Storm surge and rain from Hurricane Irene added millions of gallons of water to Pamlico and Albemarle Sounds at North Carolina's Outer Banks at Hatteras Island. Water being water seeks to find its own level, and if there isn't a convenient means of escape, it creates one:
On the outer banks, these areas where water flows from the sounds to the Atlantic Ocean (and back in again, according to tide) are called inlets. Before man arrived, they opened and closed naturally via erosion and silting/drifting. Now, with man using the Banks to dwell on and a requirement that transportation up and down the Banks be made by vehicles, such inlets as open up must be closed by heavy equipment and the road (the famous NC 12) rebuilt. So, construction companies will be busy with repair work for the next couple of weeks, getting the Banks opened back up to vehicle traffic. In the meantime, air and ferry travel will be the only way in and out.
More information here.
update: And official information from the Coast Guard can be found here.