Text & photographs by Tricky Vandenberg - February 2011
The Pa Sak River, translated the "Teak Forest River", is a major tributary of the Chao
Phraya River, draining the borderlands on the east side of the Central Plains. The source
of the Pa Sak River is situated high in the Phetchabun Mountain Range in Loei Province
and flows for hundreds of kilometers through the Central Plains of Lopburi and Saraburi
provinces until its confluence with the
Lopburi River, northeast of Ayutthaya and before
it runs into the Chao Phraya River in the southeast of the city near
Wat Phanang Choeng.

The river descends from the mountainous north in Dan Sai District of Loei Province
(1,746 m) to the south reaching its lowest point (3 m) in Uthai District of Ayutthaya
Province. Short tributaries from the east and the west, join the river on its course to the
Chao Phraya. Tributaries of the Pa Sak include: Lam Muak Lek (Muak Lek) , Huai
Nam Phung (Ban Hin Hao), Huai Pa Daeng (Ban Pa Daeng), Lam Kong (Ban Wang
Tha Di), Lam Sonthi (Ban Tha Yiam & Ban Na Som), Huai Wang Chomphu (Ban
Wang Chomphu), Huai Na (Ban Huai Na), Huai Nam Chun (Ban Fai Wang Bon), Huai
Nam Duk (Ban Pak Chong), Huai Khon Kaen (Ban Wang Khon Du), Huai Yai (Ban
Sakae Ngam), Huai Saduang Yai (Ban Thai Bun), Khlong Ban Bong (Ban Chaliang
Lap), Huai Yai (Ban Huai Yai Nua), Huai Tarang (Ban Huai Yai Nua), Huai Yai (Ban
Hin Dat), Huai Lam Narai (Ban Lam Narai), Lam Kot Thong (Ban Lam Kot Thong)
and Lam Phaya Klang (Ban Pang Hu Sua). Main cities along the Pa Sak River are
Phetchabun, Saraburi and Ayutthaya.
(Sources of the Pa Sak River)
The Pa Sak River includes both the central alluvial plain and the north-east plateau. The river
basin contains both urban and agricultural areas with the water resource being utilized mainly
for paddy irrigation. The river can be divided in four major stretches being the Upper Pa Sak,
the Petchabun section, the Middle Pa Sak and the Lower Pa Sak.

The Upper Pa Sak stretches from the river's source in the Phetchabun ridges of Loei province
to Lom Sak district in Phetchabun province. High and steep mountains are characteristic

The Phetchabun-section extends south from the Upper Basin to Muang, Nong Phai and
Wichienburi districts of Phetchabun province, through a landscape of alternating low hills and
plains on both sides of the river used for orchards and rice cultivation.

The Middle Pa Sak extends from Wichienburi and Sri Thep districts of Phetchabun, through
Chai Badan, Tha Luang and Phatthana Nikhom districts of Lop Buri province, to Kaeng Khoi
district in Saraburi province, and is characterized by hilly terrain. It provides the location of the
Pa Sak Jolasit Dam and its reservoir.

The Lower Pa Sak includes Kaeng Khoi, Muang and Sao Hai districts in Saraburi and Tha
Reua, Nakhon Luang, and Muang districts of Ayutthaya. It features low lying flood plains with
fertile soil for agriculture.
(The Pa Sak River in Saraburi Province)
Taming the river

The Pa Sak River is an inconstant waterway. One season the river is only a shadow of
itself, nearly dried up, but when the south-west monsoon rains fall across its watershed
from May till October, the river grows to serious proportions, creating devastating floods
in the lower plains and a burden for the people living in those areas. The Pa Sak River is
one of the main sources of flooding in Ayutthaya and Bangkok.

Water transportation became less important at the beginning of the 20th century and
rivers were more and more looked at in function of their irrigation capabilities due to
expanding land development and increasing agriculture in the Chao Phraya delta. The
Rama VI Dam was the first important diversion dam of Thailand. The dam was originally
named  Khuen Phra Thienracha (เขื่อนพระเฑียรฆ์ราชา) and its construction began late
1915. The barrage was completed on 1 December 1924 and its name changed into
Rama VI Dam.

Its construction was part of what is called now, the second phase of the Royal Irrigation
Department (RID) (1902-1926); a phase regarded as the early development period of
irrigation work in Thailand. It was followed in 1957 by the Chao Phraya (Chainat)
diversion dam on the Chao Phraya River. These barrages were constructed in the Lower
Chao Phraya basin to control and divert the water in the canal systems that provide
irrigation water to some 1 million hectares in this area. The dam has 6 flood gates with a
width each of 12.90 meters. The total length of its flood wall is 75 m. The canal system
straightly linked on the eastern side of the Rama VI Dam is Khlong Raphiphat, and on its
western side Khlong Chai Nat - Pa Sak.

The Raphiphat canal transmits the water from the Chao Phraya River to seven irrigated
areas: Khlong Priew-Sao Hai in the Lower Pa Sak Basin and six sub-projects in the
Lower Chao Phraya Basin; the Southern Pa Sak Basin; Nakhon Luang; Northern
Rangsit; Southern Rangsit; Khlong Dan; and Pra-ong Chaiyanuchit. The Rama VI Dam
holds the water of the Pa Sak River before it is drained into the Chao Phraya River at
Ayutthaya. After the South Pa Sak Irrigation Project was finished in 1924, farmers within
the area of Rangsit canals received more water supply and problems concerning the
shallowness of the canals occurred much less frequent. The Rama VI Dam helped in
receiving and supplying water to every part of the Rangsit canal area.
Before 2000,  the Rama VI Dam stored or held back the flood waters of the Pa Sak River,
waters coming from the north and north-east. With the creation of the Pa Sak Jolasit reservoir
Sak Jolasit Dam is the largest reservoir in central Thailand and stops the Pa Sak River at Ban
Kaeng Sua Ten, Nong Bua sub-district, Phatthana Nikhom District in Lopburi Province. The
reservoir is 4.8 Km long and stretches across the Lopburi and Saraburi Provinces. The 36.5
meter high dam is an earth-filled dam with an impervious core. The storage capacity is 785
cubic meters. The dam supplies close to 7 MW of hydro-electric power. The dam is in fact a
large irrigation project initiated by the King of Thailand in 1989.

The water reservoir is a source of water for households, factories and farms in the Pa Sak
Valley; a buffer to control flooding in the Pa Sak basin and decrease the problems of water
management in the lower provinces and the Bangkok metropolitan area. The storage of water
in the reservoir started on 15 June 1998 and the inauguration of the Pasak - Jolasit project
was held on 25 November 1999. The storage capacity of the reservoir is at maximum at 42 m
above sea level. If a higher water influx into the reservoir, the dam has to release higher
discharges for its structural safety. On the other hand, the release of water at the dam has to
be reduced if the reservoir nears it lowest operating level of 32.5 m above sea level. The Pa
Sak river's maximum natural channel capacity downstream is 1600 m3/sec. A higher release
of water at the dam pushes the river out of its banks, with flooding as result. With the
construction of the dam and reservoir 42 villages and 28 archeological sites disappeared under
the water level. All villagers were resettled and a museum was built to display the objects
found at the archaeological sites.
The Pa Sak River seems nonetheless untamable. Abnormally late monsoon moisture over
the Mid-October the Pa Sak Jolasit Dam was already releasing its water at 2600 cubic
meters a second, a sturdy 1000 cubic meters a second more than the river could channel
downwards. The Pa Sak River banks busted.

On 19 October 2010 the central provinces started to brace for more floodwaters as the
Drainage and Sewerage Department stated to intend to release floodwaters at the dam at
a rate of 3,000 cubic meters a second as the reservoir was at is maximum limit and any
additional water might give problems with the stability of the dam. The water level was
the highest recorded in the 11 years since the dam was operational. In Lop Buri the
situation was unable to reach marooned villages. Thailand's death toll rose at 257 people
and a massive damage amounting to dozens of billions of baht. The houses of about
700,000 families were flooded for at least one week. The floods ravaged 11.26 million
rai (1.8 million hectares) of farmland in 74 provinces between August 1 and December 9.
Of this farmland, about 5.82 million rai - mostly paddy fields - was destroyed. In the
same period, 190,432 rai of aquatic-animal farms in 68 provinces also suffered
flood-related damage. [1]
The Lower Pa Sak River

This author made the descent of the Lower Pa Sak River by kayak in February 2011, and will
shortly describe the stretch of this river part.

The Lower Pa Sak River turns between the foothills of the most western limits of the
Sankamphaeng Range; one of the mountain ranges separating Eastern Thailand from the
northeast and being home to Khai Yai National Park. This range is the southern arm of the
Dong Phaya Yen Mountains merging with the Dângrêk Mountains in the east.

We started near the Pa Sak Jolasit dam at the Wat Kaeng Suea Ten river landing. Just
opposite the temple is a large plant - locals said a sugar factory - spoiling the environment
south of the Dam. Dust residue covered plants, temple, streets and houses, in fact the whole
human habitat in that area. The air, filled with irritating dust, had a foul smell and was far from
pleasant to breath. The plant discharges its wastewater straight into the river and a brownish
foam, drifting on the water was still visible 60 Km further down stream.
The Pa Sak River has quite a serious rising in the rainy season. At Hin Son we noticed that the stairs at the landing of the Wat Hin Son - North Monastery a
spectacular 12 m.

Major floods of the Pa Sak River in the last 50 years were in 1964, 1978, 1995 and 2010. The river current in the rainy season must have been very strong,
as much devastation due to river erosion was seen along the river banks until Saraburi. Many restoration works were ongoing along the river banks
especially at temple sites.
After Hin Son, we came on a nice stretch of water when we entered Kaeng Khoi district. The river seeks its way through the limestone formations of the
volcanic belt and brought us along some beautiful stretches of nature. But alas, probably not for long, as new resorts start to mushroom here.

Once past Tha Khlo we left the rocks behind us, as we entered the Central Plains. Pump stations dotted the river banks in order to provide irrigation for the
cultivation of rice and crops. The main crop in the Lower Pa Sak basin is rice.
The first fish farms on the river we found in Ban Pa Sub-district. After a while paddling
south, a pea-green substance coloured the river, due to algal blooms as a result of an
excessive use of nutrients and fish waste by the farmers.

Close to Saraburi we encountered water management stations on the river banks
providing piped water to the households in city for domestic use. Fish farming started
again near Wat Tanod in Dao Rueang sub-district. The Pa Sak River as thus, north of the
Rama VI Dam at Tha Luang, is used mainly for industrial discharges by factory plants
and for crop irrigation by farmers.
South of the dam the river gets a new function. We enter a  more industrialized area with
factories and numbered mooring sites established along the river banks. The river is used for
transportation. Descending towards Ayutthaya we passed Ayutthaya Port & ICD (Inland
Container Depot), Thailand's first riverside private port, linking inland industries through
waterways and starting commercial operations in October 2009. The port has a 276-metre
berth, provides four cranes and other facilities with a total loading capacity reaching 450,000
TEU per year. Goods from the North and the Northeast are taken by road to Ayutthaya,
loaded on container ships here and transferred to Laem Chabang within 22 hours. Shipping by
barges or smaller vessels takes about 48 to 52 hours. The port includes a rice processing plant
with a capacity of more than 1 million tons and two bonded warehouses. The port opens the
world markets for the many manufacturers at the six nearby industrial estates of Rojana,
Hi-Tech, Bang Pa-In, Saha Rattana-Nakorn, Nong Khae and Kaeng Khoi.
There is a lot of boat activity and boat traffic in the Nakhon Luang district area from
smaller vessels, tugboats, barges until self-propelled vessels. It is a world on itself. Boat
people living store boats selling commodities such as drinking water, food and general
items are navigating between the barges, waiting the next load. It is unfortunately also a
heavily polluted area. A lot of domestic garbage finds its way into the river due to the
lack of a scheduled garbage pick-up service at the mooring sites.

Finally we arrived at Ayutthaya. We passed the mouth of Khlong Oom, a former bend
of the Pa Sak River. The Pa Sak River ran earlier through this canal bed towards
Kho Monastery into present Khlong Hantra, to enter the old Lopburi River south of
Ayutthaya. (1) (2) A shortcut has been dug to straighten the river and to let it run into the
old Lopburi River (3) Begin of the 19th century two shortcuts were dug, which led to
the creation of two islets, being Ko Chong Lom and Ko Loi and to the deviation of the
course of the Pa Sak River as we know it today.

(1) "On this eastern side where the waters of the Sak river at that time ran along the village of Ban Ma and found an exit at the mouth of Khao
San, the moat was very far from the city."
(2) Prior 1857, it was the Lopburi River which surrounded Ayutthaya. The Chao Phraya was deviated to Ayutthaya in that year. (See the essay:
Ever-changing Waterways).
(3) Prior 1584, this was known as the Front city canal or Khu Na Mueang (See the essay:
Ayutthaya's Ever-changing Waterways).


[1] The Nation - The Flooding crisis in retrospect - 30 Dec 2010.
[2] Our Wars with The Burmese - Prince Damrong Rajanubhab (1917) - White lotus (2000) - Bangkok - War 4 page 51.

Consulted documents:

[1] Water for people, water for life: a joint report by the twenty-three UN agencies concerned with freshwater (2003).
[3] Building a Self-sufficient Future Retaining a Heritage Pa Sak River Basin Development Project - RAP publication 1999/40 - Co-published by Food and
Agriculture Organization of the United Nations, Regional Office for Asia and the Pacific (FAORAP) and the Royal Irrigation Department (RID), Ministry of
Agriculture and Cooperatives, Royal Thai Government.
[4] - data retrieved 23 February 2011.
(Rama VI Dam at Tha Luang)
(Factory near Wat Kaeng Suea Ten)
(Stairs at Wat Hin Son Nuea)
(Limestone formations)
(Pump station along the river)
(Fish farming at Ban Pa)
(Ayutthaya River Port)
(The Pa Sak Jolasit Dam)
(Devastation along the river banks)
(Erosion of the river banks)
(A tugboat on the Pa Sak River)