Near East

& North Africa

Flood Risk Assessment Using GIS Tools

Land Resources Management

Flow Diagram

Input Processing

Construct DEM

Delineate watersheds

Extract Stream network

Calculate Watershed

Characteristics

Output

Risk Matrix

Vulnerability map

Runoff Hydrograph Rainfall

module SCS GIUH

0.00

2000.00

4000.00

6000.00

8000.00

10000.00

12000.00

14000.00

Time (hrs.)

Un

it H

yd

rog

rap

h F

low

(cfs

/in

ch

)

0.00

10000.00

20000.00

30000.00

40000.00

50000.00

60000.00

Flo

w (

cfs

)

S-curves are

lagged by 1 hour

and the difference

is found.1-hour unit

hydrograph resulting

from lagging S-

curves and

multiplying the

difference by 6.

Contours

Elevation and constructing of DEM

Flow Direction

128 64

1 16

2 4 8

32

Flow Accumulation

128 64

1 16

2 4 8

32

Delineating the watersheds and

Stream Networks

Delineating the watersheds and

Stream Networks

Selected parameters

Area (A)

weighted mean of bifurcation ratio (WMRB)

stream frequency (F)

drainage density (D)

shape index (Ish)

slope index (Sl)

relief ratio (Rr)

ruggedness number (Rn)

texture ratio (Rt).

Watershed Factors

Watershed size - runoff volumes and rates increase

with watershed size

Watershed Factors

Watershed shape - runoff rates tend to be

lower for long narrow watersheds than for

compact water sheds having the same area

Long “time

of concentration”

Short “time

of concentration”

Drainage Density and Stream Frequency

L N A

1 =D

=1

A

N

= F =1

Risk Calculation

x = the parameter value

xmin = the minimum value of the parameter according to all studied basins

xmax = the maximum value of the parameter according to all studied basins

1)(

)(*4

minmax

min

xx

xxvalueRisk

1)(

)(*4

minmax

min

xx

xxvalueRisk

Basin A WMRb F D Ish Sl Rr Rn Rt

Risk

Degree

1 1 4 2 2 3 3 4 4 1 3

2 5 5 2 3 3 1 1 5 5 5

3 3 4 2 3 2 1 1 3 3 4

4 2 4 2 3 2 1 1 4 3 3

5 1 4 3 1 3 1 1 1 1 2

6 1 4 3 2 2 1 1 1 1 2

7 1 5 1 3 2 2 2 3 2 3

8 1 4 3 2 2 1 1 1 1 2

9 1 5 3 3 4 2 2 2 1 3

10 1 5 2 3 3 3 3 3 1 2

11 1 1 1 1 1 3 3 3 1 1

12 1 5 3 3 4 3 4 2 1 3

13 1 2 1 2 1 3 3 3 1 2

14 1 5 5 3 2 3 3 2 1 3

15 1 4 4 3 2 4 4 3 1 3

16 1 5 4 3 3 5 5 3 1 3

17 1 3 3 4 2 5 4 4 1 3

18 1 5 4 3 2 5 5 3 1 3

19 1 4 1 5 1 2 4 3 1 2

20 1 3 2 3 1 2 1 1 1 1

21 1 4 2 3 2 3 3 4 1 3

22 1 4 3 4 5 2 3 5 2 4

N

EW

S

Nile

Suiez canal

Risk

1

2

3

4

5

20 0 20 40 Kilometers

Fig (6.6)

Risk map

Rainfall Analysis

Used Events

100 year maximum daily rainfall 49 mm for 3

hours period event.

50 year maximum daily rainfall 38 mm for 1

hour

0

30

60

90

120

0 1 2 3 4 5 6

TIME, t

DIS

CH

AR

GE

, q

D

qp

tb

tp

Area 19.375 km2

LΩ 6.01 Km

RB 5.00

RL 3.267

RA 6.223

SΩ 12.35 %

v 7.54 m/s

N 3.013489

K 0.097476

Basin 1

Basin 1 - Event 1

0

2

4

6

8

10

12

14

16

18

20

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Time, hr

Q, m

3/s

Basin 1 - Event 2

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Time, hr

Q, m

3/s

Basin 2

Area 1761.345 km2

LΩ 63.81 Km

RB 4.62

RL 2.649

RA 5.059

SΩ 1.59 %

v 2.71 m/s

N 3.279033

K 2.998812

Basin 2 - Event 1

0

50

100

150

200

250

300

350

400

450

0 10 20 30 40 50 60

Time, hr

Q, m

3/s

Basin 2 - Event 2

0

50

100

150

200

250

0 10 20 30 40 50 60

Time, hr

Q, m

3/s

Event 1 Event 2

Basin Qp

(m3

/s) Tp

(hr) Qp

(m3

/s) Tp

(hr)

1 18.40 0.8 28.23 1.0

2 421.46 8.0 217.40 7.0

3 215.55 7.0 111.76 6.0

4 150.36 6.0 78.90 5.0

5 5.22 0.6 7.93 0.6

6 17.92 2.4 21.49 1.2

7 87.14 3.4 58.18 2.0

8 6.03 1.0 9.47 0.9

9 14.61 1.6 19.33 1.0

10 22.89 2.2 27.13 1.2

11 9.17 0.8 16.41 0.7

12 3.28 0.6 6.66 0.5

13 7.29 0.6 13.28 0.9

14 3.03 1.0 4.83 1.0

15 7.98 0.6 2.82 0.6

16 7.05 1.0 11.21 1.0

17 8.01 1.0 12.42 1.0

18 8.48 1.4 12.21 1.0

19 2.85 1.0 4.51 1.0

20 3.20 1.2 5.00 1.0

21 35.10 2.6 38.94 1.3

22 89.33 3.4 57.59 2.0

Event 1 Event 2

Basin Qp

(m3

/s) Tp

(hr) Qp

(m3

/s) Tp

(hr)

1 18.40 0.8 28.23 1.0

2 421.46 8.0 217.40 7.0

3 215.55 7.0 111.76 6.0

4 150.36 6.0 78.90 5.0

5 5.22 0.6 7.93 0.6

6 17.92 2.4 21.49 1.2

7 87.14 3.4 58.18 2.0

8 6.03 1.0 9.47 0.9

9 14.61 1.6 19.33 1.0

10 22.89 2.2 27.13 1.2

11 9.17 0.8 16.41 0.7

12 3.28 0.6 6.66 0.5

13 7.29 0.6 13.28 0.9

14 3.03 1.0 4.83 1.0

15 7.98 0.6 2.82 0.6

16 7.05 1.0 11.21 1.0

17 8.01 1.0 12.42 1.0

18 8.48 1.4 12.21 1.0

19 2.85 1.0 4.51 1.0

20 3.20 1.2 5.00 1.0

21 35.10 2.6 38.94 1.3

22 89.33 3.4 57.59 2.0

N

EW

S

Nile

Suiez canal

Risk

1

2

3

4

5

20 0 20 40 Kilometers

Fig (6.6)

Risk map

2

N

EW

S

Nile

Suiez canal

Risk

1

2

3

4

5

20 0 20 40 Kilometers

Fig (6.6)

Risk map

N

EW

S

Nile

Suiez canal

Risk

1

2

3

4

5

20 0 20 40 Kilometers

Fig (6.6)

Risk map

20

Event 1 Event 2

Basin Qp

(m3/s)

Tp

(hr) Qp

(m3/s)

Tp

(hr)

1 18.40 0.8 28.23 1.0

2 421.46 8.0 217.40 7.0

3 215.55 7.0 111.76 6.0

4 150.36 6.0 78.90 5.0

5 5.22 0.6 7.93 0.6

6 17.92 2.4 21.49 1.2

7 87.14 3.4 58.18 2.0

8 6.03 1.0 9.47 0.9

9 14.61 1.6 19.33 1.0

10 22.89 2.2 27.13 1.2

11 9.17 0.8 16.41 0.7

12 3.28 0.6 6.66 0.5

13 7.29 0.6 13.28 0.9

14 3.03 1.0 4.83 1.0

15 7.98 0.6 2.82 0.6

16 7.05 1.0 11.21 1.0

17 8.01 1.0 12.42 1.0

18 8.48 1.4 12.21 1.0

19 2.85 1.0 4.51 1.0

20 3.20 1.2 4.02 1.0

21 35.10 2.6 38.94 1.3

22 89.33 3.4 57.59 2.0

N

EW

S

Nile

Suiez canal

Risk

1

2

3

4

5

20 0 20 40 Kilometers

Fig (6.6)

Risk map

Conclusions

The proposed methodology proved to be suitable for the arid wadi system especially when detailed data is not available

The selected geomorphological parameters for risk assessment are well matched with the results from estimated runoff hydrograph when both peak discharge and time to peak are considered

GIS has proved to be an easy and efficient tool for watersheds flood risk assessment.

The risk classification presented provides a prioritization skim for flood control and flood protection programmes.

The study presents an integrated approach for flood risk assessment for Al-Sokhna area, and should be reflected in development plans for the area

Thank You

29

Geomorphologic

• Uses stream network topology and probability concepts

• Law of Stream Numbers

range: 3-5

• Law of Stream Lengths

range: 1.5-3.5

• Law of Stream Areas

range:3-6

B1 R

N

N

L

1

RL

L

A

1

RA

A

N

NNR

R

WMRb

uu

Bu

Bu )( 1

1

Relief and Slope Ratios

B

rL

RR

l

lV

ES

75.0

Instantaneous Unit Hydrogaph

RR

R

L0.44 = t

0.38 -L

A

B

0.55

p

R L

1.31 =q 0.43

Lp

)hours

1(

0.871 = q

i

.4p

1.5Lr

2.5

i R A i

L =

bn

S =

2/3

1/2

IUH GIUH

ir is the intensity of effective rainfall in cm/h

AΩ is the area of the watershed in km2

αΩ the kinematic parameter for the stream of highest order

SΩ is the average slope of the highest order stream

nΩ is the average Manning roughness coefficient of Ω

bΩ is the average width of the highest order stream, in m

Risk Assessment Parameters

Area

Perimeter

Basin length

Valley length

Length of overland flow

Ruggedness number

Texture ratio

Stream frequency

Drainage density

Stream order

Sum of stream number

Sum of stream length

RB

RL

RA

WMRb

Slope index

Circularity ratio

Elongation ratio

Relief

Internal relief

Relief ratio

Shape index

sinuosity

Watershed characteristics Stream morphology Topographic and shape