International Dredging Review

International Dredging Review
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In May RLB Contracting Inc. of Port Lavaca Texas started dredge work along Aransas Bay in Texas to reconnect Cedar Bayou and Vinson Slough to the Gulf of Mexico. The natural pass has been primarily closed for decades and will be reopened by October 15 of this year.

RLB’s 12-inch cutter suction dredge Pat Lundin is performing the dredge work at the Cedar Bayou/Vinson Slough Restoration Project along with excavators and off-road trucks for inland work.

“The entire Vinson Slough/Cedar Bayou system works in unison to provide as much water flow to adjacent bays and marshes as possible. The Cedar Bayou channel provides circulation to the adjacent 20000 acres of Vinson Slough marshes and Vinson Slough facilitates flushing of Cedar Bayou based on the hydrodynamics of the system” said Aaron Horine P.E. senior coastal engineer at Coast & Harbor Engineering which performed feasibility studies and engineering work on the project.

Cedar Bayou Before

Cedar Bayou was predominantly open until 1979 when an exploratory well in the Gulf of Mexico blew out spilling more than 3.3 million barrels of oil into the Gulf. As the oil moved toward Texas under emergency action the state closed Cedar Bayou. Since then it has remained closed 70 percent of the time except for brief periods when it was dredged in 1987 and 1995 and opened by storms in 2003.

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RLBs cutter suction dredge Pat Lundin dredges along Cedar Bayou to reopen a pass connecting Aransas Bay and the Gulf of Mexico.

While closing the bayou saved it from a serious threat the lack of water exchange between Aransas Bay and the Gulf stunted fish and wildlife productivity in the bay.

In 1987 the Texas Parks and Wildlife Department first attempted to reopen Cedar Bayou removing approximately 300000 cubic yards of sediment. The project worked but only briefly; the pass was closed again by 1993. The state department made a second attempt in 1995 but came up short in funding to finish the project.

Local communities and government have long supported reopening Cedar Bayou invigorated by the Aransas County Cedar Bayou Advisory Committee who studied and supported a public/private partnership for the project in 2006. Money was invested through the state General Land Office and Save Cedar Bayou Inc. to study the area and develop a new strategy for reopening the bayou and keeping it open.

Previous dredging projects had not attempted to reconnect Cedar Bayou and Vinson Slough. From 2006 to 2008 Coast & Harbor Engineering performed a feasibility study to determine the best alternative.

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In late June a truck deposits material from Vinson Slough while a bulldozer waits to grade it.

The Coast & Harbor Engineering final report concluded that “Increasing the flow rate (reducing hydraulic resistance) especially for currents flowing from the bay system to the Gulf allows for higher velocities at the Gulf mouth of the bayou which tends to scour sediments from the channel mouth. Without regular scouring at the mouth sediments tend to build up and eventually lead to the closure of the Bayou.” Further connecting Cedar Bayou with Vinson Slough would increase the total volume of flow through the bayou.

In 2008 Aransas County took leadership of the project and obtained the needed U.S. Army Corps permit by 2011.

According to the Coast & Harbor Engineering report some of the previous disposal cites along Cedar Bayou also contributed to its perpetual reclosing. In 1987 sand was placed on the beach along Cedar Bayou but in two years the channel had migrated into the disposal area introducing extra sediment that couldn’t flush out of the channel with the tides. In 1995 dredged material was placed far away from the Cedar Bayou channel but instead was placed where the Vinson Slough channel connected with Cedar Bayou further disconnecting the two waterbodies.

Cedar Bayou After

The current disposal sites for the project are in two areas southwest of Cedar Bayou. Initially dredged material from the bayou was pumped via 12000 feet of pipeline to the disposal areas on beach and graded by a bulldozer to the appropriate elevation. The project permit requires the use of a diffuser at the end of the pipeline to prevent scour of the beach. Excavation work began in Vinson Slough and was transported by trucks to the placement area.

Horine said the main environmental concern with dredging in the area is suspended sediments and their effects on oyster populations. Silt curtains have been maintained around the active dredging areas. Also the placement areas were closely monitored for nesting turtles. RLB monitors patrolled the work area multiple times a day looking for turtles and piping plover. The whooping crane wintering season also begins October 16 and runs through April 14 during which no dredging can take place.

Dredging began in May at the north end of Cedar Bayou. In August excavation work began in Cedar Bayou and the dredging was relocated to the western edge of Vinson Slough.

By the end of August nearly 451000 cubic yards had been removed of the 540000 total which by the end of September should reconnect Cedar Bayou and Vinson Slough to the Gulf of Mexico.