Types of Storm Drains & Ponds (also called Stormwater Facilities)

There are many types of stormwater facilities. Common types are pictured below. They often look like natural features, but are engineered to move runoff away from homes and streets, and filter out pollution like vehicle fluids and lawn chemicals before it flows into our drinking water aquifers, streams, rivers, lakes or Puget Sound. For more information, see How to Identify and Maintain Your Neighborhood Stormwater Facility.

Wet ponds hold water year-round. Dry ponds may look like an open field until the rainy season. Many have underground pipes and catch basins, to move water and filter it. All are engineered to drain and treat stormwater in the area where they are built.  Learn more about  Wet & Dry Ponds.

Photo of wet pond type  Photo of wet pond typePhoto of dry pond type

Ditches, Swales & Culverts
A swale is an engineered ditch with very specific slopes, bottom width and soil requirements. A ditch is a v-shaped open channel. A culvert is a drain pipe under the road.  All three are designed to quickly move rain off of roadways. Grass helps filter pollution like vehicle fluids and lawn chemicals from runoff before it gets into our drinking water aquifer or nearby water bodies. That's why we don't fill them with rocks or dirt.  Learn more about Ditches & SwalesCurb Cuts & Sidewalk UnderdrainsCompost Amended Vegetated Filter Strips (CAVFS).

Photo of swale type  Photo of ditch type  Photo of a culvert, or underground stormwater pipe outlet

Catch Basins, Drains, Grates and Canister Filters
Catch basins are access points to the stormwater drainage system. They are underground, so the part you see is the drain or grate above.  Catch basins keep heavy debris out, while letting water in. They are connected to pipes that flow to ponds or natural areas. Some catch basins have filters that use charcoal or other types of treatment media that filter polluted runoff. Learn more about Catch Basins & Dry Wells,  Storm Vaults,  Biofiltration Systems,  Oil-water Separators,  Treatment Devices.

Photo of inside a catch basin  Photo of storm drain blocked with pine needles  Photo of storm drain grate  Photo of inside a catch basin with filter canisters


Culverts & Pipes
A culvert is a pipe under the road. It simply connects one ditch to another and is open to the environment on either end. A pipe is attached to a structure (like a catch basin or pond) on at least one end. Learn more about Pipes, Culverts & Slotted Drains and Level Spreader & Diffusers.

 Photo of a culvert Photo of a stormwater pipe  

Low Impact Development (LID) features 
These features tend to look more natural while still providing flood-control and filtration processes and include:

  • Permeable pavement has a dual purpose of providing flow control and treatment. It eliminates runoff by allowing water to seep through, and acts as a filter.
  • Rain gardens or bioretention helps filter pollutants and also reduces or eliminates runoff. 
  • Learn more about Permeable Pavements,  Bioretention and Constructed Wetlands

Photo of installed permeable pavement with an inset showing the material    Photo of a bioretention type