HomeColumbus Iselin Coeal Reef Restoration Project


Columbus Iselin Home Page

Repair of the First Two Spurs: July 21-27


The restoration team initiated work on the first of the two smaller injury areas, Sites "F" and "A." Working on the smaller sites insured that any potential problems in the design work or materials could be quickly addressed. With calm seas, work proceeded quickly as the contractors, sanctuary staff, and design engineers developed into an effective project team.

The only significant problems were delays in the cement supply, the "death" of one of the starboard engines on the sanctuary's vessel, and difficulties with the cellular phones. The contractor returned the barge to Stock Island to pick up supplies, including cement. The sanctuary vessel is getting two new engines, and the cellular phones now have new antennae.

Injury Site "F"

During the procedure heavy canvas straps secured the boulders while they were lowered over the side of the barge. The boulders were then guided into place by divers. After workers placed the boulders and the initial rebar lattice on the site, they added several tremie pours. Each pour was mixed in a concrete mixing truck on the barge and then pumped off the barge through special hoses.

Divers placed fiberglass rebar in new concrete about 20 minutes after each pour following the design drawings. After the final pour of concrete (about six cubic yards), divers carefully covered the site with surface rocks, one by one. Their work was guided by the sanctuary's resource manager, Harold Hudson. In reef restoration, rocks are placed to resemble the top of a healthy reef and to provide a better substrate for coral recruitment.

Injury Site "A"

The team shifted the crane position from Site "F" to Site "A." The first step on Site "A" was the removal of debris from Hurricane Georges. The debris was preventing effective placement of the boulders. The debris was cleared with the clamshell bucket on the 125 foot crane.

Boulder placement took several days, after initial chinking and sealing of the sides of the site. Several tremie pours were needed, each with a placement of rebar for support. The final concrete was allowed to harden enough to support some weight, yet still be soft enough to move rocks into the concrete. Surface rocks were then placed by hand (under Harold Hudson's guidance) into the concrete to give the finished injury site a coral reef appearance. This completed the structural portion of Site "A"'s restoration effort.

Worksite Images


A three to five ton boulder entering the water.

"Chinking" stones used to help seal (along with underwater concrete grout) the perimeter boulders before tremie concrete pour. Site "A".

A composite rebar lattice for stabilization of first tremie concrete pour. Site "A".


Divers setting boulder in Site"F".

"Hudson" holders, like that shown in the boulder above, are placed in perimeter boulders for increased stability. Vertical rebar provides stability between tremie concrete layers.

Divers from NOAA and Coastal Planning and Engineering (CPE) checking placement of boulder at Injury Site "A".

Partial placement of top surface rocks in final tremie pour at Injury Site "F". This is to facilitate coral recruitment and simulate the natural surface of the coral spur.



NOAA logo Revised July 31, 2017 by Sanctuaries Web Group
Many links leave the National Marine Sanctuary Web Site - please view our Link Disclaimer for more information
National Ocean Service | National Oceanic and Atmospheric Administration | U.S. Department of Commerce | NOAA Library | Privacy Policy
Contact Us | http://sanctuaries.noaa.gov/includes/sancfoot.html