Shoreline & Waterway Management

What is a groin? In the coastal sense, a groin is a narrow, elongated engineering structure built on a beachfront and deployed perpendicular to the trend of beach. Its intended purpose is to trap sediment to build up a section of beach. Sand tends to accumulate on the updrift side of the groin. Updrift is determined by the direction of the littoral transport or by the movement of sand parallel to the shoreline, orchestrated by waves and currents.

• See the beach take shape as the restored groin enables sand to accumulate

The groins at Herring Point in Cape Henlopen State Park in Lewes were originally built by the U.S. Government as part of the Fort Miles Military Reservation, an important army base which protected the entrance to Delaware Bay. The original timber and rock groins were built in the mid-1950’s to protect the sand bluff on which the fort’s gun battery rested.

ABOVE: The stone (boulders weighing up to five tons each each) used in reconstructing the North Herring Point groin.

BELOW: The Herring Point groin restoration begins in earnest as some of that stone meets the beachfront.

The 300-feet long groins were designed to control the natural movement of sand along the shoreline by allowing it to accumulate on the updrift side (littoral transport around Cape Henlopen generally moves to the north). Since then the groins have succumbed to the wear and tear of the seas and are falling apart.  They are no longer functional and have allowed erosion to narrow the beach and scarp the bluff where the historic gun battery is located—compromising its safety and diminishing recreational opportunities such as swimming and surfing.

The north jetty axis of the groin as it begins to take shape in early May.

DNREC’s Division of Soil & Water Conservation’s Shoreline and Waterway Management Section rebuilt the northernmost groin in the spring of 2007 by removing what remained of the rotted timber portion of the groin, and adding heavy stone to its western end. Accumulation of sand along the southern side of the rehabilitated groin shows that the reconstruction, completed in July, is having the desired effect.

Update: 

The Herring Point north groin has been completed for less than one year and is already in nearly full “bypass” mode. This means that the beach on the south side (to the right in adjacent photo) has fully accumulated sand, while sand also is flowing around the seaward end, feeding the beach to the north. This photo was taken Feb. 19, 2008.