MLW (mean low water): The average height of the low waters over a 19-year period.
Source: Adapted from US Department of Transportation, Port Performance Freight Statistics Program. & Port Authorities.
Note: Containership capacity refers to full ships. A port can accommodate larger ships if they are partially loaded.
Port locations and sites are preliminarily constrained by the maritime access they can provide. A core component of this access is related to the depth of the waterway system, the port access channels, and, more practically the berth depth. The above map illustrates the channel depth of major container ports in North America as well as the potential containership capacity such a depth may accommodate. This does not necessarily mean that the port has the physical capacity to accommodate those ships since it could be lacking berth space, turning basins, equipment (cranes), or yard space to do so. The North American continent, unlike Europe and China, is not very prone to inland waterway distribution and is composed of three major maritime facades:
- The Eastern Seaboard, except for the St. Lawrence / Great Lakes system, offers no significant navigable river system as the Appalachian Mountains are just a few hundred kilometers inland. The upper Great Lakes (Erie, Huron, Michigan, and Superior) offer good navigation depths, but navigation is limited by the waterways between the lakes and by ice in winter. Further, access to the Atlantic is limited to the depth and lock size of the St. Lawrence Seaway, which is closed for a few months during the winter. The St. Lawrence enables to go deep inland, but maritime vessels can go up to Montreal (draft of 37 feet and the capacity to accommodate ships up to 4,200 TEUs), which is at the same longitude as New York. There are channel depth limitations for accessing several East Coast ports, with many of them limited to ships around the Panamax class (4,500 TEUs) except for Halifax (55 feet), Baltimore (50 feet), and Hampton Roads (50 feet) to enable these ports to accommodate Post-Panamax containerships. New York was also able to reach a draft of 50 feet with substantial dredging investments. Based upon tidal conditions, it is possible for some Post-Panamax containerships in the range of 6,000 TEUs to call East Coast ports within the depth of 45 feet (Post Panamax I). For instance, ships in the range of 7,000 TEUs can call the port of Savannah. However, the Eastern Seaboard also has a complex but underused coastal waterway transport system. The Intracoastal Waterway services most of the Eastern Seaboard and consists of a series of bays, inlets, sounds, and artificial canals.
- For the Gulf of Mexico, the Mississippi inland waterway system is extensive but limited to depths of less than 15 feet for the most part. Ports have a mean low water depth of fewer than 45 feet, limiting the containership capacity to less than 6,000 TEUs. Under such circumstances, ports along the Mississippi are dominantly handling barges loaded with agricultural commodities, which implies highly seasonal traffic (end of the summer and fall). Additionally, the Mississippi system has a north-south orientation while most of the goods flows are east-west, implying a limited potential to service intermodal freight movements. As the Eastern Seaboard, there is an Intracoastal Waterway ranging from Texas to Florida.
- The Western Seaboard has four major deepwater gateways, Vancouver, Seattle / Tacoma (SeaTac Alliance), San Oakland, and Los Angeles / Long Beach, but poor waterway access to the interior because of the Sierra Nevada and the Rockies. The only exception is the Columbia River basin accessible to deep-sea ships up to Portland (draft of 42 feet), which is about 160 km inland. From Portland, container barge services go an additional 575 km inland. Most West Coast ports have the potential to accommodate ships of 12,000 TEUs and above. Prince Rupert is the container port having the deepest berth depth and can technically accommodate the largest containerships currently designed.
As the world container fleet gets upgraded with larger ships, major ports are facing the challenge of accommodating deeper vessel drafts. While a 35-foot channel could accommodate a typical Panamax containership, post-Panamax I containerships handling above 5,000 TEUS require a berth depth above 42 feet. A depth of 50 feet is required to handle ships above 10,000 TEUs. Under such circumstances, many ports are not accessible to the new post-Panamax containerships. The expansion of the Panama Canal to a depth of 50 feet and a capacity of 12,500 TEU (with its associated Neo-Panamax ships class) has also placed additional pressures. This has triggered a “race to the bottom” in the dredging of several East Coast ports such as Miami (50 feet achieved in 2014), New York (50 feet achieved in 2016), and Savannah (47 feet by 2022). Other ports have dredging plans. Yet, such projects are very expensive and require careful consideration of the marginal benefits they convey.