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.

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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

Global Warming: how can you help and save money at the same time?


global_warmingWe can ALL make a difference. Every action we take, however small it may seem, makes a difference. Whether you decide to recycle, to reduce the time you spend in the shower, or plant your own vegetables, we all have the power to make changes in our life and help reduce the harm we cause to nature. Here are some simple ways you can help reduce your negative impacts on the environment and, at the same time, on your pocket.

USE ENERGY-EFFICIENT LIGHT BULBS
If you are still using incandescent lamps, you are not only paying more than you should but also causing a lot of energy wastage and carbon dioxide emissions.

led-bulbs-vs-cfl-bulbs-vs-incandescent-bulbs

Replace your light bulbs with either CFLs (compact fluorescent lamps) or LEDs (Light Emitting Diodes). For more info about CFLs and LEDs, have a look at this Facebook post I made a little while back about CFLs and LEDs: https://www.facebook.com/media/set/?set=a.519714178069968.1073741826.116618288379561&type=1&l=d292cbd318

USE RECYCLED PAPER
Use paper products with recycled content whenever possible (for example, use  100% post-consumer recycled printer paper, recycled paper towels and napkins).

REDUCE AIR CONDITIONING USE
Air-cons use up a lot of energy to cool down the air and releases the heat into the environment. Many air conditioners also contain hydrofluorocarbons which contribute to the depletion of the ozone layer. They also have a negative impact on our bodies’ natural adaptation to hot and cold temperatures. If you are used to blazing cold air conditioning, try to raise the temperature a little bit more everyday and you will see it’s not so bad! Maybe you can even go without or use a fan instead?

TAKE SHORTER SHOWERS OR INVEST IN A SWH
If you use an electric shower, it is likely to account for a major part of your water heating costs. Taking shorter showers will not only reduce your electricity bill but also reduce the negative impact you have on the environment. Even better, invest into a solar water heater and you will only use natural heat energy from the sun to heat up your water.

CONSERVE ENERGY
unplugDid you know that by keeping your electronics plugged in, you are wasting huge amounts of energy. Save energy by making sure your phone charger, TV, blow dryer, etc. are unplugged when they are not being used!

WASH YOUR CLOTHES WITH COLD WATER AND AIR DRY THEM
When you wash your clothes, choose the cold wash setting on your washing machine for clothes that are not very dirty. You will save energy by not heating up the water. Air-drying your clothes rather than using a tumble dryer. We are lucky to have sunshine all year round, so why not make use of it!

CARPOOL WHENEVER POSSIBLE
Fuel prices are climbing at an astounding rate, so why not save some money and at the same time do something good for the environment by carpooling to work/school. Try to organise carpooling yourself and suggest it to friends. If your place of work is at walkable distance, walk or ride your bike instead.

REDUCE THE AMOUNT OF GARBAGE YOU PRODUCE
Recycle as much as you can (paper, plastic, glass…) and buy products which have less packaging when you shop. You will save a lot of carbon dioxide from being released into the atmosphere by doing those simple acts to reduce your garbage.

PLANT A TREE
Ecology-and-Economics-The-Sustainable-Future_widgetDo you enjoy gardening? Plant a tree in your yard or take a plant along to your workplace. Not only will it make you feel better, but you will also reduce the amount of CO2 in the atmosphere. A single tree will absorb a ton  of CO2 over its lifetime!

STAY AWAY FROM PLASTIC
Different kinds of plastic take different times to degrade. Most plastic bottles will sit in landfills for several hundreds of years! Even worse, bottles made with Polyethylene Terephthalate (PET or PETE) will never biodegrade. Very few plastic bottles are recycled, meaning a lot of them also end up thrown in public places or in the sea. toxicPlastic thrown into the warm sea water gets broken down more quickly with UV rays (this can be in as little as a year) and toxic chemicals such as bisphenol A (BPA) and PS oligomer are released. These either end up in the digestive systems of of sea animals or get washed up onto the shore, where we humans are most likely to come into direct contact with the toxins. Who loves a swim in toxic water?  Mauritius is blessed with lovely beaches that we are meant to enjoy safely. So, please share and either don’t go for plastic bottles, recycle them if you do use them and don’t throw them in watercourses or the sea! Use glass bottles as far as possible. Most of them can be returned to the shop where y0u buy them, and you even get some money back for doing so!

Does any of the tips above speak strongly to you? What else do you think can be done by us individuals to help reduce global warming? Let me and other fans know on my Facebook page

Emma Özsen
Sustainability Consultant & Building Design Analyst

Emma Ozsen

‘Construire Vert’ on l’Express Property blog


Emma Ozsen

My interview article which appeared on the Week-End newspaper (29/11/2009) can also be viewed on l’Express Property blog below:

http://lexpressproperty.blogspot.com/2009/11/construire-vert-par-emma-ozsen.html

Ecological competition: collection of plastic bottles at Loreto College Rose-Hill



For the second year running, AMORIS Environnement Ltd. has held a school competition to collect plastic bottles.  This year, the competition was sponsored by SOFAP, manufacturer  of ISO 140001 certified paint in Mauritius.

The students of Loreto College Rose-Hill engaged in a hunt for recyclable plastic waste, collecting more than 19,445 plastic bottles in one month! These were then handed over to AMORIS Environment Ltd., who will liaise with their partners for the recycling of the bottles.

The 19,445 bottles, laid end-to-end,  would create a 6 km long line of plastic bottles!

I say WELL DONE to the students/staff/parents of students at Loreto College Rose-Hill, and to AMORIS Environnement Ltd. & SOFAP for this great initiative!