Coastal Management: Treasure Island, Long Key Beach Renourishment Construction Details

View a slide show of the dredging operations to mobilize for beach Renourishment.

The borrow site, or the area from which sand will be dredged, is the Egmont Shoal. This is the large sand bar offshore of the entrance to Tampa Bay, and to the north of Egmont Key. The shoal will be dredged with a clamshell or bucket dredge, the “Atlantic”. A bucket dredge is essentially a floating barge with a bottom opening bucket at the end of a crane. To excavate material, the bucket is lowered into the sediment, closed, then raised to the surface. The closed bucket is then positioned over a scow, or sand barge, and opened, placing the dredged material into the scow.

Photograph of dredge Atlantic.

The bucket dredge “Atlantic” of Norfolk Dredging Company that will be used on the project.

Photograph of bucket dredge loading scows.

Bucket dredge loading scow.

The loaded scows will be pushed to the beach project area with tugboats. Once offshore of the beach, the scows will be hooked up to an unloader, the “Vicksburg”, that will pump the sand through a submerged pipeline to the beach. The project will place nearly 2 million cubic yards of sand on Sand Key. Approximately 800 scow loads will be transported from Egmont Shoals to the beach project area.

Photograph of tug pushing scow.

Scow being pushed by a tug.

Photograph of unloader.

Unloader "Vicksburg" prepares to unload a scow.

The Egmont Shoal is located about 3 miles due west of Ft. DeSoto Park. This sand shoal has been dredged numerous times in the past to place high quality beach sand on the beaches of Pinellas County. The sand meets stringent state environmental criteria. This borrow area is located far enough offshore that dredging of the shoal will not affect waves that reach the shore, and will not cause erosion of the shoreline. There are no reef or hardbottom communities in or near this borrow area that will be impacted by dredging activity.

Aerial photograph of unloader off beach.

1990 Sand Key Phase II Nourishment.

The above map identifies the Sand Key project area in relation to the borrow area.

Construction equipment on the beach. During construction, a submerged pipeline will run from the unloader to a landing point on the beach. Upon arrival of a scow, the scow will be unloaded and sand will be pumped in a slurry of sand and water to the beach. Then, beach construction will proceed to the north by adding additional pipeline along the beach. This pipeline will remain on the beach during the construction of each shoreline section. Next, the pipeline will be “flipped” and nourishment will proceed to the south. Once the entire beach section as been nourished, the landing point and pipeline will be demobilized and relocated to construct the next section. During construction, temporary sand ramps will be maintained over the pipeline at regular intervals to provide safe public access to the Gulf and newly widened beach.

Photograph of renourishment pipeline on Upham Beach.

Renourishment construction at Upham Beach, July 2004.

Photograph of pipes on Upham Beach.

Pipeline on the beach during July 2004, Long Key renourishment at Upham Beach.

Photograph of sand pumping onto Upham Beach.

Above and Right: Sand being pumped ashore at Upham Beach, July 2004.

Photograph of sand being pumped onto Upham Beach.

Bulldozers will redistribute the sand that is pumped to the beach to create a smooth wide beach. Dozers and other construction equipment will be operated around the clock, creating noise from engines and safety backup alarms, and using lights from dusk until dawn. The small, active construction area typically will move along in 7 or 8 days. Approximately 100 feet of beach will be constructed per day. The contractors will be working around the clock. Safety backup alarms are exempt from all local noise ordinances.

The beach areas in the immediate vicinity of the active construction will be closed. Construction equipment and the operating pipeline pose a safety hazard to beach goers. A powerful fountain of sand will be discharged from the pipeline. Please obey all posted signs and stay out of the construction area.

View a slide show of the tentative plan for construction equipment on the beach.

Type of sand. Expect the nourished sand to appear darker in color than the sand in place previously. Nourished beaches usually start out a slightly darker shade than the existing sand, because the sand was taken from underwater. Once the sand is exposed to the sun, it will lighten. The sand may also be coarser (larger grains) than the existing sand. The sand that will be placed on the project has met all state sand requirements for color, content, and size.

During the 1998-99 Sand Key Project, a large volume of fist-sized rocks was pumped onto the beach. An annual rock removal program was necessary in which the top 3 feet of beach sand was sifted to remove the rock. Every effort has been made to avoid placing rock on the beach during the 2005 project. A detailed rock removal plan has been developed in case the contractor discovers rock in the borrow area. The first million cubic yards of sand was screened with a large cage, or screening basket, placed at the pipeline discharge. Due to the high quality of sand so far, the screen is no longer required on the discharge pipe, but will be kept on-site. The construction contract specifically states that rocks will not placed on the beach during this project.

Photograph of rocks removed from beach.

Annual rock removal program by tilling the top three feet of sand.

Photograph of large cage, or screening basket, will be used to trap rocks and large material.

Large cage, or screening basket, will be used to trap rocks and large material.

Photograph of a screening basket in use.

The use of a screening basket will trap material preventing it from being placed on the beach.

Beach width. The beach will be constructed abnormally wide because it is well known that the beach will equilibrate soon after construction. This means that the wide beach that is constructed by the bulldozers will start to narrow immediately. The natural wave action will smooth the beach to a gentler slope, thereby causing the beach width to narrow. This process does not involve a loss of sand from the beach, rather a redistribution of sand to the nearshore area and to the sand bar. Like the existing beach, eventually about 2/3 of the new material will be underwater, acting like the foundation of a house supporting the dry beach. Although it will appear that the beach is rapidly eroding after nourishment, this is the normal process in which the beach transforms from a constructed, designed beach to a natural beach form.

Illustration of beach equilibration after nourishment.

Beach equilibration after nourishment.

Breakwaters. In the past, the U.S. Army Corps of Engineers considered installing breakwaters at various locations along Sand Key. After studying of the success of the nourishment project, the Corps has decided against breakwater installation. This letter from the Corps to Pinellas County describes the Corps’ position on breakwaters for Sand Key.

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