Here's where water in the gutter enters a pipe, which leads to the rain garden. It's necessary for residents to keep these clear of debris. It seems doubtful this small opening can handle much of the stormwater from a block of street.
During the same resurfacing project, grates were installed to drain runoff from some sidewalks and driveways into rain gardens.
The City now has a terrace rain garden program--the City will pay 75% of the costs of installing and planting a rain garden on your terrace, provided the spot meets certain standards. More details here.
Madison and the USGS also conducted research to test how well prairie vegetation, when planted in rain gardens, helped ground to absorb the water. It turns out that when you plant the proper plants, they are very efficient in draining water into the ground. More.
In my opinion, this program is a step in the right direction, but not nearly enough. Each rain garden is isolated, and the grates where water enters the garden can easily become clogged. In many cases, the terraces in Madison are not large enough--they should be enlarged to create a chain of interconnected pools.
Madison needs more than a few rain gardens per street--we need "green streets."
Unlike Madison, the City of Portland "benefits from comprehensive thinking and planning. In Portland, urban design, multi-modal transportation systems, watershed health, parks, open spaces, and infrastructure systems are all enhanced by integrated planning, design, and budgeting."
Portland is a leader in using strategies that manage stormwater runoff, enhance community and neighborhood livability, and strengthen the local economy."
In Madison, it's one band-aid at a time. Stormwater projects are planned with little thought to what else could be done upstream to reduce the problem.
Siskiyou Street in Portland, Oregon
"A street that uses vegetated facilities to manage stormwater runoff at its source is referred to as a Green Street."
In the Siskiyou Green Street project below, the street was narrowed, creating larger terraces for bigger rain gardens.
Photo: Kevin Robert Perry.
Plan for the Siskiyou Green Street Project. Click to enlarge.
"Stormwater runoff from 10,000 square feet of NE Siskiyou Street and neighboring driveways flows downhill along the existing curb until it reaches the 7-foot wide, 50-foot long curb extensions. An 18-inch wide curb cut allows this water to enter each curb extension. Once water is within the landscape area, the water is retained to a depth of 7 inches by a series of checkdams."
"Depending on the intensity of a rain event, water will cascade from one "cell" to another until plants and soil absorb the runoff or until the curb extensions reach their storage capacity. The landscape system in place infiltrates water at a rate of 3 inches per hour."
If a storm is intense enough, water will exit the landscape area through another curb cut at the end of each curb extension and will flow into the existing [storm sewer] street inlets. With the new stormwater curb extensions now in place, nearly all of NE Siskiyou’s annual street runoff, estimated at 225,000 gallons, is managed by its landscape system. In fact, multiple simulated flow tests have shown that the curb extensions at NE Siskiyou Street have the ability to reduce the runoff intensity of a typical 25-year storm event by 85 percent.
"Where communities struggle with ever-increasing impervious areas and degraded water quality, these simple landscape approaches can have a measurable positive impact." Source.
The project had benefits in addition to stormwater--beauty, calming of traffic, community education about water quality, and community spirit.
"The success of neighborhood stormwater projects like the NE Siskiyou Green Street is dependent on community involvement. The residents were active participants in the design process. Multiple "street side chats" were conducted during the summer of 2003 to determine how much parking to remove and what planting schemes they desired, as well as to answer any questions and address any concerns."
"In a unique partnership, the City and the neighborhood residents have agreed to share responsibilities in maintaining the landscaped stormwater curb extensions."
Sunset Village would be an ideal place to try the Siskiyou plan
- Low traffic & low residential density
- Residents already love their stream and want to restore it to health
- Serious stormwater problems downstream need solutions (Greenway erosion & University Ave flooding)
- Lack of curbs means lower expense modifying streets
- Gradual slopes in neighborhood are friendly to rain gardens.
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More photos from Portland.