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3/14/2024
WT Staff
FLOOD SPECIAL REPORT
Georgia: Timeline of a river flood
Thursday, March 15, 2024 updated Monday, March 18 122 pm EDT
As river flooding seems to go in Georgia, creeks, streams and rivers rise with heavy rains, the network of streamflow monitors in USGS Waterwatch dashboard lights up from the lime green of normal to blue of high flow rating, then black as the monitors detect flow breaching flood stage.
In the day following the first high flows and flood values, the creeks, streams and minor river tributaries rapidly empty their surplus volume into the main river channels. For many days afterward, even weeks after the initial inundation, the major veins of Georgia's surface water flood in a fairly predictable and orderly march through the drainage basins, moving massive volumes of water to the Atlantic Ocean, or the Mississippi River/Gulf of Mexico.
Here is how the March 2024 flood event has rolled out 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. The Ocmulgee, Ohoopee and Altamaha Rivers still flooding as of this report.
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. Over the course of one year, 2022, WTGA calculated over 10 million gallons of raw sewage reported spilled from upstream stormwater overflows and grease-clogged sewer lines entered Lake Jackson. From Lake Jackson, the Ocmulgee River 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.
Altamaha continues to flood near Charlottville to the last post near Everett City. Flooding initially began on 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 flooding was recorded upstream near Charlotteville, just after the noon hour on March 10. Altamaha flooded near Charlotteville and Baxley four days before spilling over downstream at Doctortown.
Altamaha River picks up another flooding waterway flow, the Ohoopee, joining between Baxley and Doctortown. The blackwater Ohoopee River, in flood stage near Reidsville since the afternoon of March 7, is still flooding today. Altamaha River gained more than 20% in flow volume the night before it spilled over the banks near Everett City during the afternoon of Saturday, March 16. As of this update, Altamaha River is still flooding near Everett City, six inches over.
Savannah River flooding initially broke out near Cylo around 5 pm on March 10. Flooding progressed upstream at Burton Ferry Road near Millhaven a little more than two days following. 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.
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 this morning. In all, twelve days of flooding for Flint River.
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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