Middle Fork Snoqualmie River Corridor Planning Process Chase - - PowerPoint PPT Presentation

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Middle Fork Snoqualmie River Corridor Planning Process Chase - - PowerPoint PPT Presentation

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Middle Fork Snoqualmie River Corridor Planning Process Chase Barton, Snoqualmie Basin Supervisor Engineer October 24, 2018 Department of Natural Resources and Parks Water and Land Resources Division River and Floodplain Management Section

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Middle Fork Snoqualmie River

Corridor Planning Process

Chase Barton, Snoqualmie Basin Supervisor Engineer

October 24, 2018

Department of Natural Resources and Parks Water and Land Resources Division River and Floodplain Management Section

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Agenda

  • Corr

rrido dor r Planning nning Proces rocess s Over vervi view w and d St Status us

  • Proj

roject ect Goals

  • Existing

ting Condi ditions ions

  • Pot
  • tential

ntial Tools

  • Ne

Next St Steps ps

2

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Middle Fork Snoqualmie River Corridor Planning Process

  • Existing conditions

Complete

  • Goals and objectives

Complete

  • Public input on existing conditions

Here now!

  • Draft Capital Investment Strategy

Winter 2018 - 2019

  • Public input on potential solutions

Spring 2019

3

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Middle Fork Snoqualmie River Corridor Plan Goals

  • Goal 1: Reduce risks from flood and channel migration

hazards

  • Goal 2: Reduce long-term repetitive costs of flood hazard

management

  • Goal 3: Integrate sound and sustainable flood hazard

management projects/practices that benefit the natural environment to the degree practicable

  • Goal 4: Incorporate stakeholder and community input

into the Corridor Planning process in an equitably and socially just manner

(Approved by King County Flood Control District Motion No. FCDECM2018-03.1)

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Mason Thorson Ells, January 1990 Mason Thorson Extension, January 2015

Existing Conditions: Flood Protection Facilities

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Existing Conditions: Multiple Types of Hazards

  • Flooding
  • Deep and/or

fast flowing flood waters

  • Channel

migration and erosion

Middle Fork Snoqualmie River downstream of the Mount Si Bridge, 1959 6

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  • Flooding from the Middle

Fork Snoqualmie River impacts areas in both the City of North Bend and unincorporated King County

  • Areas of flooding from the

Middle Fork and South Fork Snoqualmie Rivers are largely distinct

Existing Conditions: Flood Hazards

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  • Flooded areas with greater

than 3 feet of flooding and/or

  • Flows faster than 3 feet per

second

Existing Conditions: Flood Hazards

Mainstem Snoqualmie River near Fall City, January 2009 8

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Infrastructure at Risk Due to Flood Hazards

Mason Thorson Ells, January 2015

  • Flooded neighborhoods and homes
  • Flooded roadways

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River channels can move,

  • r migrate, across their
  • floodplains. This can
  • ccur:
  • gradually
  • as an abrupt shift
  • over many years or

during a single flood event

Channel Migration Hazards

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Infrastructure at Risk Due to Channel Migration Hazards

Downstream of Mason Thorson Ells Levee, January 2009 11

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Areas as of

  • f Co

Common mmon In Interest erest Ex Exerc ercise ise

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Next Steps

  • Prioritize problem areas
  • Evaluate applicability of

risk reduction tools

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How well does a tool or suite of tools address Corridor Plan Goals?

  • How well does it reduce flood risks?
  • Is it cost effective?
  • How well does it improve ecological conditions?
  • Is it consistent with what the community and other

stakeholders want?

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Risk Reduction Tools

Rebuild or add height to an existing levee. Strategically place wood in the river to protect a bank or divert flows away from an area. Rebuild or replace a bridge or culvert to increase flows under or through. Lift a structure so the first floor is above flood waters. 15

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Risk Reduction Tools

Construct a new levee set farther away from the river and remove the existing levee. Remove an existing levee to restore floodplain processes. Monitor levees and revetments and repair damages to maintain current levels of protection. Remove gravel from the river channel to increase flow conveyance in the channel. 16

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Problem Solving Exercise

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Preliminary Timeline

Outreach to residents and other stakeholders Draft Middle Fork Capital Investment Strategy (CIS) Gather feedback on the draft CIS Update the CIS based on feedback

Fall 2018

Winter 2018 -2019 Spring 2019 Early Summer 2019

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Questions?

Chase Barton Snoqualmie Basin Supervising Engineer 206-477-4854 chase.barton@kingcounty.gov www.kingcounty.gov/rivers