2/18/2014

1

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

3

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 :

2/18/2014

2

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

8

Rainfall - Runoff

2/18/2014

3

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

2/18/2014

4

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

2/18/2014

5

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.

19

Synthetic Hyetographs

No Short Duration Record? Bell Ratios!

SCS type II Arid zone hydrology 1st graph

Arid zone hydrology 2st graph

or similar distributions

2/18/2014

6

Bell’s Ratios used in IDF Development Synthetic Hyetographs

Synthetic Hyetographs “Arid zone hydrology”

proposes the following 1st graph:

2/18/2014

7

“Arid zone hydrology” proposes then this 2nd graph:

26

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.

2/18/2014

8

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

2/18/2014

9

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

35

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 - - - - - - - - - -

2/18/2014

10

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

39

Statistical Analysis

Why to Use Distribution Fitting? To extrapolate

To assume a population with known characteristics based on a small sample

2/18/2014

11

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

2/18/2014

12

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.

2/18/2014

13

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.

50

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

52

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

2/18/2014

14

53

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

54

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

55

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

56

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