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Best Management Practices to Maintain Catch Basins to Prevent Pollution

Photo shows a grate in the pavement of a parking space that is meant to drain rain from the pavement.
Catch basins can help protect our watersheds by preventing stormwater from washing pollutants into our rivers and streams. Learn more about catch basins and best management practices for maintaining them.

For clogged or blocked storm drains that are causing ponding water along city streets and intersections, contact Portland Bureau of Transportation 24/7 Maintenance Dispatch at 503-823-1700 or

You can help! Learn more about adopting a City storm drain near you.

About Catch Basins

Diagram of a catch basin shows infow through a pipe on left to a rectangular box that is half full of water. Water flows in at top through a grate. Sediment settles to the bottom. A pipe on the right bent downward, allows only water to flow out of the box to the right.
Properly maintained catch basins trap the sediment and debris in stormwater. 

A catch basin drains stormwater from a driveway, parking lot, or other paved area. It typically includes:

  1. A grate where stormwater enters the catch basin.
  2. A sump to capture sediment, debris, and associated pollutants.
  3. An outlet pipe tee/down turned elbow to capture floating debris and oils.

Catch basins collect stormwater and trap pollutants. Many catch basins are connected to the stormwater system and often discharge directly to surface waters such as rivers and streams. Some catch basins are connected to combined pipes, which carry stormwater and wastewater to a treatment plant. Others may discharge stormwater underground through a drywell or UIC (underground injection control) structure. However, it’s best to assume that the stormwater entering a catch basin is going directly to a river or stream and to take steps to prevent pollution. 

Catch basins must be cleaned periodically. Regular maintenance improves drainage to help prevent localized flooding, keeps pipes from becoming clogged, and reduces the risk of sediment and debris flowing into a river or stream. Regular removal of sediment, decaying organic material, and associated pollutants benefits water quality and our environment. Many pollutants, such as metals, attach to sediment. If allowed to flow to a stream, those pollutants can contaminate the water and may harm fish and other aquatic organisms.

Best Management Practices

The following best management practices are recommended to keep catch basins working properly and minimize stormwater pollution.

Catch Basin Grates

  • Graphic shows a fish jumping with words that read: Dump no waste. Drains to stream.
    Decals can be placed next to catch basins as reminders that many catch basins drain directly to a river or stream.
    Remove leaves and trash to reduce clogging.
  • Install “Dump No Waste, Drains to Stream” or similar decals next to the grates. A stencil to label the pavement next to the grate can also be used. Contact Environmental Services for free decals, to borrow a stencil, or for more information.

Catch Basin Sump

  • Diagram of the catch basin with instructions to clean debris from grate, replace broken or missing elbow, and clean when solids reach one-third of basin volume.
    Regular maintenance helps prevent blockages and improves drainage.
    The City recommends catch basin cleaning if the depth of solids reaches one-third the depth from the basin bottom to the invert of the lowest pipe into or out of the basin.
  • Slow drainage or ponding water around a catch basin grate generally means catch basin maintenance is needed.
  • Hire a vactor truck contractor to clean the catch basin. Or, if you would like to clean the catch basin yourself, use a shop vacuum, pump, or bucket to remove the standing water and a shovel to remove sediment at the bottom.
  • If you are cleaning the catch basin yourself, dispose of the water into the sanitary sewer through a shop drain, sink, or other appropriate sanitary sewer drain. Let the removed solids dry out and properly dispose of the material. Make sure the removed solids do not wash back into your catch basin. Do not dispose of them on your property or someone else’s property.
  • Catch basin sediment disposal must involve a solid and hazardous waste determination. As the “generator” of this waste, you are responsible for making that determination and deciding how to properly manage the solids. Solids removed from catch basins at commercial or industrial sites are generally not considered hazardous waste, but consider the types of activities and pollutants on site. Catch basins located in areas used for chemical or hazardous waste storage, material handling, or equipment maintenance may collect the chemicals used in these activities from spills or via stormwater runoff. Contact the Oregon Department of Environmental Quality for information regarding solid and hazardous waste determinations.
  • Repair any damage to the outlet pipe tee/down-turned elbow. Install an outlet pipe tee/down-turned elbow or tee, if one does not exist. Parts are inexpensive.

Safety Precautions

  • Remove the grate with caution. It may be heavy.
  • Do not leave an open catch basin unattended.
  • Never enter a catch basin or other drainage structure unless properly trained.
  • Implement traffic safety procedures.


  • Sweep pavement regularly to reduce the need for catch basin cleaning.
  • Install and maintain catch basin filter inserts and oil-absorbent pillows.
  • Prevent exposure of rain and stormwater runoff from chemical and waste storage areas.
  • Remember – only rain down the drain! Don't use catch basins to dispose of anything other than rainwater.
  • When washing vehicles or equipment, don't let the water flow into the catch basin.