Dredge contractor Marinex Construction Inc. positions boats
to dredge material from near the Boca Raton Inlet to widen the beach to the south.
Tim Stepien/The Coastal Star
By Cheryl Blackerby
After delays from bad weather, including high winds during most of November, the beach renourishment project in south Boca Raton finally started the day before Thanksgiving and finished pumping sand on 0.9 mile of beach Dec. 9.
“The dry beach was widened 60 feet on average the entire length,” said Jennifer Bistyga, engineer with the city of Boca Raton.
The dredge is expected to go to the north Boca Raton beach at the end of February and early March after finishing beach renourishment projects in Ocean Ridge and Delray Beach, she said.
The dredge moved from the Port of Palm Beach to Ocean Ridge on Dec. 19 to start pumping sand from borrow areas about 1,800 feet offshore onto 1.1 mile of beach, said Tracy Logue, coastal geologist for Palm Beach County Environmental Resources Management.
But the project was delayed again by weather and the holidays. The dredge returned to the Port of Palm Beach and is expected to start work in Ocean Ridge on Jan. 3, according to Dan Bates, deputy director of Palm Beach County Environmental Resources Management.
The Ocean Ridge project is expected to take 34 days, barring any weather delays. Sand will be put on the Ocean Ridge beach starting at the Ocean Club just south of the southernmost groin and end at Edith Street, she said.
Another Ocean Ridge project, the modification of five T-head groins, was completed in mid-December. These are the northernmost of eight groins south of the Boynton Inlet.
The groins were built to keep sand to the south of the inlet from eroding too much.
“The sand, which comes from the sand transfer plant and is deposited on the south side of the inlet, is supposed to filter through,” Logue said. However, “the groins were trapping too much sand.”
About two feet of the top layer of rocks of the groin “stems” perpendicular to the beach were removed to lower the groins and allow more sand to drift over them to the south.
“We took one rock layer off the top so sand can go through more easily,” Logue said.
Erosion a problem
Beaches located directly down-drift of inlets can experience persistent erosion, according to the U.S. Army Corps of Engineers. “Recession of the shoreline can occur at a high rate, and breaching becomes a possibility at inlets on barrier islands.”
The groins are built of granite boulders, about 2 to 3 feet wide and tall, and are sunk into the ground about 8 feet below the sand floor and stand about 4 and a half feet above the sand.
All eight groins are south of the inlet, and the five that were modified are south of the sand discharge pipe. The modified groins are all behind private property.
The U.S. Army Corps of Engineers managed the project and used seismic testing to monitor vibration from the excavation, she said. “Since they were running heavy equipment on the beach, they wanted to make sure there was no damage to a house, and no vibrations that could cause a crack in a pool, for instance.”
Excavators were used to remove the big boulders, some of which were deposited inside concrete panels to help reinforce the north jetty.
“Rocks had settled inside the concrete panels and there was space to put more rock in. The more rock you have, the more it weakens the force of the waves. The rest of the boulders will be stored and will probably go into artificial reefs,” Logue said.
The beach renourishment projects in Ocean Ridge, Delray Beach and north Boca Raton are U.S. Army Corps of Engineers beach projects. The Army Corps deadline for those projects is April 30, and the work should be finished well before the deadline if seas remain calm, said Bistyga.
The south Boca Raton beach renourishment is not an Army Corps project; but the city used the same contractor to save money, she said.