Rainfall Short Duration Objectives Analysis in Arid/Semi...
Transcript of Rainfall Short Duration Objectives Analysis in Arid/Semi...
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By
Eng. Khaled Asaad
Faculty of Engineering, Cairo University
Cairo, Egypt
Rainfall Short Duration Analysis in Arid/Semi Arid
Regions
Generate IDF, for each Rainfall Station for 5,10,20, 25, and 100 Years Return
Periods in KSA and Sinai .
Weighted Design Storm for Relative 2.0 hours and 24 hours depths of Each
Rainfall Stations in KSA and Sinai for 5,10,20, 25, and 100 Years.
Weighted Design Storm Relative 2.0 hours and 24 hours depths for All Rainfall
Stations in KSA, as well as Sinai .
Comparing Relative 2.0 hours and 24 hours depths of All Rainfall Stations
verses Bell’s and SCS storm type II respectively for both KSA and Sinai .
Evaluate adopting Bell’s ratios ,and SCS Storm type II in KSA and Sinai .
Generate Representive 24 hours Design Storm for KSA and Sinai as Arid Regions.
Check the relation between the Return Period and Relative 24 hours Depths for
KSA and Sinai If any.
Objectives
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INTRODUCTION
Arid and Semi-Arid Regions Arid Regions; These in which the rainfall on a given piece of
land is not adequate for regular crop production.
Semi-Arid Regions; as those in which the rainfall is sufficient for short
season crop and where grass is an important element in
natural vegetation.
INTRODUCTION :
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HYDROLOGICAL CYCLE INTRODUCTION : Rainfall Types
Frontal: Produced in conjunction with movement of large air masses (hot and cold
fronts) Precipitation produced by juxtaposition of warm, moist air, and cold air.
Cyclonic: A cyclone is a large low pressure region with circular wind motion. Strong winds can reach 200 km/hr and might produce excessive precipitation over very 1000 km2, for several days.
Convective: Due to intense heating of air at ground surface, air mass expands and rises.
Orographic: Air mass is mechanically lifted over an elevated land mass. Results in high precipitation on western slopes (BC temperate rain forest) and the shadow effect on eastern slopes of mountain ranges.
INTRODUCTION :
INTRODUCTION
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Rainfall - Runoff
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Factors Affecting Runoff
Soil and land Use
Drainage Characteristics
Rainfall Distribution Pattern
Storm Design Use point on IDF OR ONE
Design Storm Concept
A precipitation pattern defined for use in a hydrologic system. i.e., a hypothetical worst case hyetograph for a storm of predetermined duration and recurrence frequency (e.g. 6 hour, 50 year storm).
Developed from IDF curves for a location.
IDF curve does not represent a storm. It describes recurrence intervals for periods of rainfall of various intensities.
Rainfall - Runoff
Intensity-Duration-Frequency (IDF) Curves Intensity
Rate at which precipitation falls. This is generally expressed as depth of rainfall per unit of time (cm/hr)
Duration: The length of time over which a precipitation event occurs
Frequency: The “repeat” time interval for an event having the same volume and
duration.
Intensity and Duration combine to yield volume The amount of precipitation in total and as a function of time per
unit area
Intensity-Duration-Frequency (IDF) Curves
R.P.
Duration (hrs)
0.17 0.33 0.5 1 2 3 6 12 24
100 156.00 103.20 72.20 37.00 18.70 12.70 7.40 3.70 2.25
50 133.80 87.00 61.00 32.00 16.55 11.47 6.68 3.39 2.07
25 111.00 71.10 50.00 26.80 14.30 10.13 5.92 3.06 1.88
20 103.20 66.00 46.40 25.10 13.55 9.67 5.65 2.95 1.81
10 78.60 49.20 35.20 19.60 11.00 8.07 4.73 2.54 1.60
5 49.80 31.20 23.00 13.40 8.00 6.07 3.60 2.00 1.35
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Alternating Block Method
This method positions the block of maximum incremental depth at the middle of the required duration.
The remaining
blocks are arranged
then in descending
order, alternately
before and after the
central block.
Rational Formula
FCCIA
Q60.3
Rainfall Intensity
(mm/hr)
Basin Area
(km2)
Peak Discharge
Coefficient
(dimensionless)
Frequency Adjustment
Coefficient (dimensionless)
Discharge
(m3/s)
Runoff Estimation
Loss method
CN : is the Curve Number.
S : is the maximum storage depth (in mm).
P : is the accumulated depth of daily storm rainfall (mm).
Runoff Estimation Modified Talbot’s Method (a type of regression equations)
Drainage Area (ha) 25-year Frequency Rain Storm
1. 0-400 Q x S.F.
2. 400 to 1258 0.837 x C x A3/4
3. 1258 to 35,944 4.985 x C x A1/2
4. over 35,944 14.232 x C x A2/5
Q50 = 1.2 Q25
Q100 = 1.4 Q25
Runoff Estimation
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Runoff Applications Engineering:
Design of Dams, Culverts, Bridges ,…
Hill slope stability
Natural Hazards: Flood mitigation
Slope failure
Environmental Protection: Soil contamination
Surface and groundwater pollution
Wetlands
Water Resource Management for water supply purposes or for agriculture
Rainfall - Runoff Historical rainfall events; the way in which the precipitation is
distributed in time over the duration of the storm .
This can be described using a rainfall hyetograph of real storms as well as synthetic hyetograph.
The time distribution of the design hyetograph will significantly affect the timing and magnitude of the peak runoff.
Therefore, care should be taken in selecting a design storm to ensure that it is representative of the rainfall patterns in the area under study.
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Synthetic Hyetographs
No Short Duration Record? Bell Ratios!
SCS type II Arid zone hydrology 1st graph
Arid zone hydrology 2st graph
or similar distributions
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Bell’s Ratios used in IDF Development Synthetic Hyetographs
Synthetic Hyetographs “Arid zone hydrology”
proposes the following 1st graph:
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“Arid zone hydrology” proposes then this 2nd graph:
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Data Availability
& Accuracy
Data Availability
Station Region
Available Record Periods
No. Name From To Years
1 EL-SHAK ATIA Sinai 1989 2004 16
2 ELTHEMED Sinai 1990 2004 15
3 GODYRAT Sinai 1990 2004 15
4 NEKHEL Sinai 1990 1998 9
5 NUWIBAA Sinai 1990 2004 15
6 ST-KATH Sinai 1990 2003 14
7 RAWAFAA Sinai 1990 2003 14
8 SUDR Sinai 1991 1999 9
9 PR1,SUDR Sinai 1990 2004 15
10 R2,SUDR Sinai 1990 1997 8
11 R3,SUDR Sinai 1990 2000 11
12 R4,SUDR Sinai 1990 2004 15
13 R5,SUDR Sinai 1990 1994 5
14 WS,SUDR Sinai 1985 2004 20
A fourteen (14) rainfall stations located in Sinai (Egypt) with total 181
years records with average 13 years for each station maximum 20 years,
and minimum 5 years.
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Data Availability
A sixteen (16) rainfall stations located in Saudi Arabia with total 422 years records with
average 26.4 years for each station maximum 40 years, and minimum 8 years.
Station Region
Available Record Periods
No. Name From To Years
1 Turabah KSA 1976 2003 19
2 Ad-Dawadmi KSA 1977 1993 17
3 Riyadh (ST-452) KSA 1965 2003 39
4 Taif (ST- 627 ) KSA 1974 2004 25
5 Sarrar KSA 1967 2003 37
6 Hufuf No. 166 KSA 1979 2003 25
7 Zimaa KSA 1966 1995 30
8 Makkah Mokaramah(J218) KSA 1964 2000 37
9 SUFAN KSA 1972 1985 14
10 Khulays (J002) KSA 1966 2000 35
11 Kara Al Maru KSA 1986 1993 8
12 Uqlat Suqur KSA 1975 1992 18
13 Bir Arja KSA 1974 1990 17
14 Taif (TA004 ) KSA 1980 2003 24
15 Taif (TA002 ) KSA 1975 2000 26
16 Elsail Elkbir(TA003) KSA 1975 2000 26
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1,2 2,0 2,1 2,1 2,2 2,3 2,5 2,6 2,7 2,8 2,8 3,0 3,3 3,4 3,4 4,0 4,3
6,0 6,3 6,9 7,0 7,1
0,0
2,0
4,0
6,0
8,0
1:12 1:24 15:30 15:42 16:18 18:24 18:42 19:18 19:42 20:30 21:00RA
IN (
M M
)
TIME
EL SHEEK ATIA STATION
7/1/2002
7,4 8,4 8,7 8,8
5,0
10,0
22:48 22:54 23:12 23:18
RA
IN (
M M
)
TIME
EL SHEEK ATIA STATION
27/1/2002
0,6 0,7 0,7 1,2
0,00,51,01,5
21:30 21:36 23:06 23:18
RA
IN (
M M
)
TIME
EL SHEEK ATIA STATION
6/1/2002
DATE CHART
TIME (HR.)
CHART
READING
(MM)
RAINFALL
DIFFERENC
E
(M M)
1/1/02 14:00 0.6 0.0
6/1/02 21:30 0.6 0.0
21:36 0.7 0.1
23:06 0.7 0.0
23:18 1.2 0.5
7/1/02 1:12 1.2 0.0
1:18 2.0 0.8
1:24 2.1 0.1
15:24 2.1 0.0
15:30 2.2 0.1
15:36 2.3 0.1
15:42 2.5 0.2
16:06 2.6 0.1
16:18 2.7 0.1
16:24 2.8 0.1
18:24 2.8 0.0
18:30 3.0 0.2
18:42 3.3 0.3
18:48 3.4 0.1
19:18 3.4 0.0
19:24 4.0 0.6
19:42 4.3 0.3
20:12 6.0 1.7
20:30 6.3 0.3
20:54 6.9 0.6
21:00 7.0 0.1
21:30 7.1 0.1
27/1/02 22:48 7.4 0.3
22:54 8.4 1.0
23:12 8.7 0.3
23:18 8.8 0.1
29/1/02 14:13 8.8 0.0
days DAILY
RAINFALL
1 0.0
2 0.0
3 0.0
4 0.0
5 0.0
6 0.6
7 5.9
8 0.0
9 0.0
10 0.0
11 0.0
12 0.0
13 0.0
14 0.0
15 0.0
16 0.0
17 0.0
18 0.0
19 0.0
20 0.0
21 0.0
22 0.0
23 0.0
24 0.0
25 0.0
26 0.0
27 1.7
28 0.0
29 0.0
30 0.0
31 0.0
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Preparing Data
GODAIRAT 1/2/1990
DATE CHART
TIME (HR.)
CHART
READING
(MM)
RAIN.
6min.
(M M)
RAIN.
12min.
(M M)
RAIN.
18min.
(M M)
RAIN.
30min.
(M M)
RAIN.
60min.
(M M)
RAIN.
120min.
(M M)
RAIN.
180min.
(M M)
RAIN.
360min.
(M M)
RAIN.
720min.
(M M)
RAIN.
1440min.
(M M)
1/2/90 20:12 0.000 0.018 0.036 0.055 0.091 0.182 0.200 0.200 0.200 0.200 0.200
20:18 0.018 0.018 0.036 0.055 0.091 0.182 - - - - -
20:24 0.036 0.018 0.036 0.055 0.091 - - - - - -
20:30 0.055 0.018 0.036 0.055 0.091 - - - - - -
20:36 0.073 0.018 0.036 0.055 0.091 - - - - - -
20:42 0.091 0.018 0.036 0.055 0.091 - - - - - -
20:48 0.109 0.018 0.036 0.055 0.091 - - - - - -
20:54 0.127 0.018 0.036 0.055 - - - - - - -
21:00 0.145 0.018 0.036 0.055 - - - - - - -
21:06 0.164 0.018 0.036 - - - - - - - -
21:12 0.182 0.018 - - - - - - - - -
21:18 0.200 - - - - - - - - - -
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MONTH
RAIN.
6min.
(M M)
RAIN.
12min.
(M M)
RAIN.
18min.
(M M)
RAIN.
30min.
(M M)
RAIN.
60min.
(M M)
RAIN.
120min.
(M M)
RAIN.
180min.
(M M)
RAIN.
360min.
(M M)
RAIN.
720min.
(M M)
RAIN.
1440min.
(M M)
JAN 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
FEB 0 0 0 0 0 0 0 0 0 0
MAR 8 8.6 9.2 10.5 13.1 21.2 21.2 21.5 21.5 21.5
APR 0 0 0 0 0 0 0 0 0 0
MAY 0 0 0 0 0 0 0 0 0 0
JUN 0 0 0 0 0 0 0 0 0 0
JUL 0 0 0 0 0 0 0 0 0 0
AUG 0 0 0 0 0 0 0 0 0 0
SEP 0 0 0 0 0 0 0 0 0 0
OCT 4.1 4.7 4.71 4.8 5 7.3 7.3 7.3 7.4 7.4
NOV 7.6 8.6 9.9 16.3 21.8 30 30 30 30 30
DEC 6.6 6.9 7 7.3 9 9.7 12.9 13.6 18.4 22.2
MAX. RAIN
FALL DEPTH
(M M.
8.000 8.600 9.900 16.300 21.800 30.000 30.000 30.000 30.000 30.000
GODAIRAT 1994
SUDR 1985-2004
YEAR
RAIN.
6min.
(M M)
RAIN.
12min.
(M M)
RAIN.
18min.
(M M)
RAIN.
30min.
(M M)
RAIN.
60min.
(M M)
RAIN.
120min.
(M M)
RAIN.
180min.
(M M)
RAIN.
360min.
(M M)
RAIN.
720min.
(M M)
RAIN.
1440min.
(M M)
1985 1.08 1.33 1.46 2.16 2.16 2.38 2.82 4.53 4.53 4.53
1986 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
1987 5.46 5.55 5.64 5.73 7.16 7.31 7.31 9.13 10.21 10.21
1988 1.50 1.84 2.37 2.50 2.50 2.81 4.41 4.41 4.41 4.41
1989 2.26 4.11 4.78 5.13 5.13 7.42 7.42 8.56 9.02 9.02
1990 0.65 1.25 1.67 2.49 3.30 5.68 7.13 10.67 10.67 10.67
1991 2.35 3.58 3.83 4.64 8.54 13.03 16.38 20.84 25.01 25.13
1992 1.20 1.71 2.00 2.10 2.48 3.41 4.46 4.51 4.51 4.51
1993 0.83 1.00 1.11 1.21 1.73 2.58 3.01 3.43 3.43 3.43
1994 2.05 4.04 4.34 6.47 7.45 9.38 12.30 16.45 27.22 27.22
1995 4.12 4.43 4.79 5.21 5.27 5.27 5.57 7.24 7.24 7.24
1996 1.21 1.21 1.21 1.21 1.21 1.21 1.21 1.21 1.21 1.21
1997 1.86 3.49 3.84 4.20 4.21 4.21 4.21 5.91 5.91 5.91
1998 1.25 1.25 1.39 2.12 2.66 2.66 2.66 2.66 2.66 2.66
1999 1.42 2.08 2.94 3.91 6.65 8.89 11.27 13.00 13.00 13.00
2000 3.41 4.52 5.65 6.23 7.02 7.39 7.42 7.70 7.70 7.70
2001 1.37 1.66 1.66 1.66 1.74 2.02 3.05 3.60 3.60 3.60
2002 1.60 2.46 3.03 4.60 6.02 10.31 14.81 23.92 23.92 23.92
2003 1.36 1.75 1.90 2.08 2.11 2.11 2.11 2.85 2.85 2.85
2004 2.45 2.79 3.75 5.52 6.07 10.63 13.65 14.22 17.99 20.48
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Statistical Analysis
Why to Use Distribution Fitting? To extrapolate
To assume a population with known characteristics based on a small sample
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Statistical Analysis
Lack of High Quality Data for Rainfall Short Duration Record
No Specific Techniques
What statistical distribution should be used?
No Specifically Recommended Probability Distribution.
Find best estimate of design quantiles and hydrologic risk
Outliers
The Problem of Zeros
Typical Distributions Characteristics:
Type of Phenomenon
Number of Distribution Parameters
Range of Variable
Types: Normal Family (Normal (Gaussian), Lognormal)
Extreme Value Family (Gumbel)
Pearson Family (Log Pearson type III)
Choice between Distribution
Visual Comparison with Empirical Probability Plot
Moment Diagrams
Chi-Square Comparison as a Fitting Test
Akaike Information Criterion and Bayesian
Information Criterion
Procedure of HYFRAN+
HYFRAN+ DSS
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Choice between Distribution Distributions Fitting
Visual Comparison AIC and BIC Comparison Criteria
Bayesian Information Criterion (BIC): BIC = -2 log (L) +2 k log(n) Akaike Information Criterion (AIC): AIC = -2 log (L) +2 k where L is the likelihood, k is the number of parameters and n is the sample size.
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Outliers Outliers are measurements that are extremely large or small relative
to the rest of the data and, therefore, are suspected of misrepresenting the population from which they were collected.
Outliers may result from transcription errors, data-coding errors, or measurement system problems such as instrument breakdown.
However, outliers may also represent true extreme values of a distribution (for instance, hot spots) and indicate more variability in the population than was expected.
Not removing true outliers and removing false outliers both lead to a distortion of estimates of population parameters.
Statistical outlier tests give the analyst probabilistic evidence that an extreme value (potential outlier) does not "fit" with the distribution of the remainder of the data and is therefore a statistical outlier.
These tests should only be used to identify data points that require further investigation.
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Outputs
Hufuf Rainfall Station Relative Storm
R.P. Duration (hrs)
0.17 0.33 0.5 1 2 3 6 12 24
100 Yrs 152.94 104.24 72.20 37.00 18.70 12.70 7.40 3.70 2.25
50 Yrs 131.18 87.88 61.00 32.00 16.55 11.47 6.68 3.39 2.07
25 Yrs 108.82 71.82 50.00 26.80 14.30 10.13 5.92 3.06 1.88
20 Yrs 101.18 66.67 46.40 25.10 13.55 9.67 5.65 2.95 1.81
10 Yrs 77.06 49.70 35.20 19.60 11.00 8.07 4.73 2.54 1.60
5 Yrs 48.82 31.52 23.00 13.40 8.00 6.07 3.60 2.00 1.35
R.P. Duration (hrs)
0.17 0.33 0.5 1 2
100 Yrs 0.70 0.92 0.97 0.99 1.00
50 Yrs 0.67 0.88 0.92 0.97 1.00
25 Yrs 0.65 0.83 0.87 0.94 1.00
20 Yrs 0.63 0.81 0.86 0.93 1.00
10 Yrs 0.60 0.75 0.80 0.89 1.00
5 Yrs 0.52 0.65 0.72 0.84 1.00
R.P. Duration (hrs)
0.17 0.33 0.5 1 2 3 6 12 24
100 Yrs 26.00 34.40 36.10 37.00 37.40 38.10 44.40 44.45 54.10
50 Yrs 22.30 29.00 30.50 32.00 33.10 34.40 40.10 40.70 49.70
25 Yrs 18.50 23.70 25.00 26.80 28.60 30.40 35.50 36.70 45.10
20 Yrs 17.20 22.00 23.20 25.10 27.10 29.00 33.90 35.40 43.50
10 Yrs 13.10 16.40 17.60 19.60 22.00 24.20 28.40 30.50 38.30
5 Yrs 8.30 10.40 11.50 13.40 16.00 18.20 21.60 24.00 32.40
Hufuf Depth-Duration-Frequency Hufuf Intensity-Duration-Frequency
Hufuf (2) Hours Dimensionless Storm Hufuf Intensity-Duration-Frequency Curves
R.P. Duration (hrs)
0.17 0.33 0.5 1 2 3 6 12 24
100 Yrs 0.48 0.64 0.67 0.68 0.69 0.70 0.82 0.82 1.00
50 Yrs 0.45 0.58 0.61 0.64 0.67 0.69 0.81 0.82 1.00
25 Yrs 0.41 0.53 0.55 0.59 0.63 0.67 0.79 0.81 1.00
20 Yrs 0.40 0.51 0.53 0.58 0.62 0.67 0.78 0.81 1.00
10 Yrs 0.34 0.43 0.46 0.51 0.57 0.63 0.74 0.80 1.00
5 Yrs 0.26 0.32 0.35 0.41 0.49 0.56 0.67 0.74 1.00
Hufuf (24) Hours Dimensionless Storm
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R.P. Duration (hrs)
0.17 0.33 0.5 1 2
100 Yrs 0.49 0.65 0.76 0.89 1.00
50 Yrs 0.48 0.65 0.75 0.89 1.00
25 Yrs 0.48 0.64 0.75 0.89 1.00
20 Yrs 0.47 0.64 0.75 0.89 1.00
10 Yrs 0.46 0.63 0.74 0.88 1.00
5 Yrs 0.45 0.62 0.74 0.87 1.00
KSA Design Storm KSA (2) Hours Weighted Dimensionless Storm
KSA’s and Bell’s ratios
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R.P. Duration (hrs)
0.17 0.33 0.5 1 2 3 6 12 24 100 Yrs 0.32 0.43 0.50 0.58 0.66 0.69 0.77 0.84 1.00 50 Yrs 0.32 0.43 0.49 0.58 0.66 0.70 0.78 0.85 1.00 25 Yrs 0.31 0.42 0.49 0.58 0.66 0.71 0.78 0.85 1.00 20 Yrs 0.31 0.42 0.49 0.58 0.66 0.71 0.78 0.85 1.00 10 Yrs 0.30 0.41 0.49 0.58 0.65 0.70 0.78 0.84 1.00 5 Yrs 0.29 0.40 0.47 0.56 0.64 0.70 0.77 0.82 1.00
KSA Design Storm KSA’s and SCS’s ratios
KSA (24) Hours Dimensionless Storm
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R.P. Duration (hrs)
0.1 0.2 0.3 0.5 1 2
100 Yrs 0.39 0.42 0.45 0.52 0.67 1.00
50 Yrs 0.38 0.42 0.46 0.53 0.68 1.00
25 Yrs 0.36 0.43 0.47 0.55 0.70 1.00
20 Yrs 0.36 0.43 0.48 0.56 0.70 1.00
10 Yrs 0.34 0.43 0.49 0.57 0.72 1.00
5 Yrs 0.33 0.44 0.50 0.60 0.74 1.00
Sudr-WS (2) Hours Dimensionless Storm Sudr-WS Intensity-Duration-Frequency Curves
Sudr-WS Rainfall Station, Sinai, Egypt
R.P. Duration (hrs)
0.1 0.2 0.3 0.5 1 2 3 6 12 24
100 Yrs 6.02 6.44 6.96 7.94 10.2 15.3 20.3 28.3 34.9 35.4 50 Yrs 5.24 5.89 6.43 7.41 9.48 13.9 18.2 24.9 30.4 30.9 25 Yrs 4.48 5.3 5.86 6.82 8.65 12.4 16 21.5 26 26.4 20 Yrs 4.24 5.1 5.66 6.62 8.36 11.9 15.2 20.4 24.5 24.9 10 Yrs 3.49 4.45 5 5.92 7.39 10.3 12.9 16.8 19.9 20.3
5 Yrs 2.73 3.7 4.22 5.07 6.24 8.39 10.3 13 15.1 15.4
Sudr-WS Depth-Duration-Frequency Sudr-WS Intensity-Duration-Frequency
R.P. Duration (hrs)
0.1 0.2 0.3 0.5 1 2 3 6 12 24
100 Yrs
60.20 32.20 23.20 15.88 10.20 7.65 6.77 4.72 2.91 1.48
50 Yrs 52.40 29.45 21.43 14.82 9.48 6.95 6.07 4.15 2.53 1.29
25 Yrs 44.80 26.50 19.53 13.64 8.65 6.20 5.33 3.58 2.17 1.10
20 Yrs 42.40 25.50 18.87 13.24 8.36 5.95 5.07 3.40 2.04 1.04
10 Yrs 34.90 22.25 16.67 11.84 7.39 5.15 4.30 2.80 1.66 0.85
5 Yrs 27.30 18.50 14.07 10.14 6.24 4.20 3.43 2.17 1.26 0.64
R.P. Duration (hrs)
0.1 0.2 0.3 0.5 1 2 3 6 12 24
100 Yrs 0.17 0.18 0.20 0.22 0.29 0.43 0.57 0.80 0.99 1.00
50 Yrs 0.17 0.19 0.21 0.24 0.31 0.45 0.59 0.81 0.98 1.00
25 Yrs 0.17 0.20 0.22 0.26 0.33 0.47 0.61 0.81 0.98 1.00
20 Yrs 0.17 0.20 0.23 0.27 0.34 0.48 0.61 0.82 0.98 1.00
10 Yrs 0.17 0.22 0.25 0.29 0.36 0.51 0.64 0.83 0.98 1.00
5 Yrs 0.18 0.24 0.27 0.33 0.41 0.54 0.67 0.84 0.98 1.00
Sudr-WS (24) Hours Dimensionless Storm
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Hours Weighted Dimensionless Storm
R.P. Duration (hrs)
0.10 0.20 0.30 0.50 1 2
100 Yrs 0.35 0.46 0.55 0.65 0.76 1.00
50 Yrs 0.35 0.46 0.55 0.65 0.77 1.00
25 Yrs 0.35 0.46 0.55 0.66 0.77 1.00
20 Yrs 0.36 0.46 0.54 0.65 0.78 1.00
10 Yrs 0.36 0.47 0.56 0.65 0.78 1.00
5 Yrs 0.35 0.46 0.55 0.65 0.76 1.00
Sinai’s and Bell’s ratios
Sinai, Egypt Design Storm
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R.P. Duration (hrs)
0.10 0.20 0.3 0.5 1 2 3 6 12 24
100 0.25 0.33 0.39 0.46 0.54 0.71 0.79 0.92 0.98 1.00
50 0.25 0.33 0.39 0.46 0.55 0.71 0.80 0.92 0.98 1.00
25 0.25 0.33 0.39 0.47 0.55 0.71 0.80 0.92 0.98 1.00
20 0.26 0.33 0.39 0.47 0.56 0.72 0.80 0.92 0.98 1.00
10 0.26 0.34 0.40 0.47 0.56 0.72 0.81 0.92 0.98 1.00
5 0.26 0.34 0.40 0.48 0.58 0.74 0.82 0.93 0.98 1.00
Sinai (24) Hours Dimensionless Storm
Sinai’s and SCS’s ratios Sinai, Egypt Design Storm
2/18/2014
15
Page 57
Conclusion Most of Rainfall stations short duration rainfall ratios are greater than Bell’s
and SCS’s type II.
The peak rainfall ratios are higher than SCS’s type II for the weighted average of all stations of KSA and Sinai for each return period.
The peak rainfall ratios are higher than SCS’s type II for the average of weighted average of all stations of KSA and Sinai for all return period.
The weighted average/average of this ratios are in the upper limits of Bell’s ratios, while the upper limit of average is much greater than Bell’s ratios.
Appling Bell’ s / SCS’s type II ratios may be not safe.
Rainfall stations of KSA show increase in the rainfall depth ratio with return period increase, while this trend was not shown in Saini stations
March, 2011 Page 58
Recommendations Further study using more short duration rainfall data by establishing
new stations, and gathering data from the old stations in the arid regions, continuous update of the design storms to get a reliable design storms with adequate rainfall records.
Zoning and grouping of the arid regions avoiding generalizing errors.
Generate Iso-Line maps the arid regions for different return periods.
March, 2011
Thank You