بهره‌گیری از روش‌های تحلیل آب‌نمود جهت برآورد جریان پایه (مطالعه موردی: حوزه آبخیز رودخانه سیلاخور- رحیم‌آباد)

بخش مهمی از جریان رودخانه‌های دائمی از آب‌های زیرزمینی نشات می‌گیرد. تغییراتی که به‌واسطه‌ی عوامل طبیعی و انسانی در آبخیز ایجاد می‌شود نشان‌دهنده‌ی تغییرات فیزیکی و سوء مدیریت مصنوعی منابع آبی است. این موقعیت‌ها سهم آب زیرزمینی در جریان آب رودخانه را تغییر می‌دهد. بنابراین، درک جریان پایه، موجب می‌شود تا بتوان پتانسیل و پویایی سیستم آب زیرزمینی را شناسایی کرد. هدف اصلی این تحقیق برآورد جریان پایه با استفاده از چندین روش تحلیل آب‌نمود است. پژوهش حاضر شامل تخمین جریان پایه از داده‌های جریان روزانه با استفاده از تکنیک منحنی تداوم جریان (fdc)، ابزار تحلیل آب‌نمود مبتنی بر وب (what) و برنامه شاخص baseflow (bfi+) می‌باشد. به همین منظور داده‌های روزانه دبی جریان و بارش از سازمان آب منطقه‌ای استان لرستان دریافت شد. سری زمانی داده‌ها برای دبی جریان و بارش از سال 1388 تا 1399 انتخاب شد. نتایج تجزیه‌وتحلیل نشان داد که اکثر تکنیک‌های فیلتر خودکار مورداستفاده با پارامترهای فرضی، جریان پایه بالاتر از میانگین را در مقایسه با fdc تخمین زده‌اند. علاوه بر این، تجزیه‌وتحلیل fdc سهم ذخیره زیرزمینی در جریان رودخانه را کمتر از میانگین نشان داد. مقادیر bfi برای رودخانه‌ی رحیم‌آباد متناسب است و برای کل آبخیز، حدود 45 درصد تخمین زده می‌شود. درنهایت نیز با استفاده از مقایسه‌ی میانگین جرین پایه، روش‌های اصلاح‌شده rdf (یک پارامتر و دو پارامتر)، ihacres، bf-bflow، bf-chapman و bf-furey برای کل آبخیز به‌عنوان الگوریتم‌های مناسب برای برآورد جریان پایه انتخاب شدند. با توجه به نتایج به دست آمده از این پژوهش، می‌توان در سال‌های بعد با داشتن آمار روزانه‌ی دبی، از روش‌های فوق‌الذکر برای جداسازی آب پایه استفاده کرد.

using hydrograph analysis methods for base flow estimation (case study: silakhor-rahimabad watershed)

introduction understanding and knowing the hydrological processes of a watershed is one of the fundamental principles in ensuring the appropriate quantitative and qualitative management of surface and groundwater resources in a catchment area. the changes in a watershed due to natural and human factors indicate physical changes and artificial mismanagement of water resources. understanding baseflow allows for identifying the potential and dynamics of the groundwater system. in principle, the separation of base flow and quick flow is difficult to distinguish from the measured discharge data in a river because the measured discharge in a river is a combination of the two flow components. the separation of riverbed flow is essential for water resources management and can significantly contribute to the calculation of water availability in the dry season (relatively short discharge period). in addition, comparing different watersheds in terms of flow recession characteristics can provide valuable information about storage and recharge properties in the watershed. the main objective of this research is to estimate base flow using several hydrograph analysis techniques, as there has been neither organized research on groundwater resources at the watershed level nor studies on different methods for estimating the base flow contribution in these streams.materials and methods the current research includes estimating base flow from daily streamflow data using the flow duration curve (fdc) technique, the web-based hydrograph analysis tool (what), and the baseflow index (bfi+) program. using the fdc technique, the long-term annual average fraction of flow from the base flow is estimated after obtaining the values of q90 and q50. the web-based hydrograph analysis tool includes three algorithms: the local minimum algorithm, the one-parameter algorithm, and the two-parameter algorithm. the web-based what system provides an efficient tool for hydrologic model calibration and validation. baseflow information from the what system can also play an important role in sustainable groundwater and surface water management, including irrigation and industrial uses, and estimating pollutant loads from both baseflow and direct runoff. the baseflow index program also uses the following algorithms: fix interval, sliding interval, local minima, lynne-hollick, chapman, one parameter algorithm, two parameter algorithm, exp. weighted moving average, eckhardt, bflow, ihacres, and fure & gupta. for this purpose, daily streamflow and precipitation data were obtained from the regional water organization of lorestan province. the time series of data for streamflow and precipitation was selected from 2009 to 2019. also, the processing of spatial data used in this research was performed using arcgis software.results and discussion the results of the data analysis indicate that most of the automatic filter techniques used with assumed parameters have overestimated the baseflow above the average compared to the fdc. also, the fdc analysis showed that the contribution of groundwater storage to streamflow was below average. in this study, the bfimax value was set to 0.80 for alluvial streams and the filter parameter (α) was set to 0.995 for the rahim abad stream. the bfi values for the rahim abad river are consistent and are estimated to be around 45% for the entire watershed. the results obtained from bfi+ showed that the calculated baseflow values for the one-parameter and two-parameter algorithms, except for rdf-ihacres, bf-bflow, bf-chapman, and bf-furey, were higher than the mean flow. also, the long-term base-to-flow ratio or bfi is equal to the ratio of q90/q50. this ratio indicates the discharge of groundwater or other delayed sources to the stream flow. the q90/q50 ratio has an annually varying decreasing and increasing trend for flow, indicating that the contribution of groundwater to streamflow varies from year to year with decreasing and increasing changes. finally, by employing all methods, the range of groundwater contribution to rahim abad streamflow was obtained between 2 and 84 percent, and its average value was also determined to be 63 %.conclusion considering the average of all bfi values obtained from all methods with values less than the mean, an overall average of 45% was obtained, which provided a better estimate for the entire watershed. in this regard, the modified rdf methods (one-parameter and two-parameter algorithms), ihacres, bf-bflow, bf-chapman, and bf-furey were selected as the top algorithms for the entire watershed. further studies are necessary for future groundwater resource problems in the watershed. the interaction of groundwater and surface water and pollution problems, water quality management of rivers, estimation of groundwater potential using other techniques, and estimation of the contribution of groundwater under climate change are among those that can be mentioned. therefore, it is recommended that these factors be considered in future research for a more accurate assessment and better management of water resources in the studied area. also, studies should investigate the role of watershed characteristics, such as soil properties and vegetation cover, as well as their impact on base flow variations. the introduction of suitable methods of separation of daily flow in hydrological modeling, regional analysis of minimum flows, and determination of base flow share can be used. it is hoped that the output of this study will help the planning, development, and management of water resources in the silakhor watershed.