Sea ports and inter-modal transportation yards have been subject to increasing environmental regulation and must capture and treat the storm water before releasing it off the site.  In many cases a trench drain is the solution due to the need for simple slopes and long flat sites.  The constant traffic of trucks and large forklifts makes this one of the most difficult trench drain applications.  If the proper trench drain is selected, the concrete around the trench will often fail before the drain itself.

Design Considerations

Sizing the Drain

• The size of the drain will be determined by the amount of water being captured and where the outlets can be located.  The further apart the outlets are the larger the drain may have to be to convey the storm water.
• In most cases an 8", 10", or 12" wide internal drain is used.  Minimal widths are desirable in order to keep the span on the grating to a minimum and keep cost down.  Larger widths are often used more for bulk unloading areas where large spills could occur that may need to be cleaned out of the trench with a piece of equipment.
• The slope of the drain can be adjusted to decrease the size of the drain if the outlet pipes are spaced close enough to allow for this without getting into the water table.

Choosing the channels

• The channel must have the largest frame possible to carry the extreme loads in these applications.  The frame should not exert load on any prefabricated channel.  The extreme loads will crush any prefabricated channel if it bears directly on the channel.  
• Frames should have a very large bearing area and should have large concrete anchors spaced at short intervals, or the frame should be tied directly into the structural cage to eliminate any torques that may be exerted on the frame.
• Smooth channels such as fiberglass will carry more flow than a cast in place trench and can help keep depths to a minimum.  In some applications this can save a lot of cost.  Precast systems must be properly vibrated to ensure concrete gets under the frame of the system.  Voids cannot be seen so extra care must be taken at the time of installation to ensure proper consolidation is achieved.  Often times a precast trench it is not required and a simple formed concrete system can be used.  The concrete consolidation can be easily viewed with this type of trench drain.

Selecting the grate

• The grates should be ductile iron or galvanized steel.  The salt water environment is not good for other materials.
• The grates should be load tested to exceed the loads exerted with a minimum of a 2:1 safety factor.  Typically grates rated for load class E or F are used.
• Grates need to be bolted down with large anchors to ensure that they do not come out of the trench.  High speed traffic turning or breaking on the trench drains can cause the grates to come out and cause a dangerous situation if not properly secured to the trench drain body/frame.

Designing the layout

• The typical layout for a  port or inter modal application is a long straight run with multiple in line catch basins tying to the storm water piping system.  The distance between the pipes is usually between 300 and 500 feet, but can vary with site conditions.