Simulation and estimate of groundwater level fluctuations using GMS (case study: Zanjan plain)

Over recent decades, climate change and the lack of adequate and timely rainfall, leading to a lack of adequate water for irrigated plants and limited renewable land and water resources, has resulted in the heterogeneous spatial and temporal distribution of fresh water as well as rapid population growth, including in Iran, There are increasing problems in providing water resources for various uses. One of the main requirements for meeting global food needs is access to sustainable agriculture and its development. In order to achieve this, appropriate measures should be adopted to prevent damage to the system of limited resources in each region. Groundwater is always an important source of fresh water and groundwater management, at the first stage, requires the identification and operation of aquifers under natural conditions. In most hydrological questions and groundwater resource studies, the availability of groundwater resource data and statistics is of great importance. In order to assess the effects of development in existing conditions and to provide management methods for groundwater resources, both quantitatively and qualitatively, mathematical and computer simulation of these resources is a powerful tool for the optimal utilization of these resources. Numerical modeling of groundwater in aquifers is an important tool for the management of water resources. This model can be used to estimate the hydraulic parameters as well as water resource management. The aim of this study was to simulate fluctuations in groundwater levels in the aquifer Zanjan located at a latitude of 47 degrees 50 minutes 49 ° East and latitude 36 degrees 20 minutes north and 37 degrees using GMS software. This model is a combination of code Modflow and GIS using the finite difference method, the ground water level simulation. For this research the information needed to run the model that were introduced to the model, included: positions of border aquifers, at different heights above ground level bedrock aquifer; the amount of withdrawals from well tapping positions; the position of and water level in observation wells; the hydraulic conductivity layer; and nutrition. After the preparation of the conceptual model and the determination of initial and boundary conditions, the simulation will be discussed. The flow simulation model was calibrated in a steady flow. The results of the calibration results in a steady state showed a reasonable balance between the observed and calculated results in October 2002. After calibrating the nutritional value 0/000321 meters per day, it was found that this amount is 1/98 times the amount of power input to the model. The amount of horizontal hydraulic conductivity layers of sand,/silt and sand,/gravel were measured at 28.57 and 40.4 km per day, respectively, and then the unsteady flow model calibration mode for distances between 2002 and 2007, using trial and error to achieve the best balance between the level observed daily. Projected drops in groundwater levels were calculated, based on the implementation of the model for 2007 and 2015 and 2022. The root mean square error, mean absolute error and mean error, respectively, were 17/41, 15/22 and -0.6. The root mean square error and average error with respect to the amount equal to 26/29 and -8/43 showed the good accuracy of the model. The water level calculated for the converter, groundwater flow is from the southeast to the northwest of the current slope correspond area. The model was implemented with the assumption of the rate of groundwater abatement and constant nutrition for a 15-year interval from 2007 to 2022. Maps obtained for the groundwater level in the years reflect a sharp drop in the water level as the result of continued indiscriminate harvesting of the Zanjan underground water aquifer.