تحلیل فضایی- زمانی پویایی بستر و تغییرات نیم رخ طولی هلیل رود با استفاده سنجش از دور و برهم کنش عوامل طبیعی و بشرساخت (1984-2020 م) (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
دینامیک و تغییرات بستر رودخانه و مشخصات هندسی آن تابع عوامل طبیعی و انسانی به شکل محلی است و نه تنها از منطقه ای به منطقه دیگر، که در بخش های گوناگون یک رودخانه نیز تفاوت های چشمگیری دارد. به ویژه در چند دهه گذشته فعالیت ها و عملکردهای انسانی اثر چشمگیری بر ویژگی های هندسی بستر رودخانه بر جای گذاشته است؛ ازاین رو، این مطالعه تغییرات نیم رخ طولی و مورفولوژی رودخانه هلیل رود طی دوره زمانی 35 ساله (1984 تا 2020 م) و تأثیر عوامل گوناگون بر آن را با استفاده از تحلیل داده ها و تصاویر ماهواره لندست (5، 7 و 8) ارزیابی و تغییرات نیم رخ طولی آن را در GIS محاسبه کرده است. به دلیل طویل بودن و عبور از واحدهای ژئومورفولوژیکی گوناگون، رودخانه به 8 پاره تقسیم شده است. تحلیل داده ها از افزایش طول رودخانه در پاره های هشت گانه حکایت دارد. به طور خاص برخی پاره ها با افزایش طول بین 2 تا 4 کیلومتر روبرو شده اند؛ درحالی که برخی پاره ها (به ویژه در بخش های میانی) به دلیل تعادل دینامیکی و تأثیرات زمین ساختی تغییرات کمتری در نیم رخ طولی خود داشته اند. مقاومت سنگ های آذرین در پاره های بالادست سبب پایداری نسبی و رسوبات آبرفتی در پاره های پایین دست سبب دینامیک بالای رودخانه و تغییرات گسترده در الگوی پیچان رودها شده است. فعالیت های زمین ساختی اغلب در بخش های میانی با ایجاد گسل ها و بالاآمدگی های زمین شناختی، انحرافات قابل توجهی در مسیر رودخانه ایجاد کرده است. فعالیت های انسانی همچون ساخت سد، تغییرات چشمگیر در دبی آب و رسوب گذاری در پایین دست سد (پاره های ۵ و ۶) به افزایش طول رودخانه و پیچان رودهای آن و همچنین تغییر الگوی جریان منجر شده و تغییر کاربری اراضی به شکل تخریب پوشش گیاهی و گسترش کشاورزی در پاره های پایانی باعث افزایش فرسایش و تغییرات مورفولوژیکی شده است. ازنظر الگوی زمانی نیز بستر رودخانه در بیشتر پاره های هشت گانه طی سال های 1996 تا 2008 تغییرات نسبتاً کمی داشته است؛ اما پس از آن با تشدید فعالیت های انسانی همچون ساخت سد این تغییرات افزایش یافته است.Spatial-Temporal Analysis of Channel Dynamics and Longitudinal Profile Changes of the Halil-Rud River Using Remote Sensing with Regard to the Interaction of Natural and Anthropogenic Factors (1984–2020)
This study investigated the longitudinal profile changes of the Halil-Rud riverbed, highlighting the intricate dynamics of river channels influenced by natural processes and human activities. Utilizing Landsat satellite imagery from 1984 to 2020, alongside Shuttle Radar Topography Mission (SRTM) data, we analyzed spatial and temporal changes in the river's morphology across 8 distinct sections. Our findings revealed an overall increase in river length with significant variations attributable to geological, tectonic, and anthropogenic factors. Notably, sections characterized by resistant igneous rocks maintained relative stability, while downstream areas with alluvial sediments exhibited pronounced fluvial dynamics and meandering. The study identified a period of relative stability from 1996 to 2008, which was followed by significant morphological changes linked to intensified human activities, including dam construction and land use alterations. These changes had implications for hydrology, sediment transport, and sustainability of adjacent ecosystems, emphasizing the need for effective water resource management strategies to mitigate the impacts of riverbed instability on local communities and infrastructure. Keywords : Halil-Rud River, Longitudinal Profile, Satellite Imagery, River Morphology, Anthropogenic Changes, Geological Factors, Fluvial Dynamics, Water Resource Management, Sediment Transport, Ecosystem Sustainability. Introduction The dynamics of river channels and their associated fluvial morphological features represent complex, nonlinear systems influenced by a combination of natural processes and human activities, particularly at localized levels. These systems exhibit significant spatial variability with notable differences observable across diverse geographic regions and among various segments within a single river network. In recent decades, anthropogenic changes have markedly altered channel forms and dimensions. Riverine systems function not only as agents of geomorphological change, but also as critical indicators of broader landscape development. This dual role is evident in observable changes to channel planform, cross-sectional geometry, longitudinal profiles, and network topology. Typically, fluvial systems respond gradually over short temporal scales, ranging from seasons to decades; however, they can also undergo rapid and substantial morphological changes under sustained environmental stress (over centennial timescales) or during extreme hydrological events, such as floods with recurrence intervals exceeding 100 years. One of the most significant challenges in river systems is the migration of channel beds over time, which can cause substantial damage to infrastructure, human settlements, and agricultural lands. Among these changes, alterations in the longitudinal profiles of rivers—resulting from interactions among river incision, lithology, tectonics, base level fluctuations, and anthropogenic activities—are particularly noteworthy. Studying river longitudinal profiles is crucial for various practical applications, including flood control, reservoir efficiency, and watershed management. This research aimed to investigate the changes in the longitudinal profile of the Halil-Rud riverbed through the processing and analysis of satellite images and data, alongside an examination of the influencing factors. The relevance of this study lay in the significant impact that changes in the river's longitudinal profile could have on the surrounding geographic regions, affecting hydrology, sediment transport, human safety, local economies, and availability of water for agriculture and orchards. In the realm of water resource management, the dynamic behavior of river systems often leads to alterations in flow pathways and water quality, which in turn influence agricultural irrigation, industrial water consumption, and drinking water supplies. Ecologically, the structural stability of riverbeds is vital for the sustainability of adjacent ecosystems, such as wetlands and riparian forests. From a socio-economic perspective, riverbank erosion and associated morphological changes can result in the loss of arable land and other terrestrial resources, directly impacting agricultural productivity and livelihoods of local communities. Furthermore, these changes may jeopardize infrastructure, including bridges, roads, and levees, leading to increased maintenance costs and negative economic consequences for regional development. Given that rivers are inherently dynamic systems with their morphological features evolving over time due to geomorphological, geological, hydrological, and anthropogenic factors, identifying the physical processes and structural conditions that promote riverbed stability is of critical importance. This research highlighted these pressing issues. Materials & Methods To conduct this study, Landsat satellite images with a spatial resolution of 30 m were obtained from the United States Geological Survey (USGS), covering the period from 1984 to 2020. Specifically, Landsat 5 (TM) imagery was used for the years 1984 and 1996, Landsat 7 (ETM+) for 2008, and Landsat 8 (OLI) for 2020. Additionally, Shuttle Radar Topography Mission (SRTM) data with a 30-meter resolution were employed to generate a Digital Elevation Model (DEM) for slope and topographic analyses of the watershed. Image pre-processing, which included geometric and radiometric corrections, was performed using ENVI 5.3 software. To identify the riverbed and detect changes in the river channel, supervised classification methods were utilized and river boundaries were delineated using spectral indices. The processed images were then mosaicked for integrated analysis. Given its considerable length (over 400 km) and passage through various geomorphological units, the river was divided into 8 sections. For change detection, the satellite images were imported into a GIS environment, where channel changes within each segment were assessed across 4 time periods. Google Earth Pro was also employed for visual change detection and data validation. Furthermore, 1:50,000 topographic maps of different parts of the basin, 1:100,000 geological maps of the study area, and maps detailing soil, vegetation cover, and land use were utilized to reconstruct the basin and evaluate the influence of both natural and anthropogenic factors on changes in the river’s longitudinal profile. Research Findings Data analysis revealed a general increase in river length across the eight defined sections. Specifically: Increases in Length: Sections 1, 3, 5, 6, 7, and 8 showed increases of approximately 2, 2, 4, 3, 2, and 3 km, respectively. Minimal Changes: Sections 2 and 4 exhibited relatively minor longitudinal changes attributed to dynamic equilibrium and tectonic influences. Geological Influences: The presence of resistant igneous rocks in upstream sections had contributed to their stability, while downstream sections (7 and 8) demonstrated higher fluvial dynamics and extensive meandering. Tectonic Activities: Significant deviations in the river course had occurred in sections 2, 4, and 5 due to faults and geological uplifts with a notable orientation shift in section 3. Human Interventions: Dam construction had altered water discharge and sediment deposition, increasing river length and modifying flow patterns in Sections 5 and 6. Land Use Changes: Agricultural expansion and vegetation removal in Sections 4 to 7 had intensified erosion and morphological transformations. Temporal Patterns: Between 1996 and 2008, the riverbed had experienced minor changes, indicating stability, while significant morphological changes were observed from 2008 to 2020 due to intensified human activities. Discussion of Results and Conclusion The results indicated that each segment of the river had unique characteristics influenced by various factors, including lithology, tectonic activity, topography, soil type, vegetation cover, and water discharge. Interplay of Factors: Changes in the river length and morphology were governed by a complex interplay of natural factors (geology, tectonics, topography) and human activities (dam construction, land use change). Stability and Dynamics: Upstream segments with igneous rocks showed relative stability, while downstream alluvial sections exhibited extensive changes due to high dynamics and erosion. Longitudinal Profile Changes: Significant longitudinal profile changes were more pronounced in low-gradient sections with soft sediments, while steep-gradient segments exhibited less variation. Channel Dynamics: The river's shift between old and new alluvial beds accounted for high channel migration, with some areas experiencing over 3 kilometers of length increase and extensive meandering. Human Impact: Dam construction and land use changes had substantially influenced water discharge and sediment dynamics, leading to alterations in river morphology and flow patterns. These findings underscored the importance of understanding both natural processes and human impacts on river systems to develop effective management strategies for water resources and ecosystem sustainability.
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