Data quantifies dredging needs ahead of time

Chicago skyline and lake Michigan waterfront. Credit: Getty Images

Ports on the US Great Lakes will require plenty of dredging going forward, data suggests. Estimating dredging requirements ahead of time can be a tricky business. Indeed, so tricky that few have tried to do it, at least not on a regional level.

Yet the information would not be without its uses, enabling dredging companies, shipping lines and maritime authorities to plan ahead. Enter Craig Harley and his team from US engineering firm OBG, now part of Denmark’s Ramboll.

They have calculated the total dredging requirements from 2020 to 2030 for the entire port and harbour network of the US Great Lakes, consisting of no less than 171 facilities across 85,000 km of coastline.

“We estimated dredging demand in federal harbours and non-federal harbours, and in categories of maintenance dredging, environmental dredging, and improvement dredging,” Harley told the Western Dredging Association dredging conference in Chicago in early June, although currently the numbers for improvement dredging are unavailable. “We did not include major waterways in our study, […] just those ports and harbours that were on US coast of the great lakes.”

For maintenance dredging, the main information source was detailed federal government surveys of ports and harbours, something that can be guaranteed to a high degree of accuracy. From this, they were able to estimate what the requirements would be on a location by location basis.

Take the case of the town Algorma, which has a harbour containing a federally maintained channel, as well as a non-federal harbour. By taking information from surveys from the US Army Corps of Engineers (USACE), they were able to estimate that within the 2020–30 timeframe, the likelihood is that dredging will definitely be required.

“They do have an issue with their harbour in the federal channel,” Harley explained. “The last time it was dredged was in 1993 when 18,000 m3 was taken out. Luckily, lake levels are high so it’s not yet an issue for them, but if it comes down closer to average or where it was a few years ago they will need a dredge,” he explained.

Because the USACE often perform hydrographic surveys beyond just federal areas, Harley and his team were also able to use this information to examine Algorma’s non-federal harbour, along with other data sources.

“We looked at it and said they do have a sedimentation issue here,” he said. In this case, they estimated that around 25,000 m3 of sediment would require dredging and removing. For environmental dredging, the group’s primary resource was the Great Lakes Areas of Concern, as defined by the Great Lakes Water Quality Agreement. They used this data to develop estimates for dredging quantities for the period, together with some snappy analysis on individual locations.

For the port of Duluth for example, they estimated that 1.2 million m3 of sediment would need to be dealt with, although half of this would likely be capped, with contaminated material trapped under stable layers of sediment to reduce its exposure to the environment. Of the remainder that does need to be removed, around 75% of this would need to take place in the 2020–30 timeframe, equaling around 450,000 m.

The end result is that for federal ports and harbours on the Great Lakes, around 26 million m3 of material will require dredging for maintenance alone in 2020–30, indicating plenty of activity for regional dredging companies. For environmental dredging, the figure is 2.3 million m3, and for non-federal maintenance it is nearly 1 million m3.