How to Mend a River

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The East Gallatin River at Story Mill Community Park

The East Gallatin River at Story Mill Community Park. Photo by Christi Cooper-Kuhn.

The East Gallatin River is the heart of the east side of the Gallatin Valley. But after 150 years of agriculture and development, this river system has taken a bit of a beating. That’s the case at the Story Mill Community Park in north Bozeman, where the East Gallatin flows for half a mile just before its confluence with Bozeman Creek.

History

This soon-to-be city park has a long history, including Nelson Story’s famed flour mill, a stockyard, rendering plant, depot, ranch, and most recently, a trailer park.

In building these amenities over the last century, the river was also impacted. Concrete and metal rip-rap was placed along the banks—10 feet high in places—to prevent the river from moving or flooding. The East Gallatin’s floodplain was filled with several feet of dirt so the ground would be dry.

Click to enlarge.

Restoration

But this is all changing thanks to the restoration project currently underway at Story Mill Park. This restoration project is spearheaded by The Trust for Public Land, in partnership with the Greater Gallatin Watershed Council and others. Last year, restoration was completed on the East Gallatin River southeast of the Story Mill Spur Trail and Bozeman Creek south of E Griffin Drive. Right now, work is underway on the East Gallatin north of Griffin Drive.

Here, a one-acre floodplain on the north side of the river is being created, or rather re-created. Last month, heavy machinery excavated the dirt that was added to this area as fill material. The next step is to place erosion-control fabric over the exposed soil to reduce runoff and prevent invasive species while native vegetation grows in. The area will be planted with willow cuttings and seeds of riparian grasses and forbs.

floodplain

Newly re-created floodplain along the East Gallatin River. Photo by Kestrel Aerial.

This floodplain is engineered at the two-year flood level, which means that every year there is a 50-50 chance that it will fill with floodwater.

Clean Water

When this happens, fast-moving water from rain storms or snow melt will enter the floodplain at two access points from the East Gallatin River. The vegetation will create friction to slow the water down, reducing the chance of flooding downstream.

The water will then sit in the floodplain for hours or days, or longer. During this time, sediment particles from erosion and street runoff will settle out of the water. Nutrient pollutants like nitrogen and phosphorus from fertilizers will be absorbed by plants. So when the water re-enters the East Gallatin, it will be cleaner and healthier for fish, wildlife, and people.

To measure these benefits to water quality, Gallatin Stream Teams have been monitoring the East Gallatin River at Story Mill since 2013. Volunteers are measuring levels of nitrogen and phosphorus, collecting information about sediment and algae, and measuring stream flows to compare the health of the river pre-, during-, and post-restoration.

A Community Park

Finally, this re-created floodplain will include a public access for fishing and play in the East Gallatin River without contributing to erosion. This public access will tie in to the active part of the park—with a playground, sports fields, and more—off Bridger Canyon Drive. And all that added dirt that was removed from the floodplains? It’s going to be re-purposed to create the park’s play area.

 

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