The riddle of sand and currentOct 7, 2016
Tidal currents cycling day after day affect the depths in sandy areas like the Bahamas.
On Thursday Oct. 6 at the Annapolis Sailboat Show a subject receiving much discussion was the progress and effects of Hurricane Matthew, which had just pummeled Haiti and Cuba and was headed across the low-lying Islands of the Bahamas. I spoke with Hasko Scheidt, CEO of the paper and electronic chart publishers NV Charts. We looked at an NV Chart of the Bahamas and I remarked that Hurricane Matthew would probably cause enough storm surge to change the shallow, sand-laden channels of the Bahamas and require Hasko and his company to undertake a new round of surveys to correct the charts.
Hasko, a big man with a red beard, a full head of hair and often amused blue eyes, shook his head. "No. Not at all."
At first I thought Hasko was saying that the company, which is about to set to work on a new set of charts for the Mediterranean, didn't have any Bahamas surveys in the works and would not be able to do anything about any changes wrought by the hurricane. Then Hasko explained that there was no need to redo the charts because any movement of the sand caused by a few hours of hurricane-induced current, would have little long term effect compared to the repeated and relentless action of tidal currents. Over time the endless tidal cycle produces currents that push the grains of sand right back to where they were before a hurricane disrupted them. The combination of tidal current and bottom topography dictate where the sand comes to rest.
Hasko and his wife Conny, a fellow founder of NV Charts, related another story from their experience in the Caribbean. They spoke a beautiful beach near the mouth of the Indian River on the island of Domenica in Prince Rupert Bay (see chart below). One day a storm came and the waves washed away most of the sand, turning a picturesque beach into a stretch of rocks. In some places in the U.S such an event might lead to calls for the Army Corps of Engineers to replenish the beach with fresh sand trucked in at great expense. That replenishment operation didn't happen, however. According to Hasko and Conny nature took over the job. After a few years the natural currents in the area replenished the beach on their own, no intervention required.