Surface Water Topics

Catch Basin Inspections & Cleaning

What are those metal grates in my neighborhood?

The City of Mill Creek has approximately 5,000 public and private stormwater structures across 4.7 square miles designed to collect runoff from the entire surface of Mill Creek and route it to outfalls into our natural receiving waters. The image below is an example map of some of Mill Creek's catch basin locations (with dark purple representing basins locating in public streets).

Catch Basin Map of Mill Creek
It is necessary to monitor how these catch basins perform on a regular basis, and to identify when regular maintenance or, less frequently, replacement, is required.

In 2022, the City of Mill Creek began contracting with The Watershed Company, a local environmental firm, to inspect our public street catch basins.  This inspection is being performed to comply with the Ecology stormwater permit, which requires inspection of all publicly-owned catch basins every two years (the current inspection period is August 2021 to August 2023).  Information is gathered from each catch basin inspection, including the condition of the basin itself, the level of sediment in the bottom (sump) of the basin, the presence of any debris or obstructions that need to be removed, and the possible presence of pollutants in the stormwater.  This information is evaluated to plan our follow-up maintenance activities in the months after the inspection takes place.

Watch this video from the City of Bellingham to learn more about the process and how to help keep Mill Creek's streets and streams clear.

Runoff is surface water that flows from one area to another.  During rain storms, that runoff starts from where the rain lands and flows downhill however it can.

When it starts raining, even a small city of Mill Creek's size can produce and accumulate a lot of runoff water quickly.  The city is about 4.7 square miles in area (nearly 3,000 acres or nearly 130 million square feet!).  Even the grassy and other vegetated areas in Mill Creek do not absorb all the rain right where it lands. 

All that runoff that needs to be controlled and helped to flow down to North Creek.  Our combination of public and private stormwater pipes and facilities help with that, along with our natural streams like Penny Creek.

Even with nearly 3,600 street storm drains in the city to collect runoff, and nearly that same number of additional drains located in parking lots similar areas, it is common for water to pond up and not drain away quickly.  Hard surfaces like streets and driveways are particularly prone to this ponding.

What can I do?

Keep drains and gutters clear
Leaves and other debris from trees and plants tend to accumulate, sometimes very quickly, at drain grates and similar structures.  Even a small accumulation can either partially block water flow or deflect it in an unwelcome fashion.

Use rakes and remove any debris that accumulates.

Keep leaves out of the street
Do not blow leaves from yards into the street, even if you think the City street sweeper will pick up the debris.  Sweepers are not designed for that work, and City staff cannot sweep all city streets fast or frequent enough to remove excess leaves and other debris in the street.  Instead, dispose of all leaves from your yard and property as yard waste.

Prepare for winter storms
Begin planning for storm preparedness now, while you have plenty of time!

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Angela Bolton
Surface Water Program Coordinator
Phone: 425-921-5752
Email: [email protected]
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