After a week of rain, on September 21, 2009, record flooding in the metro Atlanta, GA, area produced numbers that exemplify the stark reality of a disaster. To that point, as a “flood of record” with multiple records broken, the numbers speak for themselves, and are painfully articulate: An unusual weather system of three confluent moisture areas hit north Georgia and dumped more than 20 inches of rain in six days in some areas. The storm prompted federal disaster declarations in 17 counties, where more than 50 gauges measured levels as high as 13 feet over flood stage in one- to 500-year flood events. The flooding damaged or destroyed thousands of homes, leaving more than 16,000 victims homeless and at least 11 people dead.
Metro Atlantans woke to a nightmare Monday, September 21, as a perfect storm of suffering victimized thousands in 17 declared disaster counties in north Georgia. For 11 victims, their storm stories were all too brief as they drowned in vehicles or were swept away by flood waters; in Carroll County, a father’s children were swept from his arms, and a Gwinnett woman’s last words were to 911 operators as she tried in vain to guide emergency workers to her rapidly flooding vehicle.
Executive Order for Disorder
After $10 million was requested under Emergency Watershed Protection and the Emergency Relief Program, the Governor’s request for federal disaster declaration under the Stafford Act for 17 of Georgia’s counties lists as critical, among other things, potable water and shelter in the counties it itemizes needed funds totaling $16,350,000 for such things as coordination, technical advice, individual and household assistance, and, notably, $8 million for debris removal alone. The request also details flood response implementation by the state already undertaken or in process:
- Providing personnel and equipment for numerous road closures and conducting emergency bridge inspections are listed.
- Assembling water tanker strike teams for structural fire support, and dispatching potable water tankers to Douglas County Hospital and several county water systems
- Opening five shelters to house approximately 300 people and placing dozens more in motels
- Providing 1,000 sandbags to Rockdale and Rabun Counties and facilitating transportation of 100 road closure signs from South Georgia to Metro Atlanta
- Establishing an Area Command for Cobb, Paulding, and Douglas Counties for severe flooding
- Dispatching numerous boats with personnel and canine units for active water rescues
- Identifying of animal shelters and assisting with large-animal evacuations in metro counties
- Responding to numerous requests for assistance with road closures on state and local roads
- Providing supplemental law enforcement for traffic control
- Providing air assets for rescue and damage assessment
- Providing flood-related public information and opening a Joint Information Center
- Responding to scores of requests from media, elected officials, and the public as to the state of the emergency
This list of emergency response activities provides a comprehensive picture of the nature and extent of the flood damage and the response by the state of Georgia to the event.
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Photo: Lanse Norris
An Austell home crushed and swept almost completely off its foundation |
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Photo: Lanse Norris
An Austell house that moved 120 feet across the street into a vacant lot; you don’t often see homes with framing directly on grass. |
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Photo: Lanse Norris
The former foundation of the house pictured above. |
Quantifying the Not-So-Routine
I expect that readers are familiar with routine flood control practices and municipal response, so after summarizing the flood for the Atlanta area, I will discuss not-so-routine features of the September flood in three of the hardest-hit counties and quantify the impact on three major structural categories vulnerable in floods: homes, paved surfaces, and dams. Specifically, I will focus on the US Geological Survey’s chronicling of all-time record water levels in creeks and homes in Cobb County; flooding that washed out roads and bridges in neighboring Douglas County; and, reciprocally, flooding that didn’t happen in areas of Gwinnett County because, as in areas of Cobb and other counties, Category 1 dams there prevented floodwaters from inundating homes in drainage areas that would have otherwise flooded into and beyond their 100-year floodplains.
Rainy Nights in Georgia
The dynamic weather responsible initially consisted of a system of persistent low pressure from the lower Mississippi valley that stalled over northeast Georgia from Monday, September 14, through Friday, September 18, dumping as much as 5 to 10 inches of rain in some areas. When the low-pressure system moved toward the northeast on Saturday and Sunday, it sucked Gulf Coast moisture in a training effect that caused some Atlanta areas to experience the whole length of a moisture band instead of just the width, dumping additional rain measuring from 9 to 11 inches in Douglas and Gwinnett Counties. At the same time, an Atlantic high-pressure system pushed more moisture in from the east. On Monday, rain measured from 9 to 12 inches in parts of west metro Cobb and Douglas Counties; with a seven-day total of more than 25 inches of rain for some creek basins in the area, an all too perfect storm had left its historical flood water mark as high as 15 feet on vegetation and structures in parts of the Atlanta metro area.
Average Performance and Quirky Contrast
As a result, stormwater conveyance systems throughout the area were overwhelmed; land use, hydrologic, and geologic trends largely are responsible for the relative disparities in flooding levels. The Chattahoochee River gauges measured a 1% chance exceedance (100-year) flood at the Vinings and Roswell gauges, and the Yellow River stream gauges for Gwinnett, Rockdale, and DeKalb Counties recorded peak flows between the 1% chance (100-year) and 0.5% chance (200-year) flood levels—average performances for waterways for the particular event, but at flood level, nevertheless. By quirky contrast, impervious-runoff-enhanced flows in Atlanta’s Peachtree Creek were at only a 10 year/10% chance magnitude, but “backwater” plugging effect caused by Chattahoochee flows pushed flooding in the basin over the 0.2% chance (500-year) flood mark. Illustrating the exponential magnitude of flooding where a watershed experienced the length of the training moisture band instead of the width, Carroll County’s fire chief noted that Snake Creek there is usually only 2 feet deep, but recorded depths of 20 feet on September 21. Table 1 lists water levels for the September 21 flood for metro area waterways against the record for that waterway; many new records were recorded.
Really a River: Sweet Waters Run Deep
Flooding in west metro Atlanta’s Sweetwater Creek basin broke its own record and broke USGS gages and related equipment critical in measuring rain, stage, and discharge. Although Brian McCallum, assistant director for the USGS Georgia Water Science Center, was reported in local papers as saying that the USGS ranked the flood as a less-than-a-0.2%-chance-of-exceedence event, traditionally called the 500-year-magnitude flood, he explained to me in a phone call that in actuality the flood “well exceeded” the 500-year flood mark, especially for Sweetwater Creek. Graphs from the Sweetwater Creek gauge demonstrating just that, and for the six-day “period of record,” show record flow at 28,000 cubic feet per second and depth 13 feet above major flood stage, cresting on September 22.
One of the press releases include the following: “‘These are historic floods and we know that people’s lives are at risk, so we burn the candle at both ends to try to keep our real-time gages running,’ said McCallum, USGS Supervisory Hydrologist who oversees the stream gage operations and the field crews. ‘Because many of the gages have been destroyed, we are attempting to install as many temporary gages as possible to ensure that real-time data is available to emergency managers.’” http://ga.water.usgs.gov
Regarding the USGS and Georgia’s stream gauge network: “The USGS is the science agency of the Department of the Interior. One of its major mission elements is the quantification and qualification of natural hazards, and in the case of the epic Atlanta floods, hydrologic hazards. The USGS Georgia Water Science Center maintains a network of almost 300 real-time stream gages across Georgia that measure the pulse of the rivers and streams through partnerships with other Federal, state, and local agencies. Each gage records water level, rainfall (where applicable), and stream flow data every 15 minutes and transmits that data hourly via satellites. The data are received directly at our office and posted automatically on the USGS Web site at http://ga.water.usgs.gov. During severe events, each gage transmits every 15 minutes when pre-programmed thresholds are exceeded. The data are also received directly by the National Weather Service and the US Army Corps of Engineers for flood forecasting and warning purposes.
“Stream flow data are critical for flood warning, drought monitoring, wastewater assimilation, water supply, bridge and roadway design, hydropower and reservoir operations, habitat studies, and recreational purposes. With all those uses, it is safe to say that USGS stream flow data affects the lives of every Georgian on a daily basis, whether they know it or not. It is our mission to make sure the data goes ‘from the stream to the screen’ reliably and in a timely fashion.
“Besides the real-time data Webpage, users can also receive the latest stream flow information on their cell phones and via e-mail by using our Streamail tool, or can also subscribe to automated e-mails to get the latest hydrologic conditions for any major river basin in the State. Go to the Web site above for more information.”
With six major creeks feeding it, and its low sloping, slow moving, sinuous stream flow draining a large, flat area, Sweetwater Creek’s watershed was inundated with record flow and widespread residential damage in and adjacent to floodplains, as the creek did not crest until September 22. Discussion all week around Cobb Stormwater Management focused on Sweetwater Creek being “really a river” because, sometimes, its “sweet” waters run deep.
Whole neighborhoods near the creek in Austell and Powder Springs had 5 to 15 feet of water in homes, and one three-bedroom brick home was picked off its foundation, sheared of all brick, and floated 100 feet across the street into a vacant lot. Because the flood far exceeded 100-year regulatory flood levels, many citizens without flood insurance and/or outside the 100-year floodplain are left without sufficient means to rebuild their homes, much less replace thousands of dollars worth of appliances, automobiles, and heating and air-conditioning units.
First, Second, and Third Responders
In response, Cobb and other counties initiated disaster response that involves, among other things, search and rescue; residential, commercial, and civil flooding and damage inspection of stormwater conveyance system structures like ponds, catch basins, and dams; as well as the reporting and closure of impassable roads due to flooding, fallen trees, and downed power lines.
Although fire rescue, police, Department of Transportation, Emergency Management, Community Development, Stormwater, and Water System Maintenance personnel all respond initially to the flooding, it is primarily Cobb Stormwater and Community Development that prosecute the second and third stages of flood response involving formal damage assessments and inspections supporting the Federal Emergency Management Agency (FEMA) and National Flood Insurance Program (NFIP) emergency funding and flood insurance payouts, as well as buyouts of properties deemed too demonstratively vulnerable to flood waters.
In the weeks following the initial flooding, Cobb Stormwater Management and Community Development inspectors, along with volunteers from engineering firms and municipalities as far away as Tybee Island, GA, conducted and processed the Residential Damage Survey Estimate (RSDE) program inspections of more than 600 mainly residential structures, many of which are in the basin of Sweetwater and the creeks that feed it. The RSDE process determines total damage values, which are instrumental in determining whether county building officials will permit a structure for rebuilding, permit it for rebuilding above the flood plain (3 feet or more in Cobb County), or process it for buyout and designate the lot as non-developable. The information gathered in the RSDE process is available for FEMA and NFIP emergency management and flood insurance decision making, as well.
Widespread Wrath: The Quality of Quantity
In the days following the September 21 initial flooding, as Cobb Stormwater Management and Community Development inspectors fanned out across the county notating damaged structures for follow-up RSDE damage inspections, the magnitude of the devastation took on the character of hyperbolic, widespread wrath, of a quantity with a quality all its own, to quote a World War II world leader familiar with devastation by, and the countering of, great forces. The intensity of wrath manifested itself in the contorted face of misshapen and displaced homes in the Sweetwater basin in Austell, GA; pictures show two homes swept off foundations, with one crushed and the other sheared of brick, 120 feet from where it stood. The extent of wrath unfolded as inspectors examined more and more homes; debris line levels and numbers of flooded residences more than double the numbers recorded after Hurricane Dennis five years earlier, with an October 2 estimate of 1,000 homes affected in Cobb County, and more than 600 impacted homes either inside the floodplain or outside with 4.5 feet or more flood water on outside walls.
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Photo: Gwinnett County Stormwater Management
This creek crossing was undermined by erosion. One county alone had more than $10 million in damage to roads and bridges. |
Douglas County’s Pilings of Great Cost
With many tributaries feeding heavy flowing Sweetwater Creek, Anneewakee Creek, and Dog River in metro Douglas County, 170 roads were impassable in places at the height of flooding, and more than 10.2 million dollars of damage was done to roads and bridges. Six people died in flooded road conditions. Douglas County’s Anneewakee Creek caused bridge washouts up and down its course, and the Georgia Highway 166 Anneewakee Creek crossing was compromised by 10 feet of erosion at its foundation. The bridge’s steel and concrete superstructure was built on sub-structural timber pilings set in the dirt, a common practice in 1957; such structures are unsuitable for rebuilding when compromised by deep scouring and are not compliant with contemporary code standards. The bridge will have to be rebuilt on rock 25 to 30 feet below the stream’s sand bottom, at a cost between $2 to $3 million, and could take up to a year.
Johnny Barron, stormwater manager for Douglas County, reported on October 21, that of the 140 roads actually closed in the county on September 21, 46 were still closed one month later; 20 roads had washed out completely. “Heavy rainfall and darkness combined to hide the hazardous water flowing over the roads. Dozens of cars drove into floodwater and many were swept off of roads. Fifteen people were rescued by EMS, and seven were killed. The last car was pulled from Dog River this morning by a National Guard helicopter.” Barron estimated the damages to the roads to total more than $25 million, and damage to the public water and sewer system to be about $8 million.
Neither Overtopped nor Overlooked: Safe Dams
Flooding hit northeast metro Gwinnett County hard as well, but nominal flooding in some areas there is attributed to comprehensive floodplain management, detailed in excerpts from a local newspaper. The September 25 article in the Gwinnett County News highlights the local success of the statewide Safe Dams Program, which provides retrofitting and regulatory and funding source partnerships.
The article noted that 14 dams built in Gwinnett in the 1970s to reduce floodplains on former agricultural land had performed as intended during the storm. It quoted county stormwater manager Steve Leo, saying eight of the Category 1 dams had been recently upgraded to meet new state and federal safety standards; four of them control drainage area in one of the most affected areas. Their original earthen spillways were replaced with wider, stepped-concrete structures to allow them to accommodate larger storms. Without the dams, schools, community centers, and upward of 150 homes and businesses would have been flooded. The water they held back was being released slowly over a period of a week.
The article also quoted Lynn Smarr, the acting director of Water Resources, who explained that the dams were built in partnership with the Natural Resources Conservation Service, the Gwinnett Soil and Water Conservation District, and the Upper Ocmulgee Resource Conservation and Development Council. The county uses stormwater utility revenues to maintain the dams.
Of the county’s 14 NRCS dams, the article reported, eight had been upgraded over the last eight years to meet the new requirements of the Safe Dams Act. Two met the requirements with no upgrades, and the remaining four were under construction or being designed and were scheduled to be upgraded by 2012. About one-fourth of the estimated $20.4 million needed for the work was being provided through NRCS grants.
In a follow-up e-mail message, Leo detailed some September flood-of-record statistics for Gwinnett County Stormwater Management. The organization had received about 1,300 flood and drainage complaints and responded to close to 99% of them, and had identified major culvert failures at 17 road crossings and anticipated having them open by November 1. “The upgraded watershed dams operated as designed,” he noted. Gwinnett County to the northeast and Cobb County to the northwest are both large, upper piedmont, NPDES Phase I suburban bedroom communities.
In a disaster of the magnitude of the Atlanta area floods of September 2009, large, successful stormwater management infrastructure components in Phase I counties like Gwinnett and Cobb are apt to be overlooked as other components of stormwater conveyance systems are overwhelmed, never meant to handle flows experienced during the event. Bill Higgins, Cobb County Stormwater Management division manager, remarked to me after the flood that Category 1 dams protecting drainage areas in Cobb County also contributed greatly to minimal flooding in areas and no deaths countywide.
Indeed, the highest mission of stormwater management is to manage as victimless a stormwater infrastructure as possible; to sanction, build, maintain, and plan for stormwater flows that are a low-order threat to property; and, as it so happened in the September 20–23 flood of record for Cobb County, a no-order threat to life. Delighted at least in that, Cobb County Stormwater Management is challenged to lead county government not just in its historical role to manage storm flow, but to anticipate wet-weather disaster as well, including early warning, first response maintenance, retrofitting, and increased floodplain residential buyouts.