URBAN STORMWATER FLOOD MITIGATION – A REQUIREMNT IN INDIA

Abstract:

Recurrent flood as a result of insufficient drainage system is a major problem faced by a number of cities in India. This affects large number of people living in urban areas resulting in loss of life and property, disruptions to transport and power and incidences of epidemics during the monsoons, and severe economic and infrastructure loss.

As a developing country, urbanisation is taking place at a faster rate in India. Census 2001 figured 285 million people in 35 metro cities in India, and it is estimated to cross 600 million with 100 metro cities in 2021. Unplanned urbanization and lack of proper development and maintenance of drainage infrastructure, has drastically altered the drainage characteristics of the natural catchments by increasing the volume of surface runoff. Drainage systems are unable to cope with the increased volume of water and are encountered with blockage due to indiscriminate disposal of solid wastes.

In 2005, severe urban floods were reported from 10 cities and Mumbai was worst affected. Number of affected cities rose from 22 in 2006, to 35 in 2007. It was followed by a severe flood in Mumbai and Hyderabad in 2008. Therefore, appropriate modifications on the current stormwater drainage systems are an essential requirement in most cities of the country.

As a case study on excessive flooding in urban cities, Trivandrum city Kerala state which is prone to localized flooding was selected. Study of the major storm water drains inside the city, flood discharge and flood routing was done to identify the critical locations and suggesting structural and non- structural measures for enhancing the status of drainage network. Nineteen major stations along the main drain are taken and modelled using HEC-RAS. Hydraulic analysis of the drain is carried out and the results highlighted 3 stations as the most critical sections. As a remedy to mitigate this local flooding in the study area, 6 structural measures are proposed along with few non structural measures.

Similar studies can be carried out for the other cities prone to urban storm water issues, to manage the problems in a sustainable manner. This can be done through proper management and maintenance of watershed, drainage network, and land use planning by taking into account the social and economic needs of the people.