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
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Mauritius: UNESCO conference on climate change education opens


world-300x209Balaclava, Mauritius – A three-day experts’ meeting on climate change, sponsored by UNESCO, kicked off Wednesday in the northern Mauritius city of Balaclava.

The Mauritian Education Minister, Vasant Bunwaree, who spoke at the opening session, said that education for sustainable development would pave the way for a better comprehension of issues related to durability of the planet.

“Our  understanding of education today is constantly punctuated by an awareness of the new realities and global preoccupations,’ he said.

He added ‘there is now a wide recognition that something is changing in our climatic system.’

He said that extreme climate events, such as heavy rains and tropical storms, have been increasing over the last few years, let alone the rise in temperatures, the sea level and the deterioration of the coastline as well as ‘the reduction of the water resources which are all risks we are constantly confronted with’.

Recommendations from the meeting will be turned over to the 18th United Nations conference of the Framework Convention on climate change and the UNESCO world conference on sustainable development education scheduled in 2014 in Japan.

Source: http://www.afriquejet.com/news/4075-mauritius-unesco-conference-on-climate-change-education-opens.html

The power of building codes: why fewer died in Chile’s earthquake than in Haiti’s


According to an article on Bloomberg.com: “Earthquakes, heat waves, floods, volcanoes, super typhoons, blizzards, landslides and droughts killed at least a quarter million people in 2010 — the deadliest year in more than a generation. More people were killed worldwide by natural disasters this year [2010] than have been killed in terrorism attacks in the past 40 years combined”.
This is an alarming statement!


Image copyright: BBC

Even with the most sophisticated weather tracking tools, it is not always possible to predict when a natural disaster will occur.  Although we can track how a cyclone develops, it is very difficult to tract the exact path it will take and the severity with which it might hit when it reaches land.  However, there is one thing we can do: prepare and adapt.  The way we design and build our buildings can save lives. This is the reason why we build reinforced concrete structures in Mauritius, and rightly so, because we are prone to cyclonic conditions.

When it comes to earthquakes, it is estimated that 80% of deaths that occur during an earthquake is attributed to the collapse of buildings. As an example, in Haiti, where most of the population lived in poorly built structures, about 220,000 people were killed.  In contrast, the earthquake in Chile, which was about 500 times stronger than that of Haiti, caused less than 1,000 deaths.  One of the reasons for this is better building codes and better construction.

An interesting article below from BBC, talks about a system that helps buildings stay up, called the “strong columns weak beams” system, and helped prevent Chile’s buildings from collapsing.

Link to article: http://news.bbc.co.uk/2/hi/americas/8543324.stm

Nuclear crisis in Japan: How bad is it? Depends on which nuclear expert you ask!


The last paragraph of the article (link below) quotes Tom Cochran: “We’ve watched Exxon Valdez, the BP oil spill, numerous coal mining accidents, Chernobyl, TMI, now Fukushima, slag ponds, TVA (Tennessee Valley Authority) reactors giving way. You have got to ask yourself, how many wake-up calls do you need before you get serious about building a safe, renewable-energy economy?
Yes, how many indeed!

Read the full article here: http://www.cnn.com/2011/WORLD/asiapcf/03/15/japan.nuclear/

A little bit of “green” humour :)


Green humour:  Skeptical about sustainability…

We should try and change the way we think and realise that we all need to do our bit, however small, to protect our environment and help towards creating a more sustainable world.  Remember this quote: Only after the last tree has been cut down…the last river has been poisoned…the last fish caught, only then will you find that money cannot be eaten.
– Cree Indian Prophesy

skeptical_image

Global highlights of 2010’s significant weather and climate events


Whilst several countries around the world were ravaged by drought, 2010 still broke the record for the wettest year, with highest average rainfall values worldwide since 1900. It has been an exceptionally rainy year, as we saw record-breaking deluges in Central America, India, southwestern China, eastern Asia, Borneo, and parts of Australia.

A few of the most extreme events were:
– The worst flooding in Pakistan since 1929,
– The worst flooding in Southwestern France since 1827;
– The worst flooding in Israel, Egypt and Kenya in more than a decade;
– Mexico’s wettest July since 1941…

We all wonder why we are seeing these intense swings in weather patterns. Some have speculated that global warming is to blame, while others disagree. Nevertheless, in spite of all our great achievements, we have to admit we are all pretty helpless when Mother Nature decides to let go…

You can read more about the global analysis of the significant weather and climate events of 2010 on the National Oceanic and Atmospheric Administration (National Climatic Data Center) at the page below:  http://www.ncdc.noaa.gov/sotc/global/

HOME movie: how humanity has upset the balance of the planet…


Please take the time to watch this movie and pass the link on to your friends & family.

The story: We are living in exceptional times. Scientists tell us that we have 10 years to change the way we live, avert the depletion of natural resources and the catastrophic evolution of the Earth’s climate.

The stakes are high for us and our children. Everyone should take part in the effort, and HOME has been conceived to take a message of mobilization out to every human being.

Link to watch video: http://www.youtube.com/watch?v=jqxENMKaeCU