The application of stochastic methods and mathematical models in forecasting of groundwater fluctuations in Shiraz city

Subject Areas : Regional Planning

Seyed Amir Shamsnia ¹ (Department of Water Engineering, Shiraz Branch, Islamic Azad University, Shiraz, Iran)
Nazanin Pirnia ² (M.Sc. Student of Water Engineering, Shiraz branch, Islamic Azad University, Shiraz, Iran)
Reza Afshin Sharifan ³ (Department of Water Engineering, Shiraz Branch, Islamic Azad University, Shiraz, Iran)

Received: 2022-05-03 Accepted : 2022-10-03 Published : 2023-11-22

Keywords: Shiraz, Groundwater, Model, time series, Stochastic,

Abstract :

Stochastic models will be used as a method, to study changes in time series data in the future. The purpose of this study is to analyzing the groundwater level of piezometer wells in Shiraz, simulating and short-term forecasting of its status in the future using stochastic methods. for modeling In this research, water level statistics of 14 piezometer wells that had more complete statistics from 1993 to 2019 were used and based on ARIMA model and partial autocorrelation and autocorrelation method and with evaluation of parameters and types of models and all possible patterns in terms of being static, suitable model for predicting groundwater level in each well was obtained separately. After validation and evaluation of the model, the groundwater level was predicted in the future years 2020 to 2026. The results of groundwater level forecasting in wells in Shiraz using time series models show that with assuming the consumption pattern remains constant and no noticeable change in the groundwater recharge process, during the next 7 years, on average, we will face a decrease of about 3.5 meters in the groundwater level compared to the current situation. Therefore, due to the significant drop in groundwater level in the future and the limited resources of drinking water supply in Shiraz and the need for more water in the future, appropriate decision-making for supply management and consumption management in this city, seems necessary.It is necessary to study the consumption and demand management, in order to save water and prevent its loss in the city as a basic solution.
Extended Abstract
 
Introduction
Shiraz city, has faced with the problem of water shortage due to the increase in population in recent years. Currently, the most demand of drinking water is supplied by groundwater, which has been declining in recent years. In this research, quantitative status of groundwater will be analyzed according to the available information of the piezometric wells in city, during the last three decades. Then, by using time series models, its fluctuations are investigated and by representing a suitable ARIMA model, water level situation in the future can be predicted. Considering the importance of Shiraz plain aquifer in drinking water supply and the need to predict groundwater level changes to make decisions of relevant managers, for better management of water resources on the one hand and accuracy and ease of using time series models, what has been done in Iran and the world, led to the study of ARIMA time series models in this research.Finally, the purpose of this study is to predict the groundwater level in piezometric wells in Shiraz city by using stochastic methods and time series analysis.
 
Methodology
In the study area, 14 piezometric wells have been investigated. For predicting future conditions of water level, time series models based on Box-Jenkins, in ITSM software, were used. Model were calibrated with 4 parametes like R2, AIC, RMSE and EF. In the next phase, the suitability of the model is investigated and in short term (7 years), the groundwater level is predicted.
 
Results and Discussion
Results show that during past 27 years, water level has faced an avreage of 12.7-meter decrese and the general trend of groundwater unit hydrograph is downward and indicates a continuous drop in water level. Groundwater level prediction values obtained from Arima models, show that by assuming the current trend of water withdrawal in groundwater, in the next 7 years, we will face an average of 3.54 meters decrease above groundwater level in piezometric wells of Shiraz city.
 
Conclusion
The results of this study show that the trend of groundwater level is decreasing and will face water level drop in future.
According to the results of this study, the following can be mentioned:
1-  The proposed ARIMA models predict the groundwater level well in short-term. However, the application of the proposed model is not recommended for long-term forecasts.
2-  Since the trend of groundwater level changes in the past and in the future according to the results of the predicted model is declining, it is expected that this trend will continue in the following years.
3-         By considering the trend of groundwater level changes, it can be concluded that the most important reason for this downward trend is seasonal changes and fluctuations due to reduced rainfall and uncontrolled withdrawal of groundwater resources. Both of which, Have significant affect on the process of water level changes in the future. It is necessary to study the consumption and demand management, in order to save water and prevent its loss in the city as a basic solution.

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