Storm drain blockers are devices used to filter or temporarily seal a storm drain. In sediment control, the goal is almost always to filter, not fully block, so the right product is a filter device (a bag, sack, or guard) that stops sediment while letting water drain. True blocking devices that fully seal a drain are reserved for short-term situations like containing a spill.

An inlet filter bag stops sediment while letting water drain.

Filtering vs blocking a storm drain

The phrase storm drain blockers covers two different needs. Most of the time the aim is sediment control: capture silt and debris while water keeps draining, which calls for a filter device. Occasionally the aim is to fully seal a drain for a short period, such as during a chemical spill, which calls for a solid cover. Using a full blocker for routine sediment control would back water up and cause flooding, so a filter is the correct choice for ongoing work.

A well-designed filter does more than strain the water. It slows the flow so suspended solids settle out and are captured by the bag before they reach the inlet, and good units include a built-in overflow path so heavy rain has somewhere to go rather than pooling in the street.

Filter devices for storm drains

Which device you need depends on the inlet you are protecting:

• Drop inlet bags and sacks: For flat grates, including round ones, and mountable curbs. The Dandy Bag hangs at the grate and settles suspended solids out of the slowed flow, and is available in 17 sizes to fit most municipal inlets. The Dandy Sack is an open-top silt bag designed to hang below the grate for higher-level grate filtration.
• Curb and gutter filters: For curb and median inlets. The Dandy Curb Bag is a reusable curb and gutter filter with a patented design that conforms quickly to the exact shape of the curb, plus a built-in protective overflow.
• Above-grate guards: For inlets that see heavy rain overflow. The Dandy Inlet Guard is a three-dimensional fabric filter that sits above the grate rather than below it.
• Light-duty grate filters: For lower-flow sites such as parking areas and smaller construction sites, where a lighter product like the Streamguard is sufficient.
• Framed models: Where extra strength is needed, the Dandy Sack Framed Model adds a metal frame to the standard sack design.

A curb barrier bag filters gutter flow at a storm drain.

These filters are made from safety orange monofilament geotextile, which keeps them highly visible on site and easy to inspect — useful when units need checking after every storm event. They are reusable, and optional oil absorbent pillows are available on the curb models. All Dandy products are American made in Ohio.

Keeping a filter working

Filter devices need attention after weather. Clear accumulated sediment and debris from the surface and surrounding area after each storm event, and remove the sediment that has built up inside the containment area of the unit as needed. Where oil absorbents are fitted, replace the pillow as it approaches saturation. Staying on top of this is what keeps a filter passing water instead of becoming an accidental blocker.

When full blocking is appropriate

Fully sealing a storm drain is a temporary emergency measure, most often to contain a spill so contaminants do not enter the system. It is not a sediment-control method, because a sealed drain cannot pass stormwater and will flood the area in rain. For day-to-day sediment control on a site, use a filter device sized to the inlet.

Choosing the right device

Decide whether you need to filter (almost always, for sediment control) or temporarily seal (rare, for spills). For filtering, match the device to the inlet type and size. The Inlet Protection Product Selector helps you pick the right filter, and the inlet protection collection lists the full range.

If a standard size will not fit your opening, custom-sized filters are available to suit nearly any inlet — worth asking about before settling for an approximate fit, since a filter that does not seat properly at the grate will let flow bypass it entirely.