Monday, October 5, 2009

Impact of stormwater project on Madison Street traffic expected to be negligible

For many of us in the Park, I suspect that the ongoing Madison Valley Stormwater Project has been one of those out-of-sight, out-of-mind things. Yes, there is that big billboard that the City installed on Madison Street overlooking the baseball field, but almost all of the actual project construction to date has been outside our normal field of vision. Next summer, however, planned construction will be moving much closer to home; so I decided to investigate how the final phase of the project might impact our neighborhood.

Phase I of the project, now in its final stages, involves the expansion of an above-ground stormwater holding area at 30th Avenue E. and E. John Street. This facility will have the capacity to hold 1.7 million gallons of stormwater during very large storms. In the City’s estimation, however, even with this expansion there will be an insufficient amount of holding capacity to prevent a stormwater surge of the magnitude experienced in 2006. That was the winter in which a "series of extraordinary events" led to the drowning death of audio-book narrator Kate Fleming in the flooded basement of her Madison Valley home.

Hence Phase II of the project, which will create an underground pipeline connecting the E. John Street facility to a newly built stormwater holding tank to be located near the existing baseball field in the Washington Park Arboretum (see graphic above). The pipeline is expected to run along the following route, crossing E. Madison Street at its intersection with Martin Luther King Jr. Way E. and 28th Avenue E.:

Fortunately, the City plans to use trenchless construction for the pipeline, meaning that except for the above-ground shaft locations (blue dots on the graphic above), all of the boring will occur underground. The construction method is shown in this cross-section illustration:

The area around each of the proposed shafts will be impacted by the construction in several ways. At a minimum, there will be noise, congestion, and the temporary loss of some parking spaces in the immediate vicinity. Additionally, work at the shafts will require traffic detours for all or part of the construction period, according to initial assessments. Although planning for Phase II is not completed, at this point the plan is to locate one of the shafts on 28th Avenue E., just to the north of E. Madison Street.

So what about traffic during the construction period on Madison, our neighborhood’s principal thoroughfare? According to project manager Brent Middleswart, we shouldn’t be worried about any restriction in the flow of traffic. Although there will be some early work on the south side of Madison near City People’s, “we will always maintain two-way traffic flow” along the arterial, he told me. Trenchless technology, he noted, will mitigate the need to block Madison during the construction of the pipeline. This is good, since there is really no suitable detour route.

Nevertheless, regular users of E. Madison Street will still see some traffic impact resulting from construction. Debris from the pipeline boring will be trucked out along both E. Madison and 23rd Avenue E., based on currently proposed hauling routes. If approved by the Seattle Department of Transportation, these hauling routes will alleviate the need to truck material through the Arboretum.

Construction on Phase II is likely to begin as early as June 2010, with completion scheduled for the summer of 2011. The total capacity of the integrated stormwater system at completion will be 2.1 million gallons. “Based on modeling results, stormwater would only appear in the Washington Park above-ground holding area during especially large storms like the two in August 2004 and December 2006,” states the Phase II report presented by the City at a community meeting last spring. A current conceptual landscape plan for the impacted area of the Arboretum shows a much-improved park space north of E. Madison Street:

For more information on the NW Diversion and Washington Park Stormwater Storage project, visit the Phase II website. I will be monitoring the progress of project planning and will do a posting if there are significant deviations from what has been outlined above.

[Illustrations courtesy of Seattle Public Utilities. Click to enlarge.]

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