نوع مقاله : مقاله پژوهشی
1 دانشیار گروه محیط زیست و شیلات، دانشگاه تهران، تهران، ایران.
2 دانشجوی دکتری گروه جغرافیا، دانشگاه رازی، کرمانشاه، ایران.
3 دانشجوی کارشناسی ارشد گروه محیط زیست، دانشگاه شیراز، شیراز، ایران.
عنوان مقاله [English]
Groundwater is the most important source of water in many parts of the world, used in drinking water, agriculture, industry and related ecosystems. However, the lack of control over human activities and climate change can lead to the destruction of these valuable resources.
Accordingly, in this study, the groundwater level of Parishan catchment in Fars province in the period 2008 to 2019 in relation to groundwater abstraction has been investigated and using Madflu modeling in different scenarios to reduce the level of aquifer for future years. Predict for different areas of this basin in order to show different degrees of crisis in different parts of the basin.
Parishan Lake catchment area is one of the semi-enclosed cups in Fars province (Kazerun city) between the eastern longitude of "251-52" to "501-43" and the northern latitude of "25.22" to "29.27". This basin leads from the north to the Kazerun basin, from the east to the Boram basin, from the south and west to the Jarreh and Baladeh basins. The area of this basin is 225 square kilometers, of which 40 percent (90 square kilometers) is covered with heights and 60 percent (135 square kilometers) is covered with plains and lakes. The maximum altitude of Parishan Basin is 1800 meters and the minimum altitude is 855 meters above sea level, and these altitudes extend from northwest to southeast.
Results and Discussion
In the present study, data and information from the study area such as exploitation and observation wells data including data related to 25 exploration wells and 960 exploitation wells were collected from Fars Water Resources Management Organization (Fars Water Organization Statistics, 1398). After collecting the required data, the conceptual model of the area was determined as a geometric form and based on the parameters that have the greatest impact on the aquifer. Then other characteristics of the aquifer such as permeable and non-permeable boundaries were determined using lithological properties parameters, geological characteristics and characteristics of boundary formations in the region as well as inlet and outlet flow to boundary cells in the range. And Natrova was prepared in the aquifer and by preparing intermediate maps, the amount of groundwater reduction in different parts of the zoning basin and the extent of expansion of critical areas were determined.
Madflow is a physical, three-dimensional model capable of stable and unstable simulations of free-pressed and free-pressed aquifers. The Madflu model solves the equation governing groundwater flow based on the finite difference method. In this regard, Marvdasht aquifer is networked into smaller cells, assuming that the characteristics of the aquifer are uniform in each cell. According to the law of mass conservation and groundwater movement, the equation governing groundwater flow is obtained as a second-order partial differential equation. This equation is given as (Equation 1) in unstable, inhomogeneous and three-dimensional conditions.
T_XX (∂^2 h)/(∂ x^2 )+T_YY (∂^2 h)/(∂y^2 ) +T_zz (∂^2 h)/(∂z^2 )=S ∂h/∂t±R ( x,y,z)
In this equation, ℎ: height of the hydraulic load; ((𝑥, 𝑦, 𝑧: flow directions; 𝑡: time; [𝑇]: 𝑇𝑧𝑧, 𝑇𝑦𝑦, 𝑇𝑥𝑥; aquifer transfer coefficients in the directions (x, y, z);: S storage coefficient; 𝑅 (𝑥, 𝑦, 𝑧): Power supply (positive sign (or discharge) is a negative sign
Due to the fact that abstraction of groundwater by agricultural wells is one of the important causes of water reduction in the troubled basin. In order to explain the trend of groundwater level changes, the general trend of the annual water level of all observation wells (25 piezometers) in the period 1398-1387 was studied.
The results of simulation of groundwater level reduction in Parishan basin showed that this model with high spatial variability power well determines the effect of different parameters on groundwater level in different parts of the aquifer. In the study area, 960 wells and 25 piezometric wells with different uses of agriculture, drinking and industry have been located, which are scattered in other places except in the southern parts of the plain. The concentration of these wells in the central areas is higher due to flat ground and in the northern areas due to higher groundwater levels.
In this research, the sensitivity analysis method combined with the calibration step has been used. The results of sensitivity analysis of effective parameters in calibration of Parishan Basin aquifer showed the maximum effect of hydraulic conductivity parameters and horizontal hydraulic conductivity anisotropy and a set of linear groups of waterways. Hydraulic conductivity of the aquifer is one of the parameters that has a high uncertainty in this model and by changing the values of this parameter, the model shows great sensitivity. Therefore, the reason for the high sensitivity of the aquifer hydraulic conductivity is the existence of wells with high discharge in these areas, so it is consistent with the statistics received from the Fars Regional Water Organization. Also, the anisotherapy parameter has a significant sensitivity in this model.
In order to check the accuracy of the model after the calibration step in the unstable state, it is necessary to refer to the mean errors calculated by the software. According to what has been said before, RMSE error is one of the best criteria for measuring the error rate. The following is a table of average error types calculated by the software and a series of related calculations.
The results of calculating the water balance in the aquifer of Parishan Basin, which was done during the period (1387-1388) indicate that the amount of 42.4 million cubic meters of water has been reduced from the constant storage of the aquifer. As a result, the amount of water entering the area, in addition to dependence on the physical conditions of the disturbed basin, such as hydrodynamic coefficients and gravity, is directly dependent on the amount of pumping discharge wells. Therefore, by increasing the abstraction from the aquifer, a change in the amount of exchange volume of the effective parameters in the balance can be expected.