NRCEST

Equilibrium beach

Chang Hsien Kuo

國立交通大學土木工程學系中華民國 102年 4月 11日

2

Definition of beach morphology

淺化帶 (shoaling zone); 碎波帶 (surf zone); 沖刷帶 (swash zone) ;灘線 (shore line); 海灘 (shore , beach); 海岸 (coast); 平台 (berm);內灘 (inshore); 外灘 (offshore); 沙洲 (bar); 灘面 (beach face); 灘崖 (beach scarp); 台梯 (step) ; 沙谷 (trough)

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Type of beach profile

Definition:平衡海灘斷面 (equilibrium beach profile): 在同一波浪條件長期作用下，海灘斷面將呈現平衡之狀態。Type of beach:Type A: 暴風海灘 (storm beach) 或冬季海灘 (winter beach) Type B: 中間型海灘 (transition beach)Type C: 正常海灘 (normal beach) 或夏季海灘 (summer beach)

Sunamura and Horikawa , 1974

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Slope of beachface

Sunamura (1984)4/12 50 12.0tan

bbf H

dHgT

TdgHb

5.05.0 50/

tan

f

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Classification of beach profile

Sunamura and Horikawa (1974)

67.0

0

27.0

0

0

67.0

0

27.0 50tan850tan4

Ld

LH

Ld

Experiment: 4-8Field:9-18

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Equilibrium beach: theory

Dean (1977)

hDECxt

Eeqg

hDghgH

dxd

eq/

212

81

hH hDdxdhhg eq 2

581 2/322/3

3/2xh 32

223524

/

/eq

g

D

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Brunn-Dean profile:Equilibrium beach:

Moore (1982) 64.05027.0 d

,

44.0 067.0 fWDean(1991)

Disadvantages:1. Infinity slope at shoreline2. Monotonic function: infinity depth

Kriebel et al. (1998)

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Other forms of beach profile

Bodge (1992)

mxf em

h

1tan

5

05

4

04

3

03

2

02

01

0

Lxa

Lxa

Lxa

Lxa

Lxa

Lh

Hsu e al. (1998)

Simple form?Theoretical approach?Bar shape profile?

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Advanced reference

mAxh

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A and m coefficients of Bruun/Dean profile

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A and m coefficients of Bruun/Dean profile

12

A and m coefficients of Bruun/Dean profile

Artcic beach

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A and m coefficients of Bruun/Dean profile

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Shape parameter

15

Shape parameter

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Shape parameter

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Best fitting for a1

a1=03285

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Shape parameter

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Extended equilibrium beach

Larson (1991)

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Three-parameter equilibrium profile

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Three-parameter equilibrium profile

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Three-parameter equilibrium profile

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Three-parameter equilibrium profile

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Three-parameter equilibrium profile

Goodness of fit: overall errors

25

Validity of equilibrium beach

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Validity of equilibrium beach

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Reflective natural beaches

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Surf profile

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Shoaling profile

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Comparison with field data

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Parameter

32

Discussion

1. Does an equilibrium beach exist in real beach?2. What is the application of equilibrium to coast

engineering?3. Theoretical approach ?