Reasserting the Place of Nature in Seattle’s Urban Creeks - Politics of Urban Runoff: Nature, Technology, and the Sustainable City - page 129

Urban Runoff and the Creeks of Seattle
The biological and physical condition of the creeks in Seattle is closely
related to how the city developed its drainage networks over time. As
noted in the previous chapter, the central core of Seattle continues to be
served by the nineteenth century combined sewer network designed by
Benezette Williams. Combined sewer networks serve about one-third of
the geographic area of the city, carrying a combination of sanitary and
stormwater volumes to Metro's regional wastewater treatment plants (see
fi gure 6.2). 24 A second type of drainage network is informal and consists
of ditches and culverts that cover another third of the city's geography.
These networks are prevalent in the northern areas of the city that were
annexed primarily in the 1950s. The municipal government agreed to up-
grade these facilities as part of the annexation process, but due to funding
constraints, signifi cant infrastructure upgrades have been completed only
on major arterials. And fi nally, separated or partially separated networks
handle some or all stormwater volumes separately from sanitary waste-
water volumes in the remaining third of the municipality's jurisdiction. 25
With the partially separated networks, roof drains are directed to the sani-
tary sewer and street drains fl ow to the storm sewer. The heterogeneous
runoff regime in Seattle can be understood as an ad hoc evolution of
drainage logics applied by the municipal government over time to manage
the city's stormwater volumes.
The ditch-and-culvert networks and the separated or partially separated
networks discharge directly into the city's creeks. The creeks serve as the
trunk lines for these networks because they are low-elevation features that
provide an existing and inexpensive conveyance channel for urban runoff.
These drainage networks are an ecotechnic hybrid that bind land develop-
ment to waterfl ows and their biota, including salmon. Seattle once had
some forty creeks that sustained healthy salmon populations; the conver-
sion of these creeks to drainage conduits, along with loss of habitat due
to urban development, has resulted in only four creeks that can sustain
salmonid populations today. 26
Like most U.S. cities, the municipal government in Seattle has empha-
sized conveyance and fl ood protection when designing, constructing, and
operating the three types of drainage networks. Seattle Public Utilities
(SPU) was formed in 1997 to combine the municipal government's opera-
tions of water supply, wastewater conveyance, stormwater management,
and solid waste management into one organization. 27 SPU's drainage
activities are divided into four major programs: stormwater and fl ood