15 August 2002
depth to enable them to drydock sonar equipped ships and ships of newer deep draft
design. Refer to ASCE Journal of the Waterways and Harbors Division.
Overall Factors. In hydraulic design of flooding systems, consider the
factors of waterheads, required flooding times, optimum configuration of culverts,
permissible flow velocities, and limiting sizes of sluice gates.
Heads. Hydrostatic head causing flow varies from a maximum when a
dock chamber is empty, to zero when a dock chamber is full. Mean high water (MHW)
or mean higher high water (MHHW) is used as the reference elevation for determining
Required Flooding Time. Refer to section 6-1.
Flow Velocities. The maximum desired flooding flow velocity should be
7.62 m/s (25 ft/s). This velocity may not conform to an available head that could
produce higher velocities. In such cases, either provide built-in head losses in the
system or reduce the intake area by sluice gate throttling.
Evaluation of Flooding Time. The many factors affecting flow in flooding
systems make it practically impossible to compute accurately the time required for the
flooding. Such factors include:
Variations in Hydrostatic Head. These conditions exist because of water
rise in the dock, and the difference in actual tidal conditions from those
assumed in the design.
Transitions in culvert cross sections in many cases are necessarily abrupt;
for example, at dock floor openings.
Changes in elevation and direction of the main culvert alignment.
Head losses in trash racks and gratings.
Roughness condition of culvert walls.
Entrance and discharge head losses.
Size of ship in dock.
Computation of Flooding Time. Because of the difficulty in combining
the various factors influencing flow, the entire system is treated as an entity with a
single overall flooding coefficient applied in the basic formula Equation 1.
Q = Ca√(2gh)0.5
Q = flooding rate (cfs)