near the Texas/Louisiana border as of the afternoon of Aug. 30, with additional accumulations of 7.5-15 cm (3-6 inches), and isolated amounts of up to 25 cm (10 inches), possible as the system moves northeastward. Additional rainfall totals of 5-10 cm (2-4 inches) are possible elsewhere in parts of the Mississippi River Valley and central Gulf Coast. Thunderstorms will likely continue to produce isolated tornadoes and waterspouts as heavy bands come onshore throughout the affected area.

The intense rainfall has resulted in a catastrophic flooding event in southeastern Texas. Flash and areal flooding will occur on roadways, bayous, creeks, and rivers throughout the region, including along the Brazos, Calcasieu, Colorado, Navidad, Neches, Sabine, San Bernard, San Jacinto, and Trinity rivers. As of midday Aug. 30, 54 water gauges along creeks, bayous, and rivers in Texas and Louisiana were at major or moderate flood stage. This number will likely fluctuate in the coming days as runoff drains toward the Gulf of Mexico. Water levels in small streams and bayous will likely recede faster than larger rivers throughout the region; many of these bodies of water will probably remain above flood stage into early September.

Flood-control systems throughout the region will be stressed by the water volumes, and some protection measures - such as levees and dikes - will probably fail. The levee at Columbia Lakes, located to the south of Houston in Brazoria County, was also breached Aug. 29. The area was placed under a mandatory evacuation Aug. 27 when officials forecasted the failure of the flood system.

As of Aug. 30, the US National Weather Service (NWS) maintains several flash flood watches, as well as flood and areal flood warnings for counties in southeastern Texas and Louisiana. A flash flood emergency is also in effect for Hardin, Jasper, Jefferson, Newton, Orange, and Tyler counties in southeastern Texas until at least 0030 CDT Aug. 31. The NWS will almost certainly continue to update and expand the alert coverage area as the flooding situation evolves. 

Houston Situation

A long-duration, catastrophic flooding event continues in the Greater Houston area in Texas. Many waterways have exceeded 500-year flood levels, and some are approaching 1,000-year flood levels. Water levels along most rivers, creeks, and bayous throughout the region are at moderate or major flood stage; historic flooding will likely continue in some parts of the Greater Houston area into early September. 

Flooding conditions in southeastern Texas as of Aug. 30.

The city's drainage system remains overwhelmed, some dams have been overtopped, and Buffalo Bayou has flooded portions of downtown Houston. As of Aug. 30, controlled and uncontrolled releases were ongoing at the Addicks and Barker reservoirs in West Houston, which has resulted in street and structural flooding in nearby subdivisions of the city. An estimated 4,000 nearby homes have been inundated by the releases, which will probably continue for several days. Water levels at the Addicks Reservoir are forecast to reach their peak on Aug. 30; officials do not believe any additional structures that have not already experienced flooding from the releases will become inundated. Water levels could rise somewhat along Buffalo Bayou near the reservoirs; however, only minimal rises are forecast in downtown Houston areas. 

Rapidly rising water has also forced thousands of people to evacuate their homes or move to elevated locations in multiple parts of the metropolitan area. Police have urged stranded people to climb onto roofs rather than move to attics, which can become flooded without warning, and to hang sheets or towels outside of residences so rescue teams can locate them. Flooding has forced the closure of numerous roads throughout Greater Houston, including several locations along I-10, I-45, I-69, I-610, Beltway 8, the Hardy Toll Road, and the Sam Houston Tollway. As of the evening of Aug. 30, there were over 175 routes throughout the metropolitan area experiencing high water.

Emergency responders have conducted thousands of rescues so far, and are generally overwhelmed. Response times will be delayed in even the best circumstances. Emergency staging areas have been established throughout the city, but first responders have had difficulty reaching some of these sites due to high water and streets blocked by stranded vehicles. Helicopter and boat rescues generally do not take place during darkness hours, to reduce the danger from submerged hazards. The US Coast Guard is assisting with water rescues, and has provided several hotlines to call for those in distress.

Transportation and Utilities

Widespread power and utility outages are ongoing in southeastern Texas and southern Louisiana. It could take weeks for crews to reach outage areas due to flooded and blocked roadways. Outages can be expected in the Entergy service areas in Texas and Louisiana, as well as the CenterPoint Energy, TNMP, and AEP Texas service areas. Estimates indicate that over 278,000 customers are without power in southeastern Texas as of Aug. 30.

Harvey will continue to cause extensive ground, air, and maritime transport disruptions throughout the affected area into at least Sept. 1. Traffic and commercial trucking delays are highly likely on regional highways in the US, including along portions of the I-10, I-12, I-20, I-30, I-35, I-37, I-45, I-49, I-55, I-59, and I-69 corridors. Secondary and low lying roads will be inundated by floodwaters; authorities will likely close roads to traffic, especially those along the coast or in frequently flooded locations of urban areas. Flooding could wash away roads and bridges, and repairs could take several weeks to complete. Standing water will probably block some low-lying roads for several days following Harvey's dissipation. Strong winds will pose a hazard to high-profile vehicles.

Both Houston George Bush Intercontinental Airport (IAH) and Houston Hobby Airport (HOU) resumed limited operations Aug. 30. Authorities have said that both airports will likely resume full operations by Sept. 2. Airports in Louisiana will likely experience significant flight disruptions as Harvey moves through the state Aug. 30-31. As of 1400 Aug. 30, all major airports in the state remain open except for Lake Charles Regional Airport (LCH), which is expected to reopen in the evening Aug. 30. Significant flight disruptions are continuing at other regional airports that handle a high volume of flights from the Houston area (IAH, HOU). Significant airline network disruptions are expected to persist through at least Sept. 2.

Temporary port closures have occurred in Corpus Christi, Ingleside, Freeport, Galveston, Texas City, Houston, Sabine Pass, Port Arthur, Port Neches, Nederland, Orange, Beaumont, and Lake Charles. As of Aug. 30, the US Coast Guard maintains Port Condition "Zulu" - which suspends all inbound and outbound traffic - for the ports; the conditions are expected to persist through at least Aug. 30. The Port of Corpus Christi is conducting damage assessments and recovery operations; estimates indicate the facilities could reopen on Sept. 4. Container terminals and general cargo facilities will remain closed at Port Houston through at least Aug. 31.

Regionwide Government Response

Coordinated federal, state, and local rescue and recovery efforts are ongoing to deal with the life-threatening effects of Harvey in Texas, particularly the ongoing catastrophic flooding situation in Houston. Texas Gov. Greg Abbott has declared a state of disaster in 50 counties, and at least 18 of these have also been declared federal disaster areas. These decrees have allowed for the rapid deployment of state and federal resources, including thousands of personnel. Over 14,000 Texas Army National Guard members have been mobilized and sent to affected areas, including Corpus Christi, Houston, and Victoria. The federal government is prepared to send up to 30,000 additional National Guard troops to the area if needed. More than 400 Humvees and high-water vehicles have been deployed, and at least 30 military aircraft are conducting search and rescue missions.

Nearly 2,000 Federal Emergency Management Agency (FEMA) personnel and more than 400 US Coast Guard (USCG) members are also supporting operations. The USCG has deployed nine shallow-water rescue teams and at least 15 helicopters in the region to conduct rescues. Mobile medical teams and equipment - including air ambulances - have been sent to the region, as some local hospitals have been forced to close due to flooding. Police and first responders in Houston have responded to tens of thousands of emergency calls and conducted hundreds of water rescues; however, the city lacks boats capable of conducting night-time rescues. Dozens of aid-group and government-operated shelters have been opened in the Greater Houston area and other localities impacted by the storm. Authorities have also asked the public to assist in recovery efforts -  including participating in search-and-rescue operations and clearing debris - as long as it is safe to do so.

Disaster preparations have been underway in southern Louisiana, as heavy rainfall from Harvey is expected to cause destructive flooding in these areas as well in the coming days. At the request of Louisiana Gov. John Bel Edwards, the federal government has pre-emptively declared five parishes - Beauregard, Calcasieu, Cameron, Jefferson Davis, and Vermillion - as emergency disaster areas; additional declarations could be issued as conditions worsen. These measures will allow FEMA to coordinate relief efforts in these localities. Due to the extent and severity of the flooding, local, state, and federal recovery efforts will likely persist for months or years, following the passage of the storm.

Health Concerns

Avoid immersion in floodwaters, if possible. The floodwaters have increased threats from mosquito-borne disease and water-borne contaminants, especially from vehicles and industrial sites that have been inundated. Floodwaters also become vectors for the spread of disease. Take precautions to avoid mosquito bites; the threat from insect-borne disease will increase as waters recede.

Rapidly Moving Water

Even water that appears shallow or slow moving may have swift undercurrents or very deep segments due to erosion or missing manhole covers. Never attempt to cross standing water. If you cannot see the road or its line markings, do not drive through the water. As little as 30 cm (1 foot) of water can move most cars off the road, and as little as 15 cm (6 in) of fast-moving water can sweep a person off of his or her feet.

Hypothermia

Prolonged exposure to cold or cool water or mud can lead to hypothermia and decreased survival time even in temperatures as high as 27 C (80 F). Between 21-27 C (7-80 F), survival time is estimated to be as little as 3 hours for some, with exhaustion and unconsciousness occurring between 3 and 12 hours' time. In areas where the water temperature is between 4-15 C (40- 60 F), the survival time is reduced to 1 to 6 hours. Keeping dry is very important to surviving in most flood prone environments.

Mechanical Hazards

Floodwaters are very strong and can displace large structures, breaking them apart in the process of washing them away. Hidden in murky waters may be exposed glass and metal that can cause serious injury, as well as nails and other sharp objects. Continually shifting waters may cause entrapment by large moving objects unexpectedly pinning a victim. Additionally, electrical lines may be broken, and charged power lines may remain in flood waters, causing electrical hazards. Until the power is turned off at the main breaker, assume the lines are still active. This includes flooded basements and dwellings.

Toxic Spills

Flooding may occur near industrial sites, raising concerns of toxic chemicals and hazards being released in an uncontrolled manner into the environment and contaminating the surrounding ecosystems. Poisonings caused by the release of above or underground chemicals that may combine inadvertently may occur immediately or may take months following exposure. Avoiding contaminated floodwaters and using personal protective clothing and equipment to prevent contact with water are the best means of preventing illness and injury.

Food

Food can be contaminated easily by floodwater contact; contaminants with pathogens and chemicals may cause illness. Any food that has been in contact with floodwaters should be treated as if it is contaminated. All food should be cooked thoroughly. Food may only be salvaged if it is in a commercially canned metal or rigid sealed plastic container and can be washed in a solution of warm clean water and detergent. The entire container should then be sanitized by soaking in a solution of one tablespoon of bleach in a gallon of clean water. Products should be relabeled with any information from the original label. Even cans with "easy open" tops should be considered unsafe and discarded, as bacteria may enter at the seams.

Water

Sealed and bottled water is preferred for consumption as drinking water. There are several methods to treat water if sealed and bottled water is not available. Add 8 drops of sodium hypochlorite (bleach) to clear water or 16 drops to turbid water in a one gallon, standard sized container and agitate. Wait 30 minutes before drinking. You can also treat clear water with water purification tablets per manufacturer's directions. 

  • Take care when considering boiling water for disinfection. Remember that if the water is chemically contaminated, boiling will merely concentrate the toxic chemicals, not eliminate them.
  • Add 5 drops of a 2-percent iodine solution to one liter of water and let stand at least 30 minutes, or longer if colder than 25 C (77 F). Do not use iodine if there is an allergy, if pregnant, or if thyroid disease is present.
  • Use portable water filters per manufacturer's directions. These do not filter all chemicals and viruses. Check the manufacturer's guide.

Disease Threats

Disease hazards following a flood will vary depending upon location. The most common threats will be due to waterborne disease risks from bacteria or viruses carried from poor sanitation and agricultural disruption. Illnesses such as Campylobacter, Giardia, and Cryptosporidia are possible pathogens to be found. Tetanus, normally occurring in the soil and on debris, is also a high risk. In temperate climates, mosquito-borne threats are a problem several weeks following floods when waters recede and standing pools have yet to be absorbed into the soil, yielding plentiful breeding grounds for disease vectors. Dengue, Zika, and chikungunya may present in this area, although as reported cases of these diseases were negligible prior to the event, it is unlikely they will pose a risk. West Nile virus and other vector-borne disease may pose a greater threat, and care should still be taken against mosquito and tick bites. It is important in any case to maintain a good sense of personal hygiene, wash hands frequently, use mosquito repellent and insect-treated nets when unable to stay indoors, and ensure that all immunizations are up to date. Seek medical attention promptly for any fever, general symptoms or gastric illness lasting longer than several days, despite treatment.

Other Potential Hazards

Combustible or Poisonous Gases: Hurricanes can damage natural gas and fuel lines. As a result, explosive gas vapors may be present in buildings. Methane gas may also accumulate due to decaying materials. Open all windows upon entering a building. If you smell gas, leave the building immediately, and notify authorities. Do not smoke or use electrical equipment or telephones (including mobile phones) while in any building in which a gas smell is present. Do not use gasoline or other fuel burning equipment within buildings, or within 3 meters (10 feet) of doors, windows or air intakes (operating fuel burning equipment within a building will cause poisonous carbon monoxide to accumulate, even if doors and windows are open and fans are running).

Safe Use of Electrical Equipment: Electrical equipment that has been exposed to salt water will be unreliable even if it seems to be working properly. Be sure equipment is properly grounded and connected to a ground break-equipped electrical source.

Mold, Bacteria, and other Microorganisms: Floodwaters contain many infectious organisms, some of which can become airborne. The greatest respiratory risk is probably due to mold, and people with asthma or chronic lung disease are most likely to be affected. Mold can survive in structures that appear completely dry═ż complete drying of a building may require removal of ceilings, walls, insulation, flooring, and other materials. Wear rubber gloves and boots, goggles, an N95 respirator (if available), or a dust mask for protection during cleanup.

Resources

Weather/Road Conditions
National Hurricane Center: www.nhc.noaa.gov
National Weather Service: www.weather.gov
National Meteorological Service (Spanish): smn.cna.gob.mx
Louisiana Road Conditions: www.511la.org
Texas Road Conditions: drivetexas.org
City of Houston Office of Emergency Management: houstontx.gov/oem

Houston Emergency Operations Center: www.houstonemergency.org
Harris County Flood Information: www.harriscountyfemt.org

FEMA Asset List: www.fema.gov

US Coast Guard emergency telephone numbers: 281-464-4851; 281-464-4852; 281-464-4853; 281-464-4854; 281-464-4855

Airports
Houston Airports: www.fly2houston.com
Louis Armstrong New Orleans International Airport: www.flymsy.com

Utilities
CenterPoint Energy: www.centerpointenergy.com
TNMP: www.tnmp.com
AEP Texas: www.aeptexas.com
Entergy: www.etrviewoutage.com

Related Advice: How to prepare for a hurricane/tropical cyclone/typhoon
Related Advice: How to prepare for thunderstorms and cope with them safely
Related Advice: What to do before, during, and after a flood
Related Advice: How to prepare for and survive a tornado

 

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