The Pa Sak Jolasid Dam and Reservoir are at the centre of the Pa Sak River Basin Development Project. Dams and infrastructure projects which require large-scale dislocation are understandably a matter of public concern. For this reason, the Government established a committee to plan and monitor project implementation. In addition to expert personnel from government agencies, academics and representatives of non-governmental organizations (NGOs) were involved in the planning and monitoring process.
Thailand's largest earthfill dam, the Pa Sak Jolasid Dam blocks the natural flow of the Pa Sak River at Ban Kaeng Seua Ten in Nong Bua sub-district, Pattana Nikhom district, Lop Buri province and Ban Kam Pran, Wang Muang district of Saraburi province.
The dam was designed to collect and store surplus water from the upper reaches of the river during the rainy season as well as to reduce runoff and the likelihood of flooding in the lower reaches of the river. During the dry season, water stored in the reservoir will be released according to demand from the agricultural sector as well as from industrial and domestic sectors.
It provides an supplementary supply of water for existing farmlands of 2.2 million rai (3520 km2) in the Lower Chao Phraya East Bank, reducing the current demand of water from the Chao Phraya River.
Supplemental water will be supplied to Lop Buri and Saraburi for domestic uses (Lam Narai, Pattana Nikhom, Wang Muang, Kaeng Khoi, and nearby small communities), as well as more water for industrial use in Lop Buri and Saraburi provinces. Additional water for domestic use will also be supplied to surrounding areas.
The project will prevent serious downstream flooding of the Pa Sak River and reduce the likelihood of flooding in the Lower Chao Phraya Basin including Greater Bangkok and adjacent areas. Further benefits include expanded water transport in the Lower Pa Sak Basin, reduced water pollution and expanded freshwater fisheries. Tourism and recreational opportunities will be enhanced.
The dam and related structures
The main components of the project are an earthfill dam (zoned type) 4860 m long and 187 m wide with a reservoir of 960 million m3 storage capacity at high water level. This is Thailand's largest earthfill dam. It has a service spillway, a river outlet, and an auxiliary spillway.
Additional structures
Additional project structures include village protection dikes at Khok Salung (4.3 km in length) and Tha Luang (1.8 km in length), new access roads around the reservoir replacing portions of Highway 2256 (Chaibadarn-Darn Khun Thod) and Highway 205 (Chaibadarn Lamsonthi), and a new 24.3 km railway line which crosses the reservoir (replacing inundated track from Kaeng Seua Ten to Suranarai stations on the Kaeng Khoi-Bua Yai route). The roads and railroad serve both normal local traffic requirement and increased access for tourism.
Pa Sak Jolasid Dam
Service spillway
+35.00 - +42.00 MSL 3900 m3/sec capacity
River Outlet (drop inlet type, 80 m3/sec capacity 3 m diameter)
Auxiliary Spillway 65 m3/sec capacity
Irrigated areas, existing and new
Benefiting from the project are three new pump irrigation schemes in a newly developed agricultural area of 131 300 rai in Lop Buri and Saraburi provinces: Kaeng Khoi-Ban Moh, Pattana Nikhom and Pattana Nikhom-Kaeng Khoi. Existing irrigated areas which will receive supplemental waters are Khlong Priew-Sao Hai in the Lower Pa Sak Basin plus six sub-projects in the Lower Chao Phraya Basin - Southern Pa Sak, Nakhon Luang, Northern Rangsit, Southern Rangsit, Khlong Dan and Pra-ong Chaiyanuchit areas.
To reduce construction time, the “design-build” method was applied. It means that design and construction was by the Royal Irrigation Department itself, including procurement and supervising procedures, which considerably speeded up completion.
| Existing irrigation areas | Rai ('000s) | New irrigation areas | Rai ('000s) | ||
|---|---|---|---|---|---|
| Total area | 2654 | (4246km2) | Total Area | 131 | (209km2) |
| Khlong Priew-Sao Hai | 135 | Kaeng Khoi-Ban Moh | 76 | (121km2) | |
| Southern Pa Sak | 241 | Pattana Nikhom | 35 | (56km2) | |
| Nakhon Luang | 267 | Pattana Nikhom-Kaeng Khoi | 20 | (32km2) | |
| Northern Rangsit | 446 | ||||
| Southern Rangsit | 530 | ||||
| Khlong Dan | 525 | ||||
| Pra-ong Chaiyanuchit | 510 | ||||
Project Timetable
A feasibility study and an environmental impact assessment were carried out during 1993–94. Design and construction of the dam were initiated in 1994, while construction was completed in 1999. Construction of the extended irrigation system will begin in 2000 and is scheduled for completion by stages in 2005. The following describes in detail how the project progressed.
Prior Project
In 1954, the Royal Irrigation Department began to implement small-scale irrigation projects to counter water shortage problems on tributaries of the Pa Sak River. In 1965 a preliminary study for the Pa Sak River Basin Development Project was completed. However, due to required high investment costs and other factors, the project came to a halt.
Phase I (63 months)
Project Preparation:
Project Preparation. On the initiative of His Majesty the King, the project was revived on 19 February 1989. Preparation extended through engineering and economic feasibility studies, government approval and an environmental impact assessment ending in May 1994.
Phase II (58 months)
Project Implementation:
Project Implementation. From May 1994 to March 1999, design, land acquisition, procurement, construction on the dam and its appurtenant structures took place, concurrent with relocation activities.
Phase III
Project Operation and Maintenance
Project Operation and Maintenance, For the dam and reservoir, operations began in 1999; full operation of the irrigation system will be completed by stages in 2005.
Development of the Pa Sak River Basin Development Project was efficient and integrated at all stages, from study to planning, procurement, design and construction. Today the major elements of the project are reality. Construction was completed within the designated time and budget, with the full cooperation, shared effort, technical integrity and dedication by all parties involved.
Despite Thailand's economic downturn, various factors have contributed to the successful completion of the project: effective management, detailed study and planning, efficient design and construction, and a management team which worked effectively together.
Effective project management by the Royal Irrigation Department integrated all components, from planning, design and construction to completion and operational status in a timely and cost-efficient manner, achieving quality and full transparency in all aspects of procurement and implementation.
Efficient project administration was achieved by effective management, directed by a Government-established committee overseeing and supervising seven subcommittees: public relations, land procurement, relocation, transport infrastructure, construction, environmental control and career development.
Established criteria to determine the most appropriate site to build the Pa Sak Jolasid Dam followed His Majesty's concern to achieve maximum benefit with a minimum negative impact on homes, the economy, the cultural and historic heritage and the environment.
Following preliminary surveys, three most potential sites were considered: Site 1, Ban Tha Sa Bok, Tha Klao sub-district, Kaeng Koi district, Saraburi province; Site 2, Manao Wan, Pattana Nikhom district, Lop Buri province; and Site 3, Ban Kaeng Seua Ten, Nong Bua sub-district, Pattana Nikhom district, Lop Buri province. Engineering concerns and cost-effectiveness as well as minimizing impact to local people and the environment were the major selection criteria.
The results of further extensive surveys and studies assessing of the strengths and weaknesses of the short-listed sites were evaluated as follows: Site 1 offered a large storage capacity, but the reservoir would have inundated 174 000 rai (278 km2), requiring the relocation of 66 villages. The resultant compensation costs would have been relatively high.
Site 2 would have a too small storage capacity for flood protection and year-round irrigation. The site was furthermore structurally unsound, due to the poor quality of underlying soil formations. Deemed as a poor investment, Site 2 was therefore removed from further consideration.
Site 3 was found to have sufficient storage capacity for both downstream flood control and to provide enough water for year-round irrigation in the project area. The reservoir covers 114 119 rai, which meant that only 42 villages needed to be resettled. The smaller number of affected families (compared to Site 1) meant reduced family and community inconvenience and less costly compensation. In the dry season, Site 3 reduces water diversion from the Chao Phraya Dam by 225 million m3 per year. Irrigable areas of the Greater Chao Phraya Project gain surplus water, and flood relief is provided at Kaeng Khoi and Muang districts of Saraburi. Furthermore, compared to Site 1, Site 3 causes less damage to Thailand's heritage, submerging fewer archaeological sites.
The Royal Irrigation Department therefore selected Site 3 because of its high potential for reserving and supplying enough water to the irrigable areas while yielding the least amount of dislocation and adverse effects on the environment and archaeological resources.
To reduce the loss of local and national heritage, a stipulation was made to the effect that artifacts from all culturally important sites scheduled for inundation were to be properly excavated and that all recovered artifacts should be archaeologically conserved before the Pa Sak River's waters could be blocked. Among those who took a direct interest in the conservation was Her Royal Highness Princess Maha Chakri Sirindhorn, daughter of His Majesty the King, and an expert archaeologist in her own right. A museum has been built to house the resulting collection of more than one thousand objects from 28 archaeological sites.
Apart from significantly higher benefits in the irrigable areas due to reliable and increased water supply the reservoir also creates a significant new aquatic ecosystem for fisheries and other aquatic fauna populations, improving the nutrition potential and providing fisheries as an additional income to local communities.
As it is connected to the Chao Phraya River, released water from the Pa Sak Jolasid Dam in the dry season helps improve downstream conditions by countering saline intrusion. Low water flow in the Chao Phraya River during the dry season allows salt water intrusion from the Gulf of Thailand to penetrate upstream, leading to poor water quality. Water allocation from the Pa Sak Jolasid Dam means that such salt water intrusion is reduced, resulting in maintained high crop yields and better water quality for other uses.
Negative effects from the Pa Sak Jolasid Dam are minor, manageable or temporary. As is normal with dams, silt accumulation in the reservoir means some loss of natural replenishment of fertile silt. In addition, covered vegetations have been planted to help control downstream erosion.
Normal and flood season operations are monitored at a state of the art control centre situated atop the dam. From this vantage point, Royal Irrigation Department engineers and technicians physically monitor the dam and its spillways 24 hours a day, every day. The latest computerized telemetering system monitors and automatically measures rainfall and water levels throughout the Pa Sak River Basin and the project area, evaluating the situation, warning of changes in the condition of the river, enabling effective water releases.
All Royal Irrigation Department personnel connected with the Pa Sak Jolasid Dam and its operations are fully-trained in operating procedures and safety measures. Normal operating procedures and guidelines are supplemented by emergency procedures for operating the spillways when the water level in the reservoir rises too rapidly in order to maintain the highest levels of safety.
In normal conditions, 90 percent of the reservoir water will be allocated for agricultural production, 4 percent for domestic and industrial uses, and 6 percent for water quality control. Releases will be made satisfy all needs as long as the stored water is sufficient, and reduced in critically dry seasons, which are expected to take place every five years after the Basin has been fully developed.
In flood conditions, particularly when the inflow to the reservoir is higher than 200 m3/hr, the reservoir operating staff will be on duty for flood operation.
Pre-established emergency procedures provide assurance that effective responses to flood situations will be made in a timely and safe manner. The Pa Sak Reservoir can fully control high floods - including 100-year maximum flood cycles - with a maximum release of 1600 m3 of water per second (the river's maximum natural channel capacity downstream) before floodwaters reach the flatlands upstream of Kaeng Khoi district.
With higher flood levels, peak inflows to the reservoir may exceed 3000 m3/sec and major flood operations will necessarily be carried out. Inflows, reservoir levels and outflows will be closely monitored and the spillway gate operation will be adjusted as the situation requires. The reservoir can maintain its flood control function to release the outflow at the full discharge rate of 1600 m3/sec for five days. Emergency measures will be executed to move local residents and their movable property from the flood plain. After that the dam must release higher discharges for its structural safety. The releases will be as high as 3000 m3/sec on Day 6, Day 7 or Day 8, depending on the incoming floods - whether they are at 500, 1000 or even a 10 000 year return period - and maximum outflows will be controlled at 3000, 3400 or 4200 m3/sec respectively.
Weather forecasting provides related emergency response information so that the reservoir can extend its flood attenuation function and releases can be adjusted as necessary.
Storage Fluctuation of the Pa Sak Jolasid Reservoir
The Reservoir will be operated to control its water storage to be within its active storage, not more than the Full Supply Level (FSL) of 42.0 m mean sea level (MSL) and not less than the Lower Operating Level (LOL) of 32.5 m MSL. When reservoir storage reaches the FSL, Flood Operating will start and the dam will release water at appropriated discharges higher than the downstream demand to decrease the reservoir level to be at the FSL. In dry years, reservoir releases must be carefully managed to maintain the reservoir storage at above LOL; therefore, some reduction of releases will be made to downstream demand to maintain the reservoir water level.
Inflow and Outflow Flood Hydrographs of the Pa Sak Jolasid Dam
Solid lines show flood inflow hydrographs of the dam. The Flood Operation Manual provides guidelines for operators to manage flood situations. As long as it can be confirmed that a flood is not more than a 100-year flood, releases from the reservoir will be controlled at more than 1600 m3/sec to keep discharges within the river banks. Higher floods, however, require higher outflows than the limit at the end of Day 5 as shown as the dotted lines.
The total cost of the Pa Sak River Basin Development Project was 23.3 billion baht (US$583 million) including 7.8 billion baht for construction 9.9 billion baht for land acquisition 3.4 billion baht for environmental management and 2.2 billion baht for railway and road relocation and construction.
| ACTIVITY | COST | % | |
| 1. | Construction | 7831 million baht | 34% |
| - Dam and appurtenant structures | (2656 million baht) | ||
| - Irrigation systems | (4000 million baht) | ||
| - Other components | (1175 million baht) | ||
| 2. | Land procurement | 9894 million baht | 42% |
| 3. | Environmental management | 3387 million baht | 14.5% |
| 5. | Railway and road relocation and construction | 2224 million baht | 9.5% |
| Total | 23 336 million baht | 100% | |
(As of November 1999)
