Document Type : Research Paper
Authors
1
M.Sc. Department of Water Engineering, Faculty of Agriculture, Shahrekord University, Shahrekord, Iran.
2
Associate Professor, Department of Water Engineering, Faculty of Agriculture, Shahrekord University, Shahrekord, Iran.
3
Associate Professor, Department of Irrigation and Reclamation, Faculty of Water and Soil, Tehran University, Karaj, Iran
4
Assistant Professor, Faculty of Natural Resources, Shahrekord University, Shahrekord, Iran.
5
M.Sc. Geology, Water Resource Protection Department, CHB Water Regional Company, Shahrekord, Iran
Abstract
Introduction
Groundwater level is strongly falling due to dependence of agricultural, industrial, and urban water on this resource. The increasing population growth, industrialization progress, and agriculture intensification have all resulted in ever-increasing water demand for various purposes. Artificial recharge and discharge optimum management can recover the groundwater resource. The artificial recharge to the groundwater aims at augmentation of ground water reservoir by modifying the natural movement of surface water through suitable civil construction techniques.
Numerical modeling of the groundwater is an important tool in groundwater engineering practice. Modflow software as a finite difference three-dimensional model can simulate the underground flow under steady and unsteady conditions in anisotropic and non-homogeneous porous media. Modflow is designed to simulate aquifer systems in which saturated-flow conditions exist, Darcy’s Law applies, the density of groundwater is constant, and the principal directions of horizontal hydraulic conductivity or transmissivity do not vary within the system. MT3D is a three-dimensional solute transport model for simulation of advection, dispersion, and chemical reactions of dissolved constituents in groundwater systems.
The groundwater of Ab-barik (Bam, Iran) was simulated to assess the artificial recharge project and the future situation of the aquifer. Modeling by Modflow show that artificial recharge has caused to recharge 12.6 mm3 into the aquifer annually during 1996-1999. But despite this condition, the drawdown has been continuing on. In north-eastern of Khuzestan province (Baghmalek), the basic information of water resource including physiography, geology, sedimentation, hydrogeology, hydrochemistry, and hydrology was studied and then potential regions for artificial recharge were determined.
A program for risk management has been studied in the contamination of the groundwater resulting from leachate in landfills at Mar del Plata (Argentina). Modflow and MT3D were used to simulate the groundwater flow and contaminant transport of the uncontrolled sanitary landfill area of the city of Pocos de Caldas, Brazil.
The paper reports the modeling process of Shahrekord aquifer using Modflow and MT3D and then analyzes the quantitative and qualitative situation of aquifer after the artificial recharge scenarios.
Material and methods
The Shahrekord plain with an area of 551 km2 is located in the CHB province, Iranwith 32° 07" to 32° 25" latitude and 50° 38" to 51° 10" longitude.
The Shahrekord aquifer was simulated to study the effect of artificial recharge using PMWIN 5.3 in two steps:
1. Flow treatment modeling with calibration of hydrodynamic coefficients such as hydraulic conductivity and specific yield by Modflow model.
2. Nitrate transport simulation by MT3D model, also monthly water sampling from 10 points of aquifer. The nitrate concentration was measured in the samples.
Figure1 shows the situation of artificial recharge and sampling points in the Shahrekord aquifer. The model developed in duration of July 2007 to May 2008. The study year divided into some stress periods that data is changed in every period and was also defined 12 monthly stress periods with daily time steps. 10 stress periods used for calibration and two last month applied for the model verification.
The 10 scenarios of artificial recharge specified in different areas and the effect of wastewater injection on around groundwater was described.
Figure 1. Position of 10 artificial recharge and sampling points of the Shahrekord aquifer
Results and discussion
The input variables to be specified are specific yield, hydraulic conductivity, water table level, and topography of ground surface and impermeable layer. Simulation results by this model include hydraulic head and drawdown terms. Transmissivity is assumed to be calculated from hydraulic conductivity and geometrical properties. Some of the indeterminatecoefficients of the aquifer were calibrated in the first step of the simulation process. Table 1 shows these values for the groundwater flow and nitrate transport models. Values mapping for the hydraulic conductivity (2-16 m/day) and specific yield (0.03-0.08) in plain surface show that the north of the aquifer has a soil with heavy texture, slower flow, and lower discharge capability in comparison to the southern parts.
Table 1. Calibrated Parameters by the model
Values range
Parameters
2 - 16 m/day
Hydraulic conductivity
0.03 - 0.08
Specific yield
0
Effective molecular diffusion coefficient
5
Longitudinal dispersivity
0.0001
Distribution coefficient
The first scenario of the 10 ones is the artificial recharge around the Shahrekord wastewater clean-up system. Table 2 presents the location of recharge and nitrate concentration before and after the model performance and results extractor. According to the table, nitrate concentration has increased equal to 5 mg/l in this site. The groundwater flow moved nitrate in downstream and affected the water quality about 500 m distance. It seems that this site is suitable for artificial recharge because of agricultural landuse and soil properties.
Table 2. Nitrate concentration before and after the wastewater recharge in station 1
UTM: 487480 , 3569210
2046.88 m
Water table Height
63.95 m
Aquifer thickness
11 m/day
Hydraulic conductivity
0.062
Specific yield
0.27
Effective porosity
39 mgr/lit
Nitrate concentration before artificial recharge
44 mgr/lit
Nitrate concentration after artificial recharge
Conclusion
The results show that the central and south parts of plain have a better situation for through artificial wastewater recharge. Because, injecting the water in this area increased both the water table to a radius of 6 km and the nitrate concentration to about 15 mg/lit. It predicates that the effect of nitrate plum would spread up to one kilometer from the plant in all scenarios and of course a considerable volume of water will be added to the aquifer.
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