The GIS system provides a more detailed picture that covers the spatial variation of pollution levels
over the three seasons (Figures 2-4). Figures shows that the pollution level is minimal in the hot (and
typically dry) season. Figures &4 show that the water quality degradation is observed in the cool and
especially in the rainy seasons. This seasonal pattern indicates the controlling role of runoff. Additionally,
WQI index show the same trend of GIS as shown in Table 3. The area around Ko Moeng is the most
polluted in every season which can observe from dark brown color. However, in rainy season the color is
clearly light brown in area of Ko Moeng (Fig 4). It is indicated that in cool season Figure 2 has the most
polluted and in rainy season has less polluted (Fig 4). It should be due to the amount of water from other
rivers and from rain which could cause less pollution in this area.