a method used to evaluate potential effects on flooding

Using HECUsing HEC--RAS to Project Effects RAS to Project Effects of Increased Flooding with the of Increased Flooding with the

Placement of Large Woody Placement of Large Woody DebrisDebris

Jeff Burkey Jeff Burkey –– King County DNRPKing County DNRP

Project Team: Dan Eastman, Doug Chin, John Bethel, Project Team: Dan Eastman, Doug Chin, John Bethel, Meredith RadellaMeredith Radella

(May 2008)(May 2008)

Increasing Roughness Suggests Increasing Roughness Suggests Flows may seek alternative Flows may seek alternative

paths?paths?



(May 2008)(May 2008)

Effects to stream flooding with Effects to stream flooding with the introduction of solid phase the introduction of solid phase matter in large quantities of matter in large quantities of

CCxxHHxxOOxx??



(May 2008)(May 2008)

A Method Used to Evaluate A Method Used to Evaluate Potential Effects on Flooding with Potential Effects on Flooding with the Placement of Large Woody the Placement of Large Woody

MaterialMaterial


Project Team: Dan Eastman, Doug Chin, John Bethel, Project Team: Dan Eastman, Doug Chin, John Bethel, Meredith Radella, Jeff BurkeyMeredith Radella, Jeff Burkey

(May 2008)(May 2008)

Tributaries in basin with projectTributaries in basin with project

Add complexity and you might Add complexity and you might get thisget this

Examples of complexityExamples of complexity

Site LocationSite Location

Site ConditionsSite Conditions

•• 26 Square Miles26 Square Miles•• Land Use Land Use ––

–– AgriculturalAgricultural–– ResidentialResidential–– Forest ManagementForest Management–– CommercialCommercial

Relevant Site ConditionsRelevant Site Conditions

•• Subbasin Flow RatesSubbasin Flow Rates•• River Stage ConditionsRiver Stage Conditions•• TopographyTopography•• Expected flow pathsExpected flow paths

Translate to Model SetupTranslate to Model Setup

•• Boundary ConditionsBoundary Conditions•• Landscape roughness Landscape roughness •• Channel GeometryChannel Geometry•• Overland GeometryOverland Geometry

Upstream Boundary ConditionsUpstream Boundary Conditions

Newaukum Creek Peak Annual Flow FrequencyUSGS 12108500

(Water Year 1945 - 2006)

Return Period (years)

1 10 100

Pea

k A

nnua

l Flo

w R

ate

(cfs

)

0

500

1000

1500

2000

2500

3000

Observed(Gringerton PP)17BUpper/Lower CI

2600 cfs

Does this flow create a steady-state condition?

Not likely…



(Water Year 1945 - 2006)


1 10 100

Pea

k A

nnua

l Flo

w R

ate

(cfs

)

0

500

1000

1500

2000

2500

3000


2600 cfs


Not likely…

Newaukum Creek February 1996 Storm EventAssumed Steady state

Time (hourly increments)

2/4 2/5 2/6 2/7 2/8 2/9 2/10 2/11 2/12 2/13 2/14 2/15

Hou

rly M

ean

Flow

Rat

e (c

fs)

0

500

1000

1500

2000

2500

3000



(Water Year 1945 - 2006)


1 10 100

Pea

k A

nnua

l Flo

w R

ate

(cfs

)

0

500

1000

1500

2000

2500

3000


2600 cfs


Not likely…



2/4 2/5 2/6 2/7 2/8 2/9 2/10 2/11 2/12 2/13 2/14 2/15

Hou

rly M

ean

Flow

Rat

e (c

fs)

0

500

1000

1500

2000

2500

3000

Newaukum Creek February 1996 Storm Event(USGS 12108500)

Time (hourly increments)2/4 2/5 2/6 2/7 2/8 2/9 2/10 2/11 2/12 2/13 2/14 2/15

Hou

rly M

ean

Flow

Rat

e (c

fs)

0

500

1000

1500

2000

2500

3000

50 hrs20 hrs


2600 cfs


Not likely…



2/4 2/5 2/6 2/7 2/8 2/9 2/10 2/11 2/12 2/13 2/14 2/15

Hou

rly M

ean

Flow

Rat

e (c

fs)

0

500

1000

1500

2000

2500

3000

Newaukum Creek February 1996 Storm Event(USGS 12108500)

Time (hourly increments)2/4 2/5 2/6 2/7 2/8 2/9 2/10 2/11 2/12 2/13 2/14 2/15

Hou

rly M

ean

Flow

Rat

e (c

fs)

0

500

1000

1500

2000

2500

3000

50 hrs20 hrs

Downstream Boundary ConditionsDownstream Boundary Conditions

191000 192000 193000 194000 195000 196000

145

150

155

160

Plan 03

Main Channel Distance (ft)

Ele

vatio

n N

AV

D88

(ft)

Legend

WS PF 1

WS PF 2

WS PF 3

WS PF 4

WS PF 5

Ground

ROB

40.4

20

40.4

729*

40.5

25

40.5

913*

40.7

62

Green River Mainstem

Estimates of Over Bank RoughnessEstimates of Over Bank Roughness

USGS n = 0.10Newaukum Over bank area

(n = 0.10)

Model GeometryModel Geometry

•• Existing LiDARExisting LiDAR•• Existing LiDARExisting LiDAR•• Conducted SurveyConducted Survey•• Composite (LiDAR + Composite (LiDAR +

Survey) TINSurvey) TIN

•• Existing LiDARExisting LiDAR•• Conducted SurveyConducted Survey

Expected Flow PathsExpected Flow Paths

•• Main ChannelMain Channel•• Main ChannelMain Channel•• Over bank pathsOver bank paths

HoweverHowever……

LiDAR shows a Historical DeltaLiDAR shows a Historical Delta

Existing Conditions Model DesignExisting Conditions Model Design

•• CrossCross--section section alignmentalignment


•• Divide not absoluteDivide not absolute


•• Divide not absoluteDivide not absolute•• Flows Exchange Flows Exchange

between reaches at between reaches at higher flood flow higher flood flow ratesrates


•• Divide not absoluteDivide not absolute•• Flows Exchange Flows Exchange

between reaches at between reaches at higher flood flow higher flood flow ratesrates

•• Low point in divide Low point in divide shown with red arrowshown with red arrow

Numerical Representation of Placed Numerical Representation of Placed Large Woody MaterialLarge Woody Material

•• Concept Abstracted Concept Abstracted from Tim Abbyfrom Tim Abby

•• Multiple vertical Multiple vertical obstructions allows obstructions allows flow around, and overflow around, and over

•• Modified to assume Modified to assume 1010--percent porositypercent porosity

•• Paired CrossPaired Cross--sections sections with obstructions.with obstructions.

0 100 200 300154

156

158

160

162

164

166

168

Plan 39River = Mi ddl eNewauk Reach = R

Stati on (ft)

Elevation (ft)

.1 .04 .1

An example of Placements of Large An example of Placements of Large Woody MaterialWoody Material

164.15 118.42

96.93* 88.79*

62.34

948.89

902.47

872.16 849.39 822.97

798.44 765.06

681.22 653.30

639.26

609.39 583.85

564.95 547.59

484.19 467.29

452.33

422.82 394.28 376.383*

367.63

343.03

311.81

278.80

261.33

206.47 196.68*

186.89

Full 5Jam 100yr

Legend

Ground

Levee

Bank Sta

Ground

Ineff

Design of models are dependant on Design of models are dependant on the questions askedthe questions asked

•• Is there an increase in over bank flooding in the pasture Is there an increase in over bank flooding in the pasture area as a result of the proposed LWM?area as a result of the proposed LWM?

•• With the landscape berm in place, what is the expected With the landscape berm in place, what is the expected 100100--year water surface elevation of the impoundment year water surface elevation of the impoundment area?area?

•• At what frequency is the over bank flooding expected to At what frequency is the over bank flooding expected to occur in the proposed impoundment area?occur in the proposed impoundment area?

•• What are the projected benefits gained from this project What are the projected benefits gained from this project design with respect to flooding extents?design with respect to flooding extents?

Design Methods for Design Methods for Simulating Flow ExchangesSimulating Flow ExchangesExisting Conditions Landscape Berm: Full Containment

Design Methods for Design Methods for Simulating Flow ExchangesSimulating Flow ExchangesLandscape Berm: Short Loop Reach

Landscape Berm: Extend Cross-sections

Projection of FloodingProjection of Flooding

Results attempt to Results attempt to answer the flowing answer the flowing questions:questions:

•• Where will flooding Where will flooding occur?occur?

•• At what flow rates will At what flow rates will flooding occur?flooding occur?

•• How deep will How deep will flooding be?flooding be?

Results are under review.

Thank you!Thank you!

Photos shown were taken by Photos shown were taken by Project team membersProject team members

a method used to evaluate potential effects on flooding

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