Seattle Parks heating up pipes for Foster Island Trail vegetation

Seattle Parks and Recreation expects to have a de-winterization project for a water line running from the Foster Island Bridge to under the State Route 520 Bridge completed later this month.

SPR is being reimbursed for the roughly $60,000 cost of the project, which was requested by the Washington State Department of Transportation for its State Route 520 Bridge Replacement and HOV program.

“A lot of the plants that have been planted for the 520 replacement are under the bridge, and they don’t receive rain,” said SPR project manager Katie Bang.

The main irrigation system was installed along the stretch of the Foster Island Trail two years ago, for a restored portion of Foster Island that coincided with WSDOT’s West Approach Bridge North Project. Around 19,500 native plants were planted there. WSDOT reports about 13 percent died, which is slightly above the normal mortality rate of new plants — a contractor will replace those by mid-November.

WSDOT requested SPR’s water line be turned on during a warm week near the end of January, but the weather took a turn a week later and a pipe burst, Bang said. Due to a lack of irrigation, a number of plants ended up dying off.

Crews started working on the de-winterization project at the beginning of October, which includes digging a trench to reach the pipe and then affixing heat tape to it, so the line won’t freeze.

“But, in order to have heat tape, we have to have a power source,” Bang said, “so that’s what this project is all about.”

The nearest power source is the Washington Park Arboretum maintenance shop, and so part of making that connection includes making a saw cut across East Foster Island Road, just west of the back entrance to Broadmoor — which is involved in this collaborative effort — for running a conduit.

SPR owns the Arboretum, which includes the trail running under the SR-520 Bridge, while the University of Washington owns the plant collection.

Foster Island has a cultural significance to several tribes, and is considered a sacred site. A portion of the Arboretum, along the Foster Island Trail, was granted back to the tribes for ceremonial purposes two years ago, Bang said.

WSDOT has an on-site archaeologist to monitor work and any artifacts that are found. Work stopped briefly after some historical period artifacts were found, but work started again after conferring with the Departments of Archaeology and Historic Preservation, according to WSDOT. Nothing tribal was found — mostly old bottles and dishware, some of which dated back to the early 1900s.