Connecticut Department of Transportation

CLIMATE CHANGE & EXTREME WEATHER PILOT PROJECT

Off ice of Strategic P lanning and Projects

LITCHFIELD HILLS

Lake Waramaug, Warren/Kent/Washington

LITCHFIELD HILLS

• Northwest corner of Connecticut, historic, pastoral landscape at the foothills of the Berkshires (Appalachian range) • Population: 185,000 • Land area: 920 sq. mi. • Density: 206 people/sq. mi.

• Manhattan: 66,940 people/ sq. mi. • Economy: tourism, dairy farming,

manufacturing • Older transportation infrastructure

LITCHFIELD HILLS

Covered Bridge, Cornwall

LITCHFIELD HILLS

• Today’s roads follow path of many Native American trails:

• Northwest Path is similar to Route 44

• Berkshire Path

is like Route 7 • Old

Connecticut Path is similar to Route 6

STUDY STRUCTURES

• More than 135 structures were identified in the study area that met the review criteria

• Average structure age: 81 years • 52 Structures underwent hydraulic evaluations • 34 study structures satisfy hydraulic design criteria

• *13 of those vulnerable to scour due to velocity • 18 study structures do not satisfy hydraulic design criteria • 19 structures are critical

ASSESSMENTS

• 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

CRITICALITY MATRIX

Structure: 06712 Location: Watertown

Year Built: 1966 Criticality Ranking: 4

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

Example: Little to No Adaptive Capacity

Criticality Score: 7

02315

Example: Significant Adaptive Capacity

Criticality Score: 8

05417

Legend • Low Risk

• Moderate Risk

e High Risk

National Highway System

Study Region

0 5 20 - - -=====-- - - • Miles

10

Litchfield Hills Study Structures Criticality Rankings

• •

•

N

A

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

19

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 updating regression equation with USGS and seek funding to study

• 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

Stephanie Molden Stephanie.Molden@ct.gov

Michael Hogan, P.E. Michael.Hogan@ct.gov

David Elder, AICP, GISP

David.Elder@ct.gov

0

2

4

6

16 14 12 10

8

18

STRUCTURE NO. 02423 HEADWATER DEPTH VS. PEAK DISCHARGE

20

0 500 1000

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).

1500 2000 2500 3000

PEAK DISCHARGE (CFS)

3500

HEA

DW

AT

ER

DEP

TH (

FT.)

O V

ERTO

PPI

NG

BEG

INS

HW

/D =

1.5

FREE

BO

AR

D =

1 F

T.

100-

YEA

R D

ISC

HA

RG

E

INLE

T SU

BM

ERG

ED

500-

YEA

R D

ISC

HA

RG

E

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