April 12, 2024
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WT Staff

Georgia: Timeline of the river flooding in progress
Day 30

Thursday, March 15, 2024 update Friday, April 5 138 pm EDT

March 2024 has been a conundrum of extremes for Georgia. Rains in the north started the creeks and rivers rising with the first flooding in the upper basins of the Atlantic and Mississippi/Gulf of Mexico basins before the first full week was out, March 6. Even with all the major rivers overflowing on both sides of the state divide came days with low relative humidity and high fire danger warnings from the National Weather Service.

As tracks streamflows and flooding in Georgia, we thought it would be a good idea to describe the progression of the flooding with the time lapsed between flood breaches from one USGS monitor to the next. In some cases, the order of flooding is not from upstream to downstream, these unorthodox progressions are worth noting. Here is our report of the progression of the March 2024 flood, still spilling over in the south as of this update.

The USGS Waterwatch dashboard doesn't take long to light up when rain falls in the mountains. The colors representing flow volume change rapidly, from the red-brown of much below seasonal normal prevalent in the northwest over the winter, to lime green of a seasonal normal to blue of a high flow rating. Switching over to the flood panel, we begin to see the blue representing the highest recorded streamflows, 99th percentile, SMS alerts begin to go out when the creeks and rivers reach action stage, then the flood map takes on black tags as the monitors detect flows breaching flood stage.

In the day after the first high flows, action stage and active floodings, the creeks, streams and minor river tributaries are the first to overflow. These smaller vessels deposit their surplus volume rainwater runoff collected off the northern mountain landscape into the main river channels, the Chattahoochee and Flint Rivers on Gulf of Mexico side of the divide, the Oconee, Ocmulgee and Savannah Rivers for the Atlantic. For many days after the rain ends, even weeks after the initial inundation, the major veins of Georgia's surface flood in a fairly predictable and orderly march through the drainage basins, moving massive volumes of water and contaminants to their outlets at Atlantic Ocean and Gulf of Mexico.

Here is how the March 2024 flood event has rolled out and carries on today in the Mississippi/Gulf and Atlantic basins of Georgia.

Atlantic Ocean basin
Twin rivers Ocmulgee and Oconee start south of the state divide in north Georgia, collecting rainfall runoff from creeks and minor tributaries of the central interior, eventually meeting and merging flow near Charlotteville to form the Altamaha River. Downstream on the Altamaha, the Ohoopee River jumps on, contributing thousands of cubic feet per second to the longest free flowing river on the US east coast. This is another way of saying, there are no dams on the Altamaha River.

By the time Altamaha reaches the Atlantic coast near Brunswick, surface water runoff from more than 14 thousand square miles is deposited into the ocean near Jekyll Island, note the permanent beach advisories for e.coli under the Georgia HABs button to the right of the map. In all this drainage area, these rivers are drinking water supply, the surface water sources for hundreds of thousands of Georgians.

Ocmulgee River drains an area over 5200 square miles of central Georgia before it joins the Oconee near Charlotteville. Oconee River drains a similar area just east of the state center line.

Of the twins, the Ocmulgee River commenced flooding first, taking the rainstorm runoff collected in Lake Jackson from 2200 square miles upstream. Lake Jackson receives flow from dozens of minor tributaries and creeks collecting runoff from dense urban landscape and developed municipal areas. Contaminants transported in heavy rain runoff from the urban areas is worth noting here. Over the course of one year, 2022, WTGA calculated over 10 million gallons of raw sewage was reported spilled from overflowing manholes caused by grease blockages and rags. All of this sewage entered creeks flowing to Lake Jackson.

Through this March 2024 flood event, we have tallied up the sewage spill reports to Georgia EPD. More than 750 thousand gallons of sewage is reported overflowing from manholes in Dekalb County, with several more reports of unknown quantities that we have not included in the total. The March of sewage from Dekalb County splits off along the height-of-land divide. On the north side, sewage and stormwater head to the Chattahoochee River in the Gulf of Mexico basin. South of the divide, the stormwater overflows carry contaminants through the Atlantic Ocean drainage basin via Lake Jackson and the Ocmulgee River.

Ocmulgee River originates at Lake Jackson, flows past Jackson and on down to Macon where it first overran the channel on Thursday March 6, just after school final bell and ahead of the evening commute.

Downstream from Macon, the Ocmulgee began to swell with flood flow, spilling over at US-341 at Hawkinsville in the wee hours of March 9, having doubled its depth in the channel at US341 in just over 24 hours. The floodwater bolus pushed further down and over the channel near Abbeville around 10 pm March 10, 15 and a half hours time lapsed between the two. Ocmulgee initially behaved on the passing through Lumber City, sticking in its channel on its way to rendezvous with Oconee River, the twins teaming up to flood next near Baxley.

Oconee River started flooding March 6 around 7pm. USGS provisional data recorded the first channel breach at the monitoring station in the upper Oconee River watershed near Penfield. Downstream at Milledgeville the monitors lit up for extreme high flow however, the channel held and did not breach, containing Oconee River flow through the whole March event. Downstream at Avant Mine, flood stage was breached March 8 around 8 am, a 36 hour lapse from the first overflow at Penfield. In less than 19 hours following, flooding began near Oconee, this one coming on March 9 at around 230 am. Dropping further downstream to Dublin, flooding started up on a 52 hour delay, beginning March 11 around the morning commute, 7 am. Another day forward, March 12 around 8 pm, Oconee broke out of the channel at Mount Vernon, 37 hours lapsed from flooding recorded on the upstream monitoring station.

Oconee River gradually stopped flooding in the same order that it started, with Mount Vernon being the last station to quit, Sunday afternoon on March 17, ending 11 days of flooding. Ocmulgee River continues to flood near Abbeville, the last monitored location ahead of the confluence with Oconee, the genesis of Altamaha River.

Flooding initially began at the second monitoring station of the Altamaha near Baxley where the channel is shallower, just below 13 ft deep. The breach near Baxley occurred March 9 right before the lunch hour. Twenty-five hours later, Altamaha was recorded spilling over upstream at the first monitoring station, near Charlotteville, just after the noon hour on March 10. Altamaha flooded near Charlotteville and Baxley four days before flood hit downstream at Doctortown, March 13 around the evening commute, 5pm. Another time lapse two and a half days forward, around 230 am March 16, flooding began at Everett City.
The blackwater river Ohoopee began flooding near Reidsville the afternoon of March 7, depositing more than 3000 cubic feet per second into the over-full Altamaha system between Baxley and Doctortown. Ohoopee ran over flood stage for nearly two weeks in March, finally returning inside the channel mid-morning on March 20. Not to be outdone or forgotten, Ohoopee rose up again and overflowed on March 25, still rising on Day 21. Flooding on the Ohoopee River finally ended in early April.

The beginning of the end
Altamaha River flow volume started to taper off on March 21, first noted in the upper end near Charlotteville. The glut of flood flow had passed by the first monitor and made its way downstream, flooding all the way. As of Saturday, March 23, the flow volume at the top end was under 30 thousand cubic feet per second, and more than double, over 60 thousand cfs at the lower end near Everett City. The depth of flow above flood stage as of Saturday March 23 ranged from half a foot over at the top end of Altamaha to three feet over flood stage downstream, the monitors near Charlotteville, Baxley, at Doctortown and Everett City gradually receding with no further encouragement from flooding tributaries.

Altamaha River flood finally receded beneath flood stage near Charlotteville around 9 pm on flood event Day 17, March 23. By Day 18 mid-morning, Altamaha flooding was over at Doctortown. As the Ohoopee River kicked up a flood fuss again on March 25, Altamaha River continued to recede, ending the overflow at the bottom end near Everett City over the noon hour on the 20th day, March 26. Altamaha River finally ceased flooding near Baxlay on April 4, Day 29.

Savannah River flooding initially broke out near lower end Cylo around 5 pm on March 10. Flooding progressed backward on the Savannah River, spilling out upstream at Burtons Ferry Road near Millhaven a little more than two days later. As seen with Altamaha flood progression, the channel depth may have something to do with the order of flood breach. Minor flood stage near Cylo is 11 ft, where upstream near Millhaven the channel is 15 ft deep. The time lapse between the two breaches, downstream to upstream, 52 hours.

Savannah River flooding ended on April 4.

Satilla River began to flood at GA158 near Waycross on Day 18, the afternoon of March 24. Flooding here subsided overnight, ending early in the wee hours of March 27. Alabaha River got out of the channel at GA 203 near Blackshear the afternoon of March 23, flooding less than 48 hours in total. Little Satilla River kicked up flooding near Offerman for the second time during the March floods, overflowing Day 17 late afternoon. By Day 30, Little Satilla runs right at flood stage, looking to collapse the overflow and get in line sometime April 5. Satilla River runs over the channel at Atkinson, running more than a foot over on April 5.

Gulf of Mexico basin

On the Gulf of Mexico side of Georgia's height-of-land-divide, the Chattahoochee and Flint Rivers gather up the runoff from over 16,000 square miles, mustering at Lake Seminole, the impoundment water body created by the Jim Woodruff Dam. Water released from this dam at the Florida border is called the Apalachicola River, escorting Georgia surface water runoff across Florida and into the Gulf of Mexico.

The glut of rainstorm runoff moved quickly out of the top end creeks and streams in the headwater basins into the Flint and Chattahoochee River channels during the March flood event. Chattahoochee River started flooding in Atlanta the morning of March 6. A day-shift later the same day, Flint River started flooding. The first breach came close to the headwaters near Lovejoy, just after 6pm March 6, followed by flooding at Woolsey six hours later, just past midnight March 7. Griffin came next, flooding just after the noon hour on March 7, approximately twelve hours lapsed from the upstream flood.

With excess water building in impoundments upstream, flows released from the dams caused Chattahoochee River to flood at 14th St in Columbus around 11 pm March 8. This is a two and half day delay from the first Chattahoochee overflow noted in Atlanta. Chattahoochee flooding struck downstream Walter F George Dam near Fort Gaines on March 9th just before 5 pm, an 18 hour lag between stations. By March 12 at midnight, flooding was recorded near Columbia, Alabama, after more than three days delay.

Flint River flood progressed in tandem to the Chattahoochee. From Griffin, the flood-flow skipped past Thomaston and spilled out at US-19 near Carsonville in the wee hours of March 9, a 36 hour lapse from the start of upstream flooding at Griffin. Count forward another 24 hours, Flint was backed up overflowing at upstream Thomaston, a brief event ending 11 hours later. Flint River carried on past the flooding US-19 near Carsonville, running high past Montezuma and Oakfield to strike Albany in the wee hours of March 12. Next to flood 18 hours later, Bainbridge on March 12 at 6 pm. Back upstream, the flood caught Newton in the wee hours of Mar 13, a 24 hour delay since Albany started to flood. Later that day, just past the noon hour March 13, Flint was flooding at Riverview Plantation near Hopeful, a little over 12 hours time lapsed from the Newton flood.

From Lake Seminole, the impoundment of the Chattahoochee and Flint Rivers, also fed by a flooding Spring Creek, water released from Jim Woodruff Dam set the Apalachicola River into flood stage By March 10 at 7 pm. Flooding of the Apalachicola River got up over 100,000 cubic feet per second, ending just before noon on March 15. The flood timeline of Apalachicola River extended almost five days. Flint River took the longest time to subside beneath flood stage, the event ending at Bainbridge at 9 am March 21. Another round of flooding started up in the Line Creek tributary at Senoia, on into Flint River, flood stage breached at Lovejoy April 3-4. No subsequent flooding occurred on Flint River downstream of Lovejoy, none of the other tributaries got out of line.

Bearing in mind all the creekbank erosion and spills that are carried along with normal streamflow, the fast and furious flood events mix up sediment with a cocktail of who-knows-what, presenting a greater challenge for drinking water treatment plants. Upstream land use is a subject of interest for the mitigation of flood effects, as the surface area can be conditioned to infiltrate rainwater more effectively. Soil carbon holds four times its weight in water, and soil can be amended with time to increase stable carbon. United Nations Intergovernmental Panel on Climate Change suggests that the amendment of soils to increase carbon could capture and hold more rainfall from the increasingly heavy atmospheric river rain events, preventing the rush of surface water runoff to the rivers. More on this as we investigate climate mitigation.

USGS Provisional Data Statement
Data are provisional and subject to revision until they have been thoroughly reviewed and received final approval. Current condition data relayed by satellite or other telemetry are automatically screened to not display improbable values until they can be verified.
Provisional data may be inaccurate due to instrument malfunctions or physical changes at the measurement site. Subsequent review based on field inspections and measurements may result in significant revisions to the data.
Data users are cautioned to consider carefully the provisional nature of the information before using it for decisions that concern personal or public safety or the conduct of business that involves substantial monetary or operational consequences. Information concerning the accuracy and appropriate uses of these data or concerning other hydrologic data may be obtained from the USGS.

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