Project 3: Bellevue Side Channel Enhancement - April 2023
An additional 1,700’ of side channel habitat gets added to Big Wood River! Outstanding news for spawning trout!
Project Goals and Benefits
We are breaking ground on another river restoration project this month! We will be reactivating and enhancing two historic side channels of the Big Wood River. This project is taking place on private property in Bellevue, just below the south end of the Howard Preserve. There will not be any preserve or trail closures during the restoration process.
Excavating and improving the side channels will encourage flood conveyance at lower flows, providing flood mitigation, reconnecting floodplain, enhancing natural fluvial processes, and providing habitat for trout and other wildlife species. Side channels offer vital complex spawning and rearing habitat for salmonid species and allow fish to escape high velocity flows. The upstream floodplain side channel inlet will incorporate a large woody debris jam, providing additional habitat cover and promoting channel stability. This project is the next step in a larger design to restore a mile-long stretch of the Bellevue reach of the Big Wood River. In 2020 the Land Trust completed a bank stabilization project above Howard Preserve, and in 2021 another side channel restoration project was completed at Lower Howard Preserve. The next step in the design will take place later this year on the District 45 diversion canal dam.
Problems and Limiting Factors
In this stretch of the Big Wood, residences and property owners have been trying to mitigate flooding impacts for decades with small-scale individual projects. Private landowners have incurred heavy costs caused by flood flows mostly due to land lost from erosion. One landowner next to the project area spent $119,562 due to damages of property from 2017 flood flows. Funds from this resident were spent on emergency bank protection and property reclamation work. Another neighboring landowner lost approximately 2 acres of developable land and spent $22,425 on emergency rip-rap to protect property in 2017. Immediately upstream of the Riverside Estates neighborhood is a tight meander geometry of the river that posed a threat to the Diversion 45 canal in 2017 and required emergency rip-rap for protection.
The Big Wood River Atlas identified the reach adjacent to the City of Bellevue as having the second largest FEMA floodplain width, yet being 44% covered in bank hardening treatments. It is apparent this stretch is prone to flooding, but is unable to experience lateral expansion. The active channel has shifted many times here, preventing stable riparian succession. The 2017 flood resulted in a heavy amount of sediment aggradation within project reach, limiting flood conveyance capacity and viable high flow refuge for trout.