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"ANALYSIS OF MAXIMUM HOURLY RAINFALL FOR DESIGN OF STORM DRAIN
NETWORK OF SURAT CITY"
Prepared By: Supervisor
PINGUL JIGNESH K Dr. S.M. YADAV
CED, SVNIT, Surat
Civil Engineering Department
SARDAR VALLABHBHAI NATIONAL INSTITUTE OF TECHNOLOGY
ICCHANATH, SURAT, GUJARAT - 395007
TableofContent 1. Basic Introduction
3. Scope of Study
4. Literature Review
5. Study Area
6. Need for Study
7. Rainfall Data Collection of Silvassa
8. Analysis of Rainfall Data for Silvassa
9. Rainfall Data Collection & Analysis for
10. Storm Drain Design for Illustrative
11. Technical Visit
The circulation and conservation of earth’s water as it circulates from the land
to the sky and back again is called the ‘hydrological cycle’ or ‘water cycle’.
BasicIntroduction Precipitation : It denotes all forms of
water that reach the earth from the
The usual forms are rainfall , snowfall,
hail, frost, drizzle and dew.
Evaporation : The process by which
water changes from a liquid to a gas & is
transferred from the surface to the
Interception : The process in which, the
part of precipitation, which may get
evaporated or flow down after
interception through trees and structures.
Transpiration : Vegetation sends a part
of water from under ground surface back
Infiltration : A process in which portion
of water that reaches the ground surface
and enters the earth surface.
Runoff : The process in which the portion
of precipitation by different paths above
and below ground surface reaches the
This Runoff may cause flood in the city
areas and hence storm drain network are laid
to overcome this problem.
A storm drain system is a network of pipes
used to convey runoff from a city to a
receiving water body.
Their design involves determination of
diameters, slopes and crown elevation or
invert elevation of each pipe.
The selection of layout or network of pipe
location for a storm sewer system requires
a considerable amount of subjective
Gradually manholes/inlets are placed at
street intersections and at major changes
in grade or ground surface slope.
Objective of the study:
To find out the 1-hour maximum rainfall
depth for different return periods.
To find out rainfall intensity duration
Apart from these, to design storm drain
network for an illustrative region.
To carry out literature review for
analyzing rainfall intensity and frequency.
To carry out data collection for compiling
To carry out analysis of collected data for
Silvassa and Surat city.
To compute 1-hour maximum rainfall
Name Year Publication Description
Elsebaie I H
relationship for two
regions in Saudi
IDF relationship is a
between the rainfall intensity i,
the duration d, and the return
period T (or, equivalently, the
annual frequency of exceedance
‘f ‘referred to as ‘frequency’).
Several aspects of short time
interval rainfall data from
Indiana are investigated in this
study. The variability in rainfall
intensity estimates by different
procedures is quantified.
The purpose of this paper is to
develop an empirical formula to
estimate design rainfall intensity
based on intensity–duration–
frequency (IDF) curves for
Name Year Publication Description
Agnihotri et al
“Analysis of Rainfall
Data and Design of
storm Water Drainage
System in an Urban
Rainfall data available from
1969 to 1983 are of duration 5,
10, 15, 30, 45, 60, 75, 90
minute. Analysis of rainfall data
is carried for year 1969 to 1983
and one year flood frequency is
Harshil H Gajjar
Network Design of
Area of City of
In this paper, past 20 years
rainfall data is taken. The system
has been designed considering in
total of 65% of the impervious
Rational method has been used
for estimation of storm water
S M Yadav
“A Case Study on
Present paper discusses the steps
involved in the design of storm
StudyArea Surat city is located on the western part
of India in Gujarat. It is also called as city
The city is located at 306 km south of the
state capital, Gandhinagar on the left bank
of the Tapti River (Tapi).
Surat is Gujarat's second largest city with
a population of 2.1 million at the 2001
census and 4.6 million at the 2011 census.
Surat city is divided into 7 zones by Surat
Municipal Corporation namely:
Surat is a port city situated on the banks of
the Tapti River. The city is located
at 21°10′N 72°50′E.
The average annual rainfall of surat city
is about 1,200 millimetres (47 in) (IMD).
The general slope is from north-east to
The city is 13m above mean sea level.
The coastal line is along the villages of
Hazira, Mora, Limla, Dumas, Bhimpor,
Abhava, Gavier, Sarsana and Vesu.
In Surat, life and property are frequently
under the threat of flooding due to heavy
rainfall. The average annual rainfall of
Surat is about 1200 millimetres.
Such heavy rainfall, sometimes coupled
with high sea levels associated with storm
surges during the passage of tropical
cyclones, can cause flooding.
Apart from natural causes, sometimes
human activities may also influence the
prevalence of flooding.
Storm water drainage is an integral part of
the essential infrastructure of a modern
city. In Surat, separate systems are
provided for the collection and disposal of
storm water and sewage.
For study of rainfall intensity, yearly rainfall data
and the 24-hour maximum rainfall data were
collected from Central Water Commission (CWC)
or Municipal corporation.
Rainfall intensity and duration is calculated by
using India Meteorological Department (IMD)
1-hour rainfall has been estimated by using 24-
hours maximum rainfall, using IMD empirical
reduction formula. 1-hour maximum rainfall is
Pt = P24 (t/24)1/3
where P24 = yearly 24-hour maximum rainfall
Rainfall Data of Silvassa for 29
By using Gumbel frequency distribution
method, frequeny analysis of 1-hour
maximum rainfall is carried out.
Graph is plotted between 1-hour maimum
rainfall and Gumbel frequency factor(K).
1-hour maximum rainfall depth for
different return periods of 2, 5, 10, 20, 50
and 100 year is calculated.
Pt = Pm + K*s
where Pt = expected 1-hour T-year rainfall depth,
Pm = mean 1-hour maximum rainfall
s = standard deviation of 1-hour maximum rainfall
k = Gumbel frequency factor
1-hour maximum rainfall depth is used for
finding the t-minute rainfall depth for
different time period such as 5, 10, 15, 30
and 120 minute.
1 hour T-year rainfall depth is multiplied
by factor (taken from Journal of Indian
Water Works Association, Vol-Octo-Dec-
2007 ) to obtain T minute Rainfall Depth.
Frequency Analysis Using Gumbel Distribution method
Rainfall data of different time period ranging from
previous 50 year, 100 year and 120 year are
obtained for Surat city.
Similar calculations is executed on these data and 1-
hour maximum rainfall depth, maximum rainfall
intensity and intensity duration curve is obtained.
Estimation of Rainfall Intensity of Surat for 30 years.
Estimation of Rainfall Intensity of Surat for 50 years.
Estimation of Rainfall Intensity of Surat for 100 years.
Estimation of Rainfall Intensity of Surat for 120 years.
Design of Storm Water Drainage Network
for a rectangular plot of area 180 X 250
square meter has been carried out.
Reduced levels of all the nodes for the
illustrative region were available.
The main line passes through the centre of
the catchment area.
The runoff from other part of the
catchment area flows through the sub
branches which are connected to the main
The frequency of storm selected was once
in 2 years.
Usually, the storm drains are not designed
for peak discharges or extreme events
from economical point of view.
The design of the drain should be
economical and at the same time it should
prevent frequent flooding and it should
drain out quickly.
For designing the storm water network for
the given area the following data is
2. Rainfall intensity and duration
3. Impervious factor
4. Design of Drainage system
Rainfall Intensity and duration has been
estimated using India Meteorological
Department (IMD) method.
For the paved area, the impervious factor
is taken as 0.7
Storm water runoff has been calculated by
using Rational Method suggested by
The diameter of pipe is selected so as to
maintain the minimum velocity of 0.6 m/s
and to carry slightly more discharge
compared to the theoretical discharge.
The diameter of the pipe was selected to
maintain a self cleansing velocity.
Moreover, the velocity of flow should not
exceed more than scouring velocity.
Design of Storm drain network of an illustrative region
A site was visited at Godadara where
drainage pipes were being laid for the
removal of storm water.
The storm water has been transported to
the pumping station, treated and than
disposed of in to the Khadi.
Consultant : Mayur Shah, Assistant
Engineer Surat Municipal Corporation.
The pipes which were being laid were
spigot pipe of 500 mm diameter and the
length of each pipe was 265 mm.
The pipes were being laid at the slope of
1:500. Generally the slope in the field is
set by two methods:
1. Boning method 2.Spirit level
Analysis of Rainfall Data of 29 years for
Silvassa region has been carried out. Maximum
hourly intensity with a recurrence interval of 2
year is estimated to be 78 mm/hr.
The same analysis of rainfall data was carried
out for Surat region:
The present study helps in computing rainfall
intensity which is used to estimate storm water
The storm water runoff thus computed is very
important for the design of storm drain network.
Years Intensity (mm/hr)
30 Years 56.5
50 Years 56.309
100 Years 52.87
120 Years 51.54
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