UFC 4-150-06
12 December 2001
Datum the horizontal plane from which the dredge depth requirement is
referred, normally the local tidal datum of Mean Lower Low Water
(MLLW).
Design depth the distance below the datum that must be maintained for
safe navigation and berthing, also called the advertised, nominal, or
project depth. This depth usually appears on Navigational Charts.
Contract depth the distance below the datum that is initially dredged by
the contract and includes advanced maintenance dredging requirements
but not the dredging tolerance (allowable overdepth). Also called the
required depth, it is the depth noted on the DD-1391 Project
Documentation and indicates the minimum depth required under the
dredging contract.
Permitted depth the distance below datum to the lowest depth
authorized by the regulatory agencies and normally includes the dredging
tolerance (allowable overdepth). Planners and engineers should use this
depth to determine estimated dredging quantities.
5-6.1.6.5
Determine required dredge depths using sound engineering practice. The
design depth is determined by summing the following parameters:
Minimum water depth requirement the minimum water depth that must
be available for safe operation. For existing locations, use Appendices C
through F implemented as follows for design water level, squat, ship
motions, and underkeel clearances. For locations not addressed in the
Appendices, contact the NAVFAC Criteria Office for assistance.
Design water level the distance above the datum from which the dredge
depth is calculated. For outer channels use 0 m (0 ft). The design
water level should equal the datum to provide enough water depth and
ensure that the ship can transit at all times. For inner channels and
turning basins use a water level that ensures safe passage to the berth
or basin. This water level should be selected by the Activity based on
optimizing cost and operation. Ship operators generally accept some
minor operational restrictions and transit shallow channels at mid to high
tide levels. Therefore, the design water level should be selected so that
the carrier can transit from deep water to the berth, or vice versa, as
frequently as expected without encroaching on the minimum water depth
requirement noted in Appendix B. The user should identify for the planner
the expected ship transit speed and desired days of accessibility, realizing
that slow transits at low tide levels result in excessive dredge depths.
An example of this procedure is as follows:
5-33
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