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.