Green Stormwater Infrastructure (GSI) is an important part of building environmental resilience – a critical element of public life – for the Capitol Hill community. As Seattle’s population has grown, the built environment has continually hardened, and tree canopies, native soils, and vegetation have declined. Rainfall now flows too quickly over streetscapes, parking lots, and sidewalks on the way to the sewer system and waterways. As the water flows downhill, it picks up whatever is in its path, such as trash, dirt, oil, metals, fertilizers, bacteria, animal waste, and other impurities. These polluted waters are toxic to all living things. 

Fortunately, there's a lot we can do reduce this form of pollution! Methods known as Green Stormwater Infrastructure can slow, detain, and clean stormwater before it enters our sewers and waterways. Scroll down to learn more.

The Capitol Hill EcoDistrict seeks artists to design rain paint murals for four locations in Capitol Hill, Seattle. The deadline for submissions is November 14, 2021 at 8  p.m. PST

Join us for a Capitol Hill stormwater walking tour 

Tours were held October 16, 2021. If you missed them and are interested in future tours, sign up for our mailing list.

Join the Capitol Hill EcoDistrict and Seattle 2030 District to explore the impact of stormwater in Capitol Hill. We are hosting mile-long guided walking tours of Capitol Hill that highlight the impacts of climate change, permeable infrastructure, trees, and rain gardens on Capitol Hill. We'll also view future rain paint mural locations.

Come with us on a journey through our historically rich neighborhood to learn about how “Seattle Showers” impact our own backyard.

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Stormwater in Capitol Hill and beyond

Seattle’s reputation for being rainy is misleading, as New York City receives an average of 46 inches of rainfall annually, whereas Seattle only receives 38 inches of rain annually. Most rainfall occurs in the winter, and the summer months here are typically very dry. Seattle does, however, have an exceptionally high number of days with cloud cover, at 226 days per year.  

Below are several GSI methods and tools:


Vessels that are designed to capture roof run-off are a direct method to reduce the volume of stormwater released into the environment during a rain event. This water can later be used to irrigate gardens or for release into the sewer system.


This hardscape, intended to break the flow of surface run-off, is designed to allow for percolation. Permeable concrete or asphalt and pavers with extra-wide gaps between them are all examples of permeable paving. The sub-base for these types of paving is specially prepared to create a stable base while providing voids for water to collect and pass through on its way to native soils. These surfaces require regular cleaning or vacuuming to maintain their porosity.


Trees in our landscapes provide stormwater benefits as well as beauty, shade, and habitat. They can also soak up the rain, boost infiltration, and prevent run-off and erosion during rain events. The leaves in the canopy intercept the rain and provide a place for the moisture to evaporate. Leaves that fall to the ground create a sponge-like layer that retains moisture, provides food for the organisms that break down organic materials, and create a rich mulch. Below ground, tree roots anchor soil and absorb water that is pumped up through the tree to evapo-transpirate, or exhales water vapor from trees and stems into the atmosphere. These interventions slow the flow of surface stormwater and reduce polluted run-off.


Similar to Rain Gardens, bioswales are more like planted ditches, as they are intended to help move water from one area of a garden to another. As the water moves through them, they can slow the speed of the water, remove sediments and toxins, and often provide infiltration as well.


Rain gardens are unken gardens designed to receive stormwater from a specified area. Their primary job is to infiltrate runoff usually received from roofs, nearby pavement, or adjacent gardens. Specialized soils and plants are installed to accommodate different saturation levels. For example, the bottom of the raingarden is planted with specimens that endure saturated soils for longer periods of time. Plants on sloped sides of the garden are selected for both tolerance of moisture and drought conditions, and upland plants are less tolerant of waterlogged soils.


Bio-retention Cells are like Rain Gardens. They are a depression in the landscape where stormwater is captured. Their main purpose is to detain, not infiltrate, the stormwater. Plants and soils reduce pollutant loads before stormwater is released it into sewer system.


Stormwater planters are concrete planters that are designed to detain stormwater for release back into the sewer system. They may or may not be planted. The soils and substrate can reduce pollutant loads of stormwater.

Special thanks to our partner:

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