Short title; Author(s), Date

Modeling the Effects of Sea-Level Rise on Groundwater Levels with Implications for

Road Infrastructure in Coastal New Hampshire

Jayne F. Knott, Jo Sias Daniel, Ph.D., Jennifer M.

Jacobs, Ph.D., and Paul Kirshen, Ph.D.

UNH Department of Civil and Environmental

Engineering

“Better Safe Than Sorry” – Workshop June 21, 2016

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Climate Change Overview

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Climate Change in the Northeast Temperature

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Source: 2014 National Climate Assessment

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Climate Change in the Northeast Precipitation

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Source: 2014 National Climate Assessment

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Climate Change in the Northeast Sea-Level Rise

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Source: 2012 National Climate Assessment

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Climate Change in the Northeast Sea-Level Rise

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Coastal NH – Winter storm 2/8/2016

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Motivation for this study

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Water is a major cause of damage to roads

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The useful life of the pavement structure decreases with an increase in the percent of time

the structure is saturated.

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Source: Cedergren, 1988

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High moisture content weakens the unbound layers beneath the hot mix asphalt

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How does water get into pavement systems?

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What does sea level have to do with groundwater?

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Source: U.S. Geological Survey

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Project Objectives

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1. Create a NH Seacoast Transportation Climate Working

Group

2. Determine the effects sea-level rise on coastal

groundwater levels

3. Identify roads that may be vulnerable to damage from

rising groundwater

4. Conduct pavement performance evaluations

5. Demonstrate the value of adaptation through case

study

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Methods

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• Identify areas where the groundwater is less than 10-feet

deep using current and historical groundwater observations

• Update the USGS groundwater flow model of the Seacoast

Region of NH (Mack, 2009) using MODFLOW-2005

• Simulate various sea-level rise scenarios to identify areas

where groundwater is predicted to rise

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Political Map of Study Area

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Groundwater Observations

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Depth to GW from observations (1960-2015)

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GW table is greater than or equal to 15-ft. below the ground surface.

Observation wells

GW table is very close to the ground surface

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Depth to GW in Portsmouth, NH

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Depth to groundwater near the I-95/Rte. 16 Interchange in Portsmouth, NH

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Depth to groundwater near Route 101 in

Hampton– Evacuation Rte. From Hampton Beach

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Route 101 Route 101

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Groundwater Model Construction

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Groundwater Model

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• Calculates the groundwater flow equation for many small

areas, or cells, within the model domain

• Hydraulic properties of surficial and bedrock geology

• Groundwater recharge

• Streamflow

• Public and private water withdrawals and returns

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GW model domain and boundary conditions

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Model grid is 535 rows and 350 columns, each grid cell is 200’ x 200’

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Observation wells and CSWs

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Sea-level rise scenarios

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Time Period 2050 2100

Intermediate low 0.6 ft. 1.6 ft.

Intermediate high 1.3 ft. 3.9 ft.

Highest 2.0 ft. 6.6 ft.

From: National Climate Assessment (Parris et al., 2012) using

MSL as a reference

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Groundwater Modeling - Results

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Surface water inundation with 6.6 feet of SLR

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Groundwater rise with 6.6 feet of SLR

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Observed depth to gw and simulated depth to gw with 6.6 feet of sea-level rise

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Transect of the off-ramp from I-95 through the Portsmouth Circle

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Sections of roads where the groundwater table is already shallow are the most vulnerable

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Location of a pavement profile along Route 286

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Route 286 – Pavement Profile

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What factors make coastal road infrastructure vulnerable to changes in climate?

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Proximity to the ocean

Locations where groundwater is near the

ground surface and where groundwater is

projected to rise

Inadequate stream crossings now or in the

future

Subgrade soil types that weaken with

increasing moisture content

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Other concerns . . .

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Will drinking water supplies be harmed by saltwater intrusion?

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Area where GW is predicted to rise the most with SLR

Areas potentially at risk from saltwater intrusion with SLR

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Rise in GW with 6.6 feet of SLR

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Why doesn’t the GW rise as much here?

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Increase in GW level is reduced in the proximity of streams, but. . .

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• Streamflow will

increase.

• The freshwater/salt

water interface

may move further

inland.

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Where might rising groundwater come in contact with contaminated soils?

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Conclusions

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Groundwater modeling is an effective tool for investigating

hydrologic changes resulting from climate change.

Rising groundwater and changing flow patterns will have

important consequences for the structural integrity of

infrastructure, water supply and water quality, stream base flow,

and the health of natural ecosystems.

Adaptation strategies must consider potential damage from rising

groundwater in addition to surface water impacts.

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What actions can communities take . . .

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Formally consider groundwater predictions when:

designing or repairing road infrastructure,

establishing criteria for the cleanup of contaminated sites

permitting onsite septic systems, and

designing sea walls or other protective structures to mitigate

damage from sea-level rise

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What actions can communities take . . .

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Identify drinking water supply wells that may be at risk from saltwater

intrusion and plan for alternative sources, if necessary

Identify the critical infrastructure in your community where rising

groundwater may cause problems

Protect existing wetlands and adjacent areas to allow for wetland

expansion

Collaborate with research institutions, community planning organizations,

government, and private partners to plan for the future

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Acknowledgements

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• NH Sea Grant is funding this project

• UNH – ICNet, UCIRC, the Asphalt Research Group, the

Climate Change and Infrastructure Research Group

• NH Seacoast Transportation Climate Working Group (NHS

TCWG)

• NH Coastal Adaptation Workgroup (NH CAW)

• NH Department of Transportation (NHDOT)

• NH Department of Environmental Services (NHDES)

• Thomas Mack and Dave Bjerklie of USGS

• Gregory Barker, NH Geological Survey

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Thank you Questions?

Contact: Jayne F. Knott

University of New Hampshire jfk1011@wildcats.unh.edu

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