For Civil War earthworks, erosion is now the enemy

03/25/04

Time and erosion are their enemies now. Having once withstood the march of infantry, pitched battles and artillery bombardments, historic defensive earthworks built at the time of the Civil War around Charleston, S.C., are now giving up ground to the march of time.

Millimeter by millimeter, these earthen fortifications – some rising about 12 feet high and stretching as wide across as a football field or two – are slowly eroding, according to University of Cincinnati doctoral geology student Reuben G. Bullard, Jr. Bullard – who also has a strong background in archaeology, having worked on digs in Greece and at Troy (in Turkey) – has been documenting the rate and patterns of erosion of 12 Confederate earthworks and will report on his findings at the joint meeting of the Northeastern and Southeastern Sections of the Geological Society of America March 25-27 in Virginia. (Also presenting research at that conference will be two other UC doctoral students in geology Sean Cornell and Katherine Bulinski. Bulinski is researching how to best study and measure long-term biodiversity trends while Cornell is comparing oceanic, sediment, rock and fauna changes caused by the formation of mountains about 450 million years ago, in what is today the New York State/Ontario region vs. the Ohio/Kentucky region.)

"The Charleston earthworks are the perfect laboratory for studying erosion of hillsides and of large earthen constructions. Unlike most historic earthen structures – like the prehistoric Native American mounds or ancient tells in Britain – we know exactly when these Civil War batteries were built in 1862 and 1863, and we even have very detailed measurements of how and where they stood at the war's end in 1865," explained Bullard who credits a one-time military engineer, Union General Quincy Adams Gillmore, for making very detailed sketches and measurements of the defenses.

Building on Gillmore's work – forming a strategic alliance if you will – Bullard has been able to determine that the earthworks are gradually eroding, though he adds, "They're not falling apart. They're becoming more rounded at the crest and at the base, slowly leveling at a rate of about five millimeters a year. The slopes are becoming more gentle, and subtle features are diminishing."

The UC research is focused on a dozen earthen redoubts and fortifications on James Island just south of Charleston, built to provide defense against Union gunboats seeking to approach Charleston by means of adjacent waterways. The structures that Bullard has studied include Battery Pringle, Battery One, Battery LeRoy, Battery Tyne, Ft. LaMar and Ft. Pemberton. Bullard's final study will be shared with both the Charleston Museum and the South Carolina Battleground Preservation Trust, organizations which have aided his research, because of their interest in safeguarding the structures.

Additional assistance has been provided by UC faculty and by faculty at the College of Charleston. Bullard's work has also been assisted by an updated version of SLOPEAGE, a computer program for dating hillsides developed by UC geologist David Nash.

Bullard – who is also studying early 19th-century transportation canals in Indiana – states that, while 150 years or so is nothing in geologic time, the effects of climate, weather, ocean currents, plant growth and human activity on these man-made hillsides during that time can be extrapolated to provide a baseline that can be used in connection to other such structures around the globe – like the earthen dams the Romans constructed, giving researchers another tool for estimating the age of such mounds. "In addition, it's similar to how tombstones serve as a proxy for natural-rock bodies in studies of weathering rate. By understanding the pattern and rate of earthwork slope degradation, we can better understand natural hillslope evolution too," he explained.

Funding for the research was supplied by Sigma Xi with matching funds from UC.

Source: Eurekalert & others

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