Holy Family Parish Rain Gardens

The Holy Family Parish in West Seattle spreads across 6.8 acres, 13 property parcels, and two city blocks. Located on 20th Avenue SW and SW Roxbury Street, it is at the southern most end of the Delridge combined sewer overflow (CSO) basin. About 75% of the Parish property has impervious cover, either roof surfaces or asphalt and concrete. For this the Parish paid more than $18,000 in 2013 surface water fees, and without an intervention these will increase annually 10 to 12%.

Over the course of this RainWise project, our team will install 15 rain gardens at multiple buildings and infiltrate over 34,000 SF in combined roof surfaces. To do this we must first conduct extensive infiltration testing, which is underway.  It will be followed by rain garden design for size and location, and then construction.

We are designing this project to gain a 35% to 40% reduction in long-term surface water fees and to show how landowners with large impervious surfaces can reduce stormwater impacts to Puget Sound. We expect construction completion at the end of 2014 or the beginning of 2015. The Parish will then apply for facility stormwater credits.

Holy Family Parish and School, Sustainable Seattle, and Rain Dog Designs are the primary project collaborators.


Aerial view of Holy Family Parish property

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Holy Family School, Church, Rectory and former Convent





Boring and Soil Profile


Monitoring Well installed


Pit Excavation


Well-infiltrating glacial outwash sand found at 13 feet