T7: Flood Risk Assessment Using GIS Tools
-
Upload
food-and-agriculture-organization-of-the-united-nations -
Category
Education
-
view
407 -
download
2
description
Transcript of T7: Flood Risk Assessment Using GIS Tools
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