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In MIKE 2016, we have added state-of-the-art shoreline morphology evolution to our industry leading MIKE 21/3 Coupled Model FM software.

WHAT IS THE COUPLED MODEL?

The MIKE 21/3 Coupled Model FM provides a unified platform for consideration of fully dynamic coupling of waves and tides plus feedback from sediment transport processes, if desired. A single interface allows the user to create a model which takes account of the impact of waves and tides on each other, in two– or three-dimensions, using dynamically coupled versions of MIKE 21/3 FMHD and MIKE 21 SW. Sand or mud transport modules can be added to include the impact of sediment transport processes on the overall system. Environmental modules can also be included within the single interface when considering water quality or the fate of contaminants, for example.

WHERE DO I FIND THE COUPLED MODEL?

The Coupled Model is located in the MIKE 21/3 Integrated Models folder of the MIKE Zero New Files dialog. It is listed as Coupled Model FM (.mfm).

WHY WOULD I USE THE COUPLED MODEL?

When a project simply requires the hydrodynamics or wave climate to be described, the relevant individual module is usually an appropriate tool. However, some projects, such as nearshore sediment transport and morphology studies, are more complex and require characterisation of the interactions of waves and tides. When the impact of water level or current variations on wave propagation is important, or equally, when the effect of wave-driven currents must be included in the overall flow field, and when instantaneous feedback between the two processes is required, the coupled model is the best tool for the job. The coupled model describes the interactions of all the relevant physical processes and therefore provides the closest approximation to reality for your project.

HOW DO I ADD THE COUPLED MODEL TO MY

LICENCE?

The pre-requisites for the Coupled Model are MIKE 21/3 FMHD and MIKE 21 SW. If you have these on your licence, you can start using the Coupled Model today. Add-on modules, such as MIKE 21 FMST, can expand the range of projects for which the Coupled Model becomes your tool of choice.

MIKE POWERED BY DHI: EMBEDDING KNOWLEDGE IN TECHNOLOGY

TAKING THE COUPLED MODEL TO THE NEXT LEVEL

Introducing the MIKE 21 Shoreline Morphology Module

INCREASING PERFORMANCE WITH GRAPHICAL PROCESSING UNITS

In MIKE 2016, we have made it possible to use multiple GPU cards with both

MIKE 21 FMHD and MIKE 3 FMHD. Additionally, we employ an unique hybrid

GPU-CPU approach so that the MIKE 21/3 Coupled Model FM supports GPU

technology for hydrodynamics and multiple core CPU technology for waves,

sediments and other processes / modules.

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CASE STUDY: DAWLISH WARREN

A Practical Application of the Shoreline Model in a UK & Ireland Context

Site Description

Dawlish Warren is a small seaside resort on the south coast of

Devon in England, located at the mouth of the Exe Estuary. It has

a beach, a National Nature Reserve spanning 2 km2 and a golf

course amongst other amenities.

Dawlish is famous for its sand spit which works together with the

beach to protect the estuary from flooding and to shelter the

existing main railway line. A beach management scheme is in

place and ongoing, operated by the Environment Agency and

partner Teignbridge District Council.

The past mobility of the beach at Dawlish Warren is apparent from the presence of groynes and, being currently topical, the site provides a suitable case study to demonstrate the application and benefits of DHI’s Shoreline Morphology module.

Planning the Study

Efficient use of the SM module requires careful consideration of

the conditions you wish to represent and a good understanding of

the physical processes that govern sediment transport and

morphology. Approximations and assumptions must usually be

made in order to arrive at a model that will simulate coastal

evolution in a timely manner, for example:

The duration of the planned study must be considered and a

suitable wave climate developed.

The relative contributions of tidal and wave-driven forcing to

the nearshore sediment transport regime should be

considered and, if tidal forces can reasonably be neglected,

the new quasi-stationary FMHD solver should be used.

The speed up factor available in the FMST module should be

used whenever possible to reduce the number of time steps

required.

If tidal forcing is important, this is usually completely

independent of the wave climate and so a typical tidal cycle

can be used in conjunction with the speed up factor to reduce

run times.

It is essential that there is a good understanding of the

requirements of the study and that the methodology to achieve

those requirements is carefully planned before model

construction begins.

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INTRODUCING THE SHORELINE MORPHOLOGY MODULE

At Present

Until now, there were two traditional approaches to simulating

nearshore sediment transport depending on the timescale to

be considered.

The 1D n-line approach of the Littoral Processes FM Coastline

Evolution module is ideal for considering development on

decadal timescales but is limited to straight coastlines with

simple bathymetries due to the approximations made during

the calculation of the 2D sediment transport processes.

The full 2/3D Coupled Model with waves, tides and sediment

transport (FMHD, SW and FMST) gives detailed patterns of

sediment transport and instantaneous updates to morphology

over the duration of a storm or a few weeks at most. Model

run time is usually considered to be the key limiting factor for

the duration over which the Coupled Model is run. In fact, the

morphological evolution of the cross-shore profile breaks

down over time so the shape of the resulting coastal profile

becomes unrealistic.

The Future… is Now Available!

MIKE 2016 sees the introduction of the MIKE 21 Shoreline

Morphology module (MIKE 21 SM). The Shoreline Morphology

(SM) module introduces a new approach to modelling long-

term shoreline morphology which overcomes the limitations of

both the 1D and the 2/3D approaches outlined above.

The SM module is applied via the 2D Coupled Model as it

uses the sediment transport rates calculated by the FMST

module to overcome the limitations of the 1D approach above,

allowing more complex bathymetries and coastline shapes to

be considered. Furthermore, the SM module provides an

alternative to the instantaneous morphological updating that is

currently applied in the Coupled Model. The sediment volume

deposited during each time step is integrated across sections

of the coastline and the resulting change to the local

morphology is updated using a predefined cross-shore profile,

which eliminates unrealistic changes to the profile and allows

for long-term simulations.

Given that the SM module is an add-on to the Coupled Model,

runs times can be similar to using FMST for long-term

simulations. However, the addition of a quasi-stationary mode

for the HD module in MIKE 2016 can reduce run times under

appropriate conditions.

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Model Construction

As with all numerical models, the first requirement is data, lots of

data! With the advent of the UKHO Inspire and the EMODnet

bathymetry portals, OS OpenData from the Ordnance Survey and

opening up of LIDAR from the Environment Agency, the

availability of free online data has never been so plentiful. Using

these sources, plus the Channel Coastal Observatory for wave

observations, all the data required to construct the Dawlish model

was obtained and fed into the Mesh Generator to start the model

build process.

The Mesh Generator in MIKE 2016 has added functionality to

support the SM module. A new menu has been included which

allows the user to create the elements required for a SM module

during the mesh creation process. The image below shows the

Baseline (red), Coastline (blue) and Edge Map extent (cyan) arcs

for the Dawlish example model together with two representative

profiles (red, perpendicular to baseline). It also shows the area of

fine resolution mesh which is required within the breaker zone in

order to adequately resolve the nearshore sediment transport

regime.

Having created a suitable mesh and SM module inputs, including

the edgemap dfsu (which provides elements in the SM module

area with their corresponding vertex number along the coastline

arc) and profiles, the Coupled Model interface is used to define

the model. The three standard modules for sediment transport

modelling are chosen (FMHD, SW and FMST) and, in addition,

the check box for Shoreline Morphology is ticked. This allows

access to the SM module section of the interface where the arcs

and files created in the Mesh Generator can be loaded, as shown

below.

Model Outputs

When the SM module is activated, specified line outputs can be

selected in addition to the standard options. Transport values

along the SM module coastline

region can be exported, as well

as the evolution of the coastline

arc location over the run

duration.

Map outputs are also useful to show areas where accretion and

erosion occur as well as the overall sediment transport regime. In

this case study, the north

-eastward transport

resulting from the applied

annual wave climate

(right) can be clearly

seen in the model

outputs below, together

with areas of accretion

(yellow). This process is

a key factor in the

creation and

development of the spit over the entrance to the Exe estuary.

Additional features, including spit creation and development, time

-varying profiles and dune erosion are planned for future releases

of the SM module.

MIKE POWERED BY DHI: EMBEDDING KNOWLEDGE IN TECHNOLOGY

FURTHER READING

A comprehensive presentation of the technical background

and application of the new Shoreline Morphology module was

presented by Kasper Kaergaard at the 2015 UK & Ireland

Symposium and a copy of his presentation can be found here.

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DHI Water Environments (UK) Ltd Ocean Village Innovation Centre Ocean Way, Southampton SO14 3JZ Tel: +44 (0)2380 381961 mike.uk@dhigroup.com http://www.mikepoweredbydhi.com/

FREQUENTLY ASKED QUESTIONS

1) What MIKE Powered by DHI version do I need in order to use

the Shoreline Morphology module?

The Shoreline Morphology (SM) module was introduced in MIKE 2016 and can be only run in MIKE 2016 or later.

2) What are the pre-requisite modules for the SM module?

MIKE 21 FMHD, MIKE 21 FMST and MIKE 21 SW.

3) What should I do if I do not have all of the above modules in

my installation at present?

Any or all of the pre-requisite modules can be purchased or rented as required, together with the SM module. Please contact us for a bespoke quotation.

4) We already own LITPACK, why would we use the SM module?

The new Shoreline Morphology module addresses the main limitations of both LITPACK and MIKE 21 FMST to provide a more advanced tool for investigating long-term shoreline evolution.

5) Does the introduction of the SM module mean LITPACK is no

longer supported?

LITPACK will continue to be supported throughout MIKE 2016. As with any product, we reserve the right to withdraw it in the future as and when appropriate.

6) Do I need to keep my LITPACK installation if I purchase the SM

module?

LITPACK is a different product from the SM module so, if you envisage continuing to use LITPACK, you should maintain your existing LITPACK installation.

7) Can I upgrade from LITPACK to the SM module?

The SM module and LITPACK are distinct products so there is no direct upgrade path available.

8) If the SM module is new, has it been tested and used in real

world examples?

All our software is quality assured and the Shoreline Morphology module has been used extensively within DHI in real world projects during its development. It has now been released to our wider customer base.

9) Have any papers been published on the SM module?

You may find the following papers of interest:

Kristensen et al (2010) Long Term Morphological Modelling, International Conference Coastal Engineering, 2010.

Grunnet et al (2012) Evaluation of nourishment schemes based on long-term morphological modelling. International Conference Coastal Engineering, 2012.

Kristensen et al (2012) Morphological Modelling of the response to a ship wreck—A case study at Cape Town International Conference Coastal Engineering, 2012.

Kaergaard et al (2014) Long term morphological modelling using a hybrid concept. Coasts, Marine Structures and Breakwaters (2013)

Kaergaard et al (2013) A numerical shoreline model for shorelines with a large curvature. Coastal Engineering 74 (2013) 19-32

10) What does the Shoreline Morphology module cost?

Add-on and package pricing is available, please contact us for a bespoke quotation on +44 2380 381961 or mike.uk@dhigroup.com.

SUPPORT

As with the entire MIKE Powered by DHI software suite,

local support for the Shoreline Morphology module is

available from the UK & Ireland team of Steve Flood,

Suzie Clarke and Mark Bailes with full back up provided

by Head Office in Denmark. We are here to provide help

in getting your software up and running as well as

technical support and guidance on optimising model

construction and configuration. The UK & Ireland support

team can be contacted on +44 2380 381961 or by email

at mike.uk@dhigroup.com.

TRAINING

In addition to the

standard support

services, a

training course has been developed to ensure new users

get the most out of the new SM module, with emphasis on

hands-on exercises. This course is recommended for

anyone considering purchasing the SM module. If you

are interested in attending the training course, please just

let us know on +44 2380 381961 or by email at

mike.uk@dhigroup.com.

MIKE POWERED BY DHI: EMBEDDING KNOWLEDGE IN TECHNOLOGY