From the Panhandle

Sandpoint’s Streets Go Green

By Cate Huisman, 6-10-11

	Sandpoint's green Second Avenue under construction.

First we had green trees, then we had “green” buildings, and now, Sandpoint is about to have the first green streets in Idaho.

Green streets are engineered to deal with storm water at its source instead of letting it run off to pollute our lake. There are several approaches to this: We can reduce the amount of area that creates runoff, filter contaminants out of the water on site, and/or plant trees along our streets, explains Public Works Director Kody Van Dyk.  Narrowing the street reduces runoff, and swales along the side of the road help filter runoff—although Sandpoint’s high water table and highly impermeable soil make this a particular challenge. The trees help by absorbing water through their roots as well as by catching some rainwater on their leaves, from which it evaporates without ever hitting the ground.

Second Avenue, which will be the first green street completed in the city, will have slightly widened sidewalks and concrete-surrounded depressed planters between the sidewalk and the street. Water will flow off the street into the planters, which are filled with “structural soil”—mostly rock and some dirt, with a special hydrogel that binds the two together. This will provide a place for tree roots to grow under the sidewalk and prevent the heaving that is common in other areas of town with street trees.

The other two streets scheduled for greening—portions of Sixth Avenue and Washington Street—will look more typical, with a depressed strip between the sidewalk and the street planted with native plants. This will collect stormwater, but again, because Sandpoint’s soil is so impermeable, perforated pipe under these strips will collect runoff that will not otherwise percolate through the soil.

Van Dyk’s department will monitor the quality of water coming off these streets into Sand Creek and Chuck Slough, and, if these design features do what they’re supposed to do, they’ll be incorporated into other streets as upgrades are scheduled and funding becomes available.

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