IMPACTS OF DOI TUNG HIGHLAND DEVELOPMENT PROJECT ON WATER QUANTITY, Apr QUALITY AND FLOW REGIME

Abstract

The impacts of Doi Tung Development Project on water quantity, quality and flow regime was undertaken at the project site in Chiang Rai Province during September 1988 - August 1989, using the stream flow data measured by the Royal Irrigation Department, Region 2, Lampang Province from 30 subwatersheds which were 90° V-notch weir temporary type. For the water quality, it was collected from 9 samples of substream flowing to Huay Mae Rai (located the Royal Palace) in dry season (March 1989) and wet season (May 1989) in order to analyse some physical qualities and insecticides. The study found that the average annual runoff was 773,401 m³/km² or 773.4 mm or 35.7 percent of the annual rainfall. The wetflow was 586.6 mm or 75.8 percent and dryflow was 186.6 mm or 24.2 percent of the total flow, respectively. While the peak of streamflow was observed in September (143.5 mm) and the lowest in April (25.5 mm). This indicated adequate total flow all year round. The observation on physical quality of streamflow showed the standard results except the turbidity (74.1 J.T.U.) which was over the standard (50 J.T.U.) and water color (403.1 unit) of which the standard was 100 unit. These were resulted from soil erosion during road construction leading to the Palace. The insecticide was rarely observed and its degree of dangerous was considered lower than the standard. However, it was not the time that insecticide was used by the hilltribe. The hilltribe just started cropping. It would then concluded that during the investigation of the project, the results showed no impacts on water quantity and flow regime but the water quality was a bit affected particularly water turbidity and color. This was due to soil erosion from road construction. Insecticide showed no significant. The investigation on insecticide impact should be done again after its application by hilltribe, sedimentation would also be analysed.