MODELLING COASTAL EROSION

MSc Kotinas Vasileios, Phd Candidate, University of Athens v.kotinas@geol.uoa.gr

Miltiadis Polidorou, PhD Candidate, University of Athens

INTRODUCTION

Around 41% of Europe’s population live near the

coast (Collet & Engelbert, 2013)

Determining the physical response of the

coastline to sea-level rise is one of the most

important problems in coastal geology today

Recent estimates of future sea-level rise based on

climate model output (IPCC,2013) suggest an

increase of the rate of sea level rise

The prediction of future coastal evolution is not

straightforward. Although a quantitative

predictive approach is not available, the relative

vulnerability of different coastal environments to

sea-level rise may be quantified at a regional to

national scale using basic information Global Mean sea level rise (IPCC,2013)

CVI

The Coastal Vulnerability Indexis a relatively simple andfunctional method to estimatethe vulnerability to erosion ofany coastal zone in relation tofuture sea level rise.

It combines the sensitivity ofthe coastal zone to changes,with the ability of the coastalsystem to adapt to the newconditions.

By ranking the vulnerability ofthe coastal zone we identifythe areas that arecomparatively morevulnerable to sea-levelchanges.

HISTORICAL EVOLUTION

The Coastal Vulnerability Index(CVI) was developed by Gornitz etal. (1990). The parameters thatwere considered were: relief, rocktype, landform, vertical (tectonic)movement, shorelinedisplacement, tidal range andwave height.

The CVI was modified later byGornitz et al (1994) to includeseven physical land/marinevariables and six climatologicalvariables

Many modifications were made tothe CVI. For example, Thieler andHammer Klose in 1999 reversed theranking of tidal range.

• The CVI was used by the UnitedStates Geological Survey (USGS) toassess the vulnerability of coastalarea, throughout the United States(Thieler, 2000; Thieler and Hammer-Klose, 1999, 2000)

• The problem with the CVI approachas proposed by Gornitz et al. andadopted by the USGS is its non-consideration of socio-economicdata.

• Boruf et al. (2005) combined theSocial Vulnerability Index with theCVI to form the Coastal SocialVulnerability Index (CSoVI)

Table : Various modifications of CVI

Geometric averageCVI =

(a ∗ b ∗ c ∗ d ∗ e ∗ f)

6

Modified Geometric

average

CVI

=a ∗ b ∗ c ∗

12∗ d ∗ (

12∗ (e + f)

4

Average sum of squares

CVI =a2 + b2 + c2 + d + e2 + f2

6

Modified Geometric

averageCVI =

a ∗ b ∗ c ∗ d ∗ e ∗ f

52

Sum of multiplications CVI

= 4 ∗ a + 4 ∗ b + 4 ∗ c + 2 ∗ d + 2

∗ (e + f)

Square root of

Geometric averageCVI =

(a ∗ b ∗ c ∗ d ∗ e ∗ f)

6

The geometric average is quite sensitive to small

changes in individual ranking factors but the square root

is used to dampen the extreme range (Gornirtz et al,

1990).

CALCULATION

Rank Very Low Low Moderate High Very High

Variable 1 2 3 4 5

Relief (m) ≥30.1 20.1-30.0 10.1-20.0 5.1-10.0 0-5.0

Rock Type Plutonic,

Volcanic,

High-medium grade

metamorphics

Low grade

metamorphics,

Sandstone and

conglomerate

Most sedimentary

rocks

Coarse and poorly

sorted

unconsolidated

sediments

Fine unconsolidated

sediments, Volcanic

ash

Landform Rocky,Cliffed

coasts, Fiords,Fiards

Medium Cliffs,

Indented coasts

Low cliffs, Glacial

drift, Salt marsh,

Coral reefs,

Mangrove

Beaches(Pebbles),

Estuary, Laggoon,

Alluvial Plains

Barrier beaches

(sand),

Mudflats,

Deltas

Vertical movement

(mm/yr)

≤ -1.1 -1.0 - 0.99 1.0 – 2.0 2.1 - 4.0 ≥ 4.1

Shoreline

displacement

(m/yr)

≥ 2.1 Accretion 1.0 – 2.0 -1.0 - +1.0 Stable -1.1 - -2.0 ≤ -2.0 Erosion

Tidal Range (m) ≤0.99 Microtidal 1.0 – 1.9 2.0 – 4.0 Mesotidal 4.1-6.0 ≥ 6.1 Macrotidal

Wave height max

(m)

0-2.9 3.0-4.9 5.0-5.9 6.0-6.9 ≥ 7.0

Original CVI variables (Gornitz et al, 1990)

CVI VARIABLES (GORNITZ ET AL,1994)

CVI Very low Low Moderate High Very High

Variables 1 2 3 4 5

Elevation ≥ 30.0 20.1 – 30.0 10.1 – 20.0 5.1 – 10.0 0 – 5.0

Geology Plutonic

Volcanic

High-medium grade

metamorphics

Low grade metamorphics

Sandstones and

Conglomerates

Most sedimentary rocks Coarse, poorly sorted

unconsolidated sediments

Fine unconsolidated sediments

Volcanic ash

Geomorphology Rocky, cliffed coasts,

Fiords, Fiards

Medium Cliffs, indented

coasts

Low cliffs, glacial drift,

alluvial plains

Cobble beaches, Estuary,

Lagoon

Barrier beaches, Sand beaches,

Salt marsh, Mud flats, Deltas,

Mangrove, Coral reefs

RSL change (mm/yr) <-1.0 -1.0 to 0.9 1.0 to 2.0 2.1 to 4.0 >4.0

Mean Shoreline displacement (m/year) >2.0

Accretion

1.1 to 2.0 -1.0 to +1.0 -1.1 to -2.0 <-2.0

Erosion

Mean Tide range(m) <1.0 1.0 to 1.9 2.0 – 4.0 4.1 to 6.0 >6.0

Maximum Significant Wave

Height (m)

0.0 to 2.9 3.0 to 4.9 5.0 to 5.9 6.0 to 6.9 >6.9

Annual Tropical storm prob. (%) 0-8.0 8.1-12.0 12.1-16.0 16.1-20.0 >20.1

Annual hurricane prob. (%) 0-4.0 4.1-8.0 8.1-12.0 12.1-16.0 > 16.0

Hurricane frequency intensity index (%) 0-20 21-40 41-80 81-120 >121

Mean forward velocity (m/sec) >15 15.0-12.0 12.1-9.0 9.1-6.0 <6.0

Annual mean no. extra-tropical

cyclones

0-10.0 10.1-20.0 20.1-30.0 30.1-40.0 >40.1

Mean hurricane surge (m) 0-2.0 2.1-4.0 4.1-6.0 6.1-7.0 >7.0

STYDY AREA

Coastal zone in NE Attica at the Gulf of Marathon

7.7 km length

The balance of the sediments that are transferred to the area is affected by a Dam that is located 8 km west of Marathon

Old and stabilized dunes and beachrocks are observed along the coast

The area is characterized by a rapid and without rural planning expansion of urban activities (Xanthakis et al, 2007)

Population of the wider area : 34. 000, and in the summer much greater.

𝐂𝐕𝐈 =(𝐚 ∗ 𝐛 ∗ 𝐜 ∗ 𝐝 ∗ 𝐞 ∗ 𝐟)

𝟔

Where:

a: geomorphology

b: coastal slope

c: rate of relative sea-level rise

d: rate of shoreline erosion/ accretion

e: mean tide range

f: mean significant wave height

For the study area the CVI of Thieler & Hamar-Klose was used

Modified CVI (Thieler & Hammar -Klose,1999)

CVI Very low Low Moderate High Very High

Variables 1 2 3 4 5

Geomorphology Rocky,

cliffed

coasts,

Fiords, Fiards

Medium

Cliffs,

indented

coasts

Low cliffs, glacial drift,

alluvial plains

Cobble

beaches,

Estuary,

Lagoon

Barrier beaches,

Sand beaches,

Salt marsh, Mud

flats, Deltas,

Mangrove, Coral

reefs

Coastal slope (%) >11.5 11.5-5.5 5.5-3.5 3.5-2.2 <2.2

Relative sea level

change (mm/yr)

<1,8 1.8 – 2.5 2.5 – 3.0 3.0 – 3.4 >3.4

Shoreline erosion/

accretion(m/yr)

>2.0 1.0-2.0 -1.0-+1.0 -1.1- -2.0 <-2.0

Mean Tide

range(m)

>6.0 4.1 – 6.0 2.0 – 4.0 1.0 – 1.9 <1.0

Mean Wave

Height (m)

<0.55 0.55 – 0.85 0.85 – 1.05 1.05 – 1.25 >1.25

The Coastal Vulnerability

Index (CVI) that will be

used is the one proposed

in 1999 by Thieler and

Hammar-Klose.

It has six ranked from 1

to 5 according to the

Table

GIS Layers needed:

A.Basic:

• Contours (Topographic Map, 1:5000)

• Shoreline

• Geomorphology

B. Shoreline Analysis:

• Baseline Inner and Outer

• Historical shorelines

Outputs

Maps of CVI value for each variable,

and the Final CVI for the area.

WORKFLOW – DATA NEEDED

SOFTWARE NEEDED

A. GIS software

ARCMAP 10.1 or newer

http://desktop.arcgis.com/en/arcmap/

B. Shoreline Analysis

DSAS Tool

http://woodshole.er.usgs.gov/project-

pages/DSAS/version4/index.html

OR

R Programming Language 3.2.4

https://www.r-project.org/

With AmbuR plugin

So let’s start by launching

ARC Map 10.3

and start working with the data…

Thank you for your attention!!