MIAMI BEACH, Fla. — Some of South Florida’s most popular beaches will be particularly vulnerable to erosion and major damage if the state experiences a series of hurricanes, as it did in 2004 and 2005, because officials have run out of an important material: sand.

Miami-Dade and Broward counties are the first in the state to deplete their offshore sources of sand that can be used for beach renourishment projects, said Tom Martin, a senior coastal engineer with the Army Corps of Engineers.

None of the beaches that are renourished in South Carolina face that kind of dilemma yet. But in the longer term, with an eroding shoreline and a constant demand for sand, there is some concern.

The Corps of Engineers periodically surveys bottoms offshore of individual beaches, areas known as “borrows,” to make sure there is enough sand for the next few projects.

“We keep an eye on it,” said Lisa Metheney, Army Corps of Engineers program and project management assistant chief in the Charleston district. The Army Corps checks for quantity, but “more importantly, is it beach quality sand? Will it stay put (on the beach) for a little while?” she said.

The S.C. Department of Health and Environmental Control keeps its own tabs on potential renourishment sand offshore.

“South Carolina has been fortunate that its nearshore beach compatible sand supply has been able to keep pace with demand,” said Dan Burger, of the Ocean and Coastal Resource Management office of DHEC.

But the state also is looking to go farther out, into federal waters, for more sand. DHEC has approached beach towns and federal agencies about putting together a region-scale sediment management plan to prepare for major storm events, do large-scale beach maintenance projects and reduce potential conflicts over the sand borrow areas, Burger said.

The Charleston County Park and Recreation Commission spent $3 million to renourish the popular county park on Folly Beach’s west end so it could reopen for the July 4 holiday after being closed since 2011 after severe erosion from Hurricane Irene. Meanwhile, a $20 million federal renourishment project for the rest of the beach is expected to start in the fall. That project will use sand dredged from 3 miles offshore. A Myrtle Beach sand renourishment is also planned.

The Corps of Engineers prioritized Miami-Dade’s sand problem this week in a series of public meetings from Miami Beach to Fort Pierce, seeking input for the first phase of the process to identify a new source of sand.

“The general perception is the ocean is full of sand, but to get the sand in an environmentally responsible way, to get sand compatible with what’s on the beaches, it’s difficult at times,” Martin said.

There’s more than enough sand available off southeastern Florida for beach renourishment projects in five counties during the next 50 years, according to a new study by the engineers and the Florida Department of Environmental Protection.

However, almost all of it is in state or federal waters off St. Lucie, Martin and Palm Beach counties — not Broward or Miami-Dade.

Beach renourishment projects have continued along roughly 200 miles of southeastern Florida shoreline since the late 1970s, providing a buffer between coastal development and infrastructure and the eroding forces of ocean waves and storms. Sand for those projects typically comes from nearby sources for cost reasons.

Now that those nearby sand sources are depleted in Miami-Dade, the Corps of Engineers is considering alternatives such as inland sand mines, sand dredged from deeper offshore waters, from the Bahamas or other international sources, or the offshore sites identified farther north along Florida’s Atlantic shore.

Miami-Dade’s shoreline should hold up relatively well if there’s a storm, thanks to beach renourishment projects over the last year using the last of the available sand dredged off the county, said Matthew Schrader, a coastal engineer with the Army Corps.

Back-to-back storms or a series of stormy weather events, however, could put the county at a disadvantage until an alternative source of sand was secured, a process that could take a few years.

“If we get hit by a large storm, unlike in the past where we knew we had resources right off our coast, those simply don’t exist now,” said Stephen Blair, chief of restoration and enhancement in Miami-Dade’s department of environmental resources management. “That vulnerability is very real.”

Blair noted that Broward County shares similar concerns, and he said he would like to see the available sand managed across the region instead of by proximity to individual counties or municipalities.

Sand for short-term fixes could be trucked in from inland sand mines in central Florida, but that’s logistically difficult and not cost-effective for long-term projects or major post-storm damage, Schrader said.

Miami-Dade’s dwindling sand problem is nothing new, Martin said. Officials first started exploring the Bahamas as a source for the county in the 1980s.

Miami-Dade and Broward historically have had fewer sources of sand than other Florida counties, Martin said.

“Here we have coral reef systems that constrict the areas where we can go to retrieve sand,” Martin said. The continental shelf also narrows off Broward and Miami-Dade counties, leaving even less space available for dredging before the ocean floor drops off.

Identifying sources of sand isn’t as simple as just hauling it from the bottom of the ocean to shore.

If the grains of sand are too fine, they’ll cloud the water and smother reefs and other marine life. Grains too dark in color can get too hot, which can affect sea turtle nests. Other considerations include costs and whether dredging will impact nearby corals or fishing grounds.

Meanwhile, Congress has dictated that international sources of sand can be used only if domestic sources are not economically or environmentally viable.

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Bo Petersen of The Post and Courier contributed to this report.