The Importance of Loading Dock Trench Drains

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It’s a good idea to install trench drains in loading docks because most loading dock ramps slope downward toward the building so trucks can unload merchandise.  When it rains, runoff water will flood the lower portion of the ramp unless a trench drain or catch basin is installed to drain the loading dock.

I mention catch basins because both technically work, but I’ll focus mainly on trench drain systems and grates in this article because I think trench drains are more effective.  Why?  Trench drains have more open surface area to evacuate surface water runoff.

Finding the Trench Drain that Works for You

Each loading dock is unique, but that doesn’t stop architects from specifying the same trench drain system for all Lowe’s projects.  This is shortsighted because it assumes that weight capacity is the most important factor in choosing a trench drain.

While load rating – a trench drain’s ability to bear heavy weights without structural damage – is important, size is a better indicator of whether a trench drain will work for you.  And, to determine the drain’s size you need to be aware of how much water will be running through the drain.

The U.S. Environmental Protection Agency designed a downloadable computer program to help developers, architects and homeowners calculate annual water runoff from any given property.  The program estimates a site’s runoff based on soil, landscape and historical weather data, making it easier to design a drainage system to reduce runoff.

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Take a look at the photo above.  This loading dock trench drain not only takes runoff water from the parking lot but also from two pipes that empty onto the truck ramp.  With so much potential runoff water, this trench drain was designed large enough to handle heavy rains.

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The contractor went with a Zurn trench drain to accommodate heavy traffic and heavy water flow.  The Z812 Series is a 12” wide system made of fiberglass.  It comes in 10 foot sections, making it the perfect size for loading docks, and features a built-in frame to reinforce the system.

Although the opening is only 9.25” wide once the drain is installed, its ductile iron grate has 86.7 square inches of open surface area per foot.  That’s a lot of water capacity!

Another detail to note: that ductile iron grate used to be black.  The Zurn grate started off coated with a black coating, which has gradually worn away over the years. That has not made the grate less durable, though, because it bolts directly into the frame so snugly that it won’t come loose with repeated vehicle traffic.

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In Another Case… Foundry Grates for Loading Docks

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A simpler method to drain loading docks is a cast-in-place frame and grate system. Foundry grating is traffic rated and generally starts at 8” widths. It gets wider in 2” increments and comes in several styles, but Type A is the standard style you’ll see in high volume applications.

Most foundry frame systems don’t lock down, instead relying on weight (they’re hefty!) to keep them down.

Cast foundry systems have the added benefit of letting contractors pour and slope the drain to custom depths. But that also comes with the potential downside of an uneven slope.

Yet another… Bar Grating in Loading Docks

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If foundry grating isn’t your style, a steel bar grate can also do the trick. Steel bar grating can maintain a large percentage open area even while bearing loads across wide spans. Traffic bearing grates are typically pressure-locked or welded. Trim bands and load bearing banding will give your trench grating a finished appearance and reinforces the grates.

The above grate is a 12” wide welded steel bar grate with load bearing bars on 1.25” centers. With trim band supporting the grating sides and load bands across the end, this grate is staying strong while also offering a bunch of open area for water to flow.  Additionally, note that this grating hasn’t caught any debris.

Bar grates can lock down if you pre-plan for it, but in practice I rarely see it done this way. Usually, the grates are just installed in longer segments. The natural weight of those pieces will hold them in place.

Why Loading Dock Maintenance Matters

Trench drains do need to be regularly cleaned or the sediment particles and larger debris carried by surface runoff will build up.  If the particulates do not clog the trench drain itself, they will clog the outlet pipe and cause flooding.

The loading dock to the right, located behind several department stores, is in the same lot as the above two grates. Summer rain washes grass clippings through the parking lot. There are three loading docks in proximity to one another at these stores, but this 4.9” wide ACO drain was the only one to clog.

Structurally, the system is sound – and theoretically it should work fine.  The grate has 34 square inches of open space per grate. But ACO was the only system to clog, rendering the drain useless.

A wider drain doesn’t excuse you from doing proper maintenance, however.

The trench drain in the loading dock shown below clogged and became ineffective before a rainstorm swept through the area.  Water backed up in the truck ramp, flooding the area.

Looking closer during my visit, I noticed the drain is a standard 12″ wide foundry grate.

Moisture damages concrete over time, leading to cracks and weakened structure. Protect the long-term integrity of your building and concrete slab. Install a properly sized loading dock trench drain and make sure you clean it of debris.

For questions about loading dock drains, including recommendations and pricing, call Trench Drain Systems at 610-638-1221.