Sea-Level Rise and Tidal Flooding in Delaware

John A. CallahanDelaware Geological Survey

University of Delaware

RASCL Summit 2017Dover, DE

Hurricanes/Tropical storms +Nor’easters/Mid-latitude cyclones

Low, flat, open topography

Location of development, public infrastructure, communities

Coastal economy (e.g., beach-driven tourism)

SLR is separate from weather!…change in the average water level without storms

Long-term, gradual consequence of global warming

The data are noisy..but the trend is clear!

We are here

Relatively stable over past 4-5,000 years.

NOAA Tech Report 083 (2017)Global and Regional SLR Scenarios

for the USadapted from Kopp et al. (2016)

1. Long-term, gradual: Loss of low-lying ag fields, forested wetlands Saltwater intrusion into groundwater Wetlands to mud flats/open water; wildlife habitat change

2. Short-term, episodic: Damage to public/private infrastructure from flooding Rapid erosion, beach sand loss, dune breaches

3. Economic impacts through tourism, real estate

SLR doesn’t cause the hazards you experience,it just makes the hazards you experience even worse!

Hazards Climate Sea-Level Rise

To address the causes and consequences of climate change

Including …to avoid and minimize flood risks due to sea level rise

Delaware Geological Survey-led committee DNREC Delaware Coastal Programs sponsored Task: To update the SLR scenarios put forth by

DNREC in 2009.

Gravitational changes of Greenland

Ocean circulation changes

Glacial Isostatic

Adjustment

We are here

2.5 m – Extreme2.0 m – High1.5 m – Intermediate High1.0 m – Intermediate0.5 m – Intermediate Low0.3 m – Low

NOAA Tech Report 083 (2017)Global and Regional SLR Scenarios for the U.S.

Incorporates IPCC AR5 process models, Lewes tide gage data, and expert assessments

Full probability distribution – per greenhouse has scenario

Relative contributions and uncertainty for each component

Widely used by other states and federal agencies

SLR at 2100High = 1.53 mIntermediate = 0.99 mLow = 0.52 m

SLR at 2100High = 1.53 mIntermediate = 0.99 mLow = 0.52 m

“Long tail” effect of risk distribution SLR > 95% is still 1:20 chance Small odds vs severe consequences

High uncertainty in Antarctic ice sheet contribution

• Select an appropriate time horizon for planning or design

• Determine risk tolerance

• Identify costs and co-benefits

• Trade offs may need to be made

Next few slides from Dr. William Sweet (NOAA)…

“Then” flooding occurred during big storms.

“Now” sunny-day nuisance urban flooding is common.

Decreasing height above high tideMean Highest Tide

Mean Lowest Tide

Sink

ing

Land

Ris

ing

Seas

Abo

ve A

vg. H

igh

Tide

(m)

Nuisance Flood LevelNWS Minor CFA

General Nature of the Problem

Example from Norfolk, VA

Daily Highest Tides(Today’s Reference Frame)

-0.8 0.0 0.8

Dai

ly H

igh

est

Tid

e(P

rob

abili

ty)

Above High Tide (m)

1950s

General Nature of the Problem

-0.8 0.0 0.8

Dai

ly H

igh

est

Tid

e(P

rob

abili

ty)

Above High Tide (m)

1950s 2010s

Typical Annual Daily Max. Water Levels

General Nature of the Problem

-0.8 0.0 0.8

Dai

ly H

igh

est

Tid

e(P

rob

abili

ty)

Above High Tide (m)

1950s 2010s

steady SLR

Nuisance Level –feet getting wet

steep transition

region

Typical Annual Daily Max. Water Levels

~21 days/yr

~5 days/yr

2030~70 days/yr

2045~150 days/yr

Emission ScenarioMinor influence

until > 2045

8 map layers: - MHHW to MHHW + 7 ft

Available on Delaware FirstMap and DGS website

SLR has been occurring in DE for a long time Delaware 2017 SLR planning scenarios

Possibly should consider upper bounds of SLR Minor coastal flood frequency will significantly increase Increased risk of major coastal flooding Maps were developed from MHHW to MHHW + 7 ft

SLR Planning Scenario SLR by 2100Low Scenario 0.52 m 1.71 ft

Intermediate Scenario 0.99 m 3.25 ftHigh Scenario 1.53 m 5.02 ft

John Callahan (chair), Delaware Geological Survey, UD David Wunsch, DGS, UD Tom McKenna, DGS, UD Daniel Leathers, Dept of Geog, UD Robert Scarborough, DNREC Delaware Coastal Programs Danielle Swallow, DNREC Delaware Coastal Programs Benjamin Horton, Sea Level Research, Department of Marine and Coastal

Sciences, Rutgers University and Earth Observatory of Singapore, Asian School of the Environment Nanyang Technological University, Singapore.

Daria Nikitina, Department of Earth and Space Sciences, West Chester University Holly Michael, Department of Geological Sciences, University of Delaware Christopher Sommerfield, School of Marine Science and Policy, Oceanography

Program, University of Delaware Jennifer Volk, Dept of Plant and Soil Science, UD Kim McKenna, DNREC Shoreline and Waterway Management Mike Powell, DNREC Division of Watershed Stewardship

Thank You!

John CallahanDelaware Geological Survey

University of Delawarejohn.callahan@udel.edu

Special Thanks!

http://www.dgs.udel.edu/slr