4/11/07, Avondale Crest bio-swale issue

Attached, is a good photo of the city "bio-swale" on Avondale & NE 104th St. You are looking to the north from 104th. The Avondale Crest project is on the west-side. This swale is serpentine (not straight) to slow the water flow enough to allow filtration into the soil before draining into Bear Creek. It is a very good example of a high functioning and (apparently) well maintained bio-swale.

This bio-swale serves as a water quality measure for storm water running off of various housing projects. It functions as a water filter for removing phosphates, nitrates, and heavy metals from stormwater. The swale also re-oxygenates the water. In the end, our drinking water is cleaner and salmon healthier.

A small, but important problem was discovered with the bioswale. The swale was intended to treat the Avondale Crest stormwater draining from two wet vaults on the north along Avondale. But, I couldn't find the northern inlet pipe to the swale servicing these vaults. A development engineer graciously escorted me into the swale to look for the inlet pipe. We could not find the inlet pipe after an hour of searching and digging.

The Development Department reviewed my request for proof of a pipe inlet for more than 2 months. With some back-up from our Code Enforcement Officer cmArthy@redmond.gov and the Department of Ecology, our Public Works department was able to find and dig out the inlet pipe. They showed me a picture for proof. Though the pipe appeared smaller than the construction plans and flow does not appear fully re-directed from the Avondale pipe, some treatment may occur.

Of note, the stormwater engineer told us bio-swale earth accumulates heavy metals over time and the soil needs to be removed. Also, during floods, the water flows over the ditches by-passing the serpintine channels. During floods, treatment is significantly limited.

A pattern seems to be emerging in newer, proposed projects to eliminate bio-swales from wet vault treatment altogether. I am researching this further. But so far, I could not find bio-swale water quality measures in the 42-lot Shaughnessy Plat or 24-lot Perrigo Heights plat. In fact, it appears the Perrigo Heights vault stormwater will drain directly into Perrigo Creek for oxygenation and filtering.

Water enters the Avondale Crest swale from housing uphill and west of the swale. It treats the stormwater from older neighborhoods to the west and potential future projects. It is also designed to treat stormwater entering from the north (Avondale pipe).

I learned about this swale while appealing the proposed 9-lot Avondale Crest plat housing project just uphill. Though, appealing can be rigorous and time consuming one may often find a mistake or unintended consequence in the development process that could improve project quality....just reward for one's effort.

2007 STORMWATER MANUEL AMMENDMENTS (SEE PAGE 19) FOR BIOSWALE REQUIREMENTS. http://www.redmond.gov/insidecityhall/publicworks/technotebk07/Chapter2.pdf