Ri River erbend bend Levee ee Se Setb tback k and nd - PowerPoint PPT Presentation

Ri River erbend bend Levee ee Se Setb tback k and nd Floodplain odplain Res estora toration tion Jon Hansen, Project Manager March 28, 2017 Department of Natural Resources and Parks Water and Land Resources Division River and Floodplain Management Section

Riverbend Levee Setback and Floodplain Restoration Riverbend Elliott Reach Restoration and Mitigation Design Update May 2014

Site and Reach Overview

Neighborhood Flooding January 8, 2009 7870 cfs @ Landsburg

Project Goals • Improve quality, quantity and sustainability of salmonid spawning and rearing habitat • Reduce flood and erosion risks to people, property and infrastructure • Accommodate public use consistent with future ecological conditions on site • Balance flood and ecological benefits and other objectives with project costs

Potential Project Elements Levee Removal Existing Levee New Setback Floodplain Excavation Fill Placement New Channel (Perm, seasonal, ephem)

Alternatives Considered • Six Alternatives with combination of elements • Alternative 1 most aggressive – Full removal and setback of left bank levees and Herzman – Largest benefit for flood and habitat – Would require NEW right bank protection – High Cost and not feasible in near term • Alternative 6 Smallest scale – Limited to former Mobile Home Site – Very limited habitat, but some flood hazard reduction benefits – Easiest to implement, but not attractive to grant agencies

Alternative 6

Evaluation Process • Compare Alternatives – Benefits, Costs, Risks and fit with long term – Aided by modeling, studies and analysis • Based on Goals – Refined by objectives with metrics for each – Specific enough to differentiate – Provides enough info to make informed decision – BUT there is still uncertainty with natural processes • Selection made via “Gate” process

Evaluation Matrix

Evaluation Matrix

Evaluation Matrix

Preferred Alternative

Alternative 4 – Simple Overview

Schedule • June 2015 – Project Initiation • July 2015 – Data Collection and Analysis begins • Winter 2016 – Alternative Analysis • March 2017 – Preliminary design milestone/RCO • Fall 2018 – Final Plan complete • Summer 2019 – construction target

Potential Pond Modification