Traditional Dredging Methods vs Dragflow Dredges: Which Is Right for Your Project?

In New Zealand’s extractives industry dredging is a critical part of sand and aggregate extraction and sludge management. Yet, the methods used vary widely - from traditional digger and dump truck setups to pontoon-mounted suction dredges, and increasingly, to submersible and autonomous dredge systems. This article compares these approaches with a focus on cost per tonne extracted, product quality, and operational safety, helping quarry and mine managers make informed decisions about their dredging strategy.

Traditional Techniques: Familiar but Increasingly Costly

1. Pontoon-Mounted Suction Dredging

This method involves a pump mounted on a pontoon, drawing material through a suction hose. While common, it has several limitations:

• Suction lift constraints: The pump sits above the material on the pontoon while a suction hose is lowered to the product. This limits dredge depth to maximum suction capacity of 10m. 
• High fuel consumption: Typically diesel engines, leading to high daily operating expense and cost per tonne.
• Environmental impact: Greater energy use means higher emissions and more disturbance to the surrounding environment.
• Limited efficiency: The suction process struggles with dense or compacted material, reducing throughput.

2. Digger and Dump Truck Excavation

This setup involves a digger extracting material and loading it into dump trucks for transport to the processing plant. It’s straightforward but resource-intensive:

• Labour-heavy: Requires multiple operators and machines working in rotation.
• High maintenance: More machines and more moving parts mean more wear and tear.
• Safety risks: Increased quarry movements elevate the risk profile.
• Variable product quality: Material can become contaminated during handling.

Both methods tend to have a higher cost per tonne extracted, especially when factoring in fuel, labour, maintenance, and downtime. They also often compromise product quality due to inconsistent handling and exposure to contaminants. To explore a smarter, more efficient alternative, download the Dragflow Dredgers brochure.

Submersible Dredge Pumps: A Step Forward

Submersible dredge pumps, such as those supplied by Prime Fluid Management using Dragflow technology, offer a more efficient alternative. These electric or hydraulic Dragflow dredge pumps can be digger-mounted or suspended by winch from a floating pontoon. Because the pump descends into the material, suction lift is no longer a variable. 

Benefits:

• Energy efficiency: Suction lift is the most inefficient and limiting part of any pump system. With having a submersible dredge pump at the source of the material suction lift is no longer a factor and there is maximum return on energy draw and efficiency. 
• Reduced emissions: Lower power draw and diesel burn.
• Simplified operations: One operator, one machine.
• Improved safety: Fewer quarry movements.
• Consistent product quality: Material is pumped as a homogeneous slurry, reducing contamination.

This method significantly lowers the cost per tonne extracted by reducing fuel use, labour, and maintenance, while improving throughput and product consistency.

Remote-Controlled and Autonomous Dredges: Expanding the Possibilities

Dragflow has developed a comprehensive range of purpose-built pontoons (dredges). These Dragflow dredges are configured for applications from dredging small waterways to large-scale extraction and weed harvesting. They include remote-controlled and autonomous models.

Remote-Controlled Dredges (DRP Series) 

These dredges allow operators to control both the pump and the dredge movement from a distance. They’re ideal for confined waterways and remote sites, offering:

• Reduced labour: No need for on-board operators.
• Extended reach: Access areas traditional equipment can’t.
• Lower maintenance: Fewer mechanical components.
• Modular design: Easy transport and setup.
  
  

Autonomous Dredges

Autonomous dredges operate without direct human control, using GPS and onboard sensors to follow pre-programmed paths and adjust to site conditions. Benefits include:

• Consistent operation: Removes variability from human input.
• Real-time monitoring: Sensors track turbidity, depth, pump tilt, and voltage.
• Optimised efficiency: Maintains ideal dredging conditions automatically.
• Safety: Eliminates the need for personnel in hazardous zones.

These systems are particularly valuable in large-scale or hazardous environments, where reducing human exposure and increasing operational uptime are priorities.

Real-World Example: Waikato Sand Quarry

When a sand quarry in Waikato did the math recently for their operation, the savings projections with a Dragflow dredge were eye-opening. We’ve shared the details below, comparing their existing cutter suction dredge setup with a Dragflow DRP electric dredge, and assuming the same volume extracted:

• Old method: Two 400Hp (300kW per unit) diesel motors, $2,300/day in fuel (~$837,000/year).
• New method: One 90kW electric motor, $160/day in electricity (~$58,000/year).

Sand dredging, NZ using a Dragflow DRP120.

A switch will reduce their energy costs by a projected 93%. It will reduce quarry movements, labour requirements, health & safety risks, downtime, and vehicle maintenance – all major contributors to cost per tonne extracted. The quarry also anticipates improvements in product consistency and reduced environmental impact. They plan to lease from Prime Fluid Management initially, allowing them to realise immediate savings while planning for CAPEX.