Bellevue Side Channels
An additional 1,700’ of side channel habitat gets added to Big Wood River! Outstanding news for spawning trout!
PROBLEMS AND LIMITING FACTORS AND HISTORY
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 handowner 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.
PROJECT GOALS & BENEFITS
The project is intended to increase flood conveyance capacity and improve fish habitat conditions by reconnecting floodplain side channels. The design plan for this project was informed by the geomorphic assessment and conceptual design plan for the Big Wood River from the Broadford Road Bridge downstream to the southern extent of the Riverside Subdivision (Biota 2019) and the Big Wood River Atlas (Cardno 2020).
The following project objectives were identified based upon existing site conditions, previous geomorphic assessment, land use constraints, and fluvial system potential.
1. Reconnect and improve floodplain side channels to increase flood flow conveyance capacity.
2. Stabilize localized bank erosion with bioengineering techniques.
3. Implement treatments that reduce, or leave unaltered, the flood hazard proximate to development.
4. Identify self-maintaining treatments that maximize the ecological values of the Big Wood River.
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Specifically, the proposed restoration design plan is to restore floodplain connectivity and improve flood conveyance capacity by side channel excavation, installing an apex jam structure integrated with an existing log jam structure and constructing bank stabilization treatments incorporating bank regrading, large wood, and bioengineered revegetation treatments.