Innovating to stem flooding: Sembula

Guest authors, Annie Cheung (2nd year undergraduate Medicine) and Shreya Basu (2nd year undergraduate Mechanical Engineering), write about their experience designing a flood barrier for Tamil Nadu in India, for the Engineers Without Borders UK design challenge.

Floods cause more than $40 billion in damage worldwide annually (1). Sembula is a frugal flood barrier working semi-automatically in proportion to the weather crisis.

In collaboration with Change Makers, our team – Sembula – entered into the Engineers Without Borders UK: Engineering for People Design Challenge. This was a national competition for over 6,500 undergraduate students to put forward their design ideas for rural Tamil Nadu.

Our focus

Despite Tamil Nadu’s rapid urbanisation and growth in the IT sector, a large proportion of its GDP comes from agriculture. This is a very unpredictable sector, of course, as it is extremely weather-dependent. Monsoon season, along with lack of appropriate infrastructure and resources, often result in severe flooding, damaging crops, soil quality and thousands of homes. To give an idea of the scale of the problem, the 2015 South Indian floods caused $3 billion worth of economic losses. With Sembula, we aimed to mitigate the damaging effects of flooding and make the agricultural sector less unpredictable for Tamil Nadu’s farming communities.

‘Sembulapeyaneerar’ is actually the name of the Tamil poet who wrote the famous ‘Red earth and pouring rain’. The meaning of his name translates to ‘he of water that has rained on red fields’. Both his name and his poem celebrate the beauty of monsoon season in Tamil Nadu, which we felt perfectly fits the purposes of our design – hence the name ‘Sembula’.

Preparing for the day

During our Change Maker module, we developed rich pictures to understand the community and outline them visually. Then, we brainstormed a number of design ideas and selected the best ones. Finally, by producing a comprehensive design brief, we explored various iterations for our flood barrier designs. These steps were crucial in understanding the social, economic and environmental impacts of our design; our detailed design brief allowed our qualification through to the Grand Finale of the competition!

To further our design, we investigated the technical specification of the barrier – in particular, the materials in the original concept were environmentally unfriendly. What’s more, we actually went and sat down in a LEGO store to build a prototype to identify any obvious flaws and we decided to use it to demonstrate our idea in the competition!

How does Sembula work?

As water approaches the flood barrier, it is allowed to pass through the holes in the lower compartment of the flood barrier. Then, the flood water is absorbed by a material called Super Absorbent Polymer (SAP). SAP can swell up to 100 times its own volume as it absorbs the floodwater. Therefore, as the SAP swells, it pushes the upper compartment. This thereby prevents the floodwater from damaging infrastructure via absorption as well as via a mechanical barrier. The beauty of this frugal flood barrier is it is a semi-automatic barrier that responds in proportion to the weather crisis.

Animation of the Sembula Flood Barrier

In terms of materials, the lower compartment will be made out of ferrock, which is an innovative carbon-negative, concrete-based material. The SAP will be made of nanocellulose, which is biodegradable. Coconuts are widely found in Tamil Nadu – thus the upper compartment will be made out high-density coconut wood so it does not float. Also, when prototyping, we found that the SAP is likely to leak so we have implemented a coconut husk (coir) membrane and mesh to encase it.

To ensure the cheapest long term solution, we decided that an initial investment in setting up a factory is worthwhile to manufacture these raw materials into individual parts. The idea is to allow farmers to decide on a plot of agricultural land that they would like to protect. After some research into this area, we can then decide the perimeter along which the placement of flood barriers is best suited. A trench will be dug along the perimeter and with the simplicity of the design, the individual parts can be assembled into a functioning flood barrier on site. Our implementation plan not only ensures good production quality for the farmers but also supports local employment in other large industries such as coir.

Our flood barrier is simple, effective and truly fulfils the values of frugal innovation.

The Day

On 14th June, my teammate Shreya and I were fortunate enough to attend the Grand Finale of Engineers Without Borders: Engineering for People Design Challenge. This year’s competition focused on engineering solutions for the problems facing the state of Tamil Nadu in India. We entered with Sembula – our frugal flood barrier design!

The day started off with pitching our idea to the judges: three engineering experts listened to our 3-minute elevator pitch and asked us a number of questions. Afterwards, Shreya and I explored other students’ designs – they were innovative and exciting! Personally, my favourite designs include a simple to implement menstrual hygiene bamboo pouch for school girls and a bicycle to condense plastic for ease of recycling.

Annie presenting Sembula to the judges

After lunch, the judges came together and named the best designs. These teams were given the opportunity to present to the whole cohort and finally win the prizes.

Shreya fielding questions from the judges

Frugal innovation

Annie: Although we did not win the competition, our team recognised that we have learnt a lot. What’s more, I am truly touched by the number of fellow students who designed frugal and sustainable innovations. The values of sustainable design will always be of the highest priority to me, as I am sure my fellow competition cohort agrees!

Contextualising engineering through the Change Makers module

Shreya: As a mechanical engineering student, this was definitely an interesting design challenge to tackle in a team of students from different disciplines. With the emphasis on social and economic considerations alongside environmental impact throughout the Change Makers module, I learnt to be critical of the wider implications of any engineering solution. ‘Design for Sustainable Development’ was definitely a worthwhile addition to what I learnt in my degree this year.

Source: [1] OECD (2016), Financial Management of Flood Risk, OECD Publishing, Paris. [Online]  Available from: [Accessed 08-07-2019]

Leave a Reply

Your email address will not be published. Required fields are marked *