كليدواژه :
آب زيرزميني , تغذيه مصنوعي , سد زيرزمين , شاخص پايداري , مدل‌سازي
چكيده فارسي :
افزایش بی¬رویه¬ی جمعیت در كشور، محدودیت منابع آب سطحی و بهره¬برداری بیش از اندازه از آبخوان¬ها باعث افت شدید سطح آب زیرزمینی در بسیاری از دشت¬های كشور همچون دشت شهركرد شده است. در پژوهش حاضر جهت مدیریت بهینه دشت مذكور، مدل كمی این آبخوان تهیه سناریوهای كاهش برداشت 5، 10 درصد، ساخت سد زیرزمینی و تغذیه مصنوعی برای 3 سال آینده پیش¬بینی و تأثیر آن¬ها مدل‌سازی شده است. در نهایت دو شاخص فنی پایداری (Iu) و بهره¬برداری اصلاح شده (WEI+) جهت تعیین میزان اثربخشی سناریوها محاسبه می¬شود. شاخص پایداری نشان دهنده¬ی میزان مصرف از منابع طبیعی موجود با توجه به مقدار تقاضا است كه مقدار بهینه آن عدد 1 بوده و می¬تواند مقادیر منفی نیز داشته باشد. شاخص بهره¬برداری نیز بیان كننده¬ی مقدار فشار به منابع آب با توجه به مقدار برداشت بوده و دارای مقادیر مثبت و مقدار بهینه¬ی آن، اعداد نزدیك به صفر می¬باشد. نتایج به دست آمده نشان می¬دهد وضعیت اولیه¬ی آبخوان بسیار نامناسب و برداشت از آبخوان بیش از ظرفیت آن می¬باشد. مقدار شاخص بهره¬برداری برای حالتی‌كه سناریویی وجود ندارد، برابر با 068/1 و برای سناریوهای سد زیرزمینی، اجرای طرح تغذیه مصنوعی، كاهش برداشت 5 و 10 درصد به ترتیب برابر با 068/1، 061/1، 045/1 و 969/0 می¬باشد. همچنین مقادیر شاخص پایداری به ترتیب برابر با 070/0، 070/0، 071/0، 078/0 و 114/0 می¬باشد. نتایج نشان داد، سناریو كاهش 10 درصد برداشت، بهترین سناریو بوده و پس از آن، سناریوهای كاهش 5 درصدی برداشت از چاه¬ها در طرح تغذیه مصنوعی و سد زیرزمینی در جایگاه¬های بعدی قرار گرفته¬اند. با استفاده از دو شاخص بازتعریف شده در این مقاله می¬توان به بررسی عملكرد آبخوان¬های دیگر و روش¬های مدیریتی مختلف پرداخت.
چكيده لاتين :
Introduction: Most part of Iran is located in an arid and semi-arid region, thus in most parts of a region; groundwater is the only water resource also Population growth, limitation of surface water resources and excessive water withdrawal from the aquifers, caused a sharp drop in groundwater level in many plains of Iran such as Shahrekord plain, So it is necessary to have suitable management plans to improve the aquifer and evaluate some indicators to see the effects of the methods. In this research, many management plans were assessed for the case study.
Materials and Methods: A groundwater numerical flow model (GMS 10.2) was established by using the monthly data including hydraulic heads, depletion volume of the wells, springs and qanats, precipitation values in Shahrekord aquifer. The model was prepared and calibrated for both status of steady (October 2010) and unsteady flow (November 2010-October 2012), and verified for the following year (November 2012- October 2013). The final values of hydraulic conductivity and specific discharge were obtained by trial and error and PEST method. The water level fluctuation was predicted for three years later (until October 2016) by applying management scenarios of 5% and 10% reduction in water withdrawal, underground dam and artificial recharge. After that, two indicators of Sustainability Index and modified Water Exploitation Index (WEI+) were calculated to determine the effect of the scenarios. The Sustainability Index indicates the consumption ratio of natural resources to water demand. The optimal value of this Index is 1 and it may also have negative values. Low values of this index mean high usage of natural resources. The Water Exploitation Index shows to which extent the total water demand puts pressure on water resources. This index has positive values and its optimal value is close to zero. These two indicators were used for surface water resources in the past studies so in this article they were redefined for underground water resources.
Results and Discussion: The result of groundwater modeling shows that the hydraulic conductivity from 1 to 25 m/day and specific yield from 0.01 to 0.08 are varied also the result of prediction shows that the underground water level would be decreased about 1.34 meter per year in the next 3 years when it hadn’t any management plans in this area but after 5% and 10% reduction water withdrawal scenarios Decreasing of water level were, respectively, 1.33 and 0.71 meter for each year also, considering that there were more wells in the center of the aquifer, water level in this area increased more than other areas, after 5% and 10% Reduction scenarios. According to the results of the artificial recharge and underground dam storage prediction, groundwater head increased in upstream of underground dam and the area near the artificial recharge. Considering the results it was found that the current condition of the aquifer is inappropriate and the amount of withdrawal from the aquifer is more than its capacity. The amount of Water Exploitation Index for business as usual scenario equal to 1.068 and for underground dam, artificial recharge, 5% and 10% reduction water withdrawal, were, respectively, equal to 1.068, 1.061, 1.045 and 0.969. Also the amount of Sustainability Index for business as usual scenario equal to 0.071 and for the other scenario were 0.068, 0.071 and 0.114. , respectively.
Conclusion: Considering the values of the indicators, 10% reduction water withdrawal scenario improved both indicators and selected as the best scenario. After that, 5% reduction water withdrawal was in the second place, then the artificial recharge scenario and underground dam scenarios, respectively, were in the third and fourth place. The scenario of underground dam had any positive effect on these two indicate. Regarding the calculated values of the indicators, it can be seen that although management scenarios have improved these two indicators, the amounts obtained are also significantly different from their optimal values. Several management scenarios can be used simultaneously to bring the calculated index values closer to their optimal values. Used two indicators of sustainability and modified water exploitation can be used exploitation for other management scenarios and assess the performance of them for the other aquifers.
