Thursday, 23 June 2011
Innovative use of MIKE by DHI for morphological evolution of coastal defences

Introduction

For many years numerical models have been able to accurately represent the flood water inundation, and associated flooding risk, resulting from the failure of flood defences. Such failures are often simply described within numerical models as static ‘openings’ in defences, with little or no consideration given to morphological change and the development of a breach over time as a result of various natural processes.

In the UK, funding for new flood and coastal defences is becoming harder to attain. As such, an increasing reliance on natural defences is highly likely, augmented by the optimisation of existing flood defence structures and innovative low impact solutions that work with our natural environment.

DHI is committed to delivering a range of tools that consider the morphological evolution of coastal defenses acted upon by natural processes of storms, waves and tides, exacerbated by our changing climate. The examples below present upcoming new features in MIKE 21/3, as well as recent projects.

MIKE FLOOD (our complete 1D-2D integrated flood modelling package) is already able to represent changes to levees over time and, coupled with the new MIKE FLOOD Dynamic Hazard Mapping module, the new features and technologies presented below will further enhance the MIKE by DHI total solution capability.

Wave Overtopping and Erosion of Sandy Barriers

Work is progressing to adapt DHI's classic Boussinesq type wave model (MIKE 21 BW) to consider the overtopping and erosion of sandy barriers; linking wave run-up, overtopping and lee side down-rush to the morphological evolution and potential breaching of coastal defences.


Overtopping of a uniform alongshore barrier

The present animation (above) shows results from an in-house version of MIKE 21 BW that is currently being developed under the research programme COADAPT funded by the Danish Strategic Research Council.

The animation shows that bathymetric irregularity can have a significant effect on the rates and location of overtopping; in this case, a depression / channel within a submerged off-shore sand bar predicts higher risk of wave overtopping of the barrier just shoreward of the depression.

The model can be used to predict the risk of flooding, as well as the vulnerability of softer defences, to the impacts of climate change and to guide prevention against flooding in a cost effective way.

Dynamic Dam / Dune Break & Morphological Seabed Change

We will soon be introducing a new feature into our MIKE 21/3 Flexible Mesh Series models enabling the dynamic update of a model bathymetry during a simulation (the feature works on element based topography; i.e. dfsu files).

In this example, the new MIKE 21/3 Dynamic Bathymetry Update feature has been employed to consider a breach through an alongshore dune.

Model set-up of dune break through


Flood water inundation resulting from dune break through

The animation above shows a dune break during a 40 hour storm, and the resulting inland flooding as a consequence of the failure.


Section through a breach in the direction of flow

The animation above shows morphological change during the critical erosion phase of a levee failure, and the consequential change in water level.

The model can be used to generate flood inundation and flood hazard maps, to inform emergency planning and evacuation procedures (including early warning systems), and to develop the design of remedial or preventative measures.

Erosion of Soft Cliffs

DHI’s work on the Femern Belt project (a 20 km long connection between Denmark and Germany) includes the design of 2.3km2 artificial landscape with beaches, bays, lagoons and active cliffs; created from material reclaimed from dredging operations for the preferred tunnel option.

The artificial cliffs will be established with the purpose of slowly releasing loose material to the down drift eroding coast line. The first estimates of expected retreat rates have been based on observed retreat rates at similar but natural cliffs.

Femern Belt project (Design group: Rambøll/DK, Arup/UK and TEC/NL, with DHI and Schønherr/DK as sub-consultants)

Cliff erosion is typically connected to events of high water levels and severe wave action. However, depending on the porosity of the cliff, the content of water in the cliff may also provoke collapse. Empirical methods are generally employed for the quantification of cliff erosion. However, the use of MIKE 21/3 for hind casting of waves and water levels could be relevant to assist in an analysis of erosion rates compared to the exposure.

For more information, please visit http://bit.ly/iOyVUr and http://www.femern.com/

Potential Applications for the Above Examples
  • River embankment breach and evolution
  • Dam embankment breach and evolution
  • Reliability of and failure consequences for soft coastal defences
  • Application to soft cliff erosion
  • Managed realignment schemes and removal of hard defences
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Wednesday, 22 June 2011
Release 2011 Service Pack 4

Service Pack 4 for Release 2011 (NB: Service Pack 5 for MIKE GIS 2011) is now available. Simply download and run SP4 from here or, alternatively, via the DHI Software Updater. Please refer to the release notes for information on the corrections made in Service Packs 1-4. If you have questions, please do not hesitate to contact the DHI UK support centre at mikebydhi.uk@dhigroup.com

To download Release 2011 Service Pack 4 please click below: -

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Breach Modelling in Bermondsey, London, UK by RPS

RPS is an international consultancy providing advice on the development of natural resources, land and property, the management of the environment and the health and safety of people.

RPS offices across the UK utilise the MIKE by DHI software on a daily basis for a variety of projects. In this example, the Bristol office was engaged to undertake breach modelling at the site of a proposed residential development in the Bermondsey area of London. The SFRA (Strategic Flood Risk Assessment) for the area gave a highly conservative breach flood extent and flood water level. A more realistic level was required to inform the minimum elevation at which residential development could take place. A detailed breach model was constructed in MIKE 21 to establish the 1 in 200-year tidal flood level at the site.

Five breach locations were selected along an adjacent stretch of the River Thames, each breach was 20m wide (in accordance with current guidance for a tidal river with hard defences), as shown below.

Breach Locations

A 24 hour tidal cycle was run through each breach based upon the 1 in 200-year peak tidal level. The following animation shows the final, predicted breach flood extents. None of the modelled breaches impacted the site permitting residential development at ground floor level, significantly increasing the profitability of the site.


Maximum Flood Depths (m)

The Environment Agency reviewed and accepted the findings of the MIKE 21 breach modelling, and deemed it conservative enough to offset any model uncertainties. The model findings have subsequently been used by other developers to the same effect; clearing other sites in the area from flooding as a result of a breach in the defences and allowing the sites to be developed for residential development at all levels.

RPS has also carried out more detailed modelling on the Isle of Dogs that is to be used in a similar fashion. Additionally, RPS regularly utilises MIKE 21 and MIKE FLOOD for local overland flow modelling for large and small scale developments as well as for coastal defence failure / overtopping scenarios.

For more information, please contact Daniel McLeish at RPS by phone on +44 (0)1454 853 000, e-mail daniel.mcleish@rpsgroup.com, or visit http://www.rpsgroup.com/

Maps and animations contain Ordnance Survey data (C) Crown Copyright and Database Right 2011
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Blog Update

A new static page has been added - accessed via the top menu bar - providing full contact details for UK 'Support Desk' enquiries. Please use our new mikebydhi.uk@dhigroup.com e-mail address for all UK specific support questions. Thank you.

Note: The image here is a photograph of Smeaton's Tower, The Hoe, Plymouth, Devon, UK. For information, please see: -
1) http://en.wikipedia.org/wiki/Smeaton's_Tower
2) www.plymouth.gov.uk/homepage/creativityandculture/museums/museumsmeatonstower.htm
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Welcome to DHI UK

DHI is an independent, international consulting and research organisation with the global objective of advancing technological development and competence with respect to water, in all of its environments.

Worldwide, we offer a wide range of consulting services and leading edge technologies, software tools, environmental laboratories, and physical model test facilities, as well as field surveys and monitoring programmes. Designated as a not-for-profit organisation, DHI is able to invest a considerable portion of its resources in research and development. Today we co-operate with many Universities, and research organisations, and are recognised globally for our innovation and expertise.

In the UK, DHI offers niche or specialist consultancy services in the water and environment market to government agencies, commercial entities and selected research organisations. We fulfil a research based specialist advisor role; a ‘Consultant to the Consultants’. We also supply and support the renowned MIKE by DHI suite of integrated water modelling tools.

MIKE by DHI software is the result of years of experience and dedicated development and has, in many regions, become the standard modelling tool. It transforms our science into practice and gives you the competitive edge and, through the DHI Academy, you can rest assured that there is a local team of highly skilled experts committed to train and support you every step of the way.

MIKE by DHI truly models the world of water - from mountain streams to the ocean and from drinking water to treatment plant and beyond.

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