Abstract:
Mumbai is experiencing wide variation in spatial-temporal distribution of rainfall and
subsequent water scarcity and flooding conditions. Hence, rainfall analysis was carried out in
Mumbai metropolitan region using the daily rainfall data of 20 years at Colaba and Santacruz
stations. It was observed that aberrant variation in rainfall event in monsoon months causes
heavy rainfall resulting in water logging and subsequent flooding conditions. An analysis of
monthly one day maximum rainfall, yearly one day maximum rainfall and seasonal one day
maximum rainfall of colaba and Santacruz raingauge stations showed that the study area was
facing huge variation in rainfall pattern which often causes flooding conditions. The
maximum rainfall recorded was 944.2 mm/day on 26thjuly 2005 which caused flooding in
Mumbai city which caused in loss of human life and property. By considering 944.2 mm/day,
of rainfall return period was calculated using Weibull’s formula it is observed that the highest
return period is 20 years and the lowest return period is 1 year. So we have taken this return
periods into account and generated IDF curves for 2,3,5,.10,15,20,30,50,70,100 years.
Intensity duration frequency (IDF) curves were generated by using Gumbel’s Equation. The
IDF curves at a duration of 24 hours predicted the intensity of rainfall for Colaba raingauge
station as 346.944 mm/day and for santacruz raingauge station as 821.64 mm/day, for 100
year return period . This obtained rainfall was then used to calculate runoff for Mumbai city
by using rational formula and calculated as 2072.5 m3/sec.
