For many who experienced the destruction of South Carolina’s October 2015 flood, it’s perhaps difficult to imagine that the state was plagued by a drought prior to the historic rain event. Despite the monumental devastation wrought by the flood, hydrologists who study the state’s aquifers, or the state’s usable groundwater resources, have observed a faint silver lining.
According to Bruce Campbell, a hydrologist with the U.S. Geological Survey (USGS), the Palmetto State was indeed in a drought during the fall of 2015. In fact, the state had been in a drought, on-and-off, for nearly two decades, with a few normal years mixed into quite a few dry ones.
“The stream flows have been down since 1998,” Campbell said. “Some people would say we’re still in that drought.”
Campbell’s fellow hydrologist Alex Butler of the SC Department of Natural Resources said the state’s aquifers had been declining ever since the 1990s, endangering fish populations, farm irrigation and towns that depend on streams and rivers for their water supplies. Individuals who get their water for wells had particularly been affected by diminishing groundwater.
According to Butler, prior to the flood, the state saw serious decreases in stream flow—or groundwater discharging to streams—in the lower coastal plain, which extends from the midlands to the coast.
“That is where we have a large number of people [who] rely on groundwater for their water supply,” Butler said. “So the main impact of the drought is this reduction in recharge to the aquifer system, and that can reduce the amount of water that ends up being discharged to the streams. That can add another level of stress to the aquifer system.”
When the Midlands were battered by relentless rain in October 2015, the aquifers of the upper coastal plain actually received much-needed groundwater recharge.
“That’s an increase in the volume of water that actually makes it to these aquifer systems . . . sandy soils, the water can easily penetrate it and move down, so what we saw was a large increase in the recharge for 2015. And that resulted higher levels in the groundwater . . . That’s a good thing,” said Butler.
However, according to Campbell, that relief was likely temporary. “It’s probably a little bit of a short term event,” Campbell said. “The water levels respond quickly, but then they’ll begin to equilibrate based on the local conditions.”
Butler agreed that the steady progress of smaller but consistent rains do more to refill groundwater supplies than a deluge such as the state received. Because there was only a brief window for aquifers to absorb the rain, shallow aquifers close to the surface, like the ones that feed into wells, were benefitted most.
“There’s a kind of limit on the amount that the soil can take in at one time. That consistent rain is what’s good for recharging the aquifer. When you have these large rain events, the soil at some point becomes saturated, and . . . the soil just cannot absorb anymore,” Butler said.
Ironically, many homeowners actually called USGS to ask for advice about the “boggy, soggy” conditions in low-lying areas of their property, according to Campbell. For these individuals, the excess water that couldn’t be absorbed by the aquifers had become a blight on their lawns.
“Everyone one of them I would tell, ‘just wait until March,” Campbell said. “The trees’ll leaf out, the temps will go up, water’ll start evaporating and the groundwater levels’ll drop, and you’ll be fine.”
Both Campbell and Butler expressed hope that, moving forward, groundwater in SC will be replenished under less dramatic circumstances. Groundwater recharge may have offered a silver lining to a devastating event, but in the future, afternoon showers will do.