A. Firoozi; seyed majid mirlatifi; Hamed Ebrahimian
Abstract
Introduction: Agriculture consumes a large portion of groundwater resources. In order to understand the status of groundwater resources in a basin and to optimize its management, it is necessary to carry out an accurate examination of the fluctuations in the groundwater levels. Recharging groundwater ...
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Introduction: Agriculture consumes a large portion of groundwater resources. In order to understand the status of groundwater resources in a basin and to optimize its management, it is necessary to carry out an accurate examination of the fluctuations in the groundwater levels. Recharging groundwater aquifers is one of the main strategies for water resources management which its accurate estimation plays a crucial role in the proper management of ground water resources. That portion of the excess irrigation water which becomes in the form of deep percolation should not be considered as wasted water, if its quality is not adversely reduced and it enters and recharges groundwater aquifers. The question is whether deep percolations resulting from irrigating farms with low application efficiencies and poor irrigation management in the Urmia basin would finally recharge ground water aquifers or not. In order to provide a solution to the aforementioned question, after calibrating HYDRUS-1D model, it was used to estimate the fluctuations of the levels of the water tables as a results of irrigations or rainfalls in a number of wheat, barley and sugar beet fields located in Miandoab and Mahabad regions where all agricultural practices were managed and carried out by the local farmers.
Materials and Methods: In order to ascertain the effects of irrigation on the groundwater recharge, the required field data was collected from nine agricultural fields including one wheat farm, three barley farms, and three sugar beet farms, all located in the Miandoab region and two wheat fields located in the Mahabad region. All the water balance parameters for each one of the fields were measured in the studied fields, including the depth of irrigation at each irrigation event by using WSC flumes. The Surface runoff from the studied farms was considered as negligible, since all the fields were irrigated using closed end borders. The evapotranspiration of wheat, barley and sugar beet were calculated in the regions using the CROPWAT8.0 model.
The soil texture of each of the study fields were determined by hydrometric method in the laboratory and then soil hydraulic parameters were estimated by ROSETTA model. The soil moisture of all the fields during the growing season were measured using a PR2 moisture meter instrument measuring soil moisture at various depths up to 105 cm below the soil surface. The amount of deep percolation occurring during the growing season was simulated by the HYDRUS-1D model. The soil water content measured by PR2 (Delta-T Device) probe were used for HYDRUS-1D model calibration and validation using the inverse solution method. Because of the occurrence of rainfall, irrigation and evapotranspiration, the atmospheric boundary condition was selected as the upper boundary condition and free drainage was considered as the lower boundary condition in order to estimate the groundwater recharge, assuming that water passes through and below the root zone. In areas with shallow ground water depth, constant flow with zero flux was chosen as the lower boundary condition in order to determine the fluctuations of the ground water level. Since the groundwater level in this case study was shallow, zero flux was considered as the lower boundary condition. The soil moisture content before irrigation was selected as the modelling initial condition.
Result and Discussion: The HYDRUS-1D model was calibrated by comparing the model estimated soil moisture contents with the corresponding measured values which indicated the coefficient of determination (R2) and root mean square error (RMSE) values ranging from 0.6 to 0.85 and 0.17 to 0.033 (), respectively. Another set of measured soil moisture data which was collected by using PR2 instrument and was not used for calibrating the model, was applied to verify the model simulation of the soil moisture content. Comparing the measured and simulated soil moisture contents at this verification stage resulted in coefficient of determination (R2) and root mean square error (RMSE) values ranging from 0.62 to 0.88 and 0.002 to 0.023 (), respectively. There was no significant difference between the predicted and measured soil moisture data in all the fields (P-value> 0.05). The minimum and the maximum coefficient of determinations in the validation stage were obtained in the T5 field with a silty loam soil and in the H3 field having a sandy loam soil. The accuracy of the model performance after it was calibrated and verified using the collected field data, was appropriate for estimating the soil water content during the growing season. The model was used to simulate the soil water contents from the soil surface to the depth of the water table during the growing season to evaluate the degree of aquifer recharge if any happened. The soil moisture front advanced to a depth of 0.7 m below the soil surface in the M1 field and to 4.7 m in the T1field. The amount of groundwater recharge varied from field to field depending on each field’s soil type, cultivation and irrigation management including the depth and the time of the irrigations. The amount of groundwater recharge increased by decreasing crop evapotranspiration. The percentage of ground water recharge in N1, M1 and M2 fields due to limited availability of water resources which resulted in deficit irrigation was very low. The irrigation water requirements estimated by the CROPWAT model for the aforementioned fields were more than the depths of the irrigation water applied by the farmers. The CROPWAT model estimated the irrigation water requirements during the growing season for wheat, barley and sugar beet in the Miandoab region to be 308, 273 and 736 mm, respectively. However, the depths of irrigation applied to such farms ranged from 306 to 500 mm.
Conclusion: This research was conducted to ascertain the effects of local farmer’s irrigation management practices considered as poor management in some areas with plenty of water resources available and rainfall on the amount of the groundwater recharge occurring in the regions studied located in the Lake Urmia basin. The simulated groundwater recharge by the HYDRUS-1D model indicated that the amount of recharge varied from field to field depending on soil type, cultivation and irrigation management practices. In all the fields, the highest amount of groundwater recharge occurred when the crop evapotranspiration was low and therefore, enhancing deep percolation to take place. The highest percentage of groundwater recharge was 28% of the sum of the irrigation and rainfall depths which occurred in the barley field (H3).
Mehrnaz Amini; Hamed Ebrahimian
Abstract
Introduction: Water scarcity is an important challenge worldwide, especially in arid and semi-arid regions. Water-scarce countries will have to rely more on the use of non-conventional water resources to partly alleviate water scarcity. The reuse of wastewater for irrigation is considered to be beneficial ...
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Introduction: Water scarcity is an important challenge worldwide, especially in arid and semi-arid regions. Water-scarce countries will have to rely more on the use of non-conventional water resources to partly alleviate water scarcity. The reuse of wastewater for irrigation is considered to be beneficial for crop production, and due to its nitrogen and phosphorus content, it can help to reduce the requirements for commercial fertilizers. However, under certain conditions, this type of water if not well managed, can have negative impacts on cultivated crops and soils, particularly on soil salinity and sodicity, and may pollute groundwater, as a result of high nitrogen concentration of most treated wastewater. Besides nitrogen (N) contamination of surface and ground waters has become a serious and global environmental problem. The risk of groundwater contamination by N depends largely on the N input to agricultural fields in the form of inorganic fertilizers and on its effective use of agricultural crops. Improvement of irrigation and nitrogen application management during the growing period can be achieved using mathematical models. The goal of this study was to assess the effects of irrigation with raw and treated wastewater by using the HYDRUS-1D model for simulation of water and nitrate transport in a maize field.
Materials and Methods: The experimental station of the College of Agriculture and Natural Resources, University of Tehran, was considered as a case study. The information of maize growing season in 2010, as well as raw and treated wastewater of Ekbatan housing complex was considered as a source of irrigation water for simulation of water and nutrient movements in the soil by HYDRUS-1D software package. HYDRUS-1D numerically solved the Richards equation for describing the variably-saturated water flow in a radially symmetric domain and the convection-dispersion equation for solute transport. The soil hydraulic properties were described using the van Genuchten-Mualem model. Since the direct measurement of soil hydraulic parameters in the field or laboratory is time consuming and costly, they were estimated using the ROSETTA model, using particle size and bulk density data determined on soil samples taken from depths of 0-20, 20-40, 40-60 cm.
Results and Discussion: The results showed that water contents increased after any irrigation event, and then decreased gradually during the following hours and days, until the next irrigation took place. Deeper depths showed smaller water content variations since root water uptake and soil evaporation were more pronounced at shallower depths. Simulated plant water uptake was estimated to be 80% of the water application, indicating the high irrigation efficiency of the system. Cumulative deep percolation (DP) values increased rapidly at around 43 days after planting. This is obtained due to higher irrigation water depth applied at irrigation events after this time because of rapid growth of maize crop that is occurring due to increase air temperature at this time. Simulated deep percolation reached 6.98 cm which is 13% of the total amount of water applied during the growing season. Simulation results showed that N leaching at 60 cm depth for about 7.61 and 2.64 kg N ha-1 for raw and treated wastewater, respectively. Nitrogen concentration for raw and treated wastewater decreased due to root nutrient uptake. The results also showed that the crop N uptake was 76.2% and 81.9% of total N input (TNI) during the growing season, while 19.4% and 14.5% of TNI was retained in the soil at the end of the season for raw and treated wastewater, respectively.
Conclusion: The HYDRUS-1D model was used to simulate the transport of N-NO3- under the raw and treated wastewater application in the soil. Simulation results provided detailed moisture and N regime, as well as bottom boundary flux for percolation and N leaching estimation. N leaching is closely correlated with vertical water flow. The N leaching distributions at the bottom of the soil profile (60 cm) are similar to the corresponding water flux distributions. The results also showed that the crop N uptake was 130 and 60 kg N ha-1 during the growing season for raw and treated wastewater, respectively. As the results showed wastewater can use as a source of N for crops and it can help to reduce the requirements for commercial fertilizers, and decrease their negative environmental impacts. It is suggested that the model parameters can be measured practically, in order to be used for model calibration and validation. Besides, the simulation can be done for a longer period of time to evaluate the effect of rainfall and different cultivations on solute transport.
M. Farasati; S.M. Seyedian
Abstract
Dispersivity is an important property of a porous medium and Advection-Dispersion equation (ADE). It is used in solving problems related to pollutants migration by groundwater. Numerical models are frequently used for simulation of water movement in soils. In the present study, the dependence of NaCl ...
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Dispersivity is an important property of a porous medium and Advection-Dispersion equation (ADE). It is used in solving problems related to pollutants migration by groundwater. Numerical models are frequently used for simulation of water movement in soils. In the present study, the dependence of NaCl dispersivity on thickness of the aquifer materials has been investigated. In orther to perform it, 5 different thickness of soil column (20, 40, 60, 80 and 100 cm) selected. The physical model used in the study consisted of a cylindrical tank with inner diameter of 6cm and 5 thicknesses 20, 40, 60, 80 and 100 cm of soil column designated by T1, T2, T3, T4 and T5 respectively. Sodium chloride with an electrical conductivity (EC) of 3 dSm-1 was selected as conservative pollutant. For calculation of dispersivity Brigham model and for simulation of NaCl movement HYDRUS software used. Results of the study indicated that the dispersivity of sandy porous was not dependent on the thickness. The result of HYDRUS showed that with increase of aquifer length, dispersivity increased but it was not significant.
