Nuisance Flooding In Charleston - The Not So New Normal
A guard unchains a locked metal fence topped with barbed wire at the edge of the cruise ship terminal in Charleston. In this protected area is a tide gauge made up of a hollow white PVC pipe connected to computer equipment. A gauge like this one has been measuring water levels in Charleston Harbor for nearly a century.
The tidal gauge sticking out of the water captures the water level every six seconds and transmits that information to the National Oceanic and Atmospheric Administration, where Doug Marcy works.
“The tube basically acts as a stilling well. It keeps the water surface still and measures the water level as it goes up and down,” he said.
The gauge also measures how much the land is sinking. Marcy explains subsidence and sea level rise are both factored into how much higher the water level is. At this spot the water is one-foot higher than it was 100 years ago.
“It actually adds together,” he said. “Probably half of that is global sea level the rest is subsidence.”
One way to measure the impact to the city is through nuisance flooding or so called sunny day flooding, That’s when water from high tides or backed up drains inundates streets. In the last 60 years those events have increased 400 percent. And the flooding is worse for the lowest parts of the city which weren’t always dry land.
“A lot of flooding mimics where the old shoreline was,” Marcy said. “A lot of the downtown Charleston area was filled in.”
Professor of historic preservation at the American College of the Building Arts Christina Butler said that fill, “is a mixture of historic garbage. Animal remains, rice chaff, lumber mill waste.”
“And human bodies,” Butler’s husband and Charleston County Library Historian Nic Butler adds. “Since the beginning of the town, the poorest people have been buried in the lowest lying areas and then built over. We’ve got a lot of evidence from the early 18th century that poor people were being buried on the west side of the peninsula which is now a very nice neighborhood.”
Christina has spent years researching how the city created land. Since the Charleston’s founding in 1680 records indicate hundreds of acres on all three sides of the peninsula have been filled in. In the colonial and antebellum periods the city wasn’t regulating the expansion, so individuals were just dumping whatever they had in the marshes.
“They put six inches of sand on top of it and two months later somebody builds a house there and digs a footing,” Christina said. “By the 20th century we know better. We know about germ theory. Slowly but surely the city gets better about public health and regulating fill.”
Butler said by the 1960’s the city has stopped the major fill projects. But to this day, those areas are some of the lowest in the city. Roads, shops and buildings on the east and west sides of the city are sitting on top of decomposing garbage in what used to be tidal creeks.
Parts of those creeks are still intact today. Charleston Waterkeeper Andrew Wunderley steps onto an unstable rock on the edge of a creek littered with tires and plastic bottles.
“This is the headwaters of Newmarket creek as it exists right now,” he said standing under the overpasses for Highway 17 and Interstate 26. “I think this is the most intact tidal creek system on the Charleston peninsula.”
He said the pluff mud and spartina grass in the marshes have an infinite capacity to absorb water in a way that fixed structures like drains and roads can’t.
“Nobody is suggesting we dig up all these creeks and return them to a natural state, that can’t happen,” he said. “There are certainly opportunities for restoring creeks to make them function like they should.”
Wunderley said it is important protect and preserve the parts of the old tidal creek system we have left as more of downtown is developed.
Some of the lowest lying parts of the city such as Ashley Avenue and Broad Street cut off what used to be natural creeks.
The homes and businesses sitting on top of what used to be Cummings Creek will flood now when the water level reaches two or three feet above the highest average tide line.
That’s what happened October 27, 2015. The king tides that day reached the fourth highest levels recorded at the NOAA tidal gauge in the Charleston harbor. The highest ever recorded was during Hurricane Hugo in 1989. During that storm the water reached close to seven feet above the highest average tide.
NOAA scientist Doug Marcy said the high water level during the 2015 flood is significant because it shows how sea level rise is causing nuisance flooding to approach levels previously seen during major storms.
This story has been updated at Monday August 22, 2016 at 3:41 PM to clarify a tidal gauge has been measuring water levels in Charleston Harbor for nearly a century.