August 13th, 2026
Catch basins have been part of stormwater systems for so long that they can sometimes be overlooked.
They aren’t the most exciting stormwater asset. They don’t get the attention that rain gardens, green roofs, or other green infrastructure often receive, and they don’t typically come with educational signage or feature prominently in stormwater demonstration projects.
But catch basins do something important: They are often the first step in a stormwater treatment train. For many jurisdictions and property owners, they represent a relatively simple opportunity to improve system performance, protect downstream infrastructure, and get more value out of routine maintenance dollars.
Before we dive deeper, what exactly is a catch basin?
A catch basin is an underground structure that collects stormwater runoff from streets, parking lots, and other paved surfaces. As water enters through a grate or inlet, sediment, debris, and other pollutants settle into a sump at the bottom while the water continues through the stormwater system. In simple terms, it acts as a first line of defense by capturing material before it can travel farther downstream.
One of the biggest advantages of catch basins is that they are relatively straightforward to inspect and clean. When sediment fills approximately 60% of the sump, which is the collection area at the bottom of the catch basin, cleaning is vital to maintain the structure’s function and prevent accumulated material from moving farther downstream. Catch basins are generally easy to access, making routine inspection and cleaning much simpler than maintaining larger or more complex stormwater facilities.
Compare that with swales, wet ponds, and bioretention facilities, which can require more involved inspections, specialized maintenance, vegetation management, and sediment removal. Keeping a catch basin clean may be a relatively simple maintenance task, but it can prevent big problems.
Catch basins don’t just protect the structure itself. They can help protect everything downstream. By capturing sediment before it reaches swales, wet ponds, bioretention facilities, and other treatment systems, routine catch basin cleaning can reduce sediment loading and help extend the useful life of those assets.
The amount of sediment captured can add up quickly. Studies have reported annual sediment removal ranging from approximately 30 to 180 pounds per catch basin in industrial areas, 70 to 120 pounds in commercial areas, and 60 to 100 pounds in residential areas, depending on cleaning frequency and site conditions. That makes routine catch basin maintenance a relatively small investment compared to the cost of rehabilitating a larger downstream facility. Ask yourself, would you rather regrade a swale because of sediment accumulation every 10 years, or every 20?
Catch basins can provide another benefit that is easy to overlook. They can become useful monitoring points. Tracking sediment accumulation at multiple catch basins over time can give stormwater managers a better understanding of what is happening throughout their system. This provides a relatively low-cost way to identify trends and compare conditions between different areas.
That information can also help inform stormwater management planning and reporting. For example, changes in sediment accumulation may help identify the effects of traffic patterns, development, erosion control enforcement, street sweeping, or other changes within a drainage area.
Instead of maintenance data simply showing that a catch basin was cleaned, it can help answer a bigger question: What is happening in the system, and why?
Catch basins can also be paired with additional technologies to improve their performance. Fabric inlet systems and other inlet protection products can provide additional sediment removal in appropriate applications. These types of improvements can be considered when a jurisdiction or property owner is looking for ways to improve water quality without completely replacing existing infrastructure.
The right solution depends on the system, the site, and the pollutants being managed. But because catch basins are already part of most stormwater networks, they can be a practical place to look for improvements.
Catch basins may not be the most exciting part of a stormwater system, but they are an important one. Regular inspection and cleaning can reduce sediment loading, protect downstream facilities, extend asset life, and help stormwater systems continue functioning as designed.
For jurisdictions and property owners looking to make the most of their maintenance budgets, catch basins are worth a closer look. Sometimes, improving stormwater performance doesn’t require a new system or a major capital project. It starts with taking care of the infrastructure already in place.
Riparia has been selected as the preferred vendor for the catch basin cleanout programs in both Clark County, WA, and the City of Shoreline, providing practical maintenance solutions that help keep stormwater systems functioning as intended, reduce sediment buildup, and extend the life of downstream stormwater facilities.
Learn more about these programs:
https://clark.wa.gov/public-works/catch-basin-cleanout-program
For more information or insight on catch basins, please reach out to our team at [email protected]!
References:
City of Seattle NPDES Phase I Municipal Stormwater Permit. Street Sweeping Water Quality Effectiveness Study. Final Report. 2018
Technical Memorandum. City of Portland. Nonstructural Stormwater BMP Assessment. 2006
Pitt, Robert., Clark Shirley. Interaction between Catchbasin and Street Cleaning In urban Drainages and Sediment Transport in Stormwater Drainage Systems.