Determining Water Conditions in the Northeastern Rivers of Thailand Using Time Series and Water Quality Index Models

Abstract

Dissolved oxygen, biochemical oxygen demand, nitrate-nitrogen, total phosphorus, fecal coliform bacteria, and suspended solids were used to evaluate water quality in the northeastern rivers of Thailand: Lam Chi, Lam Pao, Lam Seaw, Loei, and Nam Oon. The mean observed values of the six water quality parameters in each river over a 5-year period (2003–2007) were used to compute the present water quality index (WQI_present) of each river in the wet (June–November) and dry (December–May) seasons. The mean observed values of the study parameters of each river by season over a 14-year period (1994–2007) were used to build a set of time series models for predicting the values of the associated parameters of each river in the next 5-year period (2008–2012). These mean predicted values were used to compute the WQI_future by season for each river. According to the results, the water quality at many sampling stations was in good condition. However, the water quality in Lam Chi and the Loei River will tend to decrease in the next 5-year period unless proper management is undertaken to reduce the concentrations of certain contaminants such as total phosphorus and fecal coliform bacteria in the rivers. This study revealed that the time series models with the best predictions among the stations were often not the same types. Several time series models should be used and their prediction accuracy should be compared. Water quality parameters considered in developing a WQI and the index use may be limited to a watershed for which it has been developed.