بررسي تاثير عوامل جغرافيايي در نوسان آب زيرزميني دشت پارس آباد مغان

The Evaluation of Geographical Factors Impact in Groundwater Fluctuation in Parsabad of Moghan Plain

در سال هاي اخير، نوسان و بالا رفتن سطح آب زيرزميني در دشت پارس‌آباد مغان منجر به بروز مشكلاتي نظير زهدار شدن و شور شدن زمين‌هاي كشاورزي و نيز تخريب پي ساختمان‌هاي شهري و روستايي و نشست جاده‌ها و بناها در اين مناطق گرديده است. در اين تحقيق با در نظر گرفتن عوارض جغرافيايي و نحوه تاثير آن بر نوسان سطح آب زيرزميني از طريق سيستم اطلاعات جغرافيايي (GIS)، روند آن مدل‌سازي شده كه با تغيير در نحوه سيستم آبياري در منطقه مي‌توان تاثير اين فرايند را به حداقل رساند. براي پايش نوسان سطح آب زيرزميني از آمار 30 حلقه چاه مشاهده‌اي به صورت برداشت‌هاي ماهانه، داده‌هاي زمين‌شناسي، توپوگرافي، خاك و منابع ارضي و داده‌هاي اقليمي منطقه مورد مطالعه استفاده شده است. با استفاده از اين داده‌ها كه متعلق به دوره آماري 92-81 مي‌باشند، روند نوسان سطح آب زيرزميني و هيدروگراف تراز رسم گرديد. سپس ارتباط بين عوامل مختلف جغرافيايي و نوسان سطح آب زيرزميني بررسي شده است. در اين راستا همبستگي پيرسون و مدل رگرسيون چند متغيره بين عوامل موثر در نوسان آب زيرزميني و تراز آب زيرزميني بدست آمد كه معيارهاي عملكرد (0/97=R2 و 0/07=RMSE) در دوره آزمون نيز حاكي از كارايي اين مدل مي‌باشند. نتايج به‌دست آمده نشان‌ دهنده افزايش روند سطح آب زيرزميني در اين دشت مي‌باشد كه جريان آب زيرزميني از جنوب به سمت شمال و خصوصاً شمال شرقي مي‌باشد. در اين ميان عوامل ارتفاع، شيب، جنس زمين (تخلخل و قابليت انتقال) با تاثيرگذاري بيشتر و نفوذ ‌پذيري، بارش و تبخير با تاثيرگذاري كمتر و عمق آب زيرزميني نيز بي‌تاثير در نوسان آب زيرزميني شناسايي شده‌اند. با اعمال زهكشي‌هاي مداوم در اكثر نقاط دشت و تغيير سيستم آبياري از سنتي به مكانيزه مي‌توان از شور شدن خاك‌هاي مزروعي و نشست برخي منازل جلوگيري نمود.

Introduction Groundwater resources are the most important and the cheapest water resources the proper recognition of which and their exploitation principles can lead to sustainable development and economic activities, particularly in arid/semi-arid areas. The groundwater level reduction and human activities are reducing the groundwater resources level. Fluctuations study are the most important management strategies can be useful in this case. Parsabad of Moghan plain due to its form and geomorphic structure is a flat plain. By considering the slope, elevation, quaternary sediments, old and new fluvial terraces and alluvial fans, groundwater levels have fluctuated a lot. At the same time, this fluctuation has taken a positive trend in recent years. Therefore, groundwater level in the plain has reached near the surface of the Earth caused many problems for people. Consequently, swamp lands and salinization of agricultural land, destruction of urban and rural buildings and sinking the roads and buildings may be caused due to the problem. So, to overcome this status, it seems necessary prediction of the groundwater level fluctuations accurately. Material and Methods Obtaining a suitable model to predict the behavior of water resource taking into account the factors affecting these phenomena is one of the most important approaches in water resource management. These important factors include slope, elevation, porosity, permeability, transmissibility, precipitation and evapotranspiration. Therefore, in this study, observational wells data, meteorological stations data, geological data, topographic maps and satellite images of ETM+ have been used for variables mapping. Influenced factors maps is provided in GIS using digital elevation model and Kriging. The effects of geographical factors on fluctuating groundwater level have been explored by Pearson correlation. After determining the affected factors on fluctuations of groundwater level, its trend had been anticipated by taking these factors and multivariate linear regression model. In this context, through analysis of variance {ANOVA), sum of squares, degrees of freedom, mean square, Fisher's exact test and a significance level of regression have been examined. Discussion The results showed slope, elevation, transmissibility and porosity and in contrary, the permeability, precipitation and evaporation are in high and low significance level of correlation with fluctuating groundwater levels, respectively. Also, no significant correlation is between groundwater depths and groundwater level, therefore, have no effect on the groundwater level fluctuations. The results implied the consistencywith reality about the direct/indirect influence of considered environmental factors in the groundwater level fluctuation. So, the groundwater level have been decreased by increasing slope, height, transmissibility and evapotranspiration. But, the porosity, permeability and precipitation have a direct relationship with groundwater level. Standard deviation parameters, standardized coefficients, t test, and significance level have been investigated in regression model. The significance level (Sig) is 0.000 or near to zero in all parameters. Thus, the model implemented in this study have been significant, so, prediction map of groundwater level fluctuations based on the model have been produced by spatial analysis and overlapping raster. Conclusion Due to the region characteristics, slope and elevation are the most important factors affected the groundwater level fluctuation. Since the slope of study area is close to zero in the northeast regions and the Beach of Aras River, so the motion of groundwater in these areas have been very slow. On the other hand, the formation of this area is clay and silt causes slowing down the movement due to their heavy soils characteristics. Beside the geographical features affected in groundwater fluctuating, extensive networks of water supply with canal to irrigate the agricultural areas are more important factor, too. For evaluating the model, relationships between estimated and observed groundwater level have been investigated by correlation, RMSE and R2 • In this study, these criteria implied R = 0.988, RMSE = 0.07 and R2 = 0.9712, so, the results reflected high efficiency of the process model of groundwater level fluctuations. Due to the lack of these models in the country, this study can be used as a prelude to develop prediction models of groundwater level.