Coastal protection in the Pacific: Desktop review and testing of …star.gsd.spc.int/images/presentation17/Presentations... · 2017-12-05 · Coastal protection in the Pacific: Desktop

Coastal protection in the Pacific: Desktop review and testing of low cost solutionsTom Shand1, Matt Blacka2, James Carley2, Oliver Whalley3, Lorena Estigarribia4

1Tonkin + Taylor International; 2Water Research Laboratory; 3The World Bank; 4The PRIF

STAR Conference

Nadi 25-29 July 2017

Outline

• Pacific overview

• Material availability

• Protection types

• Technical review

• Economic review

• Physical model testing

• Development of guidance report

Coastal protection in the Pacific STAR Conference 2017 Nadi 25-29 June 2017

Background

• Part 1: Desktop Assessment

• Part 2: Modelling

• Part 3: Design Guidance Document

• Part 4: Field Trial?


Background

• Ocean covers ~30% of earths surface

• 30,000 Islands

• 50,000 km coastline

• Dynamic environments

• ~3.5M inhabitants, most live within 10km of the coast

• Population concentration

• Increased pressure to hold the line

• Limited local materials

• High transport costs

Changes in vegetated shoreline on Tepuka Island, Funafuti

Atoll, Tuvalu 1896-2005 (Webb and Kench, 2010)

Ebeye RMI ~1944

Ebeye RMI 2015

Jones and Barkett Publishers LLC, 2009



Coastal protection methods

Major issues with the commonly used solutions within Pacific Island Countries

• Use of local beach sand exacerbating shore sediment deficit

• Outflanking and end erosion• Undersize rock• Low strength and lightweight concrete• Failure of structural members such as gabion wire

or bonds between polypropylene woven bags• Toe scour and loss of material• No geotextile behind the wall resulting in loss of

material• Walls under-height allowing waves to overtop• lack of backshore protection results in land

damage


Technical analysis

Technical criteria for coastal protection structures have been established including:

• Engineering criteriathe ability of the protection measure to provide shoreline protection

• Social criteriathe degree to which the protection method affects the local population

• Environmental criteriathe effect of the protection method on the local environment


Technical analysis

Technical CriteriaRating

1 3 5

Engi

ne

eri

ng

Design wave characteristics Single wave height/period Range of heights All heights and periodsDesign life <2yrs 5-20 years >50 yearsTime period to become effective > 2 years Within 2 years Immediate

Effectiveness at protecting land

Limited protection of backing land, or often fails

Moderate protection, or sometimes fails

High level of protection of backing land reported in all cases

Effect on overtoppingLarge overtopping volumes or runup level high

Moderate overtopping volumes

Low overtopping volumes or decreases runup

Toe scour High toe scour occurs Moderate toe scour Low levels of toe scour occur

Design guidence available None Some Complete

Resilience to climate changeNo adaptation - replacement required Modification required

Provision for a specified level of climate change

Construction complexityRequires international contractor

Requires local contractor

Semi skilled or unskilled local labour

Construction plant requiredLarge and/or expensive plant required

Some construction plant required

No construction plant required

Scalability Highly site-specificSite-specific modification required Very generic


Technical analysis

Technical Criteria

Rating

1 3 5

Soci

al

Use of local labourLocal labour cannot be used

Use of some local labour

May be completed using local labour

Beach accessProhibits access

Access unchanged or still possible Enhances access

Aesthetic

Significantly differs from existing

Slightly differs from existing

In keeping with existing environment

Cultural acceptability Never usedSometimes used already

Already widely used


Technical analysis

Technical Criteria

Rating

1 3 5

Envi

ron

me

nta

l

Seabed occupation

Large occupation area (<3 x design wave height)

Moderate occupation area (1-2 x design wave height)

Small occupation area (less than 1 x design wave height)

End effectsEnhances erosion of adjacent land

Rates of background erosion remain constant

Reduces erosion of adjacent land

Effect on sediment budgetDepletes sediment budget

Not effect on sediment budget

Enhances sediment budget

Effect on ecosystemsSignificant adverse effect

Neutral or both positive and negative effects

Significantly improves ecosystems

Impact of construction activities

Significant and/or long-term adverse effects

Some and/or short-medium term effects

Negligible adverse impacts


Technical analysisRevetments Vertical Seawalls Offshore Low cost or local materials Other

Ro

ck r

evet

men

t

Geo

-co

nta

iner

s

Art

icu

lati

ng

con

cret

e b

lock

s

Tetr

apo

d

arm

ou

r u

nit

s

Sam

oa

sto

ne

Seab

ees

CO

PED

Mas

s co

ncr

ete

Rei

nfo

rced

co

ncr

ete

Tim

ber

ret

ain

ing

wal

l

Shee

t p

ile w

all

San

d S

aver

Ree

f B

alls

Gro

ut

fille

d s

and

b

ags

Gab

ion

bas

kets

an

d m

attr

esse

s

Gro

ute

d r

ock

Stac

ked

co

ral

Ru

bb

er t

yres

Co

ncr

ete

pip

es

Fille

d d

rum

s

Bea

ch

rep

len

ish

men

t

Bru

sh s

tru

ctu

res

Bio

rock

Pla

nti

ng

man

gro

ves

and

ve

geta

tio

n

Technical Criteria

Engi

ne

eri

ng

Design wave characteristics 5 3 2 3 4 5 3 4 3 2 2 1 3 1 1 2 1 1 2 1 4 1 3 1Design life 5 3 3 4 4 4 4 4 4 3 3 3 3 2 2 2 1 1 2 1 2 1 3 4Time period to become effective 5 5 5 5 5 5 5 5 5 5 5 3 2 5 5 5 5 5 5 5 4 2 1 1

Effectiveness at protecting land 5 4 4 5 5 5 3 4 4 3 3 2 2 2 3 2 1 1 1 1 3 1 1 2

Effect on overtopping 4 2 3 5 4 3 3 1 1 1 1 1 3 1 3 2 3 3 1 1 5 3 3 4Toe scour 3 2 3 3 3 3 3 1 1 1 1 3 5 1 2 1 3 2 1 1 5 3 3 4

Design guidence available 5 4 3 4 4 5 2 4 4 4 3 3 2 2 3 2 1 1 1 1 4 1 3 2

Resilience to climate change 3 2 2 3 2 3 3 1 1 1 1 2 2 1 1 1 1 1 2 2 4 4 5 4

Construction complexity 3 3 3 2 2 3 2 3 2 3 3 4 2 4 4 4 5 4 3 4 3 5 2 5

Construction plant required 2 4 3 2 2 4 2 4 4 3 2 3 2 4 5 4 5 3 3 4 3 5 4 5

Scalability 4 4 2 2 3 3 2 3 2 3 3 3 2 4 4 4 4 3 3 3 1 4 2 4

Soci

al

Use of local labour 2 3 3 2 2 4 2 3 3 3 2 2 3 4 4 4 5 3 3 4 2 5 3 5Beach access 3 4 4 2 4 4 2 2 1 2 1 4 3 2 3 2 2 1 1 1 5 2 4 2

Aesthetic 3 3 3 2 3 3 2 1 1 3 1 3 3 2 3 3 3 1 1 1 5 2 5 2

Cultural acceptability 4 3 3 2 3 3 3 2 2 3 1 3 3 3 3 3 4 1 1 1 5 4 5 4

Envi

ron

me

nta

l Occupation of seabed 1 2 1 1 2 2 1 4 4 5 5 3 1 3 3 4 4 4 4 4 1 4 1 1

End effects 3 3 3 3 3 3 3 1 1 2 1 3 4 2 2 2 3 2 2 2 5 3 3 4

Effect on sediment budget 2 2 2 3 3 3 3 2 2 2 2 4 4 2 2 2 2 3 2 2 4 5 5 4

Effect on ecosystems 3 2 3 2 2 2 2 1 1 1 1 2 4 1 2 1 2 2 1 1 4 3 5 5Impact of construction activities 4 3 4 4 4 4 4 4 4 3 2 4 4 2 2 2 2 2 3 2 4 4 4 5


Financial analysis

Methodology

Material costs ($/m3)

Generic designs Hs = 0.7m, 1.5m, 3m

Typical coastal protection cost

($/li m)

Transport costs ($/m3)

Design life (no maintenance)

Annual cost ($/li m/year)

Cost relative to local rock revetment (base)

Cost by location ($/li m)


Financial analysis

Coastal protection: indicative comparative costingProtection method Details Design

life2

(years)

1. Rock revetment – high density Assumes basalt or similar > 2600kg/m350

1b. Rock revetment – low density Assumes limestone, coral or similar) ~ 2200kg/m320

2. Mass concrete Assumes local aggregates are used 20

3. Reinforced concrete High strength (50Mpa) marine-grade concrete 30

4. Grout-filled bag wall Bags secured with a grout mix 5

5a. Geosynthetic container - Single Assumes 0.75m3 containers for low wave and 2.5m3 for moderate wave

10

5b. Geosynthetic container - Dbl 20

6a. Seabees – Imported materials Includes concrete cap and rock toe 30

7a. Tetrapods – Imported concrete Includes rock toe 30

8. Grouted coral wall Assumes 1:3 ratio concrete:coral block 5

9. Beach replenishment Assumes 1:12 slope and 20% loss of material/year 5

10. Timber wall Assumes piles driven and H6 Marine grade timber 15

11. Gabion Basket Assumes local aggregates and PVC coated wire 5

12. Terrafix Blocks Assume T60 blocks 20

13. Small hand-palced GSC Assume placed long-axis out – required assess 2-5


Low wave energy (Hs = 0.7m)

Moderate energy (Hs = 1.5m)

High wave energy (Hs = 3m)

650 3000 11000

850 4200 N/A

2000 9100 N/A

2000 8000 N/A

1750 N/A N/A

1850 4000 N/A

3500 7000 N/A

900 3500 12500

N/A 5000 30000

800 N/A N/A

1000 4500 17500

2400 N/A N/A

1250 N/A N/A

1300 N/A N/A

330 N/A N/A

Financial analysis

Protection option

Design life

(years)

Comparative cost (AUD/li m)

Base LocalPrimary Port

Remote Location

1. Rock revetment - Volcanic 50 665 1393 2605 45451b. Rock revetment - Limestone 15 850 1120 1570 22902. Mass concrete - local aggregates 20 2050 2208 2470 28903. Reinforced concrete 30 2010 2262 2682 33544. Grout-filled bag wall 5 1730 1843 2030 23305a. Geo-container - Single layer 10 1860 1941 2076 22925b. Geo-container - Dbl layer 20 3340 3477 3704 40686a. Seabees – Imported materials 30 890 1198 1710 25306b. Seabees - local materials 15 1223 1259 1318 14137a. Tetrapods – Imported materials 30 N/A N/A N/A N/A8. Grouted coral 5 780 823.5 896 10129. Beach replenishment 5 1000 1000 1000 100010. Timber wall 15 2400 2760 3360 432011. Gabion Basket 5 1240 1396 1556 172212. Terrafix Blocks 20 1310 1469 1734 215813. Small hand-placed GSC 2-5 330 360 405 480

Comparative cost/li m for low wave environment (Hs = 0.7m)


Financial analysis

Protection option

Design life

(years)

Comparative annual cost (AUD/li m/year)


Remote Location

1. Rock revetment - Volcanic 50 13 28 52 911b. Rock revetment - Limestone 15 57 75 105 1532. Mass concrete - local concrete 20 103 110 124 1453. Reinforced concrete 30 67 75 89 1124. Grout-filled bag wall 5 346 369 406 4665a. Geo-container - Single layer 10 186 194 208 2295b. Geo-container - Dbl layer 20 167 174 185 2036a. Seabees – Imported materials 30 30 40 57 846b. Seabees - local materials 15 82 84 88 947a. Tetrapods – Imported materials 30 N/A N/A N/A N/A8. Grouted coral 5 156 165 179 2029. Beach replenishment 5 200 200 200 20010. Timber wall 15 160 184 224 28811. Gabion Basket 5 248 279 311 34412. Terrafix Blocks 20 66 73 87 10813. Small hand-placed GSC 2 166 180 202 238

Comparative annual cost for low wave environment (Hs = 0.7m)


Financial analysis

Protection option

Design life

(years)

Costs/year (proportion of local rock revetment)


Remote Location

1. Rock revetment - Volcanic 50 1.0 2.1 3.9 6.81b. Rock revetment - Limestone 15 4.3 5.6 7.9 11.52. Mass concrete - local concrete 20 7.7 8.3 9.3 10.93. Reinforced concrete 30 5.0 5.7 6.7 8.44. Grout-filled bag wall 5 26.0 27.7 30.5 35.05a. Geo-container - Single layer 10 14.0 14.6 15.6 17.25b. Geo-container - Dbl layer 20 12.6 13.1 13.9 15.36a. Seabees – Imported materials 30 2.2 3.0 4.3 6.36b. Seabees - local materials 15 6.1 6.3 6.6 7.17a. Tetrapods – Imported materials 30 N/A N/A N/A N/A8. Grouted coral 5 11.7 12.4 13.5 15.29. Beach replenishment 5 15.0 15.0 15.0 15.010. Timber wall 15 12.0 13.8 16.8 21.711. Gabion Basket 5 18.6 21.0 23.4 25.912. Terrafix Blocks 20 4.9 5.5 6.5 8.113. Small hand-placed GSC 2 12.5 13.5 15.2 17.9

Relative annual cost for low wave environment (Hs = 0.7m)


Financial analysis

Protection option

Design life

(years)



Remote Location

1. Rock revetment - Volcanic 501b. Rock revetment - Limestone 152. Mass concrete - local concrete 203. Reinforced concrete 304. Grout-filled bag wall 55a. Geo-container - Single layer 105b. Geo-container - Dbl layer 206a. Seabees – Imported materials 306b. Seabees - local materials 157a. Tetrapods – Imported materials 308. Grouted coral 59. Beach replenishment 510. Timber wall 1511. Gabion Basket 512. Terrafix Blocks 20

Relative cost/year for moderate wave environment (Hs = 1.5m)

1.0 2.1 4.0 6.94.6 6.0 8.3 12.17.4 8.0 8.9 10.44.4 4.9 5.8 7.3N/A N/A N/A N/A6.3 6.5 6.9 7.45.8 6.0 6.3 6.81.8 2.4 3.3 4.85.1 5.2 5.4 5.82.8 3.5 4.6 6.4N/A N/A N/A N/A13.9 13.9 13.9 13.9N/A N/A N/A N/AN/A N/A N/A N/AN/A N/A N/A N/A


Financial analysis

Protection option

Design life

(years)



Remote Location

1. Rock revetment - Volcanic 501b. Rock revetment - Limestone 152. Mass concrete - local concrete 203. Reinforced concrete 304. Grout-filled bag wall 55a. Geo-container - Single layer 105b. Geo-container - Dbl layer 206a. Seabees – Imported materials 306b. Seabees - local materials 157a. Tetrapods – Imported materials 308. Grouted coral 59. Beach replenishment 510. Timber wall 1511. Gabion Basket 512. Terrafix Blocks 20

Relative cost/year for high wave environment (Hs = 3m)

1.0 2.1 4.0 7.1N/A N/A N/A N/AN/A N/A N/A N/AN/A N/A N/A N/AN/A N/A N/A N/AN/A N/A N/A N/AN/A N/A N/A N/A1.9 2.4 3.3 4.6N/A N/A N/A N/A5.0 5.8 7.2 9.5N/A N/A N/A N/A16.4 16.4 16.4 16.4N/A N/A N/A N/AN/A N/A N/A N/AN/A N/A N/A N/A


Conclusions of desktop review

• Pacific islands dynamic features – at odds with fixed infrastructure and assets

• Coastal works difficult due to • lack of local materials, construction plant and expertise

• Long distances and high transport costs

• infrequent very large wave events means oversize structures or accept failure during low probably events

• generally low-value assets requiring protection

• Hazard avoidance or relocation most effective solution• Cost and social effects must be considered

• Sometimes not possible


Changes in vegetated shoreline on Tepuka Island, Funafuti

Atoll, Tuvalu 1896-2005 (Webb and Kench, 2010)


• Low-cost ‘local’ protection structures have technical limitations and short design life resulting in very high annual cost

• Rock always lowest annual cost when available locally or short transport distances (adds <150/m3)

• Concrete armour units become more efficient when transport costs exceed ~$250/m3 (lower for higher wave height)

• For more remote locations• Large GSC (similar annual cost to rock for remote location)

• Mass or reinforced concrete (hard substrate)

• Sand replenishment where sustainable source available depending on site-specific conditions



• Identified potential to use a range of more affordable alternative materials as revetment armouring on low energy coastlines, where the materials:• Are readily available, or

• Have established supply lines,

• Can be built without heavy machinery, and

• Can use local/semi-skilled labour

• Two potential options identified • Small hand-placed sandbags

• Concrete masonry building block

• Lack of design guidance • limiting wave conditions unknown


Physical model testing

• Objectives• Investigate the stability limit of both geotextile sand filled containers (GSCs) and

concrete masonry blocks (CMBs) for conditions experienced on low-energy coastlines of the Pacific Islands (atoll lagoon coasts for example)

• Investigate the impact of placement patterns and detailing

• Investigate failure mechanisms

• Test conditions• Typical lagoon seabed profile (South Tarawa, Kiribati for eg.)

• Spectral peak wave periods of 3 s, 5 s and 10 s

• Range of water depths – up to 2.3m at revetment toe

• Wave heights ranging from Hs = 0.4 to 1.2m (depth limit of waves)



• Concrete Masonry Block Revetment Testing


Long axis shore parallel

Long axis cross shore

Alternating courses


• Concrete Masonry Block Revetment Testing



Concrete Masonry Block Revetment Testing

• Non-overtopped stability Hs<1.1m





• Stability with 5% block damage


Pre-Test Photo

Post-Test Photo







Pre-Test Photo

Post-Test Photo







Pre-Test Photo

Post-Test Photo






• Wave overtopping l<0.2 l/s/m


Tp

(s)

Hs

(m)

Ave. Over-topping rate

(L/s/m)

Damage to Top 3 Block Courses

Crest Photo After Test

5 0.4 0.0 0%

5 0.7 0.2 6%

5 0.8 1.3 36%

5 0.9 2.5 43%

5 1.0 7.5 52%







• Wave runup characteristics









Small Geotextile Bags (40kg)



















• Non-overtopped stability Hs<0.4-0.6m










• Non-overtopped stability Hs<0.4-0.6m



Bag Placement Pattern


Summary

• Concrete masonry block revetments found to be stable in waves up to a Hs ~1.1 m for wave periods of Tp = 3, 5 and 10 seconds

• Upper wave height limit not reached, however, the strength/integrity of the blocks may be the limiting factor

• Having ~5% of blocks damaged/removed had little impact on the armour layer stability, however, 10% of blocks damaged had a significant impact on the integrity of the armouring

• Crest blocks start to become unstable when overtopping exceeds ~ 0.2 L/s/m



Summary

• Small (~40 kg) sand filled geotextile containers were found to have a much lower stability threshold, and are likely only suitable for very mild conditions where design wave heights remain less than Hs~0.4 m.

• The stability of the bags within the revetment face was found to be the limiting factor even for overtopped structures, as opposed to units at the crest.


Development of guidance report

• Overview of the design process

• Assessing design conditions

• Design fundamentals

• Effects assessment

• Concept designs for a range of coastal protection works• Design considerations

• Material specifications

• Typical construction methods

• Monitoring and maintenance

• Climate change adaptation

• Concept Drawings


AcknowledgementsName OrganisationChris Brown Chris Brown consulting

Helen Sykes Marine Ecology Fiji

Cliff Juillerat Ocean Caraibes Coastal Consultant

Angus Gordon Coastal Zone Management and Planning

Yusuke Taishi UNDP

Niels B. Holm-Nielsen The World Bank

Sofia U. Bettencourt The World Bank

Gillian Cambers SPC

Nicolas Desramaut The World Bank

Heather O’Keeffe GHD

Alessio Giardino Deltares


Hugh Milliken Downer New Zealand

Dr Jacqueline Bell Bioresearches Group

Misti Hood TropSEA Engineering & Environmental

Linz Watson Go Logistics (NZ) Ltd

Dr Yann Balouin BRGM, French Geological Survey,

Simon Restall International GeoSynthetic Resources

Steven Sapalo The World Bank

Ian Iercet Public Works Department, Vanuatu

Siulai Fioana Elisala Tuvalu

John Hughes Ministry of Infrastructure Development, Soloman Islands

Ken Munro Ministry of Infrastructure Development, Soloman Islands

Coastal protection in the Pacific: Desktop review and testing of …star.gsd.spc.int/images/presentation17/Presentations... · 2017-12-05 · Coastal protection in the Pacific: Desktop

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