W Washington St. Watershed Drainage Improvements

Firm:Clark Dietz, Inc.

Other Consultants:Engineering & Research International, Inc., Hitchcock Design Group, Ardmore Roderick, Huff and Huff, Inc., Stark Excavating

Owner:City of Champaign

Description:The West Washington Street Watershed has a long history of flooding that dates to at least 1927. Over the past decade, frequent rainfalls caused severe flooding that made streets impassable and flooded residences. Stormwater infiltration into the sanitary sewer system caused sewage backups in basements and sanitary manhole overflows onto the ground. Pollution from sanitary overflows and non-point pollutants from the watershed mixed with the floodwaters during heavy rain events to create health and safety problems and water quality issues in the Copper Slough Channel, the receiving stream.

The watershed is 408 acres in size with approximately 1,400 households located within the boundary. The watershed has approximately 74,000 feet of storm sewer that collects and transports stormwater to the Copper Slough Channel, located approximately a half mile to the west. Watershed modeling indicated that approximately 40 acre-feet of stormwater floods the watershed during a 50 to 100-year storm event. Flooding was attributed to undersized storm sewers and localized low areas that trap water. In 2009, the Champaign City Council established the West Washington Street Watershed as one of three watersheds that needed stormwater infrastructure improvements.

This award entry is for the full design, construction, and implementation of Phase 2 and Phase 3 improvements to the West Washington Street Watershed. Phase 2 improvements included a 19 acre-feet detention basin located along Glen Park Drive and 6,000 feet of new storm sewers to convey stormwater from the watershed to the detention basin. The work included sustainable infrastructure components, such as native plants along the detention basin side slopes and dry detention basin, wetland plugs along the shoreline, a bio-swale, and four large rain gardens/bioretention features. The inclusion of sustainable infrastructure helps with flood control and collection of non-point source pollutants from the watershed. The detention basin also functions as a sediment removal feature which improves water quality in the Copper Slough Channel. Phase 2 improvements provided the watershed a 40-year flood protection level. Phase 3 improvements included 5,500 feet of new sewers and 5,100 feet of lined sewers to convey stormwater to the new detention basin. It also created additional bio-swales and ten rain gardens to increase runoff storage and delay flooding downstream.

The primary goal of Phase 2 and Phase 3 improvements was to improve flood protection levels and stormwater storage in the watershed. Secondary goals were to create an enhanced space for public recreation and public safety. All three objectives were successfully achieved. The approach taken to enhance the entire contributing watershed corridor resulted in 12,300 feet of water main replacement, roadway removal and replacement including concrete, asphalt and brick streets, and new/replaced sidewalks and pathways. Public recreation space was expanded by incorporating park amenities around the detention pond and lighting was enhanced with original replica historic streetlights to shed light on previously dark corridors.

Project stakeholders have attested that the Phase 2/Phase 3 drainage improvements to the West Washington Street Watershed have had a transformative impact for flood mitigation and enhanced quality of life by providing a new getaway and destination point that can be admired.

City of Champaign

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