Chennai is a coastal metropolitan city in India which faces severe flooding at times due to drainage congestion. It consists of largely flat landscape and pockets of low-lying areas. The average elevation of the city is not more than 7m above mean sea-level and the average slope varies at less than 0.7m per km. Most of the localities are just at sea-level and drainage in such areas remains a serious problem. Two major rivers Adyar and Cooum, which normally drain runoff from the upland areas, also cause back water inundation due to sea water influx. Preparing a Master Plan for the Chennai city is therefore a challenging task .
In order to expedite the preparation of Master Plan of 174 sq km city landscape with more than 1500 km existing and proposed drain survey with stipulation of 6 months time frame provided by Corporation of Chennai (CoC), the consultant (Aarvee Associates) opted for using GIS, SWMM software for the first time in India for a storm water drainage project in a massive way. The study format consists of segmenting Chennai area into 12 storm water drainage catchments and later joined to form 4 drainage basins. The survey data using total station are directly linked to GIS along with road network, existing storm water drain configuration, land use land cover information and rainfall data. Using thematic maps generated from survey data and Rational Method for urban runoff estimation, assessment of run-off from the drainage catchment is carried out in GIS platform. In the next step, thematic maps and runoff are directly transferred to US EPA SWMM software for hydraulic analysis for estimation of size of drains and carrying capacities using the options available in the software.
This city Storm Water Drainage Master Plan is the first project approved by the Government of India, under the Jawaharlal Nehru National Urban Renewal Mission (JNNURM) scheme using EPA SWMM and GIS for a total amount of Rs 1447.91 crores to CoC for implementation.