Incorporating Climate Change Projections

into Culvert Design

1

A project funded by the North Pacific Landscape Conservation Cooperative

18 May 2016

Determine how to incorporate the effects of climate change into WDFW’s culvert design and permitting processes.

Project Purpose

Provides design guidance for the protection of fish life and fish habitat.

Issues permits for the installation of culverts. Enforces regulations.

Designs culverts for its own lands and other clients. Reviews designs.

WDFW’s Role in Ensuring Fish Passage

4

Unimpeded fish passage is mandatory in Washington. Statewide effort to replace fish-passage barrier culverts. Climate change will result in higher (and lower) stream flows. Undersized culverts can become fish passage barriers. Until now, WDFW has lacked the capacity to address climate change in culvert design.

Why this Project Now

Jane Atha, Geomorphologist, WDFW

George Wilhere, Research Scientist, WDFW

Timothy Quinn, Chief Scientist, Habitat, WDFW

Lynn Helbrecht, Climate Change Coordinator, WDFW

Don Ponder, Engineering Section Manager, WDFW

Kevin Lautz, Hydrologist, WDFW

Ingrid Tohver, UW Climate Impacts Group

Jennie Hoffman, Adaptation Insight

Project Team

1. Assess climate sensitivity of current culvert design process.

2. Project changes in instream flow due to climate change.

3. Convert stream flow projections into stream channel width – an important culvert design parameter.

4. Develop approaches for applying findings in policy and practice.

Major Steps

8

14,000 known culvert barriers in database 35,000 estimated culvert barriers state-wide

A Severe and Urgent Issue

• Provides design guidance for the protection of fish life and fish habitat.

• Issues permits for the installation of culverts. Enforces regulations.

• Designs culverts for its own lands and other clients. Reviews designs.

WDFW’s Role in Ensuring Fish Passage

Geomorphic Approach to Culvert Design

• Emphasis on continuity of stream processes.

• "By measuring the channel width, one takes a measure of the watershed, its area and rainfall, its vegetation and substrate."

BFW

1.2*BFW + 2ft

Stream Simulation (<15 ft BFW)

BFW

No-slope (<10 ft BFW, gradient <3%)

Bankfull width (BFW) is a key parameter

12

Culvert Design

2011 2014

Width Matters

Width Matters

Projecting Future Changes in

Bankfull Width Due to Climate Change

15

Climate Change

Temperature Precipitation

Runoff

Streamflow

Channel Form

Culvert Size

Fish Passage Fish Habitats

winter peak flows spring peak flows

channel width

width

snow rain

Global Climate Models

future projections: temp. and precip.

Hydrologic model projects runoff

Estimate bankfull flow

Predict bankfull width

UW

WDFW

Modelling Process

Global Climate Models

• Projections from 10 independent models

• 1 global emissions scenario: moderate A1B

• Down-scaled and bias-corrected for PNW

• Climate projections for 2 future time periods

2030−2059 (2040s) 2070−2099 (2080s)

Hydrological Model

Temperature

Precipitation

Global Climate Model Outputs

19

Variable Infiltration Capacity Model (VIC)

Future Mean Daily Flow

Hydrological Model

Temperature

Precipitation

Historical Weather Data

20

Variable Infiltration Capacity Model (VIC)

Historical Mean Daily Flow

Validation of Flow Projections

Ratio of 100-year Flood to Mean Annual Flood

VIC USGS HCDN

Q100 /

Q2

Stream Gauge Station

VIC Grid Cells

1/16 degree ≈ 5 x 7 km ≈ 12.6 mi2

5,270 grid cells in Washington

22

VIC Output

1/16 degree ≈ 5 x 7 km ≈35 km2

≈ 13.5 mi2

5,270 time series of mean daily flow

050

100

150

200

250

300

350

45_53125_-122_21875

years

cfs

1 2 3 4 5 6 7 8 9 10

Years

2 future periods for 10 models

historical period 1916−2006

2030−2059

HADGEM1

CFS

45.53125, -122.21875

200

300

400

500

600

Return Interval (years)

Ret

urn

Leve

l (cf

s)

1.2 2.0 3.0 5.0 10.0

Estimating Bankfull Discharge (QBF)

45.53125, -122.21875

2030−2059

HADGEM1

Bankfull Flow Recurrence Intervals

Q1.5

Q1.5

Q1.2

Q1.5

Q1.4 Q1.2

200

300

400

500

600

45_53125_-122_21875

Return Interval (years)

Ret

urn

Leve

l (cf

s)

1.2 2.0 3.0 5.0 10.01.5

45.53125, -122.21875

2030−2059

HADGEM1

QBF

Estimating Bankfull Discharge (QBF)

Bankfull width = aQb

Q = QBF = Q1.2 or Q1.4 or Q1.5

Predicting Bankfull Width

a and b determined empirically r2 = 0.76 to 0.87

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% Change in Bankfull Width

Projected Mean Daily Flow

2030 - 2059 2070 - 2099

Projected Historical

Mean Daily Flow 1916 - 2006

Predicted Bankfull Width 2030 - 2059 2070 - 2099

Predicted Historical

Bankfull Width 1916 - 2006

Predicted % Change in

Bankfull Width 2030 - 2059 2070 - 2099

Estimated Bankfull Flow 2030 - 2059 2070 - 2099

Estimated Historical

Bankfull Flow 1916 - 2006

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• Where?

• How large?

• How likely?

Projected Changes in BFW

Mean % Change BFW: 2070 − 2099

-20 – -14 -14 – -9 -9 – -4 -4 – 0 0 – 4 4 – 8 8 – 12 12 – 16 16 – 24 24 – 38

30

Global Climate Models

future projections: temp. and precip.

Hydrologic model projects runoff

Estimate bankfull flow

Predict bankfull width

Dealing with Uncertainty

Uncertainty

Uncertainty

Uncertainty

+

+

r2 > 0.75

10 GCMs

Uncertainty in 2070 − 2099

Number of models projecting >BFW: 0 5 10

Incorporating Climate-based

Bankfull Width Projections into Culvert Design

33

Chehalis River Basin

Culvert Projects in Chehalis River Basin

Polson Camp Road on Big Creek

Area = 1.85 mile2 BFW ≈ 12 ft

Area weighted average of

QBF1

QBF2

QBF3

QBF4

11 bankfull widths

QBF2

QBF4

QBF1

QBF3

A1

A3

A2

A4

Perc

en

t C

han

ge in

BFW

b

etw

een

N

ow

an

d 2

07

0-2

099

Projections of 10 models

% Change in Bankfull Width

Mean % Change

• mean projected change in BFW = +9.5%

• range of projected change in BFW between -6 and 34%

• 7 of 10 models project an increase in BFW

• 6 of 10 models project an increase greater than 5%

BFW

1.2*BFW + 2ft

Stream Simulation (<15 ft BFW)

BFW

No-slope (<10 ft BFW, gradient <3%)

Bankfull width (BFW) is a key parameter

38

How Engineer might use it

How Engineer might use it

Pro

ject

ed

Fu

ture

Ban

kfu

ll

Wid

th in

2

07

0-2

09

9 (

ft)

Current BFW

• current BFW = 12.2 ft

Mean Future BFW

• mean % change in BFW = 9.5%

• mean future BFW = 13.3 ft

• 6 of 10 models project an increase greater than ½ ft

Cli

mate

A

dap

ted

C

ulv

ert

W

idth

s f

or

20

70

-20

99 (

ft)

How Engineer might use it

Stream Simulation Culvert

• mean future BFW = 13.3 ft

• “climate adapted” culvert width = 18 ft

climate adapted

• current BFW = 12.2 ft

• culvert width = 17 ft

not climate adapted

Construction Cost of Wider Culvert Assume:

• one-lane, gravel road • stream simulation design • round, steel culvert • and many other details

BFW (ft)1.2 x BFW

+ 2 ftCulvert

Diam (ft)

Est. Project

CostCost

Increase% Cost

Increase12.2 16.6 17 $117,030 $0 0 13.3 18.0 18 $124,125 $7,095 6 13.8 18.6 19 $144,303 $27,273 23

Potential Costs of Undersized Culvert

• Increased maintenance

• More repairs

• Early replacement

• Damage to aquatic resources

Not yet quantified

What is a Manager to do?

• Risk how bad (cost or damage) how likely (uncertainty)

• Weigh Trade-offs pay more now, or maybe pay a lot more later

• Manage Risk What risk is “actionable” ?

How Bad: Mean % Change BFW

-20 – -14 -14 – -9 -9 – -4 -4 – 0 0 – 4 4 – 8 8 – 12 12 – 16 16 – 24 24 – 38

44

How Likely: Model Agreement

Number of models projecting >BFW: 0 5 10

Actionable Risk: 2070-2099

How Bad

How Likely

actionable risk

Polson Camp Road Project

Actionable Risk: 2070-2099

How Bad

How Likely

actionable risk

Actionable Risk 2070 − 2099

Actionable Risk Mean % change in BFW ≥10% Models Projecting Increase ≥ 5

• Bankfull width is projected to increase in many watersheds due to climate change.

• Many culverts are at risk of being undersized.

• We now have a spatially-explicit, state-wide assessment of the magnitude and likelihood of change in bankfull width.

• We have developed a framework for addressing uncertainty inherent in climate change projections.

The Bottom Line

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2. Work with managers of WDFW lands to incorporate climate projections into culvert projects.

Next Steps for WDFW 1. Learn from collaboration on climate-adapted culverts in Chehalis Basin projects.

3. Continue to disseminate our results to organizations that replace or install culverts.

4. Explore development of voluntary guidance.

5. Explore funding opportunities to provide easier access to information for users.

Thank You

For more information: jane.atha@dfw.wa.gov