1. Dredge Line Presentation
SRS Crisafulli
Dredge Line Presentation

2. Flump – Remote Controlled, Unmanned Electric Dredges

3. Features and Capabilities
Electric powered
Direct drive from motor to pump increases efficiency
Electricity from the grid eliminates refueling and is usually the cheapest source of power
Remote sites require a generator or installing electrical service
All power is transmitted to the dredge through a single cord
Wireless remote control
Handheld transmitter controls pump, speed, direction, and depth
Operator does not need to be floating out in a lagoon
Limit switches and automatic sequences are available, limiting the amount of supervision that is necessary
FLUMP
Features and Capabilities

4. Features and Capabilities
Cable traverse only
Simple, straight, repeatable dredging passes
Lowest power requirements
Traverse distances over 500ft (150m) are not recommended
Requires more tension and stronger anchors to keep cable tight
If the cable droops below the water surface, the floating discharge line may float over it and get tangled as the dredge approaches
Slack in the cable allows the dredge to drift side-to-side or twist
FLUMP
Features and Capabilities

5. Rotomite SD-110 and 6000
Manned Diesel Dredges

6. Features and Capabilities
Diesel powered
Self-contained power system
No power cord to string out with the discharge line
Self-propelled by hydraulic thruster
Discharge length not limited by traverse cable or power cord lengths
Optional cable traverse drive can supplement self-propulsion
Operator on board for better situational awareness
Optional air conditioned cab enhances operator comfort
Foam-filled aluminum (SD-110) or steel (6000) pontoons
Variable-speed pump powered by hydrostatic drive
Rotomite SD-110 and 6000
Features and Capabilities

7. Cable Traverse System – Drawing of a four-post layout
ANCHOR POINT
Cable Traverse System – Drawing of a four-post layout

8. Cable Traverse System Setup Considerations
Figure out:
Which direction to dredge
How the discharge line should be routed
How the electrical power gets to the dredge
Where to put the anchors
How everything will adjust as the area is covered
Cable Traverse System
Setup Considerations

9. Cable Traverse System Operation
Begin dredging
Adjust speed and depth for optimum solids flow
Ideally, those settings can be maintained and the dredge will not require further operator input until the end of the traverse is reached
Cable Traverse System
Operation

10. Cable Traverse System Operation
At the end of a dredging pass:
Flush discharge line with water
Turn off pump and reverse dredge
After the dredge has returned to start:
Lower cutterhead to new depth and resume dredging forward along the traverse cable
After the desired depth has been reached:
Adjust the lateral cables so the dredge follows a new path next to the previous one
Cable Traverse System
Operation

11. Traverse Anchoring Methods: Stakes

12. Traverse Anchoring Methods: Concrete Blocks or Equipment

13. Traverse Anchoring Methods: Bollard Posts

14. Cable Traverse System Considerations
Most effective and efficient system for rectangular lagoons
Effortlessly keeps the dredge going in a straight line
Less power required to keep the cutterhead pushing forward
Allows the dredge to travel back and forth in the same path, digging deeper with every pass
Less pronounced effects of wind/current pushing on the dredge
Traverse distances over 500ft (150m) are not recommended
Requires more tension and stronger anchors to keep cable tight
Sagging cable may get tangled with the discharge line
Slack in the cable allows the dredge to drift side-to-side or twist
It is MUCH easier to install and operate the dredge if the water is deep enough for it to float over the material.
Cable Traverse System
Considerations

15. Notice the traverse cable and dredge being pushed out of line.
This happens when the dredge cut is not symmetrical.
The effect is more pronounced as the traverse distance increases.

16. Floating Discharge Line
Rigid floating pipe with hose flex sections in between.
Solid foam floats are pressed onto the pipe and extremely durable.

17. Liner Protection System
Removable wheels and cage keep the cutterhead from digging down through a solid lagoon bottom or snagging part of the liner.

18. Liner Protection System

19. Dredge Performance: What Gets the Job Done
All discharge photos pictured here are from Crisafulli dredges.
Dredge Performance:
What Gets the Job Done

20. Dredge Performance:
Pumping Water

21. Getting into the Sludge
Dredge Performance:
Getting into the Sludge

22. About as thick as it can get.
Dredge Performance:
About as thick as it can get.

23. 4% -5% by weight
Dredge Performance

24. ~15% by weight
20% - 30% by weight
Dredge Performance
The best way to compare dredges is to see how their pumps perform in a material with universally understood properties: water. (Next Slide)

26. Dredge Performance: Budgetary Estimates
Centrifugal pumps are limited to fluids with a specific gravity less than A dredge can usually be operated to maintain 1.3.
Dredging at 15% solids is usually very good.
Wastewater sludge is not just dirt mixed with water.
There are other effects such as viscosity that are hard to account for.
The same Flump that produced 20% solids has had trouble producing 6% solids in wastewater.
Settled sludge usually can’t be pumped at its original consistency
Thinning the sludge with water increases its volume
1 cubic meter at a 1.5 specific gravity doubles in volume to 2 cubic meters of sludge after it is mixed with water to a specific gravity of 1.3
Dredge Performance:
Budgetary Estimates

28. There are many different methods for dewatering
There are many different methods for dewatering. Which is best depends on many factors and cannot be determined until all aspects of a system have been evaluated—which is a job for consulting engineers.
Non-Mechanical: Geotextile Tubes, Drying Beds
More simple in nature, no moving parts
Requires less energy, but more space
Mechanical: Filter Press, Belt Press, Centrifuge
Smaller footprint, maybe less affected by rain
Subject to breakdowns and maintenance
Dewatering Methods

29. Ecotube Geotextile Bags
Geotextile fabrics are designed to filter water out of mud and other sludges.
Pump the slurry into them and let water drain out.
Dewatering:
Ecotube Geotextile Bags

30. Ecotube Geotextile Bags
Flocculants and coagulants are usually added to the mixture to make the solid particles settle faster.
Dewatering:
Ecotube Geotextile Bags

31. Ecotube Geotextile Bags
The water that seeps out of the bags can be collected and pumped back into the lagoon.
That extra water will keep the dredge floating and mixing the material to a proper pumping consistency.
Dewatering:
Ecotube Geotextile Bags

32. Requires Further Research
Geotextile bags are usually the best choice for dredging operations, as they are extremely easy to understand and use and are able to handle directly whatever flow the dredge can produce.
This is the first (and currently only) method SRS Crisafulli evaluated for this project. Research into other possibilities is still underway.
Preliminary Results:
As reported to SRS Crisafulli, the total volume of all San Jose and Pampa de Perros primary, secondary, and tertiary lagoons equals well over 400,000 cubic meters of material.
The bags alone to contain that volume will easily cost over $3 million. Hiring engineers to determine the best system would be a worthwhile investment!
Dewatering Method:
Requires Further Research

33. Determine the acceptable balance of cost and speed for this project.
How much funding is available for this project if it takes one year?
What if it takes two years? Five years?
How much of the project must be done right away?
Will it be sufficient to dredge a portion of the lagoons immediately, then use a slower, smaller-scale method for the rest?
Will these lagoons need to be cleaned again in 15 years?
How will it be done then?
Will a continuous dredging process and permanent dewatering facility be set up to keep this situation from happening again?
What is the next step?

34. For large projects like this, dewatering is always more costly than dredging.
Geotextile tubes will cost the same whether the project takes one year or two because they hold a limited volume and cannot be reused.
Drying beds will increase in size and cost as the rate of dewatering increases.
Mechanical dewatering systems can be purchased in varying sizes and quantities to accommodate the desired dewatering rate.
Mechanical dewatering systems are not one-time use and can be permanent installations or portable facilities.
The optimum size and quantity of dredges can easily be matched to the dewatering system that is chosen.
Deciding Factors