The Role of Erosion Control on the Panama Canal Expansion Project
Every erosion control project is mission critical, but the Panama Canal expansion project, completed in June 2016, is arguably in a class by itself, given the scale of the undertaking and the waterway’s strategic importance to international commerce. The dirt-and-rock slopes created from the dredging of nearly 50 million cubic meters (65,400,000 million cubic yards) of underwater material during the construction had to be stabilized to prevent sediment runoff into the canal and new locks. Failure would lead to environmental violations and a costly cleanup to keep the canal waters clear.
Contractors initially addressed the issue by hydraulically seeding a combination of grass seed and wood fiber mulch on the 30- to 45-degree slopes, followed by installation of costly turf reinforcement mats or erosion control blankets over the treated areas to help hold the seed in place. This was critical during Panama’s eight-month rainy season and common three- to four-hour downpours, totaling nearly 137 inches of rain annually.
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Early in the project, however, that two-step process and associated costs were eliminated by switching to Profile Products’ Flexterra High Performance-Flexible Growth Medium (HP-FGM)—a patented, hydraulically applied, fully biodegradable solution that bonds instantly to the soil, promotes rapid vegetation growth, and delivers 99% erosion control performance on slopes as steep as 90 degrees.
Over the next eight years, through multiple contractors handling different phases of the project, Flexterra HP-FGM was used to control erosion, facilitate germination and grass establishment, and protect water quality throughout the construction corridor. It was eventually applied to nearly 300,000 square meters (75 acres) of bare slopes.
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“It was important to stabilize the surface of the excavated slopes quickly to prevent erosion and sediment that would have settled in the canal waters,” says Maximiliano De Puy, geotechnical section general manager for the Panama Canal Authority (PCA). “With the approach we used, vegetation has been permanently established, soil loss has been minimal, and we have avoided the costs and complications of having to dredge sediment from the canal.”
The $5.25 billion Panama Canal expansion doubled the capacity of the iconic connector between the Atlantic and Pacific Oceans by adding two new sets of locks and associated approach channels, widening and deepening existing channels to allow larger ships to pass. The expansion also raised the maximum operating level of nearby Gatun Lake to increase the supply of water available for the additional lock operations required to support the extra ship traffic.
The project took nearly 10 years and the muscle of 40,000 workers to complete. A key goal was to accommodate newer ships that can carry up to 14,000 shipping containers, more than twice as many as the previous generation, to help Panama maintain market share and increase shipping revenues that generate roughly half of the country’s annual budget.
The monumental scope of the job prompted officials to divide the work into five separate construction projects, each individually bid to contractors. Erosion control in the first phase was handled with the wood fiber mulch and turf reinforcement mats mentioned earlier. Erosion control blankets replaced mats in the second phase. Both blanket types required significant soil preparation and installation time, as well as material and labor costs over and above hydraulic mulching.
A Better Solution
Early in phase two, the Panama-based subcontractor scheduled to handle phase three erosion control suggested replacing both the mulch and the rolled blankets with Flexterra HP-FGM for several reasons. First, the product’s hydraulic application would be faster and provide better coverage. Second, Flexterra’s proprietary blend of recycled wood fibers, ceramic particles, polymers, water absorbents, and interlocking biodegradable fibers would create a continuous, porous, flexible blanket that had been shown in multiple independent tests to provide superior erosion resistance, seed-to-soil contact, and vegetation establishment. In addition, it would eliminate blankets and associated overhead while improving worker safety.
PCA engineers were skeptical, in part because of the poor performance of a different hydromulch claiming similar benefits some years before, but they agreed to a demonstration after further discussions with subcontractor Grasstech Corp. and Profile Products.
“The Panama Canal Authority couldn’t risk an erosion problem on this project, and they thought they needed something anchored to the ground to stop soil loss,” says Paul Gonzalez, manager of international business for Profile Products and vice president of the IberoAmerican chapter of the International Erosion Control Association. “We had to prove that Flexterra could perform the functions of both a mulch and a blanket, and do it as well as, or better than, their existing two-step process.”
Test Site Success
In September 2008, to provide that proof, Grasstech hydroseeded a 500-square-meter (5,400-square-foot) test area on the canal property with a mix of Flexterra, fertilizer, and Brachiaria decumbens and Brachiaria humidicola tropical grass seeds that are widely used in Panama and Central America. The test location at Corte Culebra, the massive “snake cut” through the central mountain ridge that links the locks on the Atlantic and Pacific sides of the canal, was selected by PCA engineers because it was heavily eroded with a series of gullies where soil had washed down into the canal.
“They deliberately gave us one of the most challenging slopes to test on,” notes Gonzalez. “Their thinking was, if you can succeed here without a blanket, you can succeed anywhere along the canal.”
Despite the degraded condition of the slope and the timing at the height of the rainy season, the new solution performed as promised. The area began to show signs of grass germination in a matter of days. It was substantially covered with vegetation within a month without mats or blankets to hold the seed in place. And there was no perceptible erosion, despite the fact that Corte Culebra traditionally had the worst sediment runoff along the canal reach.
$1 Million Savings
Based on those results, the PCA adjusted the erosion control specifications on the expansion project to reduce blanket use. Every erosion control subcontractor on the project from phase three onward applied Flexterra, saving as much as $1 million in blanket and related labor costs from 2008 until the expanded canal opened for ship traffic in 2016.
Today, all slopes treated with Flexterra are fully vegetated and virtually erosion free, with sediment runoff estimated at just 1%.
“This project had exceptional challenges, from the sheer scale and the tropical climate with 3,467 millimeters [136.5 inches] of annual rainfall, to the strict environmental guidelines under which the canal operates, and engineers’ initial wariness of solutions without some kind of anchoring mat,” says Gonzalez. “The fact that we were able to provide an effective erosion control solution sends a powerful message to the industry.”