شبیه‌سازی و تعیین ضرایب هیدرودینامیکی و بیلان آبخوان با مدل ریاضی modflow (مطالعه موردی: دشت کرمانشاه)

در مناطق دارای آب و هوای خشک و نیمه خشک، آب‌های زیرزمینی یکی از منابع اصلی تامین آب کشاورزی، صنعت و شرب می‌باشند. هدف این پژوهش بررسی ضرایب هیدرودینامیکی، بیلان دشت وضخامت آبخوان در محدوده مطالعاتی کرمانشاه از طریق شبیه‌سازی آبخوان با استفاده از مدل modflow می‌باشد. دراین روش ابتدا مدل مفهومی و سپس مدل عددی در دو حالت ماندگار و غیرماندگار ساخته، سپس واسنجی و صحت سنجی گردید. نتایج نشان‌دهنده بیشترین ضخامت آبخوان در ناحیه شمال و شمال‌شرق دشت به ضخامت حدود 160.96 متر و کمترین ضخامت در نواحی جنوب‌غربی و غرب دشت به ترتیب 118.14 و 120.69 می‌باشد. همچنین ضریب هدایت هیدرولیکی بین 0.09 تا 40 متر در روز و ضریب آبدهی ویژه بین 1 تا 35 درصد متغیر می‌باشد. محاسبات بیلان منفی بودن موازنه آبی در نواحی غربی و جنوب غربی دشت و مثبت بودن بیلان در نواحی شمال و شمال شرقی وجنوب شرقی را نشان می‌دهد.

simulation and determination of hydrodynamic coefficients and aquifer balance with modflow mathematical model (case study: kermanshah plain)

introduction in areas with dry and semi-arid climates, groundwater is one of the main sources of water supply for agriculture, industry and drinking. it is verynecessary to prepare a simulation model to predict changes in the groundwater level and extract the components of the groundwater balance forbetter management of the operating of these resources. the aim of this research is to investigate hydrodynamic coefficients, plain balance and aquifer thickness in the study area of kermanshah through aquifer simulation using modflow model.methodology in this research, based on information and data related to piezometers, operation wells, rivers, well logs, geophysical sections, bedrock map, topography and geology of the area, etc., a conceptual model of the plain was built. the numerical model developed based on the conceptualmodel of the plain was calibrated and validated in two steady and unsteady states, and the optimal values of hydraulic conductivity and specific yield were extracted. then, balance components were extracted based on inflows and outflows from the aquifer, withdrawal from wells, recharge rate and seepage from rivers, feeding from the plain surface and boundary conditions and evaporation from the plain, and the most importantbalance parameters with the largest volume of exchanges were introduced.results and discussionthe results show that the thickness of the aquifer in the north and northeast of the plain is about 160.96 meters, and the lowest thickness in the southwest and west of the plain is 118.14 and 120.69 meters, respectively. also, the coefficient of hydraulic conductivity varies between 0.9 and 40 m/day and the coefficient of specific yield varies between 1 and 35%. based on the balance of the steady month (october 2016), the input of the aquifer was 2871427.5 cubic meters and the output of the aquifer was 2871472.3 cubic meters. the amount of input to the aquifer through the boundaries (general head cells) is 2500444 cubic meters and the output is 1653545.7 m3/month. the amount of inflow through the river was 7202.1 m3/month and the outflow from the river was 863470.4 m3/month. the amount of extraction from the wells was 261246.1 cubic metersand the amount of recharge was 363781.2 m3/month.conclusion this research showed that the modflow model can simulated the average level and the groundwater level of different areas of aquifer alongwith the balance of the plain, including the exchange of the aquifer with the river, the inflow and outflow from the boundaries of the aquifer, the parameters of withdrawal and recharge. in this simulation, the value of the root mean square error (rmse) was calculated as 428 mm in the steady model and 535 mm in the unsteady model. that is, in the whole plain, the difference between the observed and simulated groundwaterlevels in the piezometers was less than one meter.