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Sedimental journey
Dredging clears the ugly buildup in lakes and ponds, but all that muck has to go somewhere.
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Geotextile tubes are used for dewatering. Material can then be hauled to another location or graded at the current location. |
Water is essential for golf courses, with lakes and ponds providing a pleasing course aesthetic as well as water to irrigate turf. Built up sediment in these lakes, however, causes a variety of problems.
Trouble may first show up as shallow water near the head of the lake or at the ends of the coves where drainage enters. Unsightly weeds begin to emerge. At first limited to a small area, over time this area grows farther into the lake and the lake starts shrinking.
Next, water quality begins to deteriorate. After rainfall or high winds, more sediment is deposited and resuspended. The water takes longer to clear, often taking on a murky brown color. The water quality declines noticeably, and this reflects on the aesthetics of the entire course.
Finally, irrigation problems develop. Sediment clogs up sprinkler heads and water quantity declines in high-usage months. As sediments fill the lake, less water is available for irrigation because the sediments take up space once occupied with water.
The process that occurs when sediment fills a lake is known as eutrophication. It’s a natural process that evolves over years. Eutrophication accelerates when ground cover vegetation is disturbed within the drainage basin. During a construction project in which no effective erosion control measures are put in place, what might occur naturally over a period of 100 years or more can occur in a matter of months. Silt fence and other erosion control measures often are not properly installed or maintained after installation, which leads to topsoil runoff and, over time, causes the lake to disappear. Long before it disappears, however, the lake declines and becomes an eyesore.
So what’s a superintendent to do? Typically they’ve taken several paths to solving the problem.
Drain the lake
This method will usually require building a haul road across the golf course to provide access for heavy trucks to haul sediment offsite. Additional inconveniences include disturbing golf play, regrading the haul road and regrassing the area.
Weather can affect the process of draining a lake. Because water will naturally drain to this area, even a small rain may affect the schedule for an extended period. It may take weeks or months for the material to dry enough to excavate and haul offsite.
Another consideration is the undetermined amount of time until the lake is restored and filled again with water. Depending on the size of the drainage basin and the amount of rainfall, it may take several months for the lake to fill back to capacity.
Mechanical removal from the shoreline
This method doesn’t require draining the lake, but addresses the sediment issue from the shoreline. Heavy excavation equipment is hauled to the shoreline, and surrounding trees and other obstructions are removed and leveled so the equipment can work safely.
Mechanical removal avoids the issue of refilling the lake, but is limited by the reach of the dragline or long-reach excavator. Most mechanical excavators used in this kind of excavation reach 40 or 50 feet from the shoreline, so candidates for this type of dredging are small ponds or the end of the coves.
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Portable hydraulic dredges that float on the water remove sediment by pumping dredged material through a temporary pipeline to an offsite location, often several thousand feet away. |
Portable hydraulic dredging
A more modern solution for removing sediment from the lake bottom is a small hydraulic dredge. A hydraulic dredge has many advantages over mechanical excavation. The dredge floats on the water and pumps the material through a temporary pipeline to an offsite location, often several thousand feet away. This dredge acts like a giant floating vacuum, removing sediment precisely.
The dredge discharge line and possibly a return line are the only disturbance to the golf course. You can run these lines under golf car paths or lay back a small strip of turf and trench the pipe across the fairways. Other than this, the dredge, which is not much larger than a boat, is the only visible machine. This unobtrusive method avoids disturbing the shoreline and requires one trip in to put the dredge in the water and one trip out when the project is complete.
Sediment disposal
Hydraulic dredging produces a sediment slurry that is pumped through a pipeline to a disposal area and dewatered. This dewatering can be accomplished in a variety of ways.
Settling basin
The least expensive method of disposal is to construct a temporary settling basin. This basin allows the material to settle while the clear water flows over a weir to return to the lake. When the dredging is complete and the material has had ample time to dry, you can level and seed the area. In addition, you can load out the material and use it to fill low areas or as topsoil around the course.
Geotextile tubes
Geotextile tubes are another creative dewatering method. The slurry is pumped into large fabric tubes, which might be 6 to 8 feet tall when filled and may be 100 to 300 feet in length, depending on the area available. The sediments stay in the tubes and the water filters out through the geotextile membrane. Depending on the type of sediment, a chemical polymer may enhance the dewatering of the material.
Geotubes are most suited to projects that have a limited area available for dewatering and sediment placement, which is often the case on golf courses. For smaller quantities of sediment, you can lay the tubes in parking lots until the material is hauled offsite. Depending on the area available for the deposit of sediments and the long-term plans for the area, you can bury the tubes in place, cut them open and level them, haul them to another site, or use them to create a structure such as an island or to control erosion or stabilize the shoreline.
Mechanical equipment
A third dewatering method uses mechanical dewatering equipment. This option often allows the most rapid dewatering, but also is the most expensive. Mechanical dewatering equipment allows the material to be dewatered and hauled off as it’s being dredged.
Each dredging project is unique. On a golf course, where lakes are surrounded by expensive turf and landscaping, limited area for deposition of sediments and a sensitive environment, it’s important to work with a professional contractor who has many years of experience in solving such problems. Many of these solutions may not be apparent at first and often require creativity and innovation.
Eutrophication will not go away on its own. While dredging may be an investment, you must fully evaluate all alternatives and decide if it’s right for your course.
10 questions to ask your dredging contractor
• How many years of hydraulic dredging experience do you have working on similar types of projects?
• Can you supply references for all the projects you’ve completed in the last five years?
• Is hydraulic dredging a sideline to your core business such as excavating or dock work?
• Do you own your own equipment? Do you own more than one dredge?
• Can you bond the project?
• Do you have adequate marine insurance and can you name our course as an additional insured on your policy?
• How quickly can you mobilize for a project?
• Do you have a professionally trained mobile workforce?
• Do you have proper environmental controls in place as standard procedures?
• Do you have a good safety record and policies in place for accident prevention?
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