Thailand Flood 2011: Short- and Long-term Plan for Flood Management 1. Thailand (TH) at a glance (1) Location: 5°-20°N latitude and 97°-106°E longitude (2) Area: 513,115 km 2 (3) Population: 65.4 million (2010) (4) Climate classification: tropical monsoon (all average monthly temperatures greater than 18°C and precipitation less than 61 mm/month found in one or more months) (5) Average rainfall: 1,160-2,560 mm/year (Fig. 1.1) (6) Seasons: summer season occurs in March-April-May with respect to the average maximum temperature, pre-monsoon season is in May-June-July due to the Inter Tropical Convergence Zone (ITCZ) moving from the Indian Ocean to China, monsoon season is in August-September-October due to ITCZ moving back to cover TH, and dry season lasts from November to April with dry and cold weather in December-January- February influenced by the northeast monsoon (7) Average runoff: 213,423 million m 3 (MCM)/year (183,001 MCM/year in wet season from May to October) (Fig. 1.1) (8) Capacity of reservoirs: 71,388 MCM (9) River system: there are 9 groups of 25 major river basins sub-divided into 254 sub-basins (Fig. 1.2 and Table 1.1) (10) Floods in TH: it can be divided into 3 types: (1) flash (fast) floods caused by heavy rainfall on the hills or steep-slope areas, which are deforested; (2) inundated floods caused by runoff overflowing from rivers and canals to villages and developed areas; and (3) storm floods occur in the coastal areas caused by cyclones and monsoons. (11) Cyclones hitting TH: from 1951-2011 (61 years), there were 186 cyclones including tropical depression, tropical storm and typhoon, of which 20 cyclones (10.8%) were observed in August, 47 cyclones (25.3%) in occurred in September, 51 cyclones (27.4%) occurred in October, and 31 cyclones (16.7%) were in November. The remaining 37 (19.8%) occurred in April-July and December. (12) Damages by floods in TH: from 1989-2010, total cost was Baht 132,107.50 million with a maximum cost in 2010 of Baht 16,338.77 million, a cost in 2002 of Baht 13,385.32 million and damage in 1989 estimated to be Baht 11,739.60 million (Table 1.2).
Transcript
Thailand Flood 2011: Short- and Long-term Plan for Flood Management
1. Thailand (TH) at a glance
(1) Location: 5°-20°N latitude and 97°-106°E longitude (2) Area: 513,115 km2 (3) Population: 65.4 million (2010) (4) Climate classification: tropical monsoon (all average monthly temperatures greater than
18°C and precipitation less than 61 mm/month found in one or more months) (5) Average rainfall: 1,160-2,560 mm/year (Fig. 1.1) (6) Seasons: summer season occurs in March-April-May with respect to the average
maximum temperature, pre-monsoon season is in May-June-July due to the Inter Tropical Convergence Zone (ITCZ) moving from the Indian Ocean to China, monsoon season is in August-September-October due to ITCZ moving back to cover TH, and dry season lasts from November to April with dry and cold weather in December-January-February influenced by the northeast monsoon
(7) Average runoff: 213,423 million m3 (MCM)/year (183,001 MCM/year in wet season from May to October) (Fig. 1.1)
(8) Capacity of reservoirs: 71,388 MCM (9) River system: there are 9 groups of 25 major river basins sub-divided into 254 sub-basins
(Fig. 1.2 and Table 1.1) (10) Floods in TH: it can be divided into 3 types: (1) flash (fast) floods caused by heavy
rainfall on the hills or steep-slope areas, which are deforested; (2) inundated floods caused by runoff overflowing from rivers and canals to villages and developed areas; and (3) storm floods occur in the coastal areas caused by cyclones and monsoons.
(11) Cyclones hitting TH: from 1951-2011 (61 years), there were 186 cyclones including tropical depression, tropical storm and typhoon, of which 20 cyclones (10.8%) were observed in August, 47 cyclones (25.3%) in occurred in September, 51 cyclones (27.4%) occurred in October, and 31 cyclones (16.7%) were in November. The remaining 37 (19.8%) occurred in April-July and December.
(12) Damages by floods in TH: from 1989-2010, total cost was Baht 132,107.50 million with a maximum cost in 2010 of Baht 16,338.77 million, a cost in 2002 of Baht 13,385.32 million and damage in 1989 estimated to be Baht 11,739.60 million (Table 1.2).
Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar
300
200
100
0Rainfall (mm)
Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar
0
10000
20000
30000
40000
50000
Runoff (MCM)
Fig. 1.1: Average annual rainfall and runoff in Thailand
Fig. 1.2: The 25 major river basins in Thailand
Table 1.1: River system in Thailand
Group Area (km2) Major river basin
1. Mekong River system 188,645 (1) Mekong (2) Kok (3) Chi (4) Mun (5) Tonle Sab
2. Salawin River system 17,918 (6) Salawin 3. Chao Phraya-Tha Chin River system
157,925 (7) Ping (8) Wang (9) Yom (10) Nan (11) Sakae Krang (12) Pa Sak (13) Chao Phraya (14) Tha Chin
4. Mae Klong River system 30,836 (15) Mae Klong 5. Bang Pakong River system 18,458 (16) Prachinburi
(17) Bang Pakong 6. Gulf of Thailand system (east coast) 13,829 (18) East coast gulf
rivers 7. Gulf of Thailand system (west coast) 12,347 (19) Petchaburi
(20) West coast gulf rivers
8. East coast system of south Thailand 50,930 (21) East coast rivers of south Thailand (22) Tapi (23) Songkhla Lake (24) Pattani
9. West coast system of south Thailand 20,473 (25) West coast rivers of south Thailand
Table 1.2: Statistics of damages by floods in Thailand from 1989-2010
(1) Location: 13°-16°N latitude and 99°-101°E longitude that is in central TH (2) Tributaries: 4 major tributaries include Ping, Wang, Yom and Nan Rivers merging at
Nakhon Sawan. The portion above the confluence at Nakhon Sawan is called the Upper Chao Phraya River Basin (UCP). The portion below the confluence to the Gulf of Thailand is called the Lower Chao Phraya River Basin (LCP). Moreover, the Chao Phraya-Tha Chin River system also includes Sakae Krang, Pa Sak and Tha Chin Rivers (Table 1.1).
(3) Water resources development: there are 3 main reservoirs that are Bhumipol reservoir (1964) located on the Ping River with a maximum storage capacity of 13,462 MCM, Sirikit reservoir (1970) located on the Nan River with a maximum storage capacity of 9,510 MCM and the Pa Sak Cholasit reservoir (1999) located on the Pa Sak River with a maximum storage capacity of 960 MCM. Several irrigation projects along the Chao Phraya River and its tributaries e.g. Chao Phraya dam and Rama VI dam are operated by the Royal Irrigation Department (RID) of TH.
2.1 Focusing on LCP
(1) Area: 20,523.42 km2 originating from Nakhon Sawan province and moving down south to pass through the plain area of central TH, then flowing into the Gulf of TH. The LCP has 4 tributaries, which are Noi River, Suphanburi River, Klong Bangkeaw and Lopburi River (Fig. 2.1).
(2) Population: 11.32 million (2009). (3) Climate: from 1971-2000 over 5 meteorological stations, average annual temperature was
estimated of 28.1°C, average maximum temperature found in April was 37.5°C, and average minimum temperature observed in December was 20.0°C. An average annual humidity was calculated by 72.6%. An average annual evaporation was 1,617.0 mm.
(4) Average rainfall: 1,076 mm/year (from 293 stations) (see Fig. 2.2 for the isohyets and Fig. 2.3 for average monthly rainfall).
(5) Average runoff: 1,774.31 MCM/year (from 5 stations) with 1,528.29 MCM/year in wet season (Fig. 2.3).
(6) Capacity of other reservoirs: there are 380 projects of irrigation and water resources development (2001) that can store water of 164.61 MCM/year. The area that obtains benefit from these projects covers 11,612.8 km2.
(7) River system: the LCP can be further divided into 2 sub-basins including Beung Boraphet (4,292.34 km2) and Chao Phraya plain area (16,231.07 km2). The capacity of rivers/channels is shown in Fig. 2.4.
(8) Land use change: a maximum land use is paddy field covering 55.38% of area in 1999 and 54.60% in 2002 (Table 2.1).
(9) Floods: it can be divided into 2 types (1) flash (fast) flood in the upper part of LCP (e.g. Nakhon Sawan and Chai Nat) caused by heavy rainfall on the hills or steep-slope areas; and (2) inundated flood in the lower CP that is a plain area and has an inefficient drainage system due to shallow and long rivers and canals.
(10) History of floods:
In 1942, a big flood was caused by heavy continuous rainfall, which simultaneously affected high water level in the Chao Phraya River and overflowing along both banks. The water level at the Memorial Bridge was 2.27 m above mean sea level (MSL), which is the biggest flood before the construction of Bhumipol and Sirikit reservoirs in the Ping and Nan river basins upstream of Nakhon Sawan.
In 1975, several depressions hit the upper area of central TH and caused an inundated flood in Bangkok.
In 1978, two cyclones called Bess and Kit hit the upper CP in August and September respectively. Furthermore, the large water volume drained from the Pa Sak River Basin caused flood in the east Bangkok.
In 1980, the high water level of 2.00 m above MSL at the Memorial Bridge and the 4-day consecutive rainfall were recorded as the causes of an inundated flood in Bangkok.
In 1983, several cyclones hit the north and central TH from September-October. Total annual rainfall of 2,119 mm compared with an average rainfall of 1,200 mm/year influenced a longest flood of 4 months in the CP. The cost of damage was estimated to be Baht 6,598 million.
In 1986, the long spell of rainfall caused a flood in Bangkok. However, it didn’t cause a huge damage due to the efficient drainage system and low (tide) sea water level.
In 1990, two tropical storms namely Ira and Lola hit northeast, east and central TH in October. The heavy rainfall of 617 mm in 15 days occurred in Bangkok, which caused 30-60 cm flood lasting 1 month. The damage was about Baht 177 million.
In 1995, several storms passed by the north, central and northeast TH influencing the heavy rainfall with long consecutive days. The high water level of 2.27 m above MSL was observed at the Memorial Bridge. In Bangkok, the flood level of 1.00 m lasted by 2 months, which caused a trouble in the transportation.
In 1996, the heavy rainfall in the north and central TH influenced the flood lasting from November to December.
(11) Flood control system in Bangkok:
Structural measurement: o Royal projects e.g. monkey cheeks or retention ponds. o In Bangkok: 158 pumping stations with a total capacity of 1,584 m3/s 21 monkey
cheek sites with total storage capacity of 12.75 MCM, 7 drainage tunnels with pumping capacity of 155.5 m3/s and concrete wall of 77 km for flood protection.
o River and canal dredging to increase the efficiency in drainage. o Maintenance of pumps and machines.
Non-structural measurement: o Weather forecasting by TH Meteorological Department (TMD) using Mesoscale
Model (MM5) and Weather Research and Forecasting Model (WRF). o Real-time weather monitoring using SCADA by the Flood Control Center (FCC)
of Bangkok Metropolitan Administration (BMA). o Telemetry system and installation of flood forecasting and early warning (RID)
Fig. 2.1: Map of the Lower Chao Phraya River Basin
Nakhon
Sawan
Chai Nat
Sing Buri
Ang Thong
Ayuthaya
Pathumthani
Nontha Buri
Bangkok
Samutprakarn
Lop Buri
Utaithani
Suphan
Buri
CP River
CP River Noi River
Lop Buri River
Noi River
CP River
Fig. 2.2: Map of isohyets in the Lower Chao Phraya River Basin
Nakhon
Sawan
Chai Nat
Sing Buri
Ang Thong
Ayuthaya
Pathumthani
Nontha Buri
Bangkok
Samutprakarn
Lop Buri
Utaithani
Suphan
Buri
CP River
CP River Noi River
Lop Buri River
Noi River
CP River
Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar
300
200
100
0Rainfall (mm)
Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar
0
100
200
300
400
500
600
700
Runoff (MCM)
Fig. 2.3: Average annual rainfall (293 stations) and runoff (5 stations) in the Lower Chao Phraya
River Basin
Fig. 2.4: Capacity of the main Chao Phraya River system (m3/s)
Chai Nat
Chao Phraya
Dam
Sing Buri
Lop Buri
River
Ang Thong
Rama VI Dam
Ayuthaya
No
i R
iver
Nonth
aburi
BKK
Chao
Phra
ya
Riv
er
Klo
ng B
ang L
uan
g
Borommathat Gate
Lopburi Gate
Sea level BKK Port
Capacity at river bank
with high tide 1,400 m3/s
with low tide 2,900 m3/s
Capacity at flood protection
with high tide 3,000 m3/s
with low tide5,300 m3/s
Table 2.1: Land use change in the Lower Chao Phraya River Basin
Land use 1999 2002
Area (km2)
% of area
Area (km2)
% of area
Paddy field 11,365.99 55.38 11,205.53 54.60 Vegetable crops 113.97 0.56 40.77 0.20 Field crop 4,319.56 21.05 3,749.18 18.27 Orchard and perennial 885.15 4.31 1,041.19 5.07 Other agriculture e.g. pasture and farm
house, aquatic plant, aqua-cultural land and integrated farm/diversified farm
315.71 1.54 278.39 1.36
Forest 965.88 4.71 807.59 3.93 Other land use e.g. urban and built-up
land, water body and miscellaneous land
2,557.16 12.46 3,400.78 16.57
Total 20,523.42 100.01 20,523.43 100.00
3. Thailand flood 2011
(1) Damages from the big flood 2011: it costs of Baht 1.44 trillion with agricultural area of 11.2 million rai (17,920 km2) and deaths of 657 people.
(2) Hydrologic data: average rainfall over TH in 2011 was 1,947.9 mm. The average rainfall over central TH was 1514.4 mm. In July, there was 1 tropical storm hitting TH namely Nock-Ten. Other tropical cyclones, e.g. Haima (25-26 June), Nesat (28 September-5 October), Haitang (28 September-5 October) and Nalgae (5 October) weakened to become low pressure when they passed by TH (Fig. 3.1-3.2). However, the CP was influenced from these cyclones, in particular last three cyclones that hit TH at the same period. Total rainfall in 7 days over north and upper central TH was 400 mm. Due to large amount of water over the capacity of reservoirs, the discharge of 4,700 m3/s that was released from Bhumipol, Sirikit and Pa Sak Cholasit reservoirs flowed to the CP during 45 consecutive days.
(3) Causes of big flood 2011: (1) natural cause e.g. anomalous annual and monthly climate in terms of rainfall (Fig. 3.3-3.5) and runoff (Fig. 3.6-3.8), and topography of basin i.e. width and slope of channel; (2) non-natural cause e.g. land use change (Table 2.1), inefficient water management and planning (Fig. 3.9-3.10), and non-integrated flood control system.
Fig. 3.1: Pacific typhoons in 2011
TD: tropical depression W: tropical depression monitored by the United States’ Joint Typhoon Warning Center
Fig. 3.2: Cyclones hitting TH in 2011
Haitang
Sep Nock-Ten
Jul
Haima
Jun
Nesat
Sep-Oct
Nalgae
Sep-Oct
Low pressure
Tropical depression
Tropical cyclone
Typhoon
Date at 7:00am
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0
400
800
1200
1600
Rainfall (mm)
1971-2000 Averages
2008
2009
2010
2011
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0
400
800
1200
1600
2000
Rainfall (mm)
Fig. 3.3: Monthly accumulated rainfall in the north (top) and central (bottom) TH and comparison of 1971-2000 averages with the observations from 2008-2011
Haima
(25 Jun)
Nock-Ten
(30 Jul)
Haitang, Nesat, Nalgae
(28 Sep-5 Oct)
Fig. 3.4: The 2011 rainfall (left) and the 2011 rainfall anomalies (right) estimated with respect to
1971-2000 average rainfall
2011 Rainfall
(mm)
Max=5,496.3 mm
Min=684.8 mm
2011 Rainfall Anomalies
(mm)
Max=1,811.7 mm
Min=622.6 mm
May
June
July
August
September Fig. 3.5: The 1950-1997 average monthly rainfall (left) and 2011 monthly rainfall (right) from
May-September
Fig. 3.6: The 1964-2011 accumulated monthly inflow to the Bhumipol reservoir
Fig. 3.7: The 1974-2011 accumulated monthly inflow to the Sirikit reservoir
2011 Inflow
19
64-2
01
0 I
nfl
ow
(co
lors
rep
rese
nt
dif
fere
nt
yea
rs)
J F M A M J J A S O N D
MC
M
2011 Inflow
19
74-2
01
0 I
nfl
ow
(co
lors
rep
rese
nt
dif
fere
nt
yea
rs)
MC
M
J F M A M J J A S O N D
Fig. 3.8: The 1999-2011 accumulated monthly inflow to the Pa Sak Cholasit reservoir
