Living With Fans Living With Fans –– Challenges of and Challenges of and Strategies for Rehabilitating Alluvial FanStrategies for Rehabilitating Alluvial FanStrategies for Rehabilitating Alluvial Fan Strategies for Rehabilitating Alluvial Fan Processes in Human Modified SettingsProcesses in Human Modified Settings

Presented by  Christina Presented by  Christina AvolioAvolio,,i l C li l C l

Glacier Creek, WA at old SR 542 bridge  Forest Falls Debris Flow, CA, 1999

Herrera Environmental ConsultantsHerrera Environmental Consultants

OutlineOutline Alluvial fan processes and land use

OutlineOutlineAlluvial fan processes and land use impacts

Restoration considerations in modified Restoration considerations in modified settings

Case study examples Case study examples

Lessons learned 

2 Emerald Lake, near Golden, BC (AGU blog post)

What are Typical Alluvial Fan What are Typical Alluvial Fan Chara teristi s?Chara teristi s?Characteristics?Characteristics?

Abrupt change in sediment transport capacity

Sedimentation

Flooding

Channel avulsions Channel avulsions

Bifurcated stream channels

3

channelsSource: National Academies Press 1996

Development Often Occurs in Alluvial Development Often Occurs in Alluvial Fans Posing Many RisksFans Posing Many RisksFans, Posing Many RisksFans, Posing Many Risks

1995 20001995 2000

4Alluvial fan in North Coastal Range of Venezuela. Photo courtesy of Reinaldo Garcia.

WatershedWatershed‐‐Scale Land Use Impacts to Alluvial Fan Scale Land Use Impacts to Alluvial Fan PPProcessesProcesses

Land Use ChangeLand Use Change Impacted ProcessImpacted Process Geomorphic Geomorphic Land Use ChangeLand Use Change

Logging

Impacted ProcessImpacted Process

Volume/ frequency of

ConsequenceConsequence

Slope instabilityLogging

Roads

Volume/ frequency of runoff (stormwater)

Frequency/timing of

Slope instability

Erosion

Development

Climate Change

Frequency/timing of sediment‐transporting 

eventsIncreased 

sediment  supply

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Landslides from clear‐cut logging, Lewis County, Seattle Times, 12/2007.

LocalLocal‐‐Scale Land Use Impacts to Alluvial Fan Scale Land Use Impacts to Alluvial Fan ProcessesProcessesProcessesProcesses

Land Use Land Use  Impacted ProcessImpacted Process ConsequenceConsequenceChangeChange

Channel 

Impacted ProcessImpacted Process

Sedimentation Sedimentation 

ConsequenceConsequence

AvulsionAvulsionrealignmentConfinementCl i

within drainage within drainage networksnetworks Conveyance/ Conveyance/ 

flood problemsflood problemsClearing

Loss of LWD recruitment

Increased flood Increased flood inundationinundation

Human/ property Human/ property exposure to exposure to 

hazardhazard

6

Sunset Creek alluvial fan flooding of SE 30th St in Bellevue, WA.

Problems with some approaches to Problems with some approaches to alleviating exacerbated fan processesalleviating exacerbated fan processes

Heavy focus on local scale solutions

alleviating exacerbated fan processesalleviating exacerbated fan processes

Heavy focus on local‐scale solutionsLocal‐scale solutions can neglect gwatershed processes  not sustainablesustainable

Frequent sediment removal can Frequent sediment removal canadversely affect stream ecology

7

Rehabilitation of Alluvial Fan ProcessesRehabilitation of Alluvial Fan ProcessesRehabilitation of Alluvial Fan Processes Rehabilitation of Alluvial Fan Processes can be key to achieving Watershed can be key to achieving Watershed 

R t ti G l !!R t ti G l !!Restoration Goals!!Restoration Goals!!

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Continuum Continuum of Pof Processrocess‐‐based Alluvial based Alluvial FFan an RR h bilit tih bilit ti AA hhRRehabilitation ehabilitation AApproachespproaches

Si l t R h bilit tSimulate fan 

processes

Rehabilitate fan 

processes

Process‐ based approach: processes processes

All natural solution

Bounded natural l ti

Fully engineered 

l ti

Solution continuum

9

solutionsolution continuum

Project ExamplesProject Examples

PROJECT 1:

Project ExamplesProject Examples

PROJECT 1: Glacier and Gallop Creeks(35 mi2)

Washington State Departmentof Transportation

Alluvial fan risk analysis

3

21

Upper SkagitPROJECT 2Hansen Creek (9 mi2) Upper Skagit 

Indian Tribe

Hansen Creek (9 mi2)

Alluvial Fan and WetlandRestoration

City of Bellevue

PROJECT 3Sunset Creek (1.4 mi2)

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City of ellevueStream Restoration, Flood‐Control, and Sediment Management

Project 1: Glacier and Gallop Project 1: Glacier and Gallop Creeks Creeks ‐‐ChallengesChallengesChallenges Challenges 

Scale: Mountainous/Small townScale: Mountainous/Small townScale: Mountainous/Small town Scale: Mountainous/Small town 

Land Use: logging, minor Land Use: logging, minor developmentdevelopment

Project Site

Relief: 10,000ftRelief: 10,000ft

Habitat: Key fish spawningHabitat: Key fish spawningy p gy p g

Process Challenges: Process Challenges: 

Maintain SR 542Maintain SR 542Maintain SR 542Maintain SR 542

Continued loggingContinued logging

Reduce sediment managementReduce sediment management

11

Reduce sediment managementReduce sediment management

Reduce flood/avulsionReduce flood/avulsion

Project 1: Glacier and Gallop Project 1: Glacier and Gallop Creeks Creeks ‐‐AnalysisAnalysis

Analysis tools = field, 

Analysis Analysis y ,

aerials, GeoHMS, FLO‐2D, Parker bed evolution (2004)

Watershed analysis

Debris floods, not debris flows common Failing levee notflows, common

Hazard and Risk Sensitivity Analysis

Failing levee not maintained

y

Artificial fan behind SR 542

Avulsion risk to hotel 

12

downstream of SR 542Evaluation of Glacier Creek avulsion risk

Continuum Continuum of Pof Processrocess‐‐based Alluvial based Alluvial FFan an RR h bilit tih bilit ti AA hhRRehabilitation ehabilitation AApproachespproaches

Si l t R h bilit tSimulate fan 

processes

Rehabilitate fan 

processes

Process‐ based approach: processes processes

All natural solution

Bounded natural l ti

Fully engineered 

l ti

Solution continuum

13

solutionsolution continuum

Project 1: Glacier and Gallop Project 1: Glacier and Gallop Creeks Creeks ––Approa h All Nat ral ( ith En ineerin )Approa h All Nat ral ( ith En ineerin )

Process Approach:

Approach = All Natural (with Engineering)Approach = All Natural (with Engineering)

Process Approach:  Could not alter upper watershed 

processes

Remove some structures

Natural fan process rehabilitation

Water Depth Water Depth Scenario 4Scenario 4

p

Design Solution:  Partial levee removal Partial levee removal

Phased elongation of SR 542 bridge span

C i t b l f i k d t tAggradation Aggradation Scenario 4Scenario 4

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Communicate balance of risk and cost to community

Scenario 4 Scenario 4 (blue = (blue = aggagg, , red = scour)red = scour)

Project 2 Project 2 –– Hansen Hansen Creek Creek ––ChallengesChallengesChallengesChallenges

Scale: Foothills/ AgriculturalScale: Foothills/ AgriculturalScale: Foothills/ AgriculturalScale: Foothills/ Agricultural

Land Use: logging, farming, Land Use: logging, farming, residentialresidential

Project Site

Relief: 4,000ftRelief: 4,000ft

Habitat:  Aquatic and TerrestrialHabitat:  Aquatic and Terrestrialqq

Process Challenges: Process Challenges: 

SR 20 downstreamSR 20 downstream SR 20 downstreamSR 20 downstream

Dredging and downstream Dredging and downstream floodingflooding

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Dredging HydromodificationsHydromodifications and and simplified habitatsimplified habitat

Project 2 Project 2 –– Hansen Hansen Creek Creek ––AnalysisAnalysisAnalysisAnalysis

Analysis tools = field, GeoHMS, FLO‐2D, Syvitski sediment

Watershed analysis

Erosive geology

Landslides and mass‐wasting common

Hazard and Risk Sensitivity AnalysisAnalysis

Future park land use

SR20 bridge = fan outlet

16

SR20 bridge   fan outlet

High suspended sediment –influence avulsion timing

Continuum Continuum of Pof Processrocess‐‐based Alluvial based Alluvial FFan an RR h bilit tih bilit ti AA hhRRehabilitation ehabilitation AApproachespproaches

Si l t R h bilit tSimulate fan 

processes

Rehabilitate fan 

processes

Process‐ based approach: processes processes

All natural solution

Bounded natural l ti

Fully engineered 

l ti

Solution continuum

17

solutionsolution continuum

Project 2: Project 2: Hansen Hansen Creek Creek ––Approach =Approach = BoundedBounded NaturalNaturalApproach = Approach = Bounded Bounded NaturalNatural

Process Approach:  Proposed Fan Cross Section

Acquire some fan property

Perimeter protectionp

Provide tools (LWD, reveg.) to jumpstart fan processes

Design Solution: 

Remove/notch levees

Grading  encourage avulsion pathways 

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Communicate fan evolution expectations Hansen Fan/Wetland 2 years after construction

Project 3: Sunset Creek Project 3: Sunset Creek ––ChallengesChallenges

Downstream Confinement

ChallengesChallenges Scale: Puget lowland, urban

Land Use: commercial, residential

Relief: 1,000ftProject Site

Habitat:  degraded aquatic

Process Challenges: g

Minimal stormwater control

Dredging and flooding Dredging and flooding

Confinement

Hydromodifications/

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Hydromodifications/ simplified habitat

Upstream Erosion

Project 3: Sunset Creek Project 3: Sunset Creek ––AnalysisAnalysisAnalysisAnalysis

Analysis tools = field, studies, HSPF, y , , ,HEC‐RAS, sediment supply/ transport

B lk di t l

Watershed analysis

Erosive geologyBulk sediment samples Stormwater retrofits

Hazard and Risk Sensitivity Analysis

Cannot remove buildings/roads in short‐term

Habitat imrovements must

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Hydraulic Analysis

Habitat imrovements must accompany reduced sedimentation/flooding

Continuum Continuum of Pof Processrocess‐‐based Alluvial based Alluvial FFan an RR h bilit tih bilit ti AA hhRRehabilitation ehabilitation AApproachespproaches

Si l t R h bilit tSimulate fan 

processes

Rehabilitate fan 

processes

Process‐ based approach: processes processes

All natural solution

Bounded natural l ti

Fully engineered 

l ti

Solution continuum

21

solutionsolution continuum

Project 3: Sunset Creek Project 3: Sunset Creek ––Approach = Fully EngineeredApproach = Fully EngineeredApproach = Fully EngineeredApproach = Fully Engineered

Process Approach:  Sediment Trap  during construction

Upstream ‐ Stormwatermanagement; stabilize sediment h t thot spots

Local concern for precedent –setting with acquisitionsetting with acquisition

Locally simulate fan processes

Design Solution Design Solution:  Maintainable sediment trap

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Install LWD and native vegetation

Monitor downstream reaches Sediment trap two years after 

construction

Lessons learnedLessons learned

Watershed process and evaluation

Evaluate upstream drivers before local design approach

Adapt rehabilitation strategies to land use and topographic settings

Don’t underestimate the role of suspended sediment

Manage expectations

Just because it hasn’t happened yet doesn’t mean it won’t…

Anticipate episodic flooding and sediment‐mobilizing events

Evaluate precedent‐setting once strategies involve property 

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p g g p p yacquisition

Monitoring likely required for engineered solutions

AcknowledgementsAcknowledgementsgg

Co‐author – Ian Mostrenko Herrera Co‐author – Ian Mostrenko, Herrera

Contributors –Mark Ewbank and Jeff Parsons, Herrera; Reinaldo Garcia HydroniaHerrera; Reinaldo Garcia, Hydronia

Project Sponsors – WSDOT

Upper Skagit Indian Tribe

Skagit County

City of Bellevue

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