BED, BANK & SHORE BED, BANK & SHORE PROTECTION - CHAPTER 6 doc

Wave motion in periodic, unbroken wave... Validity of wave theories... Wave run-up irregular waveH s = significant wave height ξ0 = breaker parameter based on T m-1,0 For smooth slope...

BED, BANK & SHORE

PROTECTION

Lecturer: Pham Thu Huong

Faculty of Coastal Engineering

Chapter 6

(6 class hours)

6.1 Introduction

6.2 Non breaking waves

6.3 Breaking waves

6.4 Wave on the slope

6.4 Reduction of wave loads 6.5 Summary

Examples of wave loads

In which:

(A) - standing wave

(B) - breaking wave on a mild slope

(C) - breaking wave on a steeper slope

Wave motion in periodic, unbroken wave

Validity of wave theories

Application of linear theory

gradient in filter under breakwater

Friction under waves

friction factor and cf

2 1

ˆ sinb

u = u ω t

ab: wave amplitude at bottom

ω : angular frequency

in waves (=2π/T)

Near-shore effects

¾ Shoaling

Near-shore effects

¾ Shoaling

¾ Refraction

Near-shore effects

¾ Shoaling

¾ Refraction

¾ Diffraction

the Iribarren number

(surf similarity parameter)

breaker types

(sóng cồn, sóng dâng)

bore and hydraulic jump

2

0.1

R r

small ξ Æ less reflection

Kr = 1 Æ seawall (standing wave)

Loads due to breaking

γb = H/h = 0.78 (solitary wave limit)

γb = 0.88 (Miche formula)

change of distribution in

shallow water

run up

Hunt’s Formula (for regular waves)

CUR/TAW, 1992 (for Irregular waves)

Wave run-up irregular wave

H s = significant wave height

ξ0 = breaker parameter based on T m-1,0

For smooth slope

friction values

Sand-asphalt

blocks with grass

Shallow foreshore

γf = H2% / 1.4H s

What is the wave run-up?

1:3

1:3 2m

HS = 1 Wave Slope = 0.01 R

u ?

) The wave run-up, finally, is then: R u2% = 1.5*0.9*0.75*1*2 ≅ 2m

above the design level.

Ostia, Italy

Samphire Hoe,

United Kingdom

Overtoping in Jaade Siel, Germany

22-12-1954

Measured overtopping (breaking)

Measured overtopping

(non-breaking)

Seaward slope seadike Haiphong

Sea dike near Haiphong

After Durian (2005)

wave impacts on slope

Load reduction

reflection absorption

transmission Waves

Coastal line

Linear wave theory

definitions and behaviour of

hyperbolic functions

standing wave

Relative depth Shallow Water

20

1

<

L h

Transitional water depth

Wave Celerity

c L T

g h

L T

g T kh

2 π

L T

2 2

π ρ

z h

linear wave theory basic equations

parameters

in linear wave theory

definition of H and T

wave definitions and wave height

distribution

wave height and wave period

wave registration in the North Sea

Tm-1,0 = m-1/m0 = spectral wave period ≈ 0.9

spectrum types

two types of spectra

wave spectra across shallow bar

tanh 0.578

0.077 1.20 tanh 0.833 tanh

2

tanh 0.833

w s

w

w s

w

gF u

u

gF u

wave height as function of wind,

depth and fetch

wave period as function of wind,

depth and fetch