Promontory Point’s Natural Rocks Are Effective Shoreline Protection

On Thursday, the Promontory Park Conservancy released the results of an independent condition study it commissioned from McLaren Engineering Group. McLaren had its engineer-divers inspect the Point from above and below and concluded that the limestone blocks currently in place along the Point’s shoreline are structurally sound, function as intended, aren’t in danger of collapse and provide critical shoreline protection for the inland park and south lakefront.

“It is McLaren’s professional assessment that … with maintenance and repairs, the service life of the structure can be significantly extended, obviating the need for major demolition and replacement,” the study said.

Among McLaren’s key findings:

• The vast majority of limestone blocks at the Point are generally in good condition. Less than 25% would need to be replaced.
• Shifting and displacement of the current limestone blocks is almost entirely due to the loss and erosion of replaceable underlying (“subgrade”) earth and material. Repairing and restoring this layer — and providing for continual maintenance — would halt deterioration.
• Furthermore, much of this “deterioration” is purely aesthetic and not necessarily deleterious to the protective structure or function of the Point, according to the report.

Resilient Materials

As the McLaren study notes, just because limestone revetments aren’t typically used as solutions today doesn’t mean they’re ineffective, outdated or derelict.

“Structures like the Point are not common today … because few municipalities have the initiative and funding to build structures from this sort of material,” McLaren said. “The current condition of this structure and the condition of the upland park are testaments to the quality of design, the workmanship, and the use of resilient materials.”

Indeed, McLaren continued, the resiliency of those materials, particularly in the context of climate change, should place even greater priority on retaining rather than replacing the limestone.

“It is worth noting that concrete production is the world’s third highest producer of man-made carbon dioxide and, once employed in the built environment, (concrete) significantly intensifies the urban heat island effect,” the study said. “The limestone currently in use, conversely, meets the environmental justice criteria of sustainability, durability and cost-effectiveness.”

“There are lots of reasons for reusing limestone,” Hammond said, not the least of which is sustainability, but it would also give Chicago something to brag about.

“This could be a world-class solution for a world-class city,” she said.

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Additional Media Coverage

• Block Club Chicago "Promontory Point’s Limestone Is Still Protecting The Lakefront And Can Be Preserved, Advocates’ Study Finds"
• Chicago Sun-Times "Promontory Point limestone seawall can be saved, study says"