Cities around the world are restoring urban streams that had previously been decked or canalized, often with a roadway on top.
Streets-to-streams projects are transformative, presenting an opportunity to implement high-performance water quality management practices, while creating inviting and active public spaces. These spaces can become destinations in themselves, giving people in cities access to a new kind of waterfront.
Existing Conditions
The street, initially designed as a primary corridor aligned with a stream, has been decked over or channelized, often into a large subsurface pipe or aqueduct.
Substandard or missing sidewalks and no bike facilities create an inhospitable and dangerous environment for all users. Vehicles routinely park on poorly defined curbs. Speeding is a consistent issue.
Poor or depleted pavement quality along the flow line contributes to frequent ponding, further degrading pedestrian accessibility and pollutant accumulation.
The complete absence of tree canopy contributes to a local heat island effect.
Stormwater is directed entirely to the graywater system, resulting in regular overflows that send untreated runoff into the regional watershed, degrading water quality and putting greater strain on offsite treatment facilities.
Recommendations
1Restore the natural drainage swale and daylight the stormwater flows to fully express water in the streetscape, provide street beautification, and create usable public space.
Large stormwater facilities create space for innovative or high-performing stormwater facilities, including water quality treatment, fish and amphibian habitat restoration, and recreation space. Design facilities for the appropriate context, including local flora, drought risk, and community needs. Continue streams through crossings and connect with regional waterways.
2While upstream flow is directed into the median stormwater stream, local street runoff is directed into curbside green infrastructure, including curb extension planters and pervious surface on the raised bikeway. Subsurface infrastructure can direct overflow into the median drainage swale.
3Direct gutter flow along raised crossings to appropriately sized inlets to mitigate risk for pooling; cover inlets with metal lids to prevent wheels from entering planters.
4Pervious pavement on the bikeway infiltrates sheet flow from the sidewalk and water that falls on the bikeway. Raised cycle tracks, with raised crossings, can provide comfortable bicycling conditions for all ages and abilities when properly designed (refer to the Urban Bikeway Design Guide for additional guidance), while performing stormwater management functions and creating a more active and inviting public space.
5Trees can be planted either between the bikeway and pedestrian path, or between the bikeway and street. Design tree pits or wells to mitigate risk of pedestrians or bicyclists entering accidentally, as well as risk of bicycle pedals striking raised curbs, lips, or short fencing. Tree grates can be used to protect soil against compaction.
Ensure trees planted in sidewalk/planting zone tree wells have sufficient subgrade root space to reduce the likelihood of broken or launched sidewalks. Select trees so that branch height or width does not invade either the pedestrian path or bikeway.
Potential GSI Features
Median
Travel Lanes/Roadbed
Curb Extensions
Planting Zone
Bikeway / Shared Use Path
