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Successful Hydraulic Dredging Relies on Critical Velocity

Posted by Sam Crawford, Project Manager on August 13, 2020

As a leader in inland waterway dredging, J.F. Brennan Company (Brennan) serves as a success story for hydraulically dredging and pumping sediments over long distances and changing elevations. The goal of most dredging projects is to maximize efficiency, which means maximizing the average percent solids in the pipeline. However, there is a fine balance between maximizing percent solids and surpassing critical velocity to transport dredge slurry. Therefore, a dredge operator must understand the importance of critical velocity and how it varies as the material in the dredge cut changes.

Critical velocity, in this case, is the minimum speed at which sediment and water (slurry) must be pumped to prevent the sediment from settling and subsequently plugging the dredge pipeline. Plugging the pipeline is the bane of any dredging operation and one of the few things that will set a dredge operator trembling in their boots. After all, if a pipeline gets plugged, the dredge must shut down, which means the entire project stops.

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River Restoration: Small Dredges Prove Useful in Waterways

Posted by Paul Olander, Senior Project Manager on March 25, 2020

As the sun on the dredging season in the Midwest inland areas began to set, operations were starting to heat up on the east coast for J.F. Brennan Company (Brennan). For a third straight year, Brennan has had the opportunity to procure work in the milder maritime climate throughout New England during the winter months. These months are key for in-water work on the east coast as they provide opportunities to revitalize salt marshes, re-nourish beaches and restore navigation outside of the fish migration and spawning windows. Generally, this work has been undertaken in and near the coastal salt marshes adjacent to the smaller resort communities.

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Most-Searched Blog Topics of 2019

Posted by Kimberly Walters on January 07, 2020

Brennan blog posts were viewed 13,622 times in 2019. Reviewing our most-searched blog topics helps us construct a list of the marine industry's most critical topics and those most pertinent to our company. So, what were the most-searched topics?

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Risk, Impact, and Corporate Responsibility: Implementing an Environmental Management Program

Posted by Michael Cannell on December 16, 2019

As a marine solutions company, J.F. Brennan Company, Inc. (Brennan) faces a unique array of regulations and rules. While every company deals with regulations, most deal with rules that impact operations only on land or only in the water. We are accountable for regulatory requirements in both areas and have been for years. So, what's changed and what are we doing about it? 

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State of the Environmental Industry | June 2019

Posted by Andrew Timmis on June 20, 2019

We’re nearly halfway through 2019, and unless you’ve been in a cave or under a rock, you understand that the environmental market is exploding right now. I have been in the environmental industry for 32 years (wow that’s a long time), and I do not believe I have ever experienced this much activity. The size, scopes, and complexities of our current projects are overwhelming. J.F Brennan Company (Brennan) is extremely fortunate to have a very busy, robust workload this year with some exciting projects underway, and more that are set to begin once fish windows open. Based on our own surplus of work and activity, I wanted to share my observations and discuss the current state of the environmental community from a dredging contractor’s perspective.

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7 Cost-Drivers of a Dredging Project

Posted by Dillon Hogan on November 13, 2018

Dredging projects are complex affairs that involve many components and significant planning before execution. The intricacy of these projects means that pricing is often multifaceted. Here are seven common areas that drive overall costs on a dredging project.

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The Basics of Using Polymers on Dredging Projects

Posted by Dillon Hogan on October 16, 2018

Why Add Polymers?

 

One of the biggest challenges on a dredging project is managing the water that is excavated and transported with the sediment. On hydraulic dredging jobs where sediment and water are pumped through a pipeline as a slurry, water can account for 90+ percent of the volumetric flow. After the slurry reaches the disposal area, the water must be separated from the sediment, collected, and often clarified or treated. This process must happen as fast as the water is being pumped, which for a 12-inch cutterhead dredge could be 5,000 gallons per minute.

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The 4 Basic Steps of a Wetland Restoration

Posted by Dillon Hogan on July 24, 2018

Our experience in wetland habitat restoration began 30 years ago with the Upper Mississippi River Restoration Program (UMRR), the largest restoration program ever undertaken on a major waterway, worldwide.  Since then we have carried out many more restorations along the inland waters of the United States, including restoration after large-scale environmental remediation.  

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The Leverman's Challenge

Posted by Dillon Hogan on May 29, 2018

The Bureau of Labor Statistics classifies a dredge operator as a person who removes sand, gravel, or other material in order to excavate and maintain navigable channels in waterways. In the industry, we call the dredge operator a leverman. This is a historical remnant of the days when the pilothouse, or lever room, was full of mechanical levers that controlled various parts of the dredge. The levers eventually gave way to computerized control systems...

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QC-ing the QC Equipment

Posted by Dillon Hogan on April 03, 2018

All Systems Go

At Brennan, we utilize hydrographic survey systems to measure progress on all of our dredging projects. These systems typically include a positioning system, such as RTK-GPS, and a multi-beam echo-sounder. The Real Time Kinematic, Global Positioning System, or RTK-GPS, is a precise satellite navigation tool, whereas an echo-sounder is a sonar device for measuring depth. Combining the two allows us to achieve very accurate measurements on the location of the river bottom. We take the data points created during these measurements and create a 3-dimensional model using Hypack® software. By running a survey before we dredge, and then one afterward, we can create two models and compare them to one another. The difference between the two models is the total volume of in-situ yardage that we have removed. Typically, we are paid by the in-situ volume of sediment (in cubic yards) that we remove so it is very important that these measurements are extremely accurate. Therefore, establishing quality control checks on the equipment before we survey is an extremely important step in achieving accurate measurements.

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