Flood Mitigation Master Plan for Chao Phraya DeltaINWEPF 2007

Suphat Vongvisessomjai

Professor, Water and Environment ExpertTEAM Consulting Engineering and Management Co.,Ltd.

e-mail : suphat@team.co.th

Abstract

Master plans of flood mitigation for Chao Phraya Delta, rice bowl of Thailand, are as follows :

First master plan of flood mitigation for Bangkok developed after 1983 flood from the King’s initiation by King’s Dike to protect rainwater from northern and eastern boundaries

and the Chao Phraya river water from the west Second master plan of flood mitigation for Chao Phraya Delta

after 1995 flood, Initially developed by AIT,DHI and ACRES for World Bank, further developed in details by JICA, and

finally developed in Thai by Crown Property Bureau. The proposed master plan of flood mitigation for Chao Phraya

Delta after 2006 flood, with new diversion using AIT river network model.

1.Introduction

The Chao Phraya Delta,rice bowl of Thailand FAO study in 1948 recommended that Thailand’s economic

strength lay in exporting rice to alleviate world-widefood shortages due the war.

1950,Thailand secured a World Bank loan1952,commenced work on the Greater Chao Phraya

1957,first phase completion of Asia’s largest irrigation project.1961,additional component : Bhumibol dam and irrigation canal.

1977,Sirikit dam finished for 25 year irrigation program and Thailand is ranked first in rice export.

AIT river network model was developed by Vongvisessomjai and Suppataratarn 1998 and used as tool for Chao Phraya flood

management review for World Bank and forecast future floods especially 2006 flood

2. Literature Review

2.1 The First Master Plan for Bangkok

The King recommended King’s Dike to protect Bangkok after 4 months flood in 1983 due

to heavy rainfall

Figure 1

Eastern Bangkok Polder (JICA 1986)

2.2 The Second Master Plan for Chao Phraya Delta

After 1995 flood with extensive damage, World Bank requested AIT,DHI, and ACRES to conduct a Chao Phraya flood management review JICA provided assistance to develop an Integrated Plan for Flood Mitigation based on recommended work plans of World Bank report Crown Property Bureau reported in Thai the framework of water resources management which proposed 3 mitigation measures for water shortages, floods and pollutions

Diversion Diversion

Figure 2: Short, Medium and Long Term Flood Mitigation Measures in 5, 15 and 25 years respectively (Crown Property Bureau 2000)

Urban Polder Reservoir Operation

Short Term in 5 year

Reservoir Construction Chao Phraya Delta Retention

Medium Term in 15 years

Reservoir Construction

Upstream Retention

Long Term in 25 years

3. Methodology

The proposed master plan is developed from 2006 flood data

3.1 Important Data of 2006 Flood

(1) Severe floods occurred more frequently, i.e. in 1995,2002 and 2006 due to invasion of upper catchments, and insufficient drainage of flood flow

resulted in extensive damages at Singhburi,Angthong,Ayutthaya and Bangsai which is a bottle-neck that limit the flow less than 3,500 m3/s resulted

In flooding upstream in all areas of Ayutthaya

(2) Flood waves in 2006 from Chao Phraya Dam to Bangsai :At Chainat, 7 m. and peak at 17.50 m.At Singburi, 6 m. and peak at 13.14 m.At Angthong, 5 m. and peak at 8.19 m.At Ayutthaya, 2 m. and peak at 4.70 m.At Bangsai, 1.5 m. and peak at 3.60 m.

Figure 3

2006 Flood Hydrographs of the

Chao Phraya River from Chao Phraya Dam to

Bangsai and the Decreased Water Levels due to Diversion of 500

and 1,000 m3/s at Bangsai

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2.00

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อ�างทอง(ปั�จ้จ้�บั�น) อ�างทอง(ผั�น500cms) อ�างทอง(ผั�น1000cms)

อย�ธยา(ปั�จ้จ้�บั�น) อย�ธยา(ผั�น500cms) อย�ธยา(ผั�น1000cms)

บัางไ ทร(ปั�จ้จ้�บั�น) บัางไ ทร(ผั�น500cms) บัางไ ทร(ผั�น1000cms)

Daily Highest Water Level (m.MSL)

Date from 16 September to 15 November

16 Sep. 21 Sep. 26 Sep. 1 Oct. 6 Oct. 11 Oct. 16 Oct. 21 Oct. 26 Oct. 31 Oct. 5 Nov. 10 Nov. 15 Nov.

Chao Phraya Dam (Present)Singhburi (Present)Angthong (Present)Ayutthaya (Present)Bangsai (Present)

Chao Phraya Dam (-500 cms)Singhburi (-500 cms)Angthong (-500 cms)Ayutthaya (-500 cms)Bangsai (-500 cms)

Chao Phraya Dam (-1,000 cms)Singhburi (-1,000 cms)Angthong (-1,000 cms)Ayutthaya (-1,000 cms)Bangsai (-1,000 cms)

(3) Satellite images of 1995 and 2006 in Figs 5&6 showed severe floodings in Chainat,Singhburi,

Angthong and Ayutthaya

Undrained water’s at Bangsai inundated Chao-chet,Pakhai and Sena,then flowed to the Tha Chin and flooded Banglen to the mouth of

the Tha Chin at Krathumban and Muang of Samut Sakhon.

Figure 5

Flooded Area and Maximum

Water Level in 1995

Nan Basin

Kanchanaburi

Nakorn Pathom

Ratchaburi

Gulf of Thailand Bang Pakong Basin

Chachoeng Sao

Prachinburi

Nakorn Nayok

Saraburi

Pasak Basin

Samut Songkhram

Chonburi

Figure 6 Satellite Image of 2006 Flooded Area

in the Chao Phraya River (Contributed by GISTDA from

Summary Report on Satellite Imagery of

Flooding in 2006)

3.2 The Proposed Master Plan

(1) The leftover mitigation, the diversion, is very costly and not so effective as shown in Fig.3

(2) The river diversion is the major factor to alleviate flooding

(3) It can be seen in Fig.4 that the Tha Chin river flows from ChaoPhraya Dam parallel to the Chao Phraya river. Its capacity is only10 percent (350 m3/s) of the Chao Phraya river (3,500 m3/s) because of 4 regulators

(Pholathep,Thabote,Samchuk&Phophraya)but downstream of Phophraya to the river month, the river

sectionsare large enough for 1,500 m3/s

(4) Therefore, a diversion canal in the upper Tha Chin is best mitigation

Fig

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Date in January 2002

Figure 7b. Three-dimensional plot of water surface fluctuation in the Tha Chin River

with respect to distance and time.

Water Level (m)

Maha Sawat 89( )

Phra Pimon (121)

River Mouth (0)

Distance (km)

Phraya Banlu 142( )

Figure 8a : Physical layout of the River

Network Model (Vongvisessomjai,S.

and Suppataratarn,P.1998)

Figure 8b : Schematization of the

River Network Model(Vongvisessomjai,S. and Suppataratarn,P.1998)

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16 ก.ย. 21 ก.ย. 26 ก.ย. 1 ต.ค. 6 ต.ค. 11 ต.ค. 16 ต.ค. 21 ต.ค. 26 ต.ค. 31 ต.ค. 5 พ.ย. 10 พ.ย. 15 พ.ย.

วั�นที่�

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สิ�งห์�บั�ร�(ปั�จ้จ้�บั�น) สิ�งห์�บั�ร�(ผั�น500cms) สิ�งห์�บั�ร�(ผั�น1000cms)

อ�างทอง(ปั�จ้จ้�บั�น) อ�างทอง(ผั�น500cms) อ�างท อง(ผั�น1000cms)

อย�ธยา(ปั�จ้จ้�บั�น) อย�ธยา(ผั�น500cms) อย�ธยา(ผั�น1000cms)

บัางไ ทร(ปั�จ้จ้�บั�น) บัางไ ทร(ผั�น500cms) บัางไ ทร(ผั�น1000cms)

Chao Phraya Dam

Singhburi

Angthong

Ayutthaya

Bangsai

Chao Phraya Dam (Present) Singhburi (Present) Angthong (Present) Ayutthaya (Present) Bangsai (Present)

Chao Phraya Dam (-500 cms) Singhburi (-500 cms) Angthong (-500 cms) Ayutthaya (-500 cms) Bangsai (-500 cms)

Chao Phraya Dam (-1,000 cms) Singhburi (-1,000 cms) Angthong (-1,000 cms) Ayutthaya (-1,000 cms) Bangsai (-1,000 cms)

16 Sep. 21 Sep. 26 Sep. 1 Oct. 6 Oct. 11 Oct. 16 Oct. 21 Oct. 26 Oct. 31 Oct. 5 Nov. 10 Nov. 15 Nov. Date from 16 September to 15 November

Daily Highest Water Level (m.MSL)

Figure 9: 2006 Flood Hydrographs of the

Chao Phraya River from Chao Phraya Dam to Bangsai and the

Decreased Water Levels due

to Diversion of 500 and 1,000 m3/s to the

Tha Chin River

(5) AIT river network model reveals that At Chainat and Singhburi, flood depths drop 2 m.

At Angthong, drop 1.5 m. At Ayutthaya, drop 1 m. At Bangsai, drop 0.5 m.

No more floodings in the Chao Phraya Delta. The reduced flow of3,000 m3/s in the river will not have overspillage. This diversion fromthe Chao Phraya Dam can flow to the river mouth without pumps dueto its high head. No more floodings from Banglen to the river mouth.

4. Conclusion

(1) Floods in the Chao Phraya Delta were caused by the in sufficientdrainages to the sea which inundated the rice bowl of Thailand The eastern diversion could not be built due to its expensive land cost and high pumping cost

(2) The new diversion was found most effective to mitigate floodin the Chao Phraya Delta. It helped minimize floodings at Chainat,Singhburi,Angthong Ayutthaya and Bangsai It also helped minimize floodings downstream of the Tha Chin

from Banglen to the river mouth.

(3) The new diversion costed less than the eastern diversion and had less impact to the people since its course was along the existing river which required less dredging and its merit of high head near to the Chao Phraya Dam which required no pumping.