India – Come monsoon, Chennaiites will face a deluge of problems with water-logged streets and clogged drainages.
In a bid to identify areas prone to flooding and to suggest flood mitigation steps, the Institute of Remote Sensing (IRS), Anna University, has undertaken flood mapping for Chennai city and its suburbs using the Airborne Laser Terrain Mapper (ALTM) technology.
“This is the first time in the country that the ALTM technology is being used for flood mapping,” IRS sources told TOI.
From an aircraft hovering over the city, laser will be beamed down which will hit the terrain and get reflected. The data, which is recorded in a sensor, is decoded and information about the rise and fall of the terrain is generated. Based on this, the digital surface model can be created.
However, the true terrain elevation could not be obtained from the digital surface model as it would also contain the elevations of buildings and trees. Hence, a terrain elevation model will be created by leaving out the elevations of buildings and trees, the sources added.
Once the slopes of the terrain are identified, places suitable for artificial recharge of the ground water with the run-off could be spotted. Besides, routes to divert the excess flood water could also be drawn.
For preparing flood risk map sheets (ward-wise) covering 500 sq km of the Chennai Metropolitan Area, high resolution images from the latest American satellite ‘Quick Bird,’ in addition to the ALTM imagery, would be used, the sources added.
As a research component of the project, the IRS team also proposes to create a hydrological simulation model ie. simulating different flood situations. “We will take up a study to identify which are the areas that will be flooded at different measurements of rainfall. The findings will be helpful in taking up flood mitigation works in vulnerable areas. This can also be used as a base for all future simulation models,” the sources added.
The water resources wing of the Public Works department has allocated Rs 2.17 crore for the one-year project. The Survey of India and the Department of Science and Technology will also assist the IRS in the research component of the project. “Based on the success of the project, the model will be replicated in other metropolitan cities, particularly in Mumbai which is frequently hit by floods,” officials said.
Velachery, Kolathur, Madipakkam, T Nagar and Vyasarpadi are some of the low-lying areas in the Chennai city that are worst hit during heavy rains. The flood mapping would help in a big way in chalking out flood mitigation works, PWD sources said.