Deadly flash flood event in Mauritius on 30th March 2013 – How SUDS can help reduce flooding risks

Deadly flash flooding event in Mauritius on 30th March 2013

Deadly flash flooding event in Mauritius on 30th March 2013

It is very saddening and shocking to see that 11 people have been victims (so far) of the tragic flash flood event on the 30th March 2013 in Mauritius. My thoughts are with the families who lost their dear ones and those who have lost their property and belongings during this event.

I am not an expert in drainage system design or flood risk management, however I would like to share some information that I have gathered during my career, regarding reduction of flooding risk through the implementation of SUDS (Sustainable Urban Drainage Systems). I am providing the information below, in the hope that the engineers/designers who will review the drainage system in Mauritius after this terrible event, might take SUDS into consideration. 

Flash floods are terrifying events, that can be very destructive and deadly, as we have witnessed. Localised heavy rains, together with inadequate drainage and increasing urbanisation can lead to severe problems due to flash flooding after sudden heavy rainfall. Cutting down vegetation to replace them by artificial surfaces such as impermeable concrete and tar means the area loses its ability to absorb rainwater. The rain is therefore directed into surface water drains instead, causing them to be overloaded and resulting in floods. Whatever we do on land will affect the hydrology of an area.

All it takes for flooding to become a problem is for 40% of vegetated area to be cleared and replaced by impervious surfaces such as impermeable concrete. The amount of surface water runoff will then double and flow twice as fast. Extreme rainfall events can cause hundreds of mm of rainwater to fall within a few hours – this amount of water flowing at high speed on impervious concrete areas will certainly overload drainage systems, which cannot dispose of the water as quickly as they are receiving it.

There are several ways of managing stormwater. The more traditional way is to divert water runoff from drains into rivers (“rapid conveyance” approach). However, the water runoff is sometimes so rapid that the rivers just cannot cope with the sudden deluge, leading to flooding downstream. When drains and rivers are blocked by debris, the water flow is impeded, worsening the flooding event.

Retention ponds hold water run-off back and slowly release it to mitigate flooding

Retention ponds hold water run-off back and slowly release it to mitigate flooding

Another way of managing rainwater runoff is to use the “control at source” concept. This means increasing the time that the water takes to reach streams by controlling it at source. This is a totally different approach from the rapid conveyance method. Water runoff is first captured and then gradually released or allowed to infiltrate the soil. Therefore, instead of a sudden, excessive water flow to areas downstream, the water flow is mitigated and reduced, making it more likely for drains and streams to be able to cope with it.

A swale

A swale

However this requires that the water runoff from the site must be similar to or less than levels before land-clearing took place. This means that developers should be responsible for limiting the rainwater discharges due to their construction when a vegetated site is changed into an artificial impervious one. Instead of merely building drains to cater channeling of rainwater away from their development site, they should contain the water instead and release it gradually or allow it to seep into the soil. We should not work against nature, but with it. We should try to mimick nature’s natural hydrological cycle through a combination of infiltration, storage and delayed stormwater flow. The approach to replicate natural drainage systems is termed the SUDS (sustainable urban drainage systems) approach, sometimes termed “sustainable drainage systems” as they are not restricted to urban areas only. SuDS have a low environmental impact by managing water runoff through collection, storage, and natural cleaning before it is allowed to be released slowly back into water courses (drains and rivers). Usually SuDS constitute a combination of water retention ponds, wetlands, underground storage tanks, infiltration, permeable surfaces, swales, and filter drains with the best combination of structures and techniques being specific to the site in question.

Permeable paving especially useful in car parking spaces to allow for subsurface infiltration

Permeable paving especially useful in car parking spaces to allow for subsurface infiltration (image courtesy of RIBA Sustsainability Hub)

The way we manage rainwater runoff should be reviewed and alternative ways of managing stormwater could be explored and evaluated, as well as the establishment of by-laws to guide the implementation of more sustainable and natural stormwater management practices, replicating natural attenuation, infiltration and drainage, rather than relying solely on concrete-lined drains. The benefits of both water storage and infiltration strategies extend beyond that of controlling water runoff. They also improve water quality, encourage bio-diversity, add amenity value and help us adapt to and mitigate the negative impacts of climate change.

Emma Ozsen
Sustainability Consultant

Sustainable building design analysis using Ecotect

If you are an architect, building designer or engineer, you might have heard of Ecotect Analysis. If you haven’t, it might be of interest to you. Students or professionals in the construction industry willing to go towards sustainable design might also find this useful in understanding the design principles through a visually responsive and interactive tool.
[NOTE: I am also planning on providing training courses on the fundamentals of Ecotect, as well as green building design concepts, in the near future (see last paragraph of this article).]


Ecotect is a tool designed to aid in the simulation, analysis and optimisation of high performance buildings, and is especially useful in sustainable building design projects. Its comprehensive analysis capabilities help analyse and simulate conceptual designs. It allows architects and engineers to test and evaluate design strategies and to study alternatives and make decisions earlier to deliver more achievable, resource-efficient building designs.

Architects, designers and engineers often find it useful to visually communicate complex design concepts and extensive datasets to other project team members and clients in an intuitive and effective way. For instance, proposing the use of a shading device might not be initially accepted by a client, until the potential savings in cooling energy due to the shading device is demonstrated. This can effectively be done through the use of Ecotect Analysis.

Using simulation software, design professionals are able to continuously study and predict how decisions will impact the performance of the building from the early phases of design through occupancy, reducing or eliminating the need for investment in mock-ups or manual calculations. Ecotect gives architects, designers and engineers the power to use performance-based criteria in their design projects.

Ecotect Analysis produces cutting-edge 3D spatial models to help users visualise  the simulation output, allowing a smooth translation of the simulation results into the project design.  A few of the outputs from Ecotect Analysis are shown below (all images courtesy of Autodesk):


If you are interested in learning how to use Ecotect for conceptual design analyses, I am planning on providing training courses on the fundamentals of Ecotect as well as an overview of green building design concepts. Courses will be MQA-approved and fees refundable up to 75% (for companies contributing to the HRDC levy grant system) . If you are interested in attending the training course and would like to be notified when the training courses are scheduled, please subscribe to this blog or to the Facebook fan page.
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Emma Ozsen - Sustainability Consultant
Emma Ozsen
Building Design Analyst and Sustainability Consultant

Beautiful earth and stone structures at the School of Visual Arts of Oaxaca (Mexico)

Image copyright, Luis Gordoa

The School of Visual Arts of Oaxaca was developed at the request of the artistFrancisco Toledo, in collaboration with the Universidad Autonoma Benito Juarez. The lack of a master plan integrating the pre-existing buildings led to the project being designed as a large garden rather than just another building. At the same time, the building under construction on the campus were producing huge amounts of earth. These contingent factors suggested raising a bank of earth to provide the isolation necessary for an art school. Due to calendar and budgetary issues, the school was planned in three stages. The first two have already been built, giving form to what’s become known as “the crater”, which defines its perimeter with regard to the rest of the campus. Continue reading

Pegasus Complex’s checkerboard facade protects it from the Indian heat

The Pegasus complex is located in Gujarat and was designed to be protected from the hot Indian sun with  what looks like a black and white checkerboard facade!
Image ©

It is actually a number of specially-oriented slats that give the illusion of a solid mass when seen from a distance.
The building was designed by Jagrut Patel of Vitan Architects.

Read the full article here:

Tropical Luxury + Green Living = Lofted Seaside Solar Home

It is a stroke of pure genius – and will keep its residence from having heat stroke as well. Lofted living and bedroom spaces, swooping architectural swimming pool and roofline curves – everything about this place speaks to casual, resort-like luxury … which makes the semi-secret sustainable wind, solar and green-roof strategies built into the project by Guz Architects in Singapore all the more impressive.

Continue reading

What is sustainable construction?

A few tips to help you incorporate sustainable practices into your next project:

Sustainable construction brings together the principles of green building methods and eco-friendly values in a bid to lighten the environmental impact of residential and commercial structures. Continue reading

French Green Building Gets Highest BREEAM Award

A multi purpose green building in France has scored a first – “Spring” in Nanterre is the first building to achieve an interim ‘Outstanding’ rating under BREEAM Europe Commercial 2009. The development by Bouygues Immobilier and Archon Group has achieved 90% – the highest ever score under BREEAM for a building at the design stage.
Read more below:

SoloPower rolls out flexible rooftop solar panels

The manufacturer of the panels claims that they are lighter than glass-encased panels and can be installed quicker than other technologies, and also that they achieved 11 percent efficiency!
Read more below:

Tongji solar power bamboo house set out for Europe Decathlon Competition

Tongji solar power bamboo house set out for Europe Decathlon Competition:
Two curve roofs, built by bamboo, run only by solar power, the bamboo
house can generate 9 kilowatt electricity, one bedroom and one living
room with whole set of facilities. This solar power bamboo house was
built by a team of our students from various departments for about half
a year, which was just completed and was going to be shipped to Madrid,
Spain, for the local 2010 Europe Decathlon Competition this June.
Read more at the website below: