Evaluation of the surface water of Khlong Luang reservoir

Surface water is widely recognized as an essential source of water for drinking and irrigation purposes in
Thailand. Khlong Luang reservoir was built from 2012 to 2017 (construction period) in Koh Chan district, Chonburi province, Thailand. It has started operating and distributing water for irrigation from 2018 up to the present. This study
was supported by the Royal Irrigation Department and aimed to evaluate the water quality index (WQI) based on five parameters such as DO, BOD, TCB, FCB, and NH3. The water samples were collected from 6 locations in Khlong Luang reservoir from 2012 to 2020. A comparison of the WQI obtained during the construction period (2012 to 2017) and operation period (2018 to 2020) was conducted. The result revealed that the water quality at the reservoir (location
1) improved from class 5 (very poor) in 2012 to class 2 (excellent) in 2020. During 2018, the first year of the operation period, the WQI indicated class 4 (poor) because of runoff from agricultural farms in the areas. Later in 2020, the result of the WQI improved to class 2. Overall, some deterioration in water quality of several locations (1,2,3, and 6) in the irrigation area was observed. The study helps to identify the significant zone of high pollution which require appropriate mitigation and control measures in the study area. Also, the result obtained via evaluation of water quality provides empirical pieces of evidence for policymakers to prescribe proper intervention measures.