Floods Happen.

by Bill Wells, Reese Library, Augusta State University. 2006.

 

“The Savannah River is a stream bold in all of its features,” wrote Augusta, Georgia ’s 1914 weather bureau officer-in-charge Eugene D. Emigh.[1]     The Savannah River is formed by the union of the Seneca and Tugaloo Rivers some one hundred miles above Augusta and has its cultural and physical ties to both Georgia and South Carolina.  Emigh wrote, for its size, the Savannah is a “restless river” with intermittent stretches of water “rushing over the granite bed” and “resting in placid pools.”   Overall the river made a rapid passage to Augusta with a 257-foot drop over the sixty-four miles immediately preceding Augusta.  The last “rapids” are about six miles above Augusta but once past the city the river turns into a slow, meandering course to the sea.  

 

Part of the river’s rush to Augusta is the up-state topography.  The “catchment” area above Augusta entails a geological formation of the Piedmont Plateau with its foundations of granite and gneiss.   The elevation of the plateau ranges from 200 feet above sea level in the east to 1000 feet in the west.  Further north, the mountains reach 2000 feet with some well beyond.  All the height, combined with hard surfaces, made natural runways for water run-off. At that time, the only factor preventing larger run-off was the dense forests of the 7,294 square mile watershed.  The denseness of the forest acted to absorb the moisture through the roots or by evaporation.  The concern was the large deforestation for agricultural purposes.  Emigh cited that the watershed above Augusta shrank during the 1859 to 1912 period from 70% to 19%.  The result was by 1909 only 25% of the catchment area remained forested.  A positive factor of the period was during the peak rainfall periods of January, February, March, and April the land was being plowed for new crops and this plowed land was “ideal” for rainfall storage.

 

The ideal river height level for the Savannah River was 20 feet.  This level afforded water transportation as well as allowing logging companies to float logs out the swampy regions south of Augusta.  River water would not enter Augusta until the 32-foot mark (pre-levee) and was not a real danger to the businesses until the 34-foot mark.  Emigh noted, “At 36 feet a wide area of the business and residence sections is covered to depths of 1 to 3 feet.”

 

It was held that water run-off was caused by two causes.  Primary was direct falling rain and secondary a gradual supply from saturated soil or from the forest floor. It was more common in cultivated lands following a slow but steady rainfall.  Emigh argued this was truer for long rivers, but the short span of the upper Savannah River “freshets” came from the delayed flow when one rain supersaturates the soil and is followed by another rain a few days later. This combination of rapid run-off and soil saturation presented the greatest possibility of flooding.  However, by 1914 the number of days the Savannah River, at Augusta, was above the 20-foot mark increased with the “expansion of agricultural and contraction of forest area.”[2] The theory that plowed ground would hold more water was shown that the forests were needed to help control run off as well.

 

Emigh’s study of rainfall versus river height produced interesting comments. He concluded,

 

   Starting from the initial stages below 16 feet, the normal amount of rise in the Savannah River at Augusta for each inch of rain in 24 hours over the catchment area with the ground in moist condition is 8.5 feet.  This remains true until rain has brought the river to its 29-foot stage.  Any surplus of water above that necessary to cause a 29-foot stage has a value of about 3 feet for each inch of rain.[3]

 

Year	Rainfall, January-April	Days of 20 feet or over.
1903	24.6	23
1906	17.8	14
1908	19.8	24
1909	18.2	12
1912	25.2	25
Means	21.1	20
Emigh, 51.

Interestingly, rises above the 34-foot level were negligible with the greater rises occurring at the 16-foot level.  He dismissed any calculation of rainfall that would not bring the level to 20-feet and theorized that it would take some twelve inches of rain during the first four months of the year to bring the river to the 20-foot mark.

Unknowingly predicting the Flood of 1929, Emigh predicted, “If precipitation be of short duration but great intensity, it occasions a high stage that keeps the river above 20 feet for several days.”  Rain, soil saturation, or run-off was not the only considerations of Emigh.  The “flashy” nature of the river itself had to be included in the estimations.

The freshets of the Savannah River have a long history.  The greatest was the flood of 1796, reaching an average of 40 feet making it the greatest pre-levee flood in the city’s history.  The 1929 (post-levee) flood marks the greatest in height, but the 1930 flood exceeded in volume of water flowing past Augusta.

 

Anthony J. Gotvald, hydrologist for the USGS Georgia Water Science Center explains how river height is determined in 2006,

 “When a streamgage is first installed, we set the gage-height to some arbitrary value. But, we try to set this gage-height value high enough so that we don't get negative gage-heights. We then tie this gage-height to a local benchmark in order to determine the gage datum. So by adding the gage datum to the gage-height, you get the water surface elevation above the National Geodetic Vertical Datum of 1929 (NGVD29).”

 

He then provides an example. “The gage datum for 0219700 Savannah River at Augusta, GA is 96.58 feet above NGVD29. . . . For the October [19]29 flood at 02197000, the gage-height peaked at a value of 45.10 feet. By adding the 96.58 feet gage datum to that reading, you get a water surface elevation of 141.68 feet above NGVD29.” [4]

 

Although Eugene Emigh provides no physical reference for his gage, the 5^th Street Bridge had been used in previous floods.[5] This structure would be the most likely guide because it would have been the limit of steam vessel navigation and just upstream from Augusta’s port facility and steam boat landings and was used locally for the 1888 flood until the river washed the bridge away.

 

The 1888 freshet was the largest since 1796 and in the interim the populace of Augusta had grown complacent.  Only the 1840 and 1865 floods reached the city proper and nearly all memory of these disappeared.  The 1888 flood was a reminder of what the Savannah River could do if unchecked.  This flood did open flooding for scientific study.  In 1892, the River and Flood Service of the Weather Bureau was established to provide some warning of dangerous high water.  Nevertheless, as Emigh would mention later, the Savannah being a “flashy” river prone to very sudden rising, any gage readings would be of no use and, as future weather forecasters would claim, there is nothing certain about the weather.  However, averages could be built with carefully acquired information.   This information can be useful and fairly accurate when predicting normal circumstances if there is enough time to analyze the computations and give warnings.   The computations were gleaned from less than a dozen reporting stations upstream from Augusta. From these the rise in river stages upstream could be translated into river height at Augusta. 

 

 

The floods of 1888 to 1929 were, as Emigh noted, from storms dumping huge amounts of rain in a short period.  Most were statewide storms effecting nearly all the river systems of Georgia.  The 1929 flood was an extreme example of sudden and terrific rainfall.

 

Emigh’s prediction of a high intensity storm came during his tenure at Augusta. With the simple description of “Hurricane No. 2,” this Caribbean Sea storm reached modern Category 4 standards packing 120 MPH  winds from September 26 to 27.  By October 2^nd, the storm reached Augusta, GA., under the meteorological heading of “extra tropical storm” with 40 MPH winds as it caused extreme rainfall. The storm had followed the Fall Line across the State and hovered at 33.50N 81.00W for most of the day. (Augusta sits at 33.47N 81.95W)  No one could have predicted the effects of the storm.  Fortunately, the Savannah River levee had been constructed after decades of debate.  The levee was built to 48-feet and at one point the river reached 47.4 feet on the levee.  The result was this wall prevented flooding waters from destroying Augusta, but the same levee also forced the water higher and into North Augusta and Hamburg, South Carolina.   The latter had taken the brunt of all previous floods and this last freshet was one cause for the end to the small town.

 

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In the current era, the three dams constructed up river from Augusta, Hartwell Dam, Richard B. Russell Dam and J. Strom Thurmond (formerly Clarks Hill) Dam offer protection from flooding damage to Georgia and South Carolina. The latter dam regulates and limits, to a degree, flooding problems.  Although Stevens Creek Dam, built in 1916, functions as a “run-of-the-river,” reservoir it has no impact on flooding in Augusta.   It was this dam that the cubic feet per second of flowing water was calculated in 1929. 

 

There remains a potential for dangerous flowing in Augusta, GA, and the city together with the U. S. Army Corps of Engineers (USACE) has made plans for disaster control from possible future floods.   Part of this plan is a proposed map of the possible flooding caused by a break in the J. Strom Thurmond (Clarks Hill) Dam has been drawn by the USACE. 

 

Although the Savannah River has not overflowed its banks at Augusta since the construction of the levee system and the construction of the three upriver dams, there have been local floods in the Rae’s and Rocky Creek sections as well as the 1990 flooding from heavy and intense rain fall.

 

The low lying areas will always have the potential of flooding.  This is why knowing the history of former floods will serve as warnings and preparatory lessons for the future.   This web site is a reminder of the clarity of the past and how the future can be as murky and “flashy” as the Savannah River during a flood.