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The account of Boston tripling in size through the leveling of hills and infilling of the estuary is practically synonymous with the story of Boston itself.[,] Yet dredging, a practice involving dredgers to create, deepen, or maintain waterways is seldom mentioned despite it being the significant other land-forming practice. Principally, dredging enhances commerce by clearing a path of least resistance to the port. Although dredging has been dynamic across temporal and spatial scales, it remains inconspicuous in aerial photos; the outlines of navigation channels are rarely delineated in conventional maps. This chapter brings dredging to the surface and explains from various angles the role it has had in shaping the city.

There is a small gap in the Northeast Atlantic's continental shelf where the Labrador Sea's cold southerly current is able to slip through and flow into a bowl shaped pocket of water called the Gulf of Maine. Sequestered from the Atlantic Ocean by Georges Bank and Browns Bank, this Gulf is sometimes called a 'sea within a sea',[,]. Comprised of, and articulated by numerous smaller banks and basins, the Gulf's geologically complex floor contributed to the formation of what is believed to have been the most productive fishing grounds in the world.[,] Tales of this phenomenal find- transmitted to Europe in the early 17th century by the likes of Captain John Smith captured the imagination of other explorers who later followed across the Atlantic in search of a new England.

Shawmut Peninsula (1600-1700)

Beginning in the 1630s the British colonized Shawmut Peninsula for many of the same reasons the site had appealed to the Native Americans: it had a spring with pure drinking water, a hill with expansive views, and a tidal channel that cleared a path to the Gulf of Maine. Shawmut was also tucked far into the estuary behind islands and headlands- which served as a primary barrier to naval attack and forces of nature.[, ] From a global perspective the site enabled  merchant sailers to participate in the Triangular Trade, which benefited from the circular, clockwise patterns of currents and winds in the Atlantic Ocean.

Epicenter (1700-1800)

Merchants redirected capital gained from commerce towards new investments in ships and ports – quickly transforming Boston into a global epicenter with trade volumes four times that of New York. The latter half of the 18th century is marked by the beginning of industry, a secession from the British Empire, and an emergent Capitalism. By 1800, the city's population had climbed to 25,000.

Metamorphosis (1800-1900)

A flood of ideas and innovations beginning in the early 1800s – such as the Amphibious Digger, steamboat, and factory system – rapidly transformed New England in this century.[,,] The map from 1907 depicts a dendritic growth that stemmed from America's Industrial Revolution (1780s-1850s). Meanwhile, by the 1850s the commercially desirable fish (Cod, Halibut) became over-fished or depleted; by the 1870s even forage fish like the Alewife (Menhaden) were being exploited.[,] While the percipitous loss of fisheries delivered a blow to the region's economy, industrialization and technology helped balance this loss.

President Roads (1822-1930)

The history of Boston would have to be rewritten in the absence of dredging; between 1820 and 1930 the city's population flourished, swelling from 43,000 to 781,000. Throughout this period dredging occurred in unison with the increasing drafts of larger ships. Starting around 1822, the principal tidal channel leading to Shawmut Peninsula was extensively deepened - with support from agents with vested interest in the economy of New England. Up to the 1930s, the extents of the North Channel and President Roads were maintained to a uniform depth of -35 ft.

President Roads (1930 - Present)

Ships having a 39.5ft draft (Panamax) started becoming common around the time of Panama Canal's opening (1914). Boston deepened a large portion of its navigation tributaries to -40ft in the late 1990s and maintains and leverages its status as the principal distribution point for regional commerce. This depth still accommodates most petroleum tankers, carriers, containerships, and LNG tankers with the caveat of larger, Post-Panamax ships having to wait on the tide for extra depth. The South Channel and the Narrows are limited to smaller ships and barges.

Mounting Geopolitical Pressures

In their 2011-12 report on logistics and supply chains, the World Economic Forum's Global Agenda Council calls the shipping industry "global trade's weakest link." Rightfully, a radical shift in maritime trade is being anticipated, and several mounting geopolitical pressures such as rising costs of transport; demographic shifts; emission mitigation efforts; the potential emergence of new Trans-Arctic shipping routes; a modernized, widened Panama Canal by 2015 are shaking up this industry. In preparation, the U.S. Army Corps of Engineers and MassPort have begun examining the feasibility of deepening the North Channel and President Roads to a depth of 45-50 feet. There is concern that a failure to meet a new global standard may lead to cascading, multidimensional losses such as decreased  purchasing power, loss of capital flows, and increased emissions from having to truck goods in and out of the city.

Developed in the 1950s, containerization is an efficient system of freight transport based on standardized units of steel intermodal containers called TEUs (Twenty-foot Equivalent Units). TEUs filled with cargo are loaded and unloaded, stacked, transported over long distances, and transferred from one mode of transport to another – intact. Initially driven by demands of a post-war boom, containerization in-and-of-itself became a driver of growth.

Top 15 U.S. customs districts along the Atlantic Coast by volume of cargo, in metric tons. Boston's trade volume is the largest in New England. The principal dry bulk cargos in Boston include salt and cement imports, and scrap and newsprint exports.

Infrastructure, logistics, and technology allows cargo off-loaded in Boston to reach Chicago in 24 hours by truck or 32 hours by rail.

The years between 1987 and 2008 – bookended by Black Monday and the Subprime Mortgage Crisis – saw a four-fold increase in the total volume of goods handled by U.S. ports. Starting in the 1990s, the rise of personal computing and an expanding internet accelerated the globalization of information flows. Concurrently, free-trade agreements such as the GATT and the NAFTA transformed business strategies while phenomena such as trickle-across, rising income inequality, the dot-com bubble and online shopping redefined patterns of consumption.[, , , ]  In the United States, the strong growth in containerized shipping peaked in 2007 and subsequently broke below it's upward trend line in 2008. The peak year for Boston's Conley Terminal was also 2007, when 220,000 TEU were handled.

In the past, dredged sediment not suitable for beach nourishment was directed to and disposed of at several locations throughout Massachusetts and Cape Cod Bays. Presently, open water disposal must conform to the EPA's Ocean Dumping Criteria. Since the 1970s, Boston has utilized the Massachusetts Bay Disposal Site for open water disposal.

Containing the costs of maintaining adequate port capacity is challenging; the U.S. Army Corps of Engineers, considers open water disposal a cost-effective and environmentally sound option.

Basin geometry, sediment supply, and oceanographic processes all contribute to the sedimentary patterns (self-organizing) observed in the Boston Harbor. Fine sediments accumulate in this estuary because of its restricted flushing and low-wave environment. 

“ Tide is the vertical rise and fall of water accompanied by the horizontal movement of the water, known as a tidal current. The moon and sun generate tidal forces. However, weather, seismic events, or other natural forces also influence tides and river flows; floods or other non-tidal currents also affect tidal currents. Current is affected by differences in bathymetry or the depth of the ocean.”

- Massachusetts Ocean Management Task Force

While tide is the regulating force that effectively mixes and renews the water in the estuary, overall health and ecological stability of estuaries may be impacted by changes in this water circulation. A simplified calculation using the volume of freshwater input can approximate the residency period (renewal period) of the water in this estuary. This equation suggests that dams, dredged channels, urbanization – as well as rainfall patterns impacted by climate change –  have effects on this exchange rate.

In Boston Harbor, turn-over time is about ten days during low flow and about two days at the mean annual rate of flow. Further increases in runoff had only a slight additional effect on the rate of the circulation.

For three hundred years, the filling of salt marsh and tidal flat habitats supported the development and growth of Boston. An examination of the historic losses of these habitats would be useful in understaning changes in the extent and quality of this valuable land, but no such data exists.

"The dual nature of sediment as both a threat and a resource to humans and the environment makes its management particularly challenging. Regional sediment management will require coordination among diverse interests, political jurisdictions, and levels of government to achieve environmental, social, and economic goals."

- United States Commission on Ocean Policy (USCOP)

Graph: Growth in the volume of container-based trade in the United States 1980-2009. 

This A to Z List of Goals represents the interests of: the Executive Office of Energy and Environmental Affairs (EEA), Adaptation Advisory Committee (AAC), Environmental Protection Agency (EPA), and the U.S. Army Corps of Engineers (USACE).

A From: Concepts, Regional Sediment Management. B-E Four Goals, Massachusetts Ocean Management Plan. F-N Management Goals, Climate Ready Estuaries Synthesis Of Adaptation Options. O-Z Cross-Cutting Strategies, Massachusetts Climate Change Adaptation Report