Flood Risk Assessment Using GIS Tools, By Dr. Omar Elbadawy, CEDARE, Land and Water Days in Near East & North Africa, 15-18 December 2013, Amman, Jordan

1. Land Resources Management
Near East
& North Africa
Flood Risk Assessment Using GIS Tools

2. Flow Diagram
Processing
Input
Construct DEM
Delineate watersheds
Extract Stream network
Calculate Watershed
Characteristics
Output
Risk Matrix
Vulnerability map
GIUH
Runoff Hydrograph
14000.00
60000.00
12000.00
10000.00
8000.00
6000.00
4000.00
50000.00
S-curves are
lagged by 1 hour
and the difference
is found.
1-hour unit
hydrograph resulting
from lagging Scurves and
multiplying the
difference by 6.
40000.00
30000.00
20000.00
10000.00
2000.00
0.00
0.00
Time (hrs.)
Flow (cfs)
SCS
Unit Hydrograph Flow (cfs/inch)
Rainfall
module

3. Contours

4. Elevation and constructing of DEM

6. Flow Direction
32
64 128
16
8
1
4
2

7. Flow Accumulation
32
64 128
16
8
1
4
2

8. Delineating the watersheds and
Stream Networks

9. Delineating the watersheds and
Stream Networks

10. 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).

11. Watershed Factors

Watershed size - runoff volumes and rates increase
with watershed size

12. 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”

13. 
Drainage Density and Stream Frequency
D=
1
A

 N  L

=1

F=
 N

=1
A

14. Risk value  4 *
( x  xmin )
1
( xmax  xmin )
Risk Calculation
( x  xmin )
Risk value  4 *
1
( xmax  xmin )
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

15. Basin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
A WMRb
1
4
5
5
3
4
2
4
1
4
1
4
1
5
1
4
1
5
1
5
1
1
1
5
1
2
1
5
1
4
1
5
1
3
1
5
1
4
1
3
1
4
1
4
F
2
2
2
2
3
3
1
3
3
2
1
3
1
5
4
4
3
4
1
2
2
3
D Ish
2
3
3
3
3
2
3
2
1
3
2
2
3
2
2
2
3
4
3
3
1
1
3
4
2
1
3
2
3
2
3
3
4
2
3
2
5
1
3
1
3
2
4
5
Sl
3
1
1
1
1
1
2
1
2
3
3
3
3
3
4
5
5
5
2
2
3
2
Rr
4
1
1
1
1
1
2
1
2
3
3
4
3
3
4
5
4
5
4
1
3
3
Rn
4
5
3
4
1
1
3
1
2
3
3
2
3
2
3
3
4
3
3
1
4
5
Rt
1
5
3
3
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
Risk
Degree
3
5
4
3
2
2
3
2
3
2
1
3
2
3
3
3
3
3
2
1
3
4

16. N
W
E
S
20
0
20
40 Kilometers
Risk
Fig (6.6)
Risk map
1
2
3
4
5
Suiez can al
Nile

17. Rainfall Analysis

18. Used Events


100 year maximum daily rainfall 49 mm for 3
hours period event.
50 year maximum daily rainfall 38 mm for 1
hour

19. 120
D
DISCHARGE, q
90
tp
60
qp
30
tb
0
0
1
2
3
TIME, t
4
5
6

20. Basin 1
Area
19.375
LΩ
6.01
RB
5.00
RL
3.267
RA
6.223
SΩ
12.35
v
7.54
N
3.013489
K
0.097476
km2
Km
%
m/s

21. Basin 1 - Event 1
20
18
16
12
10
8
6
4
2
0
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Tim e, hr
Basin 1 - Event 2
30
25
20
Q, m3/s
Q, m3/s
14
15
10
5
0
0
0.5
1
1.5
2
2.5
Tim e, hr
3
3.5
4
4.5
5

22. 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

23. Basin 2 - Event 1
450
400
350
250
200
150
100
50
0
0
10
20
30
40
50
60
Tim e, hr
Basin 2 - Event 2
250
200
Q, m3/s
Q, m3/s
300
150
100
50
0
0
10
20
30
Tim e, hr
40
50
60

24. Event 1
Qp
Tp
Basin (m3/s)
1 18.40
2 421.46
3 215.55
4 150.36
5
5.22
6 17.92
7 87.14
8
6.03
9 14.61
10 22.89
11
9.17
12
3.28
13
7.29
14
3.03
15
7.98
16
7.05
17
8.01
18
8.48
19
2.85
20
3.20
21 35.10
22 89.33
(hr)
Event 2
Qp
Tp
3
(m /s)
0.8 28.23
8.0 217.40
7.0 111.76
6.0 78.90
0.6
7.93
2.4 21.49
3.4 58.18
1.0
9.47
1.6 19.33
2.2 27.13
0.8 16.41
0.6
6.66
0.6 13.28
1.0
4.83
0.6
2.82
1.0 11.21
1.0 12.42
1.4 12.21
1.0
4.51
1.2
5.00
2.6 38.94
3.4 57.59
(hr)
1.0
7.0
6.0
5.0
0.6
1.2
2.0
0.9
1.0
1.2
0.7
0.5
0.9
1.0
0.6
1.0
1.0
1.0
1.0
1.0
1.3
2.0

25. Event 1
Qp
Tp
Basin (m3/s)
1 18.40
2 421.46
3 215.55
4 150.36
5
5.22
6 17.92
7 87.14
8
6.03
9 14.61
10 22.89
11
9.17
20
12
3.28
13
7.29
14
3.03
15 (6.6)7.98
Fig
Risk
16 map
7.05
17
8.01
18
8.48
19
2.85
20
3.20
21 35.10
22 89.33
(hr)
Event 2
Qp
Tp
3
(m /s)
0.8 28.23
8.0 217.40
7.0 111.76
6.0 78.90
0.6
7.93
2.4 21.49
3.4 58.18
1.0
9.47
1.6 19.33
2.2 27.13
0.8 16.41
0
0.6
6.66
0.6 13.28
1.0
4.83
0.6
2.82
1.0 11.21
1.0 12.42
1.4 12.21
1.0
4.51
1.2
5.00
2.6 38.94
3.4 57.59
(hr)
1.0
7.0
6.0
5.0
0.6
1.2
2.0
0.9
1.0
1.2
0.7
0.5
0.9
1.0
0.6
1.0
1.0
1.0
1.0
1.0
1.3
2.0
N
W
E
S
2
20
20
40 Kilometers
0
20
40 Kilometers
Risk
Fig (6.6)
Risk map
1 Risk
1
2
2
3
3
4
5
4
Suiez can al
Nile
5
Suiez can al
Nile

26. Event 1
Qp
Tp
Basin (m3/s)
1 18.40
2 421.46
3 215.55
4 150.36
5
5.22
6 17.92
7 87.14
8
6.03
9 14.61
10 22.89
11
9.17
20
12
3.28
13
7.29
14
3.03
Fig
15 (6.6)7.98
Risk
16 map
7.05
17
8.01
18
8.48
19
2.85
20
3.20
21 35.10
22 89.33
(hr)
Event 2
Qp
Tp
3
(m /s)
0.8 28.23
8.0 217.40
7.0 111.76
6.0 78.90
0.6
7.93
2.4 21.49
3.4 58.18
1.0
9.47
1.6 19.33
2.2 27.13
0.8 16.41
0
0.6
6.66
0.6 13.28
1.0
4.83
0.6
2.82
1.0 11.21
1.0 12.42
1.4 12.21
1.0
4.51
1.2
4.02
2.6 38.94
3.4 57.59
(hr)
1.0
7.0
6.0
5.0
0.6
1.2
2.0
0.9
1.0
1.2
0.7
0.5
0.9
1.0
0.6
1.0
1.0
1.0
1.0
1.0
1.3
2.0
N
W
E
S
20
20
20
40 Kilometers
0
20
40 Kilometers
Risk
Fig (6.6)
Risk map
1 Risk
1
2
2
3
3
4
5
4
Suiez can al
Nile
5
Suiez can al
Nile

27. 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 AlSokhna area, and should be reflected in development plans for the area

28. 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
N 1
 RB
N
RBu
( N u  N u 1 )
RBu 1
WMRb 
N
L
 RL
L 1
A
 RA
A 1
29

30. 
Relief and Slope Ratios
R
Rr 
LB
E
Sl 
0.75Vl

31. Instantaneous Unit Hydrogaph
GIUH
IUH
0.55
0.44 L  R B 
 
tp=
  RA 
qp =
1.31
L
R
- 0.38
L
qp=
0.871
i
1
(
)
hours
.4
2.5

0.43
L
R
i=
L
1.5
i r A R L  
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
1/2
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
S
=

2/3
n b

32. Risk Assessment Parameters
Watershed characteristics
Area
Perimeter
Basin length
Valley length
Length of overland flow
Ruggedness number
Texture ratio
Stream morphology
Stream frequency
Drainage density
Stream order
Sum of stream number
Sum of stream length
RB
RL
RA
WMRb
Topographic and shape
Slope index
Circularity ratio
Elongation ratio
Relief
Internal relief
Relief ratio
Shape index
sinuosity