International Dredging Review

International Dredging Review
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Smoky ash is no longer thick in the air of Chile’s Northern Patagonia but the town of Chaitén is still coping with the aftereffects of the explosion of its namesake volcano nearly five years ago.

The Chaitén Volcano exploded in a big way in May 2008 forcing the evacuation of the charming fishing village just six miles away. The volcanic ash spread over southern Argentina and floated over the Atlantic affecting air quality across a large swath of the southern hemisphere and damaging water quality on the southern cone of South America. The ash was so thick it coated a town 75 miles away with three inches of ash and the situation in the pueblo of Chaitén was even more dire as rain combined with the ash and deposited more than a meter of ash-mud there.

In the years since residents have slowly rebuilt their village. But while they’ve managed to wipe their streets and walls of volcanic soot it continues to spill through their waterways.

The nearby Rio Blanco (also called Rio Chaitén) whose headwaters flow from the glaciers of Minchinmayida and whose watershead drains through some of the areas most affected by the volcanic explosion carries tons of ash a day and deposits it straight into the Chaitén Bay. Though the river has never been navigable its deposits are making the bay difficult to navigate.

This is a problem for not just Chaitén but for the entire region. Chaitén served as the main entrance to the province of Palena which covers much of Northern Patagonia. Roads do not reach the area. The port therefore is crucial for the region’s economy which primarily consists of fishing and tourism. The port also brings in supplies food and construction material to the zone said Palena Governor Maria Clara Lazcano.

“Due to the eruption of the Volcano Chaitén we’re still accumulating sediment material in the bay and those sediments are creating an embankment in the port. So in order to maintain and ensure the connectivity of the zone we have to remove that material. And you can only do that by dredging” Lazcano said.

She said the problem had not yet prevented any ships from navigating the entrance channel to the port but that would happen if dredging didn’t occur.

The problem first became obvious in 2011 when a bathymetric study showed that the bay was losing depth due to the ash deposits. To address this Chile’s Ministry of Public Works employed its own trailing suction hopper dredge Ernesto Pinto Lagarrigue built in 1978 to remove the sediments.

But by the middle of 2012 it was clear that a second dredging cycle would be needed as the ash continued to pile up at the bottom of the port. As volcanic ash is notoriously hard on equipment when this second cycle proved necessary Public Works chose to contract out the work.

This time company Dragados S.A. Agencia was hired to dredge the port a project worth $4.2 million. They began the dredging work in November – the southern hemisphere’s spring – with its 68-meter long split hopper dredge OMVAC 10. The work was expected to be complete by early January according to Palena spokesman Carlos Sala.

It’s not clear yet whether another dredging maintenance cycle will be necessary in the coming years he said.
This time about 40000 cubic meters of ash was expected to be dredged and deposited in high seas Sala said. The port is attempting to maintain a depth of at least 10 meters or 33 feet.

Chilean media Radio Biobio reported that some fishermen were complaining that ash was washing up onto the beach from where it was deposited last time and said they were worried the same thing would happen again. However though both Sala and Lazcano were familiar with the media report they said the government had not received any official complaints about the problem.

Regardless the project must be completed if the region is to continue surviving said the mayor.

“This dredging project is very important to us because otherwise we cannot access our province” Lazcano said.