15 August 2002
DEWATERING SYSTEMS. This section deals with criteria, data, and
information on dewatering, with particular attention to basic components, basic
requirements, and pumping systems.
Requirements. Graving docks have two dewatering systems. In both
systems a large portion of the water is drained directly through a collector channel.
Secondary System. A secondary system collects the last few millimeters
(inches) of water blanketing the graving dock floor, as well as rainwater, flushing water,
and steam condensate. This system has sloping longitudinal floor drain culverts near
the sidewalls that lead to collector channels at pumpwells. The culverts may have
rectangular cross sectional areas of several square feet. They are covered by securely
anchored strong gratings.
Alternate System. As an alternative to relatively large floor culverts of
the above secondary systems, use a wall culvert to carry off the main discharge. Floor
culverts are then made smaller and are connected to wall culverts at intervals through
floor openings. Connect wall culverts to the collector channel or directly to the main
pump suction chamber.
Environmental Systems. Environmental requirements in most locations
now require that potentially contaminated water be treated prior to discharge. If
potentially contaminated and uncontaminated waters are allowed to mix, the mixture
must be handled as contaminated water. For this reason, it is usually necessary to
segregate potentially contaminated water sources in the drydock from uncontaminated
sources that can be pumped directly into the harbor. Potentially contaminated sources
can include water that contacts the drydock floor where industrial activities are
occurring. Uncontaminated sources include water pumped from the drydock during
docking/undocking operations, water that leaks past the caisson seat, ship's cooling
water, and water that leaks through dock walls or enters the dock through pressure
Design environmental systems so that system failure does not result in
flooding of the drydock floor. Environmental systems should overflow into the normal
floor drainage system before the water reaches drydock floor level.
Environmental system requirements vary by location and can be
subjective. For this reason it is critical that environmental system planning and design
be closely coordinated with the regulatory authority to ensure compliance with
DEWATERING SYSTEM COMPONENTS