CGC Dredging is a specialist dredging company based in Western Australia that has expertise in mine tailings and marine dredging industries. With operations beginning in 1980, CGC is extremely experienced and well respected in the industry with an established fleet of small to medium-sized cutter suction dredges.
Port Geographe, located in Western Australia is a canal community and small boat harbor that requires regular dredging in order to cut back seagrass wrack and accumulated sedimentation collected on the seafloor. Dredging work establishes appropriate depths and keep the channel open to navigation. In addition, the port’s seawall structure had to be redesigned because it collected unmanageable levels of seaweed and sand. CGC was tasked with dredging the footprint to desired depths to prepare the seafloor for placement of rock for the new seawall. With a tight deadline and specification to meet these goals, CGC turned to its technology partner SITECH Western Australia (WA) and Trimble for assistance.
The CGC team adopted the Trimble® HYDROpro™ Construction software, Trimble SPS461 GPS heading and positioning receivers; WA Limestone (WAL) used Trimble GCS900 Machine Control on their excavators and a SPS855 receiver with HYDROpro Navigation on a Trimble Site Tablet and a single beam echo sounder on their hydrographic boat.
- For the hydrographic survey, WAL avoided a multi-beam scanning operation
- CGC precise cutter head guidance allowed the dredge operator to dredge to the desired depth and return to the exact location where the previous day’s work ended; this avoided wasted time and costly rework
- HYDROpro software displayed the precise position of the cutter head under water within an accuracy of 10 centimeters
- Met depth guidance parameters and rigorous design measurements
Guidance System Improves Dredging Performance
Port Geographe is located in the town of Busselton in Western Australia. The harbor entrance has two seawalls, which over the years have accumulated severe sand and seaweed build up. In order to keep the channel open and maintain an attractive and usable beachfront, frequent dredging of the seafloor along the harbor entrance is required. Faced with this challenge, the local transport authority authorized a large-scale $28.15 million coastal reconfiguration project. WA Limestone, in conjunction with Italia group, were the Project managers for this larger project. They were tasked with providing stone and construction plant for constructing the new breakwaters and seawalls. A pre dredge hydrographic survey was carried out of the area prior to dredging and placing material on the seafloor. In addition to modifying the shape of the western break wall and removal of the old seawall, the team was also tasked with building a new seawall and realigning the shoreline.
“The basic rule of dredging is that you don’t want to over- or under-dredge,” said Whitcomb “Over-dredging means you spent time and money, like burning diesel, that you didn’t need to; and if you under-dredge your floor may not meet design depth specification. You really need to be precise and efficient in your work and also have the ability to make adjustments according to design parameters.”
Faced with a tight timeline for the dredging phase of less than six months, Adam Whitcomb, operations manager for CGC, explains he turned to technology partner SITECH Western Australia (WA) and Trimble for assistance. The team was looking to optimize dredging operations and improve performance. CGC worked with SITECH WA, the Trimble marine and construction technology representative for the region, to equip its “Cooper II” dredge with Trimble Site Positioning System GNSS receivers.
SITECH WA installed the Trimble SPS461 GPS positioning receiver onto the dredger along with dual Zephyr antennas to position the dredge arm. While the dredge was on the trailer they also installed the gear and precisely measured the offsets to the cutter head.
Accurate Hydrographic Survey
For the hydrographic survey, Trimble HYDROpro software and Trimble Site Tablet were used in combination with the receiver data and the echo sounder to determine real-time position, and elevation of the seabed surface. Since the GNSS receiver was so precise in the vertical plane there was no need to install a conventional Tide Gauge with their ongoing communication and maintenance issues.
“A hydrographic survey was needed to provide an accurate baseline beforehand and to check our work throughout,” said Whitcomb. “During the course of the project, we also wanted as-built updates from the dredging. WA Limestone considered using multi-beam echosounder but the cost estimates were way over budget, so SITECH WA recommended Trimble HYDROpro for collecting measurements and site positioning.”
Within days, the pre-dredge hydrographic survey was complete providing an accurate picture of the seafloor. Using HYDROpro and positioning receivers, the team met 2 centimeter accuracy requirements and captured nearly the same accuracy levels of a multi-beam system, but at significantly less cost. The survey provided a real-time heat map of depths, color binning of design compared to the existing surface, and guidance of survey lines in the map area.
Remote Support Options
SITECH WA delivered remote support and service, which Whitcomb believes was a significant advantage for his crew. It worked like this: the CGC dredge was equipped with an Internet connection and a remote viewing software application was loaded on to the on-board computer system. With that, SITECH WA support personnel could then remotely see exactly what the CGC operator was viewing during the dredging process.
“The remote support experience from SITECH was absolutely essential to the success of the project,” said Whitcomb. “Port Geographe is a three hour drive from Perth, not to mention the logistics of getting that person on the dredge; it just wasn’t a cost-effective option. Despite having no experience with Trimble marine guidance, with remote monitoring support, our operator resolved questions extremely fast.”
Reliable Vessel Positioning and Heading
Whitcomb explains that with the Trimble marine positioning system, his operator had precise dredge head positioning and real-time tracking capabilities. The receiver provided vessel positioning and heading, which is critical when working on the water. To position the cutter head underwater, the dredge was fitted with digital angle sensor on the dredge arm that goes underwater. Then, knowing the length of the arm and angle the HYDROpro software displayed the precise position of the cutter head under water within an accuracy of 10 centimeters.
Whitcomb explains that cutter head guidance is extremely important with this type of project because his operator needs the ability to re-start dredging at the precise location where the previous day’s or week's work ended. The work requires precision and is somewhat tedious when accurate positioning is not available. With the depth guidance, operators were able to meet rigorous design measurements the first time instead of performing costly rework. This high level of accuracy was needed to locate and dredge the toe of the new structure. WA Limestone and Italia Joint Venture also used their equipment whenever location guidance was needed to ensure the successful removal of existing rock by the earthworks excavation team.
“If the dredge was taken to sheltered waters or in for maintenance, the accurate cutter head guidance enabled our operator to return to the precise location the next day and continue,” said Whitcomb. “With the depth guidance, we were also able to precisely dredge to the design, and keep up with changes, which saved us more work and time―none of this would have been possible without Trimble technology or the support from SITECH WA.”