Kanyanee Pornpinatepong, Boonrueing Manasurakarn, and Somboon Pornpinatepong

pp. 901 - 915

Abstract

To prevent flooding of Hat Yai city, diversion of excess water from the U-taphao river which flows to
the town is contemplated. Diversion canal No.1 (DR.1), located at the west of the U-taphao river, is designed
based on a 25-year-flood period. For a proper economic analysis, two scenarios have been introduced and
compared: (A) drain directly towards the Songkhla lake by means of a full-length new canal (21.34 km), and
(B) use the Klong Bang Klam as a bypass, reducing the length of the canal to 13.8 km. The collected data and
the model results indicate that the two cases practically provide the same hydraulic efficiency.
Cost-benefit analysis has been performed on the two alternative scenarios (A and B). With the
discount rate of 12 percent, the results indicated that the case A would be beneficial if the flood occurs in
the first year of the project and the net present value (NPV) of the case B will be positive from year 1 to 4
(2006-2009). For the lower discount rate of 6 percent, the benefit of the case B prolongs an additional 3 years (2010-2012). For later years (the remaining 17 years of the case B), negative results are predicted. This
implies that diversion canal No.1 (DR.1) may not be worth the money for the flood protection.
For a proper decision by the authorities, the socio-economics and environmental impact aspects should
be brought into account and the diversion canal No.1 (DR.1) needs to be reviewed.