CLIMATE CHANGE & EXTREME WEATHER PILOT PROJECT

Off ice of Strategic Planning and Projects Connecticut Department of Transportation

PROJECT BACKGROUND/SCOPE A

pril

2013

Dece

mbe

r 201

4

• Draft Report

• Criticality analysis

• Data collection

• Stakeholder Outreach

• Final Report

• Action Steps

• Data analysis

• Field reviews of structures

Sensitivity analyses of structures at a systems level

Northwest Connecticut chosen as study region • Historically susceptible to extreme weather events

Presented to peers

and stakeholders

STUDY STRUCTURES

6 FEET

20 FEET

• Started with 60 structures between 6 and 20 feet • 52 were chosen for full analysis

• Data collection and field review • Hydrologic and hydraulic evaluations • Criticality/vulnerability assessments

STUDY STRUCTURES

• Average structure age: 81 years • 34 study structures satisfy hydraulic design criteria

• 13 of those vulnerable to scour

• 18 study structures do not satisfy hydraulic design criteria

• 19 structures are critical, 14 satisfy do not satisfy hydraulic design criteria, 2 have adaptive capacity

METHODS

• The hydrologic calculations were performed for this project using the following methods: • Rational Method • SCS Unit Hydrograph • USGS Regression Equations

• Precipitation estimate data vs. Climate Projections • Used TP-40, Precip.net, StreamStats

METHODS

• Hydraulic Evaluations • Performance (Rating) curves for structures:

• Headwater depth vs. peak discharge

• Velocity vs. peak discharge

• Criticality/Vulnerability Assessments: • Criticality Matrix

• Criticality ranking for structures

ANALYSIS RESULTS

• Following slides are examples of:

• Results of performance curve calculations and

adaptive capacity analyses

• Results of Criticality/Vulnerability assessments

• Maps of study and structure areas

• Low, Moderate, and High Risk structures

0

2

4

6

8

10

12

14

16

18

20

0 500 1000 1500 2000 2500 3000 3500

HEA

DW

AT

ER

DEP

TH (

FT.)

PEAK DISCHARGE (CFS)

STRUCTURE NO. 02423HEADWATER DEPTH VS. PEAK DISCHARGE

Continuing with the example presented in Figure 2, a 2-inch or an approximate 24% increase in the 100-year, 24-hour precipitation would increase the current 100-year peak discharge estimate of 881 cfs by 366 cfs to 1,247 cfs (horizontal scale), a 41.5% increase. As illustrated by the rating curve, a 2-inch increase in precipitation would move the 100-year peak discharge estimate to slightly above the current 500-year peak discharge estimate of 1,221 cfs. The resulting headwater depth would increase by approximately 1.9-ft, from 6.9-ft to 8.8-ft (vertical scale).

OV

ERTO

PPIN

G B

EGIN

S

HW

/D =

1.5

FREE

BO

AR

D =

1 F

T.

100-

YEA

R D

ISC

HA

RG

E

INLE

TSU

BM

ERG

ED

500-

YEA

R D

ISC

HA

RG

E

100-year design headwater depth is below the depths at 1-ft freeboard and HW/D = 1.5, therefore structure satisfies headwater design criteria

CRITICALITY MATRIX

Very Low to Low Moderate Critical to Very Critical

1 2 3 4 5 6 7 8 9 10

Hydr

aulic

High adaptive capacity Moderate adaptive capacity Low adaptive capacity

No history of closure History of periodic closures Significant history of closure

Scour critical

Satisfies WSE criteria Adjacent to scour critical structures Does not satisfy WSE criteria

Spat

ial Outside FEMA flood zones Within 500 year FEMA flood zone Within 100 year FEMA flood zone

Low concentration of impervious surfaces

Moderate concentration of impermeable surfaces

High concentration of impermeable surfaces

Soci

al

Low ADT & V/C Moderate ADT & V/C High ADT & V/C

0-4 accidents 5 or more accidents Emergency route

Non-NHS, non-emergency route NHS route Emergency services cluster

Structure: 06712 Location: Watertown

Year Built: 1966 Criticality Ranking: 4

0

2

4

6

8

10

12

0 50 100 150 200 250 300 350 400

HE

AD

WA

TE

R D

EPT

H (F

T.)

PEAK DISCHARGE (CFS)

STRUCTURE NO. 02200HEADWATER DEPTH VS. PEAK DISCHARGE

100-

YE

AR

TP-

40 &

PR

EC

IP.N

ET

50

-YR

DI

SCHA

RGE

OV

ER

TO

PPIN

G B

EG

INS

HW

/D =

1.5

FREEBOARD = 1

INLET SUBMERGED50

-YE

AR

TP-

40 D

ISCH

ARG

E

100-

YE

AR

PR

EC

IP.N

ET

DIS

CHAR

GE

Criticality Score: 2

02200

Example: Little to No Adaptive Capacity

Criticality Score: 7

02315

Example: Significant Adaptive Capacity

Criticality Score: 8

05417

PROJECT FINDINGS

Factors related to Resiliency: • Velocity-erosion-scour impact

vulnerability and adaptive capacity • Many structures near end of their

service life may be more vulnerable • Hydraulic design methods of older

structures are unknown • Precipitation Estimates

• Precip.net vs. TP-40 • NOAA Atlas 14 will be used when

released • Precip.net estimates higher for less

frequent storm events (500, 100, 50 year)

Example of bridge scour, New Milford

PROJECT FINDINGS

• Keep data/tools up to date (rainfall, stream gage, regression equations)

• “Check” frequency discharge should be carefully examined

• Reassess hydrologic methods and practices with or in anticipation of release of NOAA Atlas 14

NOAA Atlas 14 not available yet for Connecticut

21

NEEDS / FURTHER RESEARCH

• Precipitation projections from climate models • Uncertainty in precipitation/discharge estimates vs.

uncertainty in climate change projections • Guidelines, examples and tools to conduct risk and

cost benefit analyses • Developing and integrating cost factors into criticality

assessments

NEXT STEPS

• Outline a plan/process to better incorporate risk assessment/life cycle cost-benefit analysis into hydraulic design and asset management

• Discuss regression equation update with USGS and seek funding • Re-establish statewide “hydrology committee” • Work with municipalities on context dependent adaptation

strategies and other tools for at-risk structures • Stay current with studies, best practices, guidance, and revisions

to FHWA’s Climate Change and Extreme Weather Vulnerability Assessment Framework.

THANK YOU

Project Contacts

Michael Hogan Michael.Hogan@ct.gov

David Elder David.Elder@ct.gov

Stephanie Molden Stephanie.Molden@ct.gov