Evaluating Coastal

Erosion Structures

Lauren Hunt, Christopher Sample,

Kathleen Sullivan

December 16th, 2014

Project Sponsors: Jeff Carlson,Peter Morrison, and Mary WawroProject Advisors: Dominic Golding

Stanley Selkow

Overview

-What is Erosion

-Objectives/Goals

-What we did and how we did it

-Findings

-Conclusions and Recommendations

Defining coastal erosion is rather straightforward

Understanding coastal erosion is not as easy

What is Erosion?

What is Erosion?

Why is erosion an issue?

Threatens 300,000 homesDestroys 1,500 homes

In Nantucket 2 feet to 12 feet a

year

Sheep Pond Road Area5 houses lost10 Houses relocated

Goal

Evaluate the current condition, impacts, and effectiveness of the coastal erosion structures

Limitations

-No universal rating scale

-Erosion rates from aerial photos and CZM transect lines

-Structures which have permits

-7 weeks of onsite visits

Objectives

Categorize Data

Variety of structures

and methods

Evaluated impacts and effectivenes

s

Breakdown of Opinions

Coastal erosion

practices and policies

Island stakeholders

Create Recommendation

s

Future Policies

Erosion control

strategies

Erosion Structures

•Seawalls•Groins•Geotextiles•Offshore Breakwaters

Hard

•Beach Nourishment•Vegetation•Sand Fencing•Jute Mesh and Bags

Soft

Permitting Process

Design

Resource Areas

Impacts

Withdrawn

What we did

-Site Visits

-Google My Maps

-Database

-Effectiveness Rating Scale

Site VisitsLocated Structures

-Aerial photographs-CZM database

Documented-Notes-Photographs

Post evaluation notes

Google My Maps

Database

Good •2 Points

Fair •1 Point

Poor •0 Points

Structure Test

Property Test

Beach Test

Total

Score 0-

6

5 or 6 •Effective

3 or 4 •Adequate

0 to 2 •Ineffective

Effectiveness Rating Scale

Structure•Integrity•Condition

Property•Scouring•Holding back land

Beach •Beach present in front of property

Types of Structure

FindingsTypes of Structures

Hard Soft

42%

58%

Location of Structures

Northwest SiasconsetSouth Harbor

69%17% 7%

7%

Effectiveness Rating Scores

5 to 6 3 to 4 0 to 2

50%44%

6%

Types of Structure

Findings

Effective Adequate Ineffective0

5

10

15

20

25

HardSoft

Num

ber

of

Str

uct

ure

s

Hard

EffectiveAdaquateIneffective

Soft

EffectiveAdaquateInnefective

48%50%

2%

38%

52%

10%

Hulbert Avenue

1981 2014

East Tristram Avenue 20102011201

42001

Soft Structures

Pocomo Road Coskata Course Way

Now more likely to be permitted by

Conservation Commission

-Sand fencing -Jute mesh and bags

-Sand nourishment -Beach grass plantings

Lauretta Lane

Stakeholder Perspectives

Natural Resources Department

Nantucket Coastal Conservancy

Josh Posner, President SBPF

John Merson, Baxter Road resident

Conclusion

-Location of Structures

-Type of Structures

-Difficult to evaluate effectiveness

ConclusionSoft structures may

-Decrease erosion

-Encourage accretion

-Require more maintenance

Hard structures may

-Protect land behind them

-Cause scouring

-Distant impacts

Recommendations

Continue to inspect structures

-function as expected-limit unauthorized

Update and maintain database

Maintain systematic photographic record

Recommendations

ConCom continue to work with homeowners

Develop systematic approach to evaluate effectiveness

Acknowledgments

A special thanks to:Jeff Carlson and all of the Natural Resources Department

Sheila Lucey the Harbor Master

Mary Wawro and Peter Morrison

Harvey Young and Young’s Bicycle Shop

Andrew Mckenna-Foster and the Maria Mitchell Association

And to all those that have taken the time to talk with us

Questions and Comments

-Created database of 72 structures

with 20 fields of information

-32 Effective structures, 36 adequate structures, 4 ineffective structures

-Recommend the town maintains database with all current and future structures

-No cookie cutter way to signify one structure is better than any other, effectiveness will vary by location due to outside impacts

-Recommend future evaluations of effectiveness

Quaise Road