damping of tsunami and storm waves by ......parameterization based on easily measurable/observable...

11

Leichtweiß-Institute für Wasserbau (LWI)

Abteilung Hydromechanik und KüsteningenieurwesenTechnische Universität Braunschweig

DAMPING OF TSUNAMI AND STORM WAVES BY COASTAL FORESTS –

PARAMETERIZATION AND HYDRAULIC MODEL TESTS

S. Reimann

S. Husrin

A. Strusińska

H. Oumeraci

FZK Kolloquium, Hannover, 26. March 2009

FZK Kolloquium, Hannover, 26. March 2009S. Reimann

2. Parameterization of mangroves

3. Laboratory experiments on hydrodynamic performance of mangrove forest

1. Motivation and objectives

4. Outlook

POSITION OF THE PROBLEM

1. Motivation and objectives FZK Kolloquium, Hannover, 26. March 2009S. Reimann

MULTI DEFENCE LINE STRATEGY (Oumeraci, 2006)

> 500 m ?

250 - 500 m ?

Damped

TsunamiHWL

MWLLWL

1

2 45

Artificial reefs

Sea wallsDunes

Raised buildings

Mobile defence systems

FOREST

50 - 100 m ?

Tsunami resistant Building

• Damping performance of forest• Structural integrity of single tree

3

OBJECTIVES

1. Motivation and objectives FZK Kolloquium, Hannover, 26. March 2009S. Reimann

Generate knowledge base for better insight into physical processes involved in interaction of tsunami/storm waves with coastal forests, incl. subsequent energy attenuation

Develop generic methodology for coastal forest parameterization based on easily measurable/observable parameters

Develop and validate/verify prediction models (analytical/ numerical, semi-empirical) for hydraulic performance of coastal forests as a protection against tsunami/storm waves.





4. Outlook

REAL MANGROVE TREE AND ITS DIMENSIONS

2. Parameterization of mangroves FZK Kolloquium, Hannover, 26. March 2009S. Reimann

after Dinar et al. (2004)

bB = 3.0 - 3.2 m

hB = 3.5 - 4.0 m

hTR = 0.5 - 1.0 m

hR = 1.3 - 1.5 m

Ø root = 4 - 6 cm

Ø trunk = 12 - 18 cmMHWL

Rhizophora sp.

density of trunks = 0.8 - 1.0 trunks/m²number of prop roots = 72 - 152 roots/trunk

hM = 5.0 - 5.5 m

Ø branch = 5 - 6 cm

PARAMETERIZATION OF MANGROVE TREE

Reference Model Parameterised Models

Model Scale 1 : 20


SELECTED RESULTS OF PARAMETERIZATION TESTS






4. Outlook

EXEMPLARY MODEL SET-UP FOR FOREST WIDTH B=0.75m (1)

h=0.415m

10.0m

WG1

WG2

WG3

WG4

23.64m

13.64m 8.33m

8.33m

2.01m B=0.75m

WAVE

MAKER WG5

ARRAY1

SWL

PLATFORM

Bf=

2.0

m

WA

VE

MA

KE

R

ADV1 ADV2

WG6

WG7

WG8

WG9

WG10

WG11

WG12

ARRAY2 ARRAY3

FOREST

WG13 WG14 WG15

WG16

WG17

WG18

WG19

PLATFORM

GLAS WINDOW

~1:20

WG1

WG2

WG3

WG4

WG5

WG6

WG7

WG8

WG9

WG10

WG11

WG12

WG16

WG17 WG19

WG13 WG14 WG15

P1 P2

WG18

PT1 PT2

WA

VE

MA

KE

R

Bf=

1.0

m

~1:20PLATFORM

WG8

WG9 WG11

WG10P2PT2WG1

WG2

WG3

WG4

FT

FT

10.0m 0.40m

0.755m

1.095m 0.40m 1.08m 0.42m 1.08m

0.775m 0.76m

1.03m0.375m0.375m0.495m

0.5m

0.495m

0.539m

FOREST

WG6 WG7

PT1

WG5

P1

?m 8.33m

1.0m

hr=0.415m

ARRAY4

ADV1

3. Laboratory experiments on hydrodynamic performance of mangrove forest FZK Kolloquium, Hannover, 26. March 2009S. Reimann

TREE NUMBER: N=62

SIZE OF SINGLE TREE MODEL: 15x15cm

FOREST WIDTH: B=0.75mT

2

FTS7

FTS4 FTS5 FTS6

FTS1 FTS2 FTS3

Bf=

2.0

m

1.9

5m

1.8

m

B=0.75m

~1:20

2.0m

BE

AC

H S

LO

PE

PT2PT1

DIRECTION OF WAVE

PROPAGATION

FTS8 FTS9

P1 P2

ADV2ADV1

WG13WG14

WG15

Measuring devices:

Wave gauge

Propeller

Acoustic Doppler Velocimeter (ADV)

Pressure Transducer

Force Transducer for single tree

WG

P

ADV

PT

FTS

ARRANGEMENT OF TREE MODELS AND INSTRUMENTATION



EXEMPLARY MODEL SET-UP FOR FOREST WIDTH B=0.75m (2)

1. STAGE: Mangrove Forest

• MODEL SCALE: 1:25

• MODEL STIFFNESS: MANGROVE FOREST - stiff tree models (submergence depth up to canopy)

MANGROVE & PINE FOREST - stiff/flexible tree models (submergence depth up to canopy)

• FOREST WIDTH: B=0.0, 0.75, 1.5, 2.25, 3.0 … m

• WATER DEPTH: h=0.415, 0.465, 0.515, 0.565, 0.615m

• WAVE TYPES: storm waves (regular and irregular waves), tsunami (solitary waves and bore)

• WAVE PARAMETERS: wave height H=0.04-0.20m; wave period T=1.0-6.0s

2. STAGE: Pine Forest


EXPERIMENTAL PROGRAMME

MEASUREMENTS OF FORCE TRANSDUCERS FOR A SINGLE TREE (FTS)


REGULAR WAVES:

h=0.565m, H=0.04m, T=1.0s

FTS2

FTS1 (in front of forest)

FTS2 (in the middle of forest)

FTS1

MEASUREMENTS OF FORCE TRANSDUCER FOR ENTIRE FOREST (FT)


REGULAR WAVES:

h=0.565m, H=0.04m, T=1.0s

FT

MEASUREMENTS OF WAVE GAUGES (WG)


REGULAR WAVES:

h=0.565m, H=0.04m, T=1.0s

WG12 (in front of forest)

WG19 (behind forest)

WG19WG12





4. Outlook

4. Outlook FZK Kolloquium, Hannover, 26. März 2009S. Reimann

Preparation of equipments required for performance of the experiments (e.g. coastal pine models, gate for a bore generation in twin wave flumes)

performance of laboratory experiments on mangrove effectiveness on wave energy reduction for varying water depths and wave conditions

performance of laboratory experiments on Casuarina effectiveness on wave energy reduction for varying water depths and wave conditions

determination of hydraulic performance of both types of forest (wave transmission, reflection and energy dissipation)

Use of experimental results for the development of numerical model

THANK YOU FOR YOUR ATTENTION !

FZK Kolloquium, Hannover, 26. März 2009S. Reimann

damping of tsunami and storm waves by ......parameterization based on easily measurable/observable...

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