Figure 1. Underkeel clearance allowances

CETN I-63

March 1999

The USACE guidance (USACE 1984, 1995, 1999) defines authorized depths and widths for

navigable channels. Figure 1 shows various factors that influence the authorized channel depths

or, conversely, the maximum allowable draft under various environmental and/or transit

conditions. Water levels and currents (tidal) are reasonably well known through such efforts as

long-term measurements and predictive models by the National Oceanic and Atmospheric

Administration (NOAA) (http://www.opsd.nos.noaa.gov/) and recent development of numerical

models such as ADCIRC (Luettich, Westerlink, and Scheffner 1992). Less well understood are

the effects of waves and ship speed and resulting vessel motions in the navigable channels and

shallow waterways. The current effort will identify channel depth/width allowances caused by

waves and vessel speed through (a) prototype data studies, (b) parametric model studies,

(c) transferring knowledge and databases to the USACE ship simulator, and (d) retrofitting an

existing probabilistic vessel response model.

USACE DEEP-DRAFT CHANNEL PRACTICE: Many different parameters enter into the

planning, design, and operation of deep-draft navigation channels. For example, in the planning

of a navigation channel, a design ship, typically the maximum size ship from the projected user

fleet, is selected on the basis of economic analyses. The two main design dimensions of

navigation channels are width and depth, and these must be determined to accommodate the

design vessel (USACE 1984, 1995, 1999). Likewise, for safe operations within a channel, it is

necessary to consider the effects of winds, waves, tides, currents, visibility, and navigational aids

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