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How to Rebuild a River

October 1, 2010

Earthmovers spread river rock in a newly constructed channel defined by meandering tubes of tan-colored coconut matting wrapped around dirt and rock. Silver Bow Creek is in a temporary channel at the foot of the railroad tracks at the back of the site.

Earlier this week I got in touch with Joel Chavez, the Montana Department of Environmental Quality (DEQ) man in charge of effecting the reconstruction of the Clark Fork River. He’s got crews working now on a section of the tributary Silver Bow Creek where it runs through Durant Canyon, not far upstream from Opportunity. Chavez was kind enough to give me a tour of the Durant Canyon project and several recently completed construction sites so I could see what river reconstruction looks like from the ground up.

Soil-removal site. The top 13 feet of earth is contaminated heavily enough to merit removal.

It looks like a construction site.

The first step is to remove soils contaminated with heavy metals and arsenic. In the photo at right, you can see a cross-section of a dredge site where workers are having to remove soil 13 feet deep to get to dirt that’s clean enough to leave in place.

The dirt that goes is freighted on trains or trucked to the BP-ARCO Waste Repository site at Opportunity.

The remaining pit will be backfilled with donor soil dug up from a state-leased property nearby, and pictured below. When the state is done digging donor soil from the property, that site too will be recontoured and replanted with groundcover to mask the scar.

Donor soil dig site.

Eventually, the construction site at top will be planted with dozens of native seedlings, the creek will be shunted into its new channel, and with a little luck from the weather, in a couple of years it will look like the site below, an upstream stretch of Silver Bow that Chavez’ crews have already completed.

The coconut mats are designed to last about a dozen years and then biodegrade, and somewhere along the line the reconstructed riverbed is expected to give way to wherever the river decides it wants to go. This, to me, is one of the most interesting aspects of the reconstruction, a concept called “engineered failure.” In other words, the reconstructed riverbed is designed not to be a permanent, unadjustable structure, but as a nudge to the river toward engineers’ best guesses at how it wants to “behave.”

Recently reconstructed section of Silver Bow Creek upstream of the Durant Canyon restoration site.

Aside from the channel, the crews also grade a floodplain, wider at some points, thinner where it impinges a railroad or road, and eventually the river will find its own course within that floodplain.

The other thing I learned that struck me was that high nutrient loading in the creek—a result of imperfect wastewater treatment upstream in Butte—despite being universal acknowledged as bad from a water-quality perspective (it contributes to algae blooms, which suck oxygen out of the water, which is bad for fish), is actually a short-term good thing for river restoration on Silver Bow Creek, because the nutrients—fertilizer, basically—help the new vegetation get established more quickly.

So keep crapping, Butte. We need it downstream.

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