Bed bank and shore protection

BED, BANK & SHORE PROTECTION Lecturer: Pham Thu Huong Faculty of Coastal Engineering... The impacts cause the damages on coastal line 3.. The impacts cause the damages on coastal line •

BED, BANK & SHORE

PROTECTION

Lecturer: Pham Thu Huong Faculty of Coastal Engineering

Chapter 1

INTRODUCTION

(3 class hours)

1 General of Viet Nam coast

2 The impacts cause the damages on coastal line

3 Protect or not protect ?

4 Coastal protection structures

5 Working conditions and requirement with coastal structures

6 How to look at protections ?

7 How to deal with protections ?

Schedule 45B (15Jan – 18May)

¾ 15 Jan: Chapter 1

¾ 22 Jan: Chapter 2

¾ 29 Jan: Chapter 3

¾ 05 Feb: Chapter 3 (cont.)

¾ 12 Feb: Tet holiday

¾ 19 Feb: Tet holiday

1 General of Vietnamese Coast

Islands in Ha Long as breakwaters

Dong Chau beach (Thai Binh)

Beach at Tien Giang river mouth (Go Cong)

Sandy beach at Quang Binh

Rocky beach at Hai Van mountain pass

2 The impacts cause the damages

on coastal line

• Natural impacts:

- Winds, typhoons ⇒ bring sand land ward or sea ward

- Tides, salty water ⇒ erosion, rusted steel structures

- Currents ⇒ erosion, creation

- Waves ⇒ erosion, instability of coastal lines, damaging structures which protect bed, bank and shore

- Chemical impacts ⇒ structures are corroded

- Impacts of organisms

Erosion in Nam Dinh coast

Impacts of organisms

on culvert wall (NamDinh)

Wave action (Nam Dinh sea dike – August 2006)

2 The impacts cause the damages on coastal line

• Artificial structures impacts:

- Building dams, reservoirs ⇒ reduce sediment transport to down stream, cause coastal line erosion

Hoa Binh dam

• Artificial structures impacts:

- Exploiting sand, grave, mineral resources ⇒ inadequate sediment supply

2 The impacts cause the damages on coastal line

Exploiting sand in Tan Ba, Dong Nai river

• Artificial structures impacts:

- Deforesting, destroying mangroves ⇒ erosion, unstable coastal line

2 The impacts cause the damages on coastal line

Mangroves, Đầm Nại, Bình Thuận

• Artificial structures impacts:

- Reclamations ⇒ unstable coastal line

- Canal, culvert system ⇒ Coastal erosion

- Navigation ⇒ damage bank protections

2 The impacts cause the damages on coastal line

3 To protect or not to protect ?

Floating houses in MeKong River

Protect what ?

- Protect residential area from flood-tides, storm surge

- Prevent wave actions, erosions, slide of the slope

- Other purposes: Navigation, hydraulic works,

aquaculture, tourism, salt production, national defense

- Prevent salt intrusion*

- Prevent sedimentation at river mouths and obstacle

on draining off flood away*

* don’t mention in this lecture note

4 Coastal protection structures

- Construction: Sea dikes, revetments, groins,

breakwaters, close-dams, sea-walls, artificial dredging and creating, dams, culverts,…

- Non-construction: sand nourishments, mangrove

forests, laws, policies, institutions, organization

methods and managements; propaganda, education, convincing people…

5 Working conditions &

requirement with Coastal structures

- Working conditions of coastal structures:

• Coastal structures are under the powerful influence of waves, winds, tides, currents, uplift pressures, drifts…

• erosion, accretion

- Requirement with Coastal structures:

• Height Æ Allow overtopping ỏ Not ?

• Stable

• satisfy other purposes

When and Where ?

6 How to look at protections?

Building codes in eroding coastal line

Hue

Examples of protection

7 How to deal with protections?

Cause and effect

Designed protections

North coast Java

Failure Mechanisms

Fault tree

Load and strength for steel and granular structure

Strength increase or load reduction

Strength as a function of time and maintenance

The end of Chapter 1

Construction

Non – construction

BED, BANK & SHORE

PROTECTION

Lecturer: PhamThu Huong

Faculty of Coastal Engineering

Chapter 2

(3 class hours)

Seconds short waves seconds turbulence

Velocity field in various situations

averaged velocity values (ū = Q/A)

Reynolds dye experiment

Reynolds number

• Laminar flow occurs at low Reynolds numbers (Re<1000)

• Turbulent flow occurs at high Reynolds numbers (Re>2000)

vs - mean fluid velocity,

L - characteristic length (h: water depth)

μ - (absolute) dynamic fluid viscosity

ν - kinematic fluid viscosity: ν = μ / ρ = 10 -6 m 2 /s (water)

ρ - fluid density

2.2 Turbulence

Turbulence motion: velocity and pressure show irregular fluctuations

u = u + u v = v + v w = w + w p = p + p ′ ′ ′ ′

Turbulence variations:

Turbulence can then be expressed in various ways, such as:

total kinetic energy in a

turbulent flow fluctuation intensities of

u, v and w, relatively

2 2

inertia press visc.

Reynolds stresses:

2

inertia press visc Reynolds stresses

mean values turb fluctuations

Exchange of momentum due to turbulence

Resistance in laminar and turbulent flow

2.3 Uniform wall flow

a bed slope of 1/1000 and a roughness of 0.2 m What is the

depth, the velocity, the Chezy-value, the relative turbulence

intensity and the relative turbulent shear stress?

u= C√RI

Q* = bhu Q* = Q

Stop

non uniform flow

The growth of a boundary layer when an

infinitely thin plate is placed in a flow with u = u 0

Influence of pressure gradient on velocity

profile

Turbulence in windtunnel contraction

The total amount of turbulent kinetic energy, k, remains approximately

constant

Due to the increased velocity in the contraction, the relative turbulence, r,

using the local mean velocity decreases

Flow and velocities in jets

2

2

0.693 0

0.693 0

R b

Turbulent fluctuations in circular jet

instability of an axisymmetric jet

effect of strong pressure gradients

2.5 Combination of wall flow and Free flow

Flow separation around blunt and round body

Vertical constriction and expansion (sill)

Vertical expansion (backward-facing step)

Horizontal expansion

Horizontal constriction and expansion

(groyne)

Detached

bodies

2.6 Load Reduction

The end Chapter 2