Flash Flood — Cobb, Georgia

2021-09-07 to 2021-09-08 · near Marietta, Cobb, Georgia

Event narrative

Numerous social media posts and reports from Emergency Management indicated significant flooding over Cobb county due to anomalously heavy rainfall.

Radar estimates indicate 5 to 7 inches of rain accumulated quickly over the area resulting in the flash flooding. These amounts are between 0.1% and 0.2% chance of occurrence in a given year according to the NOAA Atlas 14.

In total, more than 250 structures, 15 roadways and more than 100 cars were inundated with floodwater. The Emergency Management reported flooding of the Roswell Road and Old Canton Road intersection, a washout of East Lake Parkway, a washed out footbridge near Chinquapin Drive and South Woodland Drive, and complete collapse and washout of Pickens Industrial Drive.

Additionally, dozens of cars were flooded in the parking lot of the Marietta Crossing Apartment homes due to flash flooding of Rottenwood Creek. Water also caused damage to the interior of the building after water inundated the apartments.

Flash flooding occurred along Columns Drive along the western bank of the Chattahoochee River, inundating multiple homes and vehicles. This flooding was also documented by a local news station traffic helicopter on Twitter.

The river gage on Sope Creek (NWS MARG1/USGS 02335870) recorded an almost 17 foot rise in 4 hours due to the quickly accumulating rainfall. The observed stage height crest in Major Flood Stage at 18.05 feet -- only 0.3 feet below the crest from the historic September 2009 floods. Two river gages on the Chattahoochee River in Vinings (NWS VING1/USGS 02336000 and NWS VIXG1/USGS 02335990) also rose above flood stage.

Wider weather episode

Thunderstorms developing along a stationary front across north Georgia produced isolated reports of wind damage in a portion of the metro Atlanta area. This front also triggered training storms that quickly dumped several inches of rain over the two-county area. Flash flooding occurred late in the evening on September 7th and continued into the early morning hours on September 8th. Afternoon showers and thunderstorms re-fired on the afternoon of September 8th with isolated flash flooding occurring again over-soggy north Fulton county.

View location on OpenStreetMap → (33.9528, -84.5710)

Source: NOAA Storm Events Database, event_id 987534. Narrative written by the NWS forecast office that issued the report.