Last year’s drought had Boston worrying anew about a longstanding problem: The foundations beneath centuries-old homes and other buildings are at risk of rotting and crumbling.
It seems counterintuitive that a lack of water would be a problem for foundations, but this odd situation is the result of an unusual facet of Boston’s history: A large portion of the city sits on man-made land. Structures built on the landfill are supported by dozens of 30- to 40-foot-long wood pilings, similar to telephone poles, that reach down through the landfill to a harder layer of clay. These pilings sit entirely below the water table, which protects them from microbes that would attack them in dry air, causing rot.
Water leaking into sewers or tunnels can drop the water table below the pilings even in wet years. But last year’s drought brought the water table dangerously close to the tops of some of these pilings, putting them at greater risk. How did Boston end up in this situation? It all started in the 17th century, not long after the city was established.
Photograph courtesy of the Norman B. Leventhal Map Center, Boston Public Library
When the Puritans arrived in 1630, much of the land that underlies some of the oldest parts of Boston didn’t exist. They settled on a small peninsula—called Shawmut by Native Americans—that covered less than 800 acres and was connected to the mainland by a narrow neck that became submerged during high tide. It had the advantage of a dependable supply of springwater, and it was well positioned for maritime commerce.
The map above shows the shape of Shawmut when Boston was established in 1630. Shortly thereafter, its inhabitants began to make their peninsula bigger.
Boston’s land-making wasn’t all about the need for more space, writes author Nancy Seasholes in her wonderfully comprehensive book Gaining Ground. Over the years there were many other motivations for making new land, including making harbor improvements, burying pollution from wastewater, safeguarding public health, building public parks, adding railroad tracks and depots, adding more shipping facilities to compete with other port cities, establishing appealing neighborhoods to entice Yankees to stay (and to counter Irish immigration), and creating space for the city’s airport.
In fact, some of that new land was the unforeseen end result of entirely unrelated endeavors. An early example of this is the story of Mill Pond. In the 1640s, a group of businessmen got permission from the city to build a dam across the mouth of a cove on the northern end of the peninsula, so that they could use the tides to power some flour mills. The dam formed what was known as Mill Pond (see map below), and the mills were up and running by the end of the decade. But they were never very productive, and the whole operation was sold off to another group by the end of the 18th century.
