Embed Size (px)
Citation preview
Impact of Growing Islands on the Flood Capacity of Tigris
River in Baghdad City
Ammar A. Ali, Nadhir A. Al-Ansari, Sven Knutsson Department of Civil, Environmental and Natural
Resources Engineering, Lulea University of Technology, Sweden
Emails: [email protected], [email protected], [email protected]
INTRODUCTION
In recent years, substantial changes have
occurred in the morphology of the Tigris
River within Baghdad City. Although huge
volumes of sediment are being trapped in
recently constructed headwater reservoirs,
the number of islands in the Tigris at
Baghdad is increasing.
The debris of bridges destroyed in the wars of 1991 and 2003 and their subsequent reconstruction have enhanced the development of these islands. As a consequence the ability of the river to carry the peaks of flood waters has been reduced. This has led to potential increase of flooding in parts of the city.
Map of Iraq showing the Tigris and Euphrates Rivers.
Tigris River
Confluence of Tigris with Diyala Rivers
Al-Muthana Bridge
Diyala River
Aerial photo of Baghdad City
DISCHARGES OF TIGRIS RIVER FOR THE PERIOD 1960-2010
200
400
600
800
1000
1200
1400
1600
1800
Ave
rag
e M
on
thly
Dis
ch
arg
e (
cu
me
cs
)
Months
Average Monthly Discharge
for years 2000~2010
(531 cumecs)
Average Monthly
Discharge for
years 1990~2010
(674 cumecs) 19% the slope of the
trend line
DISCHARGE OF TIGRIS RIVER FOR THE PERIOD 1990-2010
Mosul Dam Dokan Dam
Adhaim Dam
Hemrin Dam Samara Barrage
Baghdad City
CONTROL STRUCTURES UPSTREAM BAGHDAD CITY
BRIDGES ON TIGRIS RIVER WITHIN BAGHDAD CITY
Muthana Bridge
Al-A’ameh Bridge
Adamiyah Bridge
Sarafia Bridge
Bab Muadam Bridge
Al-Shuhada Bridge
Al-Ahrar Bridge
Jumhuriya Bridge Sinak Bridge
Jadiriyah Bridge Suspension Bridge
Twin Bridge
Al-Rasheed Bridge
Tigris – Diyala confluence
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
0500010000150002000025000
Distance (m)
Bed
Level (m
)
1976
1991
2008
CHANGES IN TIGRIS RIVER BED ELEVATIONS DURING 1976, 1991 AND 2008
15
17
19
21
23
25
27
29
31
33
35
37
39
-10
10
30
50
70
90
110
130
150
170
190
210
Station (m)
Ele
vati
on
(m
)
1976
1991
2008
CHANGES IN GEOMETRY SHAPE OF SARAI BAGHDAD GAUGING STATION
HYDRAULIC MODEL •A one-dimensional steady-flow hydraulic
model using HEC-RAS was used to predict the maximum flood capacity for the river. • The upstream condition was the average
daily discharge in Baghdad for the past ten years. • The downstream condition was the
updated rating curve at Diyala River confluence.
METHODOLOGY
River geometry • The survey
conducted in 2008 • 105 cross sections
at average intervals of 250m. • The length of the
reach 26 km, starts from Suspension Bridge at u/s till the confluence with Diyala River at d/s.
Model calibration • 59 observation points for water levels along last 15 km of
the reach were used to calibrate the model. These observations were recorded at the same day for a discharge of 400 m3/s. •Modification for Manning’s ‘n’ for the main channel and
the floodplain was included to achieve coincidences between computed water surfaces and observed one. •Minimum R.M.S.E. (0.026m) was achieved for Manning’s
‘n’ as 0.0285 for the main channel and 0.042 for floodplains. • 5 m3/s discharge for Diyala River was considered as lateral
inflow. •No precise data available for water consumption along
the reach.
METHODOLOGY
METHODOLOGY
Model application • To find out the critical discharge that can cause
inundation, a set of discharges starting from the average daily discharge for the past ten years were used in model as u/s condition with the updated rating curve at d/s.
• Most of these discharges were examined for the same area in previous studies (Geohydraulique in 1977 and University of Technology-Baghdad in 1992).
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
0500010000150002000025000
Distance (m)
Wa
ter
Su
rfa
ce
Ele
va
tio
n (
m)
400 500 800
1100 1300 1500
2500 2700 3500
4000 Banks Observed (R.M.S.E. = 0.026m)
Observed water surface elevations with the computed for different discharges of Tigris River and 5m3/s discharge of Diyala River.
RESULTS AND CONCLUSIONS • The critical elevation for inundation is 35m
at station 22+000m • The inundation could take place along
approximately 3 km reach of the Tigris River for discharges greater than 4000 m3/s. •No significant effect found for more three
lateral inflow values (25, 50 and 100 m3/s) for Diyala River on the water surface elevations in Tigris River with highest discharges.
RESULTS AND CONCLUSIONS • Since the water is eroding below the
protected banks now, this will lead to the collapse of parts of these protecting banks in future. • The bed levels fluctuation was the
minimum according to the 2008 survey relative to those of 1976 and 1991. • The average slope of the river bed became
higher in 2008 compared with previous surveys.
