The lead engineer studying the Church Creek drainage basin confirmed Tuesday what outer West Ashley residents have suspected for years: recent developments have brought more flooding problems to their neighborhoods.
But Bob Horner of Weston & Sampson Engineering explained to Charleston City Council that the analysis hasn't turned up a "smoking gun." Instead, he said a variety of forces, including new developments, have made it increasingly difficult for water to drain properly in the 5,000-acre basin.
"I think this is like a perfect storm for a problem area of drainage that’s been brought to light more frequently by multiple, significant weather events," he said.
Council passed a nine-month building moratorium in the basin in February so Weston & Sampson Engineering could study the basin's problems and recommend a new round of solutions. The firm's final report is due at the end of October.
During his progress report to council, Horner said Church Creek, a 10-foot-wide channel to the Ashley River, simply isn't large enough to handle drainage for such a large area that includes the West Ashley Circle and many subdivisions such as Grand Oaks and Shadowmoss.
During a major storm such as Tropical Storm Irma or Hurricane Matthew, storm surge overwhelms the basin's creeks, ponds and ditches. Combined with heavy rainfall, the water can't drain quickly enough and backs up into streets and homes.
In some places during Irma, the water levels rose to nearly 9 feet, and didn't return to normal for several days.
The team of engineers is using a simulation of the area to test how storm water flows during those extreme weather events as well as average rainy days. The model is helping the firm test potential solutions.
Some early results indicate the basin will need more than one main drainage channel to divert water from Church Creek. That will be the central idea behind the recommendation Weston & Sampson is submitting to council next month.
Horner said the firm will suggest installing several pump stations along the Ashley River to push out water during heavy rainfalls, and create new tidal gates to keep water from flowing into the drainage system at high tide.
When Councilman Dudley Gregorie asked how long it would take to implement all those solutions if funds were readily available, Horner estimated it could take about four to five years.