The torrential rains and catastrophic flooding of May 1-3, 2010, will be remembered for many years by Middle Tennesseans. Back-to-back record breaking rains fell on Saturday, May 1, and again on Sunday, May 2, causing widespread flash flooding and river flooding across much of the mid state. The storm killed 18 people in Middle Tennessee and at least 27 in all of Tennessee and Kentucky. Property damage estimates are hard to develop and vary widely, but they totaled at least into the hundreds of millions of dollars and helped prompt a Presidential Disaster Declaration for many counties in West and Middle Tennessee. To worsen matters, the region had several rounds of severe thunderstorms, some of which caused extensive wind damage and tornadoes.
Nashville experienced its all-time rainiest day AND third-rainiest day on back-to-back days. The National Weather Service in Nashville has rainfall data back to the early 1870s – that’s over 50,000 days of observations. Rainfall of 6.32 inches on Saturday, May 1, at Nashville International Airport was the second highest amount ever measured in a day. That ranking lasted for just one day because the rain that fell on Sunday, May 2, (7.25 inches) established a new record amount of precipitation. The total of 13.57 inches absolutely demolished the previous two-day record of 6.68 inches.
Several weather factors caused this complex disaster. The main culprit was a very slow-moving low pressure system at upper levels of the atmosphere. Also, a front stalled just west of Tennessee and we had a plume of unusually rich moisture from the tropics that took dead aim on Tennessee. A long-lived outflow boundary caused by the initial round of heavy rains on Saturday morning helped focus additional heavy rains later in the weekend.
The answer depends on your exact location. See the chart below.
A flood event that sets a new record crest is something rarely seen, especially when records date back 50 to 100 years. The Cumberland River at Nashville caused tremendous damage when it rose to almost 52 feet (crested May 3), but still fell well short of the highest crest on record - 56.20 feet. This record crest was set back in 1927, before dams controlled the flow of the Cumberland and its tributaries. It has been speculated that if there was no control of the river, the water level in the May Flood would have come close to 56 feet in downtown Nashville. A record crest of 62.58 feet was set on the Cumberland River at Clarksville, which is just over 5 feet higher than the previous record crest of 57.10 feet set in the 1979 Flood. The Cumberland River at Clarksville rose not just from the water coming down the main-stem portion of the river, but also from the significant inflows from two major tributaries – the Red River and Harpeth River.
The Red River set a new record crest of 49.48 feet at the gauge near Port Royal, and the Harpeth River reached record levels at three locations on the river. The gauge at Franklin crested at 35.32 feet, which is just a few inches above the previous record of 35.14 feet set in 1948. Downstream at the gauges near Bellevue and Kingston Springs, the river level was so high it ended up washing the gauges away. High water marks show the river level at Bellevue reached 33.32 feet, which is almost 9 feet higher than the previous record of 24.34 feet set in 1948. Kingston Springs also saw an extreme river level surveyed with high water marks indicating a crest at 46 feet, which is about 14 feet higher than the previous record set in 1946. Gauge data for the Harpeth River at Bellevue and Kingston Springs dates back to the early 1920s, which really shows the magnitude of this event.
In the Nashville Metro area, many of the creeks and streams surpassed levels not seen since the 1979 Flood. Browns Creek at the State Fairgrounds crested at 13.44 feet which is 5 feet higher than the previous record set in 1993, and Whites Creek in Bordeaux crested at 25.82 feet, which is over 6 feet higher than the previous record set in 2002. The Mill Creek at Woodbine gauge set a new record crest of 21.37 feet and the Antioch gauge set a record crest of 26.10 feet. The previous record for Woodbine was 20.63 feet and the previous record for Antioch was 23.78 feet, both set in 1979. Richland Creek crested at 19.99 feet, which is almost 5 feet higher than the 1979 Flood level of 15.13 feet.
Elsewhere in Middle Tennessee, record levels were set on portions of the Duck River and Buffalo River. The Duck River near Hurricane Mills washed away the gauge and a crest of 34.21 feet was surveyed from high water marks (previous record 30.70 feet set in 1948). Upstream at Centerville, a record crest of 47.50 feet was set which is almost 10 feet higher than the 1948 crest of 37.58 feet. The Duck River at Columbia did not set a record crest, but did reach its 7th highest level on record with 44.91 feet. The Buffalo River near Lobelville crested at 26.00 feet, which is just above the previous record of 25.23 feet set in 1991, but is a flow of almost 17,000 cubic feet per second more. Upstream of Lobelville near Flat Woods, TN the Buffalo River crested at 32.69 feet which is just half of a foot higher than the previous record set in 1991. Records for the gauge at Flat Woods date back to 1921.
Many folks faced conditions they had never before seen – from the people directly impacted by flooding to those who try to forecast Mother Nature. After the National Weather Service’s “Service Assessment” report and by participating in a series of incident reviews with other agencies, the following is a list of “lessons learned” and the actions implemented to address them:
1. Many people felt unwarned about the flood despite nearly constant NWS flood warnings.
- It can be difficult to adequately convey technical information. The NWS recognizes that it’s text-based flood warnings would be enhanced by associated graphics that would show how deep flood waters would reach on any given street. The NWS is working on a long term project with other government and private sector partners to do detailed inundation mapping which could be used to develop graphical flood warnings.
2. Lack of real-time rainfall and river level data.
- The NWS uses several new tools to monitor rainfall and river levels. Thanks in part to a multi-agency project involving Metro Nashville, the USGS, the U.S. Army Corps of Engineers, and the NWS, we now have real-time monitoring at 7 additional locations on the Cumberland River and at 7 new points on tributaries in Davidson County. Also, a new gauge has been installed on the Cumberland River at Ashland City in Cheatham County. The USGS has also worked with Metro Nashville to obtain rainfall measurements from 26 new sites across the county. When combined with a dual-polarization upgrade to the NWS radar in January 2012, all of this information will further enhance NWS Flash Flood Warnings and river forecasts.
3. Forecast of heavy rains only predicted half of what fell.
- NWS data gathering and research, along with much improved forecast models, have greatly enhanced forecasts in recent years. Although this effort continues on a daily basis, we recognize that accurately forecasting double-the-all-time-record rains will take many more years of research and model improvement.
4. Interagency coordination could have been more effective.
- The NWS and U.S. Army Corps of Engineers coordinated about water release from area dams and the associated impacts on river level forecasts at least 17 times during May 1-3, 2010. Some of these calls included other agencies (e.g., City of Nashville officials). However, to further enhance our ability to efficiently exchange critical information, NWS Nashville now sends a meteorologist to work in Metro Nashville’s Emergency Operations Center (EOC) as often as possible during bad weather situations. We also have an agreement with the Tennessee Emergency Management Agency to assist in the State EOC when activated during selected activations.