Littoral dynamics

modelling

Filipa Simões de Brito Ferreira de Oliveira

Núcleo de Estuários e Zonas Costeiras

Departamento de Hidráulica e Ambiente

Outline

• Brief introduction of LNEC-DHA-NEC

• Methodologies for evaluation and testing beach vulnerability &

protection-rehabilitation solutions: general overview

• Applications of Mike – Litpack modelling system at LNEC

• Case study: an application of Litpack

Hydraulics and Environment Department

R&D&I topics cover the whole water cycle:

• Surface and groundwater resources

• Urban, coastal and port engineering

Strategic lines of approach:

• Risk management and safety

• Hydraulic infrastructures

• Environment and aquatic systems

• Urban water

• Information technology applied to water and environment

Estuaries and Coastal Zone Unit

R&D&I areas

• Beach dynamics, protection and rehabilitation

• Management of coastal risks including erosion and flooding

• Morphodynamics and stability of inlets

• Improved design of estuarine and coastal infrastructure

• Maintenance of ports, harbours and navigation channels

• Assessment and prediction of water quality in estuaries

• Prediction and monitoring of oil spills at sea

LNEC | 44

Present SLR = 1 mSLR = 0.23 m SLR = 0.35 m

Methodologies for evaluation and testing

beach vulnerability & protection-rehabilitation solutions

applied at LNEC

1) Field work for characterisation of the site dynamics

Coastal processes field measurement

Numerical modelling of coastline evolutionTopo-hydrography

historical evolution

2) Topo-hydrography historical evolution analysis

3) Numerical modelling of medium to long-term coastline evolution

4) Numerical modelling of beach morphological

response to storm events

Vulnerability index

Numerical modelling

of beach response

Integrated video-tracer technique for

sand transport measurements

5) Physical modelling

6) Risk evaluation analysis

Applications of Mike – Litpack modelling system

at LNEC

…in international consultancy projects

Integrated solution for

environmental rehabilitation

of Rodrigo de Freitas lagoon

and Leblon, Ipanema and

Arpoador beaches, Brasil

Rehabilitation of

Hac-Sá beach,

Macau, People's

Republic of China

Detailed Modelling Studies for

Colwyn Bay Coastal Defence

Scheme, United Kingdom

Characterisation of the

coastal dynamics conditions

and impact assessment of

Marina Luanda’s

construction, Angola

…in national research & consultancy projects

Feasibility study on

the construction of a

white-sand beach at

Formosa beach,

Funchal, Madeira

Study of the

maintenance and

improvement of

Porto Santo beach

Madeira

Intervention alternatives for the

improvement of the accessibility to the

fishing harbour of Vila Praia de Âncora

Sediment dynamics in

the littoral stretch Praia

da Vieira – Praia Velha

Beach evolution in

zones of restricted

fetch: Alfeite spit

Morphodynamic study at the

location of the submarine

water intake pipelines of the

Mira Acuinova fish farm

Marine sand extraction in the

continental shelf of Algarve,

Portugal: morphodynamics and

impact at the coastline

Modelling the impact

of the extension of

the Mondego inlet

north jetty in the

adjacent beaches at

south

Hydrodynamics of

Buarcos and F. Foz

beaches

Modelling the

stability of artificial

reef modules and

adjacent seabed

evolution, Nazaré

Case study: an application of Litpack

Rehabilitation and protection

of Colwyn Bay beach, UK

Rehabilitation and protection of Colwyn Bay beach, UK

Problem

• Process of beach erosion

1946

1990

Impact

• Reduction of beach width

• Beach face and berm lowering

• Coastal defence structures degrading

• Seawall overtopping and consequent flooding of the

promenade

2009

Objectives

• Characterisation of the beach sediment dynamics and its recent

evolution

• Test and evaluate coastal protection solutions based on artificial

beach nourishment and control structures

Methodology

Characterisation of the beach dynamics

Historical evolution

• Average shoreline retreat: 13 m (1956-2007)

• Maximum shoreline retreat: 76 m (1980-1990)

• Foreshore volume loss: 40x103 m3 (2001-2007)

-80.0

-60.0

-40.0

-20.0

0.0

20.0

40.0

60.0

80.0

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

transects number

net

sh

ore

lin

e m

ovem

en

t (m

)

1956-1980 1980-1990 1990-2002 2002-2007 1956-2007W E

A

Characterisation of the beach dynamics

Sediment

• Upper foreshore: coarse-grained sands and gravel (D50=0.6-3 mm), poorly sorted (σ > 3)

• Lower foreshore:fine to medium-grained sands (D50=0.2-0.3mm), well sorted (σ ~ 1)

• Particles density: 2.7

Sea level

• Tide: 4<TR<8 m

• Maximum surge observed: 1.02 m

Characterisation of the beach dynamics

Wave climate

• 50% waves Hs<0.25 m and max Hs<3.25 m Mild climate

• Most frequent class is 3<Tz<4 s and max Tz=7.1 s

• 65% of the inshore waves reach from the Northwest quadrant, with

predominance of directions 285<Dir<345

100x103 m3/year

0

20 000

40 000

60 000

80 000

100 000

120 000

140 000

160 000

180 000

200 000

198

6

198

7

198

8

198

9

199

0

199

1

199

2

199

3

199

4

199

5

199

6

199

7

199

8

199

9

200

0

200

1

200

2

200

3

200

4

200

5

200

6

Se

dim

en

t tr

an

sp

ort

(m

3.y

ea

r-1)

Year

Longshore annual transport

West

East

Longshore sediment drift

• Significant interanual variations of the transport potential (52-188 x 103m3.year-1)

Hrms (m)

Above 2.00

1.75 - 2.00

1.50 - 1.75

1.25 - 1.50

1.00 - 1.25

0.75 - 1.00

0.50 - 0.75

0.25 - 0.50

0.10 - 0.25

Below 0.10

C:\D

ocum

ents

and

Set

tings

\FO

livei

ra\M

y D

ocum

ents

\Pro

ject

s_10

\Col

wyn

Bay

\Mod

ellin

g\Li

tdrif

t_ol

d be

ach\

Tra

nspo

rt_1

987c

_orig

inal

sed

imen

t.dfs

0

N

Calm0.10 %

5 %

Sediment balance

Hrms (m)

Above 2.00

1.75 - 2.00

1.50 - 1.75

1.25 - 1.50

1.00 - 1.25

0.75 - 1.00

0.50 - 0.75

0.25 - 0.50

0.10 - 0.25

Below 0.10

C:\

Do

cu

me

nts

an

d S

ett

ing

s\F

Oliv

eira

\My D

ocu

me

nts

\Pro

jects

_1

0\C

olw

yn

Ba

y\M

od

elli

ng

\Wa

ve

clim

ate

\Litco

nv\C

lima

te_

19

87

b.d

fs0

N

Calm35.55 %

5 %

Wave climate

Definition of optimum recharged beach profile

• Long-term submerged profile: two-slope (surf and shoaling) EBP due to the large tidal range

2S-EBP profiles: Berm configuration A

-8

-6

-4

-2

0

2

4

6

0 100 200 300 400 500 600 700

x (m)

h (

m O

D)

C31

C33

C35

C37

EBP, D50=0.75

EBP, D50=0.25

EBP, D50=0.45

ar

r

xxxhC

D

C

hX

xxhA

B

A

hx

,

0,

3

23

23

3

23

23

2S-EBP profiles: Berm configuration B

-8

-6

-4

-2

0

2

4

6

0 100 200 300 400 500 600 700

x (m)

h (

m O

D)

C31

C33

C35

C37

EBP, D50=0.25

EBP, D50=0.45

• Berm designwidth (beach protection; recreational use; recharge economy)

height (sea level frequency of exceedance)

Definition of optimum recharged beach profile

• Berm vulnerability testing: beach response to storm events – numerical modelling Extreme maritime events definition (2 criteria 2 events)

Storm Feb/90

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

1800 1900 2000 2100 2200

Cross-shore distance (m)

Ch

an

ge i

n z

(m

)

-6

-4

-2

0

2

4

6

8

EB

P i

n O

DN

level

(m)

D50=0.25mm, Spreading=1.72 D50=0.45mm, Spreading=2.1D50=0.25mm D50=0.45mm

Main findings:

• Only the 50 m width and 1:100 slope berm revealed enough resilience to prevent direct wave action on the seawall

• Importance of the geometrical spreading for the erosion process

Long-term Shoreline Modelling

• Two long-term coastline evolution numerical models with different characteristics and capacities (complementary)

• Calibration• coastlines (Oct/01, Oct/02, Jul/03, May/04 & Jul/05)

• synoptic hydrodynamic data (wave series & sea level)

• Alternative solutions• 2 solutions of beach nourishment

• 6 solutions of beach nourishment (2.5x103 m3 for D50=0.25mm) with control structures

3.3x106 m3 for D50=0.25mm 2.2x106 m3 for D50=0.45mm

Classical groynes

Detached breakwaters

Fishtail groynes

Construction of the terminal groyne (eastern end of the frontage)

Beach recharge

Thank you for your attention !

2016