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Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Avenue, Suite 1000, Portland, OR 97204

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Stormwater Conveyance

Storm sewers in the Balch subwatershed are located primarily in the eastern third of the watershed to support the developed portions of the subwatershed. In the headwaters of the subwatershed, stormwater flows are conveyed in open channels, natural stream corridors, and ditches along NW Cornell Road. High erosion rates in the upper channels are confirmed by accumulated debris, cobbles and dirt in the lower ends of the stream. This increases demand on maintenance teams to keep the culverts obstruction free and flowing at full capacity (BES, 1999).

Upper Balch Creek ends at a large trash rack and culvert at Lower Macleay Park, an area that has documented flooding problems associated with debris blockages. Flows pass through an 84-inch diameter storm sewer and are discharged into the Willamette through Outfall 17.

Model outputs predict that street flooding will occur in the SW portion of the subwatershed along NW Thurman St from NW Gordon to NW 30th Ave and south along NW 32nd and 33rd Ave. Surcharging is also predicted at the NW 29th Ave/Nicolai St diversion manhole. Up until the publishing of the PFP (BES, 1999), there were only fifteen instances of basement flooding reported, predominantly around the area of NW 30th and NW 34th Avenues.

Stormwater from many industrial sites in monitored and managed under private NPDES permits. Under these permits, some stormwater may be discharged to the CBWTP even though it is carried in separated storm line.

CULVERTS (NUMBER OF) LENGTH OF CULVERTS (FT) PIPE AGE CLASS PIPE AGE LENGTH (FT) PIPE DIAMETER CLASS
PIPE LENGTH (FT)   
90.0 5281.0 1867-1899 0.0 1" - 12" 12078.0
1900-1945 7234.0 13" - 24" 11342.0
1946-2001 16709.0 > 25" 13419.0
No Data 26331.0 No Data 13436.0
90 5281   50274   50275
Maps & Files

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