Vjti Paper Abstract

ANALYSIS OF RAINFALL INTENSITIES AND TIDES FOR STORM WATER MANAGEMENT IN MUMBAI Shashikant D. Chawathe, Consultant Vidyadhar N. Sontakke, Operations Director Manasi S. Bapat, Project Engineer MWH India Private Limited, Mumbai Abstract Sustainable development is a pattern of resource use that aims to meet human needs while preserving the environment, so that these needs can be met not only in the present, but also for future generations. In the case of storm water management for metro cities and satellite townships, the major objectives of sustainability is to reduce the risk of flooding in vulnerable areas to levels acceptable to all stakeholders, even under future climate change scenarios and to reduce the socio-economic and health damage. Unacceptable flooding also affects the sustainability of various environmental protection measures and infrastructure projects as is very clear from the unprecedented havoc created by 26/07/2005 torrential rainfall in Mumbai. From 1990 to 1993, Watson Hawksley (now called MWH), in association with AIC India Pvt. Ltd. carried out a major study of the storm drainage system in Mumbai. The BRIMSTOWAD (Brihan Mumbai Storm Water Drainage) study was an in-depth investigation into all aspects of the storm water drainage system and formulated comprehensive proposals to alleviate the chronic flooding problems in Mumbai. Due to the limitations of funds, very few of the recommendations have been implemented. After major flooding event caused by the extreme rainfall on 26 July 2005, a Fact Finding Committee (FFC) was set up by the Maharashtra Government to investigate the causes and suggest measures for immediate relief. In addition, the Municipal Corporation of Greater Mumbai (MCGM) also requested that MWH update the original Brimstowad study to include updated hydraulic modelling, flooding solutions, engineering designs and economic analysis. Fresh rainfall and tidal analysis are two of the most important parameter studies required for updating the original Brimstowad study. The hydrological analysis of rainfall has now been updated by extending the original data set to a period of 38 years (1969-2006) from Colaba and Santacruz observatories. IntensityDuration-Frequency (IDF) relationships for rainfall in Mumbai have been developed based on methodology given in CPHEEO manual on sewerage. For hydraulic modelling, the IDF relationships are further converted into time varied rainfall profiles using the ‘Chicago’ method. The tidal analysis now carried out, updates the original analysis by extending the data set of tidal levels to 22 years (1986-2008) from the tidal gauges at Apollo Bunder and 4 years (2004-2008) from Trombay.

Average high and low tides were calculated from the available predicted July to September tidal data and these were used to develop ‘base’ tidal curves (Sine Curves) for use in modelling. Adjustments were carried out for global warming, storm surges and wave action and for using predicted data in the place of observed data. ‘Base’ tidal curves were thus converted into final long-term sea-level rise curves for use in modelling. The present paper discusses the methodology used for the updated rainfall analysis as well as tidal analysis and presents the developed IDF and Chicago curves. Also the final tidal variation curves to be further used in the modelling exercise are presented.