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The Crab Bank shorebird rookery has eroded from more than 18 acres to less than an acre over the past 25 years. Plans to renourish it have Mount Pleasant concerned. Grace Beahm Alford/ Staff

 Grace Beahm Alford/Staff

The shifting sands of Crab Bank won't stand still, and neither will the town of Mount Pleasant.

The town will commit as much as $100,000 to study whether the renourishment sand that washes from the shore bird rookery in Charleston Harbor would block the mouth of nearby Shem Creek — the town's valuable commercial fishing hub, tourist destination and restaurant row.

That's even as the Army Corps of Engineers will study the silting pattern before any renourishment takes place.

"We have a duty to represent the interests of the town and our shrimping fleet, to know what’s going to happen here," said Mayor Will Haynie.

"The $100,000 for the study pales in comparison to the potential losses or the cost of redredging Shem Creek or Hog Island Channel,” he said.

The Crab Bank rookery is an eye-catching crowd of shorebirds nesting by the hundreds in the harbor close to the Mount Pleasant side. It's a critical mid-state link among a handful of publicly owned and protected rookery islands in the state for threatened species of shorebirds.

It's also a sought-out natural destination in a tourism economy worth billions of dollars per year. But over the past 25 years erosion from the seas, storms and ship wakes have reduced it in size from more than 18 acres of nesting high ground to less than 1 acre.

The Army Corps' Charleston District has been given the go-ahead from headquarters to renourish the bank to 28 acres of high ground using 660,000 cubic yards of dredging soils from the coming harbor deepening project. Conservation and birding interests have pushed hard for the renourishment.

Some of the sand lost to erosion apparently sifts in the tides along the bottom toward Shem Creek, less than a quarter mile away. Getting in and out of the creek already means weaving around sand bars that occasionally strand boats, even though the creek was dredged as recently as 2014.

Town residents and officials worry more sand means the expense of more dredging, to keep the creek navigable for the shrimp boat fleet and other commercial fishing vessels at its docks, plus the horde of recreational power and paddle craft launching from its landings.

No one has put a dollar figure on the value of Shem Creek, but it's easily in the millions.

The Army Corps maintains the erosion will continue at the same rate it has since the island first was created by dredging soils in the 1950s. Its staff will do a computer-driven numerical estimate of where the renourishment sand is likely to go once it erodes, said spokesman Sean McBride.

The town wants more.

"The Corps is going to deposit the equivalent of 50 acres of sandbar at the mouth of the creek, on an already unnatural bank," Haynie said.

"It has disappeared because nature doesn’t want it there. It is (the state's) only such designated rookery that is not natural. The Corps acknowledges that due to the fact that because only 65 percent of the spoil (dredging soils) is sand, 35 percent or the equivalent of 20 acres will dissipate immediately," he said.

"Shouldn’t we know where it will go?" Haynie asked.

The conservation community, which must raise an estimated $2 million to pay the local share of the renourishment project, is treading lightly around this dispute, which could potentially delay or derail the project.

"Our primary goals are to protect Crab Bank and Shem Creek," said Caroline Bradner, the land, water and wildlife project manager for the Coastal Conservation League.

"We support the town’s decision to study siltation as long as it doesn’t slow down or impact this once-in-a-lifetime opportunity to save Crab Bank and restore critical nesting habitat," she added. "Ideally, we believe the town can work collaboratively with the Army Corps."

Reach Bo Petersen Reporter at Facebook, @bopete on Twitter or 1-843-937-5744.

Science and environment reporter. Author of Washing Our Hands in the Clouds.