Coastal Engineering Technical Note I-63
March 1999
Deep-Draft Coastal Navigation
Entrance Channel Practice
by Zeki Demirbilek and Frank Sargent
PURPOSE: The Coastal Engineering Technical Note herein summarizes U.S. Army Corps of
Engineers (USACE) deep-draft coastal navigation entrance channel design practice and describes
elements of a USACE research effort for improving this practice.
NEEDS AND BENEFITS: Entrance channels are the initial points of entry to ports and
harbors. Almost all of United States overseas trade by weight, and approximately 50 percent by
value (air transport accounts for a greater fraction of precious cargo), moves through our
Nation's ports and harbors. The waterborne commerce through U.S. ports and harbors has
increased continuously over the last four decades (U.S. Department of Transportation 1997;
Webster 1992), and many ports are expanding to serve larger vessels. Economics of scale and
increased containerization of cargo are producing containerships of increased size (U.S.
Department of Transportation 1997), exceeding the dimensions of Panamax class ships (Panama
Canal maximum ship dimensions are 965-ft length, 106-ft beam, and 39.5-ft draft). The
economics of scale is applicable to all cargo classes and has fueled demand for port expansions,
infrastructure capable of rapid on-and-off loading, larger stockyards, and efficient land-based
facilities for truck and rail transport. With the ever-present political and economic pressures to
serve larger vessels, ports are faced with planning for costly infrastructure upgrades,
deeper/wider channels, larger turning basins and berthing areas, and open and modernized
terminals. To attract waterborne commerce and decrease shipping costs, many U.S. ports and
harbors are now planning for the next generation of vessels with increased draft even though
these ports are not equipped to accommodate such vessels through channels leading to them.
DEEP-DRAFT ENTRANCE CHANNEL RESEARCH: Although USACE (USACE 1984,
1995, 1999) provides detailed guidance for the design of inland waterways, the guidance for
coastal entrance channels is not as comprehensive. The design guidance for coastal entrance
channels, particularly underkeel clearance allowances (principally squat and waves as defined in
Figure 1), appears to be overly conservative. Consequently, differences exist between USACE,
States (Harkins and Dorrell, in preparation), and other international design guidelines
(Permanent International Association of Navigation Congresses (PIANC) 1997). Recent work to
update EM 1110-2-1613 "Hydraulic Design of Deep-Draft Navigation Projects" revealed the
need to develop verified guidance for the design of approach, entrance, and bar channels where
vessels are subjected to waves and other coastal conditions. The absence of a verified design
methodology often leads to conservative estimates on channel size, which gives rise to increased
initial/maintenance dredging costs. Recent advances in measurement and modeling allow for
improvements in the USACE channel design guidance.
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