Application of Time Series Modeling to Study River Water Quality

Water deficit problem originates from two factors: population increase and water pollution. However, studying and forecasting the quality of water are necessary to avoid serious problems in future through managerial works. In present study, using time series modeling, the quality of Madian Rood River is studied at Baraftab station using time series analysis. Nine parameters of water quality are studied such as: TDS, EC, HCO₃^-, Cl^-, SO₄²⁺, Ca²⁺, Mg²⁺, Na⁺ and SAR. Investigation of observed time series shows that there is a common increasing trend for all parameters unless Na+ and SAR. The order of models for each parameter was determined using Auto Correlation Function (ACF) and Partial Auto Correlation Function (PACF) of time series. The ARIMA model was used to generate and forecast the quality of stream flows. Akaike Information Criterion (AIC), Determination Coefficient (R²), Root Mean Square Error (RMSE) and (Volume Error in Percent (VE %) criteria were referred to evaluate the generation and validation results. The Results show that time series modeling is quite capable of water quality forecasting. For the majority of forecasts, the value of R² was greater than 0.6 between predicted and observed values.