King County has selected 31 streets in two West Seattle neighborhoods for “further evaluation” to install rain gardens in hopes of reducing combined sewer overflows into Puget Sound at the Barton CSO facility near the Fauntleroy ferry dock.

Westwood and Sunrise Heights residents (the area defined by 35th Ave to the west, Barton St. to the south, Othello St. to the north and 30th Ave S.W. to the east) attended a public meeting on March 28, hosted by the King County Wastewater Treatment Division, to learn about how their streets will change once the county starts installing rain gardens, or bioswales, starting in 2013.

While the project involves only these two neighborhoods, King County has expressed their intent to create more rain garden projects in other neighborhoods in the future.

Another meeting, with the same presentations and topic, occurs on Saturday, March 31 from 10 a.m. to 12 p.m. at the High Point Community Center (6920 34th Ave S.W.).

The meeting opened with Barton CSO Project Manager Mary Wohleb directly addressing a number of neighborhood concerns about the project. Wohleb reiterated comparing the West Seattle project to a Ballard rain garden system that did not go so well is off base, since the “Ballard project was fast-tracked” and more time and money has been poured into the Barton version.

She said that difference in approach should ensure rain gardens drain quickly, look attractive, do not bring critters into the neighborhoods (rat and mosquito infestation worries have arisen), and will not pose a drowning threat to children in the neighborhood. Wohleb also said the county will do continual maintenance on the bioswales, just as they would with any other facility, and referenced the High Point rain gardens as a preview of what is to come.

She did not discuss the concern over dropping property value at the meeting, but did address it in a recent Herald article.

One change King County fully acknowledged, and what became the focus of the meeting for many, is that some residents will lose access to on-street parking in front of their homes.

How the streets were chosen
King County discussed the criteria for selecting 31 streets for further evaluation, providing details for those immediately affected and a blueprint for residents of future projects in our area.

-Flatter streets. The less elevation change on a block, the more effective bioswales are at catching the water.

-Wider planting stips. Wider planting strips between sidewalks and the street were given preference because it will reduce the amount of curb bump-outs to fit a bioswale in. Bump-outs will equal a loss of parking in many cases.

-Where curb bump-outs are required, they are trying to select locations where parking is already off limits – basically near intersections. However, if a traffic circle is located at the intersection, they will not be able to install a bump-out to ensure ample space for traffic to navigate.

-Bioswales are more likely to be installed on the lower elevation end of blocks to catch more runoff. In this case, that generally means the south end of north-south running blocks.

-If streets are crowned and one side is lower than the other, bioswales are more likely going in on the lower elevation side to catch more water.

-Areas with mature trees and established root systems will be avoided as much as possible.

-Blocks with fewer driveways and areas where testing has shown greater runoff accumulation are more likely to be selected for rain garden installation.

Bioswale characteristics
Certain areas will have a series of rain gardens in a row, with a gap in between planted with walk-on-friendly vegetation. The general dimension for each "cell" is 35 feet long, 9 to 15 feet wide with water depth (when the rain is falling hard) from 0 to 12 inches at the deep end.

Multiple cells are connected with inlets and outlets in the curb, so if one reaches capacity, water will flow into the next available cell.

From there the water goes into an underdrain, travels to a catch basin and into deep infiltration wells that take water below the hardpan, a hard soil layer that makes natural infiltration difficult and results in the occasional overflow.

For residents unable to attend the public meetings who would like a map of the proposed sites for rain gardens on their block, contact the King County Barton CSO Project’s community liason Kristine Cramer at (206) 263-3184 or Kristine.cramer@kingcounty.gov.

Wohleb said the next step is block-by-block community outreach where King County officials will meet with residents of the selected streets to discuss their specific plans and landscaping options for the rain gardens. Those meetings will start up in early summer.