Ironic Twist to Cleaner Water Presents Engineering/Financial Challenges

Often considered the termites of the sea, and collectively known as marine borers, this aquatic creature has made a comeback in the waters of NYC since the implementation of the Clean Water Act in 1972.  Gribbles and shipworms are the two most common types of borers found in the NYC harbor, and together they’ve caused considerable damage to the wooden infrastructure holding up piers, bridges, and roads.

Nationwide, marine borers have caused billions of dollars in damaged infrastructure, and New York City is expected to spend roughly $300 million in the next five years to repair and reinforce damaged pilings.  With renewed interest in the waterfront for parks development, it is not unusual for the vast majority of the cost to go to reinforcing damaged pilings.  Gribbles undermine wooden infrastructure by boring horizontally, while shipworms bore into a piling and then bore either up or down, eating the structure from the inside out.

Ship captains and others have been plagued by shipworms for centuries.  Christopher Columbus reportedly lost two ships in present-day Panama in the early 1500s to shipworms.  According to legend, the Little Dutch Boy plugged a hole in a wooden dike that was made by shipworms.  Reportedly, so little wood was found on the sunken Titanic because of shipworms.  And ancient Greek literature even mentions the pest as far back as 350 BC.

As New York City became industrialized in the 19th century, its harbor was known as a “clean harbor,” meaning that when a vessel entered New York City waters, anything living on the underside would not survive due to extremely poor water quality and the ship would leave “clean.”

With the passage of the Clean Water Act in 1972, scientists began noticing evidence of gribbles in the harbor in the 1980s, and eventually shipworms.  Borers need oxygen to survive, and with steadily improving dissolved oxygen levels in NYC waterways, the borer population has exploded.  At particular risk is infrastructure in the East and Harlem Rivers, because of the FDR and Harlem River Drives, as well as numerous bridge crossings over these two waterways that are propped up by wooden pilings.

To battle against the borers and protect vital wooden infrastructure, techniques involving the application of various chemicals to pilings were tried.  However, with greater environmental consciousness, these techniques were discarded for plastic wrapping around pilings, although this reportedly made the problem worse.  Finally, in the mid 1990s, engineers pioneered the first ever pier constructed of recycled plastic at Tiffany Street in the Bronx.  Initially thought to be the future of harbor infrastructure, hopes were dashed when the pier was struck by lightning and melted.

Today, at considerable cost, engineers retrofit damaged pilings with wire cages and fiberglass and then pour concrete into the molding to reinforce and lengthen the life of a piling.  This is currently the accepted best practice for dealing with marine borers.

The presence of pollution-intolerant marine borers in NYC waters is an ironic twist to increasingly cleaner waters.  With more interest in the development of waterfront parks, including areas along the East River Esplanade, protecting vital infrastructure from marine borer damage must be considered in any waterfront plans.

-PH

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