Seattle Public Utilities

12th Avenue NW Basin Drainage Project

12th Ave Neighborhood

They City of Seattle will construct drainage improvements in west Broadview.

What & Why

The 12th Ave NW Basin Drainage Improvement Project will improve the drainage system in parts of west Broadview with severe flooding issues. This project is the first phase of improvements in the Broadview Program. Visit our program webpage to learn more about the Broadview Program.

We plan to reduce storm-related flooding by building new storm system improvements where there are none, to slow runoff and improve flows. The project may use a variety of tools in City of Seattle right-of-way along neighborhood streets to address flooding issues including:

  • Installing natural drainage systems in feasible locations
  • Converting ditch-and-culvert flow to a piped system
  • Installing large, underground pipes to hold water and prevent flooding during storms
  • Locating improvements to address priority flooding and allow for future expansion

What's Happening Now?

Earlier this year, the project team completed a desktop analysis to identify potential blocks in the neighborhood where NDS may be feasible. Over the next few months, you may see crews conducting surveys and evaluating soils. We anticipate minimal disruption in the neighborhood during early geotechnical exploration activities.

Later this summer, we’ll work to narrow down the number of blocks to a select few so we can move into design. We’ll be using several criteria to help whittle down to the final block selection, including: feedback from neighbors, whether the block meets technical requirements (size, ability to infiltrate water, constructability, etc.), cost-benefit and possible opportunities for additional benefits. Throughout the siting process, we will keep you updated on progress and engage you for specific feedback. Stay tuned!

What are Natural Drainage Systems (NDS)?

NDS are engineered facilities that mimic nature by slowing or reducing stormwater runoff close to its source (streets, rooftops and parking lots). NDS helps our city act more like a forest by absorbing, filtering and cleaning stormwater runoff before it harms our waterways. NDS installed in our public spaces—such as planting strips next to the street—help absorb and clean stormwater runoff.

Learn more about NDS and why they are being installed in the Broadview neighborhood here.


The 12th Ave NW Basin Drainage Improvement Project is part of the first phase of improvements in the Broadview Program. Read about how SPU selected the 12th Ave NW Basin project, check out the Broadview Program background. 

Program Background

For more information about how SPU selected the 12th Ave NW Basin project, check out the Broadview Program background.

Project goals and benefits

The goals of the Broadview program are to:

  • Reduce sanitary sewer overflows into homes, streets, and creeks
  • Reduce the frequency and quantity of stormwater flooding to areas most impacted, especially building structures.

The 12th Avenue NW Basin Drainage project will focus on reducing storm-related flooding by slowing runoff and improving flows, seeking to maximize benefits with available budget.

Following the outcomes of our program’s options analysis process that included community input, we are now focused on making improvements along neighborhood roads, in City-owned right-of-way. As we move through design, we will work to identify where proposed improvements may require property owners to clear any encroachments beyond their property boundaries that currently extend into the City’s right-of-way (e.g. fencing, landscaping, or parking). Without doing so, we won’t be able to meet our goals.


Grace Manzano, project manager
Call our project information line (206) 409-3651, available weekdays from 8 a.m. to 5 p.m.

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Sign up for Broadview program updates.