Page History

Section

border	true

Column

width	70%

table

Wiki Markup

{table} {table-row} {table-cell:valign=top} {panel} h2.

tr

td

valign	top

Panel

'Process-based

modelling

of

shoreline

response

to

submerged

breakwaters' {panel} !bedlevelend.png|border=1! *

breakwaters'

Image Added

Procces-based

modelling

of

shoreline

response

to

submerged

breakwaters

*

Towards

design

criteria

for

shoreline

repsonse

to

submerged

breakwaters

*Background* In the

Background

In the past,

emergent

coastal

structures

like

groynes

or

detached

offshore

breakwaters,

have

been

used

commonly

as

coastal/beach

protection

measures.

These

conventional

structures

are

studied

extensively

and

applied

successfully

many

times.

Main

purpose

of

a

coastal

structure

near

or

in

the

surf

zone

is

to

counter

shoreline

erosion.

A

frequently

adopted

structure

is

an

emerged

rubble-mound

breakwater.

Primary

function

of

such

a

breakwater

is

to

reduce

the

wave

energy

in

the

lee

of

the

breakwater

and

initiating

shoreline

accretion

by

changing

the

corresponding

local

currents.

[

]

.

Amongst

others,

[

]

and

[

]

,

already

quantified

the

shoreline

response

to

(single)

emerged

breakwaters

as

a

function

of

the

dominant

breakwater

design

parameters.

Despite

the

successful

applications,

emergent

structures

are

becoming

increasingly

less

popular,

due

to

their

negative

impact

on

beach

amenity

and

aesthetics.

[

]

As

a

result,

alternatives

for

these

conventional

protection

measures

are

sought.

One

alternative

is

a

detached

offshore-submerged

breakwater.

Submerged

breakwaters

are

capable

of

providing

the

necessary

beach

protection

while

not

having

the

downside

of

adverse

impact

on

beach

amenity

and

aesthetics.

In

addition,

the

recognition

that

a

beach

protection

measure

can

be

combined

with

other

functions

has

a

wide

community

appeal

[

]

.

According

to

[

]

artificial

sub-tidal

and

sub-aerial

offshore

reefs,

which

are

similar

to

submerged

breakwaters,

can

have

different

functions,

like

beach

protection,

enhancement

of

marine

habitat,

surfing,

diving

and

swimming

safety.

In

[

]

an

example

is

given

of

such

a

multi

functional

design

of

a

submerged

breakwater

which

enhances

local

surfing

conditions.

Obviously,

a

multifunctional

beach

protection

measure,

which

combines

protection

of

the

shoreline

with

other

functions

while

not

impairing

aesthetics

or

beach

amenity,

will

be

the

preferred

choice

to

coastal

management

authorities

when

coastal

problems

arise.

*

Problem

definition

*

Despite

all

the

benefits

of

a

proper-designed

submerged

breakwater,

submerged

breakwaters

have

rarely

been

adopted

until

now,

which

is

the

reason

why

their

efficiency

is

still

largely

unknown.

An

overview

of

reported

submerged

breakwaters

is

given

by

[

]

.

From

this

overview,

it

shows

that

in

spite

of

all

effort,

in

most

cases

enhanced

shoreline

erosion

in

the

lee

of

the

submerged

breakwater

occurred.

Clearly,

a

better

understanding

of

all

the

involving

processes

around

submerged

breakwaters

is

required

before

routinely

adopting

submerged

breakwaters

for

coastal

protection.

As stated

As stated above,

before

routinely

adopting

submerged

breakwaters,

more

understanding

is

needed

of

the

effect

of

a

submerged

breakwater

on

hydrodynamic

and

morphological

processes

close

to

the

shoreline.

In

this

highly

complex

zone,

waves

and

currents

interact

with

local

conditions

like

bathymetry

etc,

enabling

morphological

changes

around

the

breakwater.

have

been

focussing

(amongst

others)

on

wave

characteristics

over

submerged

breakwaters,

[

]

,

wave

set-up

[

]

,

scour

characteristics

,

[

]

and

modelling

of

waves

and

currents

around

submerged

breakwaters

[

]

.

Less

is

known

about

the

morphological

shoreline

response

to

submerged

breakwaters.

A

first

attempt

in

quantifying

the

formation

of

a

salient/tombolo

in

the

lee

of

submerged

breakwaters

was

done

by

[

]

.

This

study

focussed

on

the

morphological

effect

of

natural

reefs

in

New

Zealand

and

Australia,

which

is

similar

to

submerged

breakwaters.

Another

interesting

study

on

the

morphological

effect

of

submerged

breakwaters

is

done

by

[

]

.

This

study

focussed

on

the

mode

of

shoreline

response,

(accretive

or

erosive)

to

a

single

shore-parallel

submerged

breakwater.

Both

studies

as

well

as

the

other

studies

mentioned

show

the

complexity

of

the

processes

around

submerged

breakwaters.

Due

to

this

complexity,

computational

models

are

often

used.

In

practise,

these

models

may

however

be

time

consuming

and

'difficult'

to

use.

In

addition,

during

preliminary

stages

of

the

design

process,

no

detailed

solutions

or

outcomes

are

needed

and

therefore

rules

of

thumb

or

(empirical)

formulas

are

commonly

preferred

instead

of

computational

modelling.

However,

universal

rules

of

thumb

or

formulas

of

the

shoreline

response

to

submerged

breakwaters,

which

include

all

the

important

hydrodynamic-,

structural

and

environmental

parameters

are

still

to

be

discovered.

*Research objective* The main objective of this MSc thesis is the development of universal engineering design criteria that can predict the magnitude of shoreline response to a given design single shore-parallel detached submerged breakwater. These criteria will quantify the formation of a salient/tombolo or erosion as a function of structural, environmental and hydrodynamic parameters. In order to come up with design criteria for shoreline response to submerged breakwaters this study will be specially focussing on: • Current literature that is available on submerged breakwaters. • Modelling of a submerged breakwater with a phase averaging numerical model (Delft3D) • Sensitivity analysis of the model results to various model characteristics (Morfac, wave-current interaction, mass-flux etc). • Hydrodynamic and morphologic processes that dominate shoreline response to submerged breakwaters. • The dependency of the magnitude of shoreline response on principal structural/environmental parameters that govern submerged breakwater induced morphological response. • Analyses of model results and translation to engineering criteria capable of predicting the magnitude of shoreline response to a design submerged breakwater *Methodology* The proposed study can be divided into the following stages: _Literature review_. First, the hydrodynamic and morphological processes that may affect shoreline response to a submerged breakwater are studied from literature. This theoretical study indicates which are the important processes and corresponding parameters that govern submerged breakwater induced morphological response. In addition, previous studies on submerged breakwaters will be summarised and conclusions are taken into account. This literature study will act as a starting point for this thesis. _Modelling with of a submerged breakwater with a phase averaging model (Delft3D)_. Second the shoreline response to a submerged breakwater is modelled by a numerical phase averaging model, Delft3D, developed by Deltares. A two-dimensional depth averaged model is set-up to study the important driving processes behind submerged breakwater induced shoreline response, without having the large computational times of a full three-dimensional and phase resolving model. Using an initial alongshore uniform profile and avoiding site-specific conditions will lead to a universal approach so that the eventual design criteria will be applicable world wide. _Sensitivity analysis numerical parameters_. Applying a numerical model introduces additional (numerical) parameters and assumptions that influence the shoreline response. In order to quantify the influence of these parameters/assumptions and to reduce the computational times, a sensitivity analysis of these parameters is performed. _Analysis of hydrodynamic and morphologic processes_. From literature most important processes that govern submerged breakwater induced shoreline changes are known. Analysing model results of Delft3D will show whether this phase-averaged and depth averaged model is capable of modelling all the important processes, ignoring detailed turbulence, while using mild slope equations. _Sunny isle Delft3D calibration case_. Next, measurements from an existing submerged breakwater are used to calibrate the Delft3D model. This field case comprises the Sunny Isle breakwater in Florida USA, a coupled breakwater system containing two detached shore normal submerged breakwaters. Fine tuning of the numerical parameters, together with the sensitivity analyses, will lead to more reliable results when comparing the influence of structural/environmental parameters, while not impairing on computational efficiency of the Delft3D model. _Structural and environmental parameters_. The next step in this study is the sensitivity analyses on the structural and environmental parameters governing submerged breakwater induced shoreline response. The influence of the most important parameters on shoreline response, followed from the theoretical study, are examined using the model set-up in Delft3D. The results of this analyses, the formation of a salient or erosion, are then quantified and a tendency is searched for. _Design criteria and comparison_. Using the tendencies of the different parameters, design criteria for submerged breakwater induced shoreline response are made. The final stage of this study will be a comparison between the proposed design criterion and previous studies on submerged breakwater induced shoreline response, followed by conclusions and recommendations for further research. {table-cell} {table-row} {table-row} {table-cell:colspan=2} {table-cell} {table-row} {table}

Research objective

The main objective of this MSc thesis is the development of universal engineering design criteria that can predict the magnitude of shoreline response to a given design single shore-parallel detached submerged breakwater. These criteria will quantify the formation of a salient/tombolo or erosion as a function of structural, environmental and hydrodynamic parameters.

In order to come up with design criteria for shoreline response to submerged breakwaters this study will be specially focussing on:

• Current literature that is available on submerged breakwaters.
• Modelling of a submerged breakwater with a phase averaging numerical model (Delft3D)
• Sensitivity analysis of the model results to various model characteristics (Morfac, wave-current interaction, mass-flux etc).
• Hydrodynamic and morphologic processes that dominate shoreline response to submerged breakwaters.
• The dependency of the magnitude of shoreline response on principal structural/environmental parameters that govern submerged breakwater induced morphological response.
• Analyses of model results and translation to engineering criteria capable of predicting the magnitude of shoreline response to a design submerged breakwater

Methodology

The proposed study can be divided into the following stages:
Literature review. First, the hydrodynamic and morphological processes that may affect shoreline response to a submerged breakwater are studied from literature. This theoretical study indicates which are the important processes and corresponding parameters that govern submerged breakwater induced morphological response. In addition, previous studies on submerged breakwaters will be summarised and conclusions are taken into account. This literature study will act as a starting point for this thesis.
Modelling with of a submerged breakwater with a phase averaging model (Delft3D). Second the shoreline response to a submerged breakwater is modelled by a numerical phase averaging model, Delft3D, developed by Deltares. A two-dimensional depth averaged model is set-up to study the important driving processes behind submerged breakwater induced shoreline response, without having the large computational times of a full three-dimensional and phase resolving model. Using an initial alongshore uniform profile and avoiding site-specific conditions will lead to a universal approach so that the eventual design criteria will be applicable world wide.
Sensitivity analysis numerical parameters. Applying a numerical model introduces additional (numerical) parameters and assumptions that influence the shoreline response. In order to quantify the influence of these parameters/assumptions and to reduce the computational times, a sensitivity analysis of these parameters is performed.
Analysis of hydrodynamic and morphologic processes. From literature most important processes that govern submerged breakwater induced shoreline changes are known. Analysing model results of Delft3D will show whether this phase-averaged and depth averaged model is capable of modelling all the important processes, ignoring detailed turbulence, while using mild slope equations.
Sunny isle Delft3D calibration case. Next, measurements from an existing submerged breakwater are used to calibrate the Delft3D model. This field case comprises the Sunny Isle breakwater in Florida USA, a coupled breakwater system containing two detached shore normal submerged breakwaters. Fine tuning of the numerical parameters, together with the sensitivity analyses, will lead to more reliable results when comparing the influence of structural/environmental parameters, while not impairing on computational efficiency of the Delft3D model.
Structural and environmental parameters. The next step in this study is the sensitivity analyses on the structural and environmental parameters governing submerged breakwater induced shoreline response. The influence of the most important parameters on shoreline response, followed from the theoretical study, are examined using the model set-up in Delft3D. The results of this analyses, the formation of a salient or erosion, are then quantified and a tendency is searched for.
Design criteria and comparison. Using the tendencies of the different parameters, design criteria for submerged breakwater induced shoreline response are made. The final stage of this study will be a comparison between the proposed design criterion and previous studies on submerged breakwater induced shoreline response, followed by conclusions and recommendations for further research.

tr

td

colspan	2

Column

width	30%

Panel
Info:

unmigrated-inline-wiki-markup

{

Metadata list

}
|| Name | Roland Vlijm||
|| Email | Roland.vlijm@Deltares.nl ||
|| Room | HH 1.17 ||
|| Software package | Delft3D ||
|| Start Date | Nov 2010 ||
|| Specialisation Programme | Coastal Engineering ||
|| Deltares supervisors | Arjen Luijendijk ||
|| &nbsp; | Rosh Ranasinghe ||
|| TU Delft professor | Prof. Marcel Stive||
{metadata-list}

Child pages

Versions Compared

Old Version 17

New Version Current

Key

'Process-based

modelling

of

shoreline

response

to

submerged

breakwaters'

Info: