Small projects that used to defy economic justification because of high dewatering and handling costs can now go ahead. Small dredges pump into geotextile tubes that contain the material in restricted areas and allow it to dewater leaving a sausage of nearly-dry solids that can be hauled away in trucks.
A project in the Midwest that saved a municipality millions of dollars in dredging and material transportation costs illustrates the value of the burgeoning geotube business to the dredging industry and the general public.
Charles Gardner is president of Eco-Marine Inc. of Luna Pier Michigan. His company bid on a project to dredge a creek where storm water and organic effluent had been deposited for 40 years. The city was cleaning up the creek in preparation for building a 30 million gallon holding tank and had planned to dredge it mechanically onto barges and ship it to a disposal area in another county.
With the help of Dean Wickoren Gardner bid the project using a “closed loop” system coming in with a bid 90 percent lower than the city had specified.
They first injected the bottom material with a bio-stimulant to neutralize the odor and then dredged it using the Regent a Model 2008 IMS which pumped more than 2100 feet using an eight-inch booster for the last 300 feet. A polymer was injected into the line before the material entered the tubes. The 22000 cubic yards dewatered to 7000 cubic yards and was hauled away.
|!|Representatives from the State Department of Environmental Quality the Department of Natural Resources the Corps of Engineers and the city were all amazed at the clarity of the discharge water” said Gardner.
The next phase will remove 140000 cubic yards from the creek bottom and Gardner has purchased a second IMS dredge for that project which will begin this spring.
Dean Wickoren has worked in dredging and dredge manufacturing and is spending his “retirement” consulting on dredge geotube jobs as an agent for Synthetic Industries (SI) who manufactures geosynthetics at their plant in Atlanta Georgia.
SI is a huge company and the dredge geotubes are a small portion of their business said Wickoren though this is a vital and growing industry for dredging and lake and pond management.
There isn’t much room for improvement in the manufacture of the fabric said Wickoren but he has come up with some changes in the design of the tie-down handles and fill ports.
|!|We’ve filled enough tubes to get some good ideas on how to improve them” he said. He has failed several tubes on purpose. A tube failure acts like a run in a nylon he said. It starts with the fabric pulling apart in one spot and then running quickly down the length of the tube. With the help of Robert Lasano at the SI factory he has suggested improvements that will make the jobs more foolproof for contractors as far as filling and handling the tubes.
Wickoren spends much of his time traveling to sites where he is setting up jobs or to conduct workshops for contractors. In January he addressed a group of SI salespeople in Milwaukee spoke to environmental contractors in Chicago and then went to Florida where he visited three municipalities about dewatering on parking lots and tennis courts.
He made informal video that shows eight projects after the fact and in progress beginning with Drakes Creek in Hendersonville Tennessee. Fourteen months after installation of a tube that dikes a containment area trees and other vegetation are growing through it and it continues to act as a stable dike.
At a golf course near Dallas 14000 cubic yards of dredged material was dredged from ponds and dewatered in a one-acre site on the driving range. Crystal clear water returns to the river and management methods are shown including stretching an elevation string across the tubes that indicate when to switch the discharge to another tube and brooming the top of the tube to break up the filter cake and increase the water flow through the fabric.
J.F. Brennan Company conducted a successful dewatering project in conjunction with Phoenix Process Equipment Company outside Clinton Iowa last summer. They used a dewatering plant for part of the project and completed the project with geotubes.
The dredge pumps into a thickening tank where the slurry is partially settled out and pumped from the bottom of the tank into the filter press. For the last part of the project Brennan pumped from the thickening tank into the geotubes and found that adding the polymer to the tank rather than the pipeline shortened the dewatering time considerably once the material was in the tubes.
Dr. Jack Fowler of Geotec Associates reached just before leaving to teach a seminar at the Texas A&M Dredging Short Course said that the geotextile fabric market is booming for dewatering dredged material and for coastal protection. He formed Geotec Associates after retiring from the U.S. Army Corps of Engineers where he had conducted research on the effectiveness of geotextiles in a number of ground stabilization and dewatering applications. A major test in the United States was at the Gaillard Island Dredged Material Disposal Island Mobile Alabama where tubes were used as barrier dikes and to create wetlands in 1992 an application that was successful.
In Colombia South America he consulted on a project to fill tubes with concrete to block a 10-meter-diameter bypass tunnel that was inadvertently left open during construction and filling of Chivor reservoir. He worked on a project in the San Antonio River Buenaventura Colombia to build a confined disposal area island for containment and dewatering of fine-grained maintenance dredged material. In 1995 he demonstrated that geotextiles are capable of filtering the municipal sewage sludge so that the effluent water passing through the fabrics meets the 30 mg/l discharge requirement in less than 11 minutes of drainage time.
His company placed tubes along the coast in Galveston Texas which were covered with sand and planted with vegetation. When tropical storm Allison devastated the area last year much of the sand was washed from the dikes but the tubes remained protecting the homes behind them to the delight and relief of the homeowners who had thought their property would be condemned prior to placement of the tubes.
On the horizon is a massive shore protection project in Louisiana where the Corps of Engineers is planning to use geotubes to stabilize the rapidly-eroding coastline.
A Louisiana law requires that all dredged material be placed along the coast but wave action washes most of it away because there is nothing to hold it said Jay Joseph who is working on the project for the New Orleans District Corps of Engineers. The multi-billion dollar coastal protection project is in the planning stages and depends on funding both from the federal government and the State of Louisiana. The Coastal Wetlands Planning Protection and Restoration Act is a source of money for the project which would enable restoration and protection of hundreds of miles of Louisiana coastline.