- The Petchburi Irrigation Project was built in the southern part of
the Central Plain of Thailand in 1942. The purpose of the project was
to divert water from the Petchburi River to irrigate the principal part
of the Petchburi Plain where lands were used for rice and upland crop
At present, however, a serious water shortage both for agricultural
and domestic uses occurs in the areas outside of the project.
The lands on the northern part of the plain are seriously in need of
water for irrigation because the available inflow of the river is not
sufficient to irrigate these lands in the wet season. As the river decreases
its flow in the dry season, there is practically no water delivered
to the southern part of the plain for domestic use. The water
shortage becomes more serious every year due to population growth and the expansion of cash crop production during the dry season.
Water conservation through dam construction and extension of
the existing irrigation system is considered a feasible way of increasing
the amount of water required in the areas where the people are
suffering from a desperate shortage of water. The additional works to
the existing Petchburi Project under the name of "Kang Krachan
Project" is proposed to fill the water requirements of the area. This
project is designed as multi-purpose and will provide supplementary
water for the existing Petchburi Project, water to irrigate new lands,
and will provide for flood control, water for domestic use, and hydroelectric
The objectives of this study are:. (1) to determine the general
economic feasibility of the proposed Kang Krachan Project through an
analysis of costs and benefits, (2) to recommend a possible method of
allocating reimbursable costs, (3) to allocate costs to various purposes.
The U. S. Bureau of Reclamation methods with some modification
of computing direct, indirect, and public benefits were used as
the basis of analysis.
The average total project benefits per rai are found to be 566
bahts of which direct benefits account for 329 bahts, indirect benefits
147 bahts, public benefits 73 bahts, benefits from preventing flood
damage 5 bahts, and benefits from domestic water amount to 12 bahts
per rai. The analysis indicates the total project benefit-cost ratio to be
6.4, while the total irrigation benefit-cost ratio is 6. 3, and the direct
irrigation benefit-cost ratio is 3. 8. These benefit-cost ratios
are very favorable. The project is, therefore, considered economically
For the allocation of the multi-purpose project costs in Thailand,
the separable costs-remaining benefits method is applicable. Because
all required data are not available, the cost allocation of the
Kang Krachan Project is not shown in the analysis.
The problem of repayment by direct beneficiaries has thus far
never occurred in Thailand. The costs of all previous projects have
been repaid by the federal taxpayers. Thai farmers have not been
charged for repayment of construction costs of primary facilities.
However, the government proposed to use a land tax for the Kang
Krachan Project area. Repayment of construction costs of this project
is proposed from a land tax, municipal tax on domestic water
use and revenues derived from the differential in the domestic and
export price of rice.
In the future, all water development projects in Thailand should
be multi-purpose. Benefit-cost analysis by the U. S. Bureau of
Reclamation methods and the allocation of project costs by the separable
costs-remaining benefits method will be useful in determining
economic feasibility and allocation of reimbursable costs to direct