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Development about to restart in one of Charleston's most flood-prone regions

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Cynthia and Gregory Martin were rescued from their home in Shadowmoss during 2015 flooding by Charleston Fire and Task Force One. File/Staff

Clusters of subdivisions started popping up in the Church Creek drainage basin in the mid-1980s. Until then, this 5,000-acre area in the outermost corner of West Ashley was mostly marshland and old phosphate mines.

Almost as soon as the first neighborhoods, such as Shadowmoss and Hickory Farms, were built, the flood waters arrived in homes, yards and streets. It was a problem that would return time and again for decades to come, expanding its reach as more developments moved in. 

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Church Creek basin in outer West Ashley

Today, the Church Creek basin is one of the most flood-ridden parts of the region. Unlike the historic Charleston peninsula, where centuries-old infrastructure is largely to blame for the flooding, Church Creek is a relatively new destination for development. Its subdivisions were planned after the creation of the National Flood Insurance Program and the flood maps that were supposed to identify the riskiest areas.

What led the area down a path of destruction was a combination of mapping errors, rampant development and a profound misunderstanding of how water naturally moves through the basin.

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For Church Creek flood story

Through a rain-soaked lens, Dawn Hale took this picture of Dave Hale as they used kayaks during a storm to check on their home on Mowler Court in Shadowmoss last year. File/Provided

The city of Charleston commissioned a number of engineering studies over the years to understand the problem, and it spent millions of dollars on improvement projects. But it's never been enough to dry out the area for good.

After the most recent $300,000 study was completed last year, the city is now pursuing another round of solutions — stricter rules for new developments and more drainage projects. The recommendations, which include a major pump system and a tidal flood gate, are estimated to cost $44 million, more than 10 times what the city has spent there in the past.

Still, further study will be needed to determine if those projects will bring enough relief to justify the costs, according to Stephen Julka, the city's floodplain manager.

And the march of development can resume as soon as next week. The temporary building moratorium in the basin will expire when City Council finalizes the new stormwater rules Tuesday, allowing four projects with a combined 352 residences to move forward across almost 200 acres. All of them are at least partly in a floodplain.

What went wrong?

In basic terms, wetlands and floodplains are nature's version of stormwater ponds. When it rains, wetlands hold whatever water isn't absorbed into the ground, and if they fill up, the water spills over into surrounding floodplains.

At high tide, when streams and rivers are fuller, floodplains serve as waiting rooms for the excess water until it can make its way out when the tide.

Problem is, Church Creek is the only stream connecting the 5,000-acre basin to the Ashley River, and it's only 10 feet wide. It's always overflowed easily in a heavy rain, even before the first bulldozers showed up to change the landscape.

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Tropical Storm Irma (copy) (copy)

The Shadowmoss subdivision of West Ashley was flooded during Tropical Storm Irma. The city is seeking solutions to flooding in the Church Creek drainage basin which is where the subdivision and other properties with flooding problems are located. File/Brad Nettles/Staff

But when the Federal Emergency Management Agency developed the first flood maps for that area of West Ashley in the early 1980s, it didn't account for the narrow stream's behavior when it fills up with rain. Like most of the maps for the region, FEMA only looked at the flooding brought on by storm surge in a hurricane. 

It also assumed that the railroad running through the middle of basin would keep everything above Bees Ferry Road dry in a major storm like that, so all the land where Shadowmoss and Hickory Farms were built looked like high ground.

That's how dozens of slab-on-grade homes, including the 32 Bridge Pointe Townhomes, got built in the middle of a floodplain. Of the 5,173 homes in the basin today, 74 have been damaged by flooding multiple times.

The first engineering firm the city hired to study the issue, Woolpert, discovered this in 2001 and helped get the maps changed. It made sure that new homes were elevated properly, but the flooding problems persisted.

About 80 percent of the basin has been developed, meaning vast areas that once stored water are now covered with pavement and homes, forcing more water to runoff when it rains.

The development changes in the Church Creek basin from 1984-2016.

Bob Horner, the lead engineer with Weston & Sampson who led the latest Church Creek study, said one of the biggest mistakes was that the city never regulated how developers used fill-dirt in floodplains.

When building homes in those areas, developers can either elevate them on stilts, or they can lift the whole site out of the floodplain by layering on tons of fill dirt. Horner said that's a really destructive method because it forces water to move elsewhere, causing more flooding in areas that haven’t been filled in.

The Post and Courier investigated the city's lack of regulations on fill dirt earlier this year. Unlike other coastal cities such as Savannah, Charleston never followed recommendations from FEMA and state agencies to monitor how developments altered the floodplains.

The new rules in Church Creek that City Council passed last month include a requirement that if developers use fill, they have to dig and leave holes on the land so it doesn’t lose its overall capacity to hold water. They also will have to use certain materials so water can soak into the soil. 

Tim and Nancy Holbach's home on Jawol Drive was severely damaged by the historic flood in October 2015, and they couldn't live there for four months afterwards. When the moratorium is lifted, the new 30-unit Middleborough Villas will be allowed to move forward on the street behind them. 

Tim said he's glad new developments will have to follow stricter fill rules.

"My main concern is ground topography," he said. "If you keep filling in all these low spots, there's no place for retention."

In the past, ponds and ditches helped store some of the excess water. But they couldn't store all of it if a storm dumped a heavy rain in a short period, as happened during the October 2015 storm.

Plus, almost all of the collection systems in the basin end up draining into the narrow Church Creek channel, which simply isn't big enough to handle that much water at one time — especially at high tide.

That's why developments will also be required under the new rules to hold their runoff water for at least 72 hours, which will mean larger, deeper ponds.

That will help add more storage capacity that's been lost over time, but with the majority of the basin already built out, it will basically only make sure that new projects don't exacerbate the issues. 

Solutions are big and expensive

Crosstowne Christian Church on Bees Ferry Road is right next to Church Creek, and it has been inundated with some of the deepest floods over the past few years. In October 2015, the water rose more than two feet inside the sanctuary. 

Paul Rienzo, the pastor, blames surrounding developments for sending more water the church's way. When Bees Ferry Road was widened and the West Ashley Circle was built, the state and local agencies building those projects weren't required to follow the basin's strict water detention rules.

"None of this happened before the redesign of Bees Ferry Road," Rienzo said. "There seems to be some sort of causal link."

He supports the new regulations, but he's afraid other developers will be able to get variances from the city to avoid following them. He said he plans to track whether any are issued.

"We want the community to know who’s making the decisions and what deals are being made," he said. "That’s the level of accountability we need here."

The strategies that will bring the most relief, according to Weston & Sampson, are large-scale projects that would divert water from Church Creek. 

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Tropical Storm Irma (copy)

The Bridge Pointe neighborhood in Shadowmoss flooded during Tropical Storm Irma. All the town homes in the neighborhood will be bought out with a FEMA grant. File/Brad Nettles/Staff

The most expensive, at roughly $26.6 million, is a new pump station that could be installed where the creek meets Bees Ferry Road. The water would be pushed through a channel straight to the Ashley River. 

Without a major investment like that, Horner said water will continue to inundate properties like the Crosstowne church. But it's still unclear if that's a realistic project.

Woolpert's 2001 study didn't recommend it. Brian Bates, the project manager at the time, said it didn't earn a high enough score on FEMA's standard cost-benefit analysis. That process is required for any drainage project to receive federal funding.

“The cost of the construction, design and the operation and maintenance of a stormwater pump station far exceeded the resulting benefit price,” Bates said.

In a written Q&A with residents in December 2015, the city also doubted the possibility of a pump station, calling it "infeasible." 

Julka, the floodplain manager, said while it would be a massive undertaking, the city's priorities have changed in recent years.

"I think that we are in a position to really attack this with whatever ability we have," he said.

One alternative is to buy and raze the properties that routinely flood and turn them back into greenspaces to store water. There's already a process in the works to buy out the 32 Bridge Pointe townhomes and a few other single-family homes in Shadowmoss. 

Horner said it would be worth pursuing buyouts of more than 100 other properties.

Until then, residents like the Holbachs are bracing for hurricane season, hoping they'll be spared this year.

Reach Abigail Darlington at 843-937-5906 and follow her on Twitter @A_Big_Gail.

Abigail Darlington is a local government reporter focusing primarily on the City of Charleston. She previously covered local arts & entertainment, technology, innovation, tourism and retail for the Post and Courier.