ارزیابی و بهینه سازی اتصال هیدرولوژیکی با هدف مدیریت منابع آب در حوزه آبخیز سامیان (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
کمبود منابع آب در برخی از استان ها به یک بحران تبدیل شده است. بر همین اساس، به تازگی توجه ویژه ای به اتصال ساختاری و عملکردی شبکه های رودخانه و منبع اصلی تأمین آب (به عنوان یکی از راه حل های مدیریتی در مقیاس حوزه آبخیز) شده است. با وجود این، به اتصال هیدرولوژیکی در ایران هنوز به طور کافی توجه نشده است؛ بنابراین پژوهش حاضر با هدف ارزیابی و بهینه سازی اتصال هیدرولوژیکی در شبکه رودخانه حوزه آبخیز سامیان برای حفاظت و مدیریت بهتر منابع آب و بهبود عملکرد هیدرولوژیکی انجام شد. نتایج نشان داد که شبکه هیدرولوژیکی رودخانه با طول کلی 73/1254 کیلومتر 173 یال و 176 گره دارد. همچنین، نسبت یال به گره (β)، اتصال گره به یال (γ)، شاخص یکپارچگی اتصال (IIC) و سنجه احتمال پیوستگی (PC) به ترتیب برابر با 983/0، 331/0، 66/5 و 151/1 به دست آمد. علاوه بر این، ساختار هیدرولوژیکی در مناطق دشتی به صورت ضعیف ارزیابی شد. در این میان، مهاجرت مرکز ثقل گردش آب پس از بهینه سازی برای سطح های مختلف اتصال هیدرولوژیکی به جنوب حوزه آبخیز انتقال پیدا کرده است. نتایج حاصل از محاسبه نسبت یال به گره (β) و اتصال گره لبه (γ) نشان داد که پیچیدگی داخلی شبکه مسیر با افزایش سطح بهینه سازی افزایش می یابد. همچنین، افزایش سطح بهینه سازی از 1 تا 4 باعث افزایش تعداد مسیرهای اتصال آب در حوزه آبخیز، پیچیدگی شبکه رودخانه و شاخص پیوستگی هیدرولوژیکی (IIC) شده است بنابراین پیشنهاد می شود اتصال هیدرولوژیکی در حوزه آبخیز سامیان تا سطح 4 بهینه سازی شود.Assessment and Optimization of Hydrological Connectivity for Effective Management of Water Resources in the Samian Watershed
Water scarcity has become a critical issue in some regions. Accordingly, increasing attention has been given to the structural and functional connectivity of river networks as the primary source of surface water supply, while this can be a potential watershed-scale management solution. However, assessment of hydrological connectivity remains understudied in Iran. This pioneering research aimed to evaluate and optimize the hydrological connectivity in the Samian Watershed to enhance protection and management of water resources and improve hydrological performance. The results showed that the hydrological network in the Samian Watershed with a total length of 1254.73 km had 173 links and 176 nodes. The river chain node ratio (β), actual bonding degree (γ), Index of Integration of Connectivity (IIC), and Probability of Connectivity (PC) were calculated to be 0.983, 0.331, 5.66, and 1.151, respectively. The hydrological structure of the Samian Watershed in the plain areas exhibited weak connectivity. After optimization, the center of gravity of water circulation shifted southward at different connectivity levels. Increasing the optimization level up to Level 4 resulted in an improvement in the hydrological connectivity indices within the Samian Watershed. While the overall connectivity showed a sudden increase after the 4th optimization level, the IIC increased but then decreased beyond Level 4. Therefore, it is recommended to optimize the hydrological connectivity in the Samian Watershed up to Level 4 for effective management of water resources. Keywords: Spatial Analysis, Minimum Cumulative Resistance (MCR), River Network Structure, Connectivity Index, Water Resource. IntroductionRiver networks are formed over long periods through the interplay of topographic, geological, hydrological, and erosional processes. However, human interventions, particularly in recent decades, have significantly altered these natural river systems. Industrialization and the growing water demands of human societies, especially in developing countries, have led to an increase in ecological disturbances, such as dam construction, river water extraction, inter-basin water transfer, and channel modification. These intense human activities have caused the deterioration of water ecosystem structure and function, exacerbating water scarcity at local, regional, national, and global levels. Considering the effects of climate change on intensifying the water crisis, various researchers and organizations have emphasized the need to restore river networks and ensure the availability of surface water resources at the watershed scale. Hydrological connectivity at the watershed level refers to the longitudinal transfer of water, sediment, pollutants, and aquatic organisms from the upstream to the downstream areas, which is related to the watershed convergence process. Evaluating the level of hydrological connectivity is crucial for increasing managers and experts' knowledge and understanding of the spatial heterogeneity in hydrodynamic and geomorphological processes, thereby promoting sustainable watershed management and conservation. Against this backdrop, the present research was conducted to investigate the structural hydrological connectivity and its optimization with the aim of river restoration in the Samian Watershed. Materials and MethodsThe study area, the Samian Watershed, covers an area of 4236 km2, representing 24% of the total area of Ardabil Province. This watershed includes 3 main rivers (Qarasu, Qori Chai, and Neor), each with several branches. The maximum and minimum altitudes are 4788 and 1200 m, respectively, with an average slope of 16.49%. The average annual rainfall in the region is estimated to be 351.52 mm. The assessment and optimization of the structural hydrological connectivity in the Samian Watershed were based on remote sensing, geographic information systems, graph theory, and binary theory. After constructing the hydrological network of the Samian Watershed, several connectivity indices were calculated to capture the internal complexity of the water flow transfer path network:River chain node ratio (β): Calculated to represent the degree of branching in the river networkActual bonding degree (γ): Determined to show the level of connectivity in the river networkIndex of Integration of Connectivity (IIC): Extracted based on binary theory using Conefor Sensinode 2.6 software to represent the overall connectivity of the transmission path networkProbability of Connectivity (PC): Also derived from binary theory to indicate the overall connectivity of the transmission path networkThe cost of water connection resistance was determined based on topographical, hydrological, and anthropogenic factors. 5 optimization levels were then defined according to the priority of optimization. The migration of the gravity center model was obtained using the mean center tool in ArcMap 10.8. Discrete water bodies were selected as optimization targets and the Minimum Cumulative Resistance (MCR) model was used to determine the optimal connection paths with the least obstacles to hydrological circulation. By combining ecological and geomorphological concepts, the optimization objectives were linked to the existing water systems to improve the overall hydrological connectivity in the Samian Watershed. Research FindingsAnalysis of the water areas in the Samian Watershed revealed that the general flow direction was from the northwest to the east, southeast, and southwest. The land surface in the southeast was relatively uneven and the water network was distributed accordingly. Water zones were mainly spread in the center of the watershed. Water resources in the Samian Watershed had been developed due to cultivation and urban development, which had led to a significant risk of excessive use and unequal distribution of water resources across different temporal and spatial scales. The results showed that the hydrological network of the river had a total length of 1254.73 km with 173 links and 176 nodes. The calculated connectivity indices were as follows:River chain node ratio (β): 0.983Actual bonding degree (γ): 0.331IIC: 5.66PC: 1.151The hydrological structure of the Samian Watershed in the plain areas exhibited weak connectivity. After optimization, the migration of the center of gravity of water circulation shifted to the south. The presence of independent water zones was observed in areas with relatively low slopes compared to their surroundings. 7 optimization objectives were considered at each level to increase the connectivity between the independent water zones. At Optimization Level 2, 14 nodes and 14 edges were added to the river network. By increasing the optimization level to 4, the hydrological connectivity indices in the Samian Watershed also increased. The overall connectivity showed a sudden increase after 4 levels of optimization, following an incremental trend. In contrast, the IIC increased but experienced a decreasing trend after Level 4. Therefore, it is appropriate to optimize the hydrological connectivity in the Samian Watershed up to Level 4. Discussion of Results & ConclusionResults of the assessment and optimization of hydrological connectivity are significant for the protection of vulnerable and discrete water bodies in watersheds and improvement of ecological processes in these water bodies. In this research, a framework was developed to assess and optimize the connectivity of natural and artificial hydrological structures at the watershed scale using graph and binary theories. Spatial analysis of cost distance and center of gravity in the watershed was also conducted across 5 optimization levels. The difference in slope in the region had led to the creation of independent water zones. These independent water zones were located separately from the main river network and, as a result, contributed little to the hydrological cycle and energy transfer in the watershed, making them more fragile. To protect these water zones from destruction and disappearance and improve the overall ecological function of the water system, they had to be integrated into the hydrological connection pattern. The analysis showed that each hydrological connectivity index exhibited an increasing trend with increasing optimization level. It could be concluded that up to Optimization Level 4, the hydrological structural connectivity indices tended to increase with the increase of optimization level. Hydrological connectivity was necessary at the first optimization level in the Samian Watershed river and the third optimization level could be a more economical and appropriate choice. The numbers of corresponding edges and nodes for small areas, such as agricultural watersheds, can be considered as effective factors in the results. Each identified natural hydraulic connection path can be managed. Therefore, the results of the current research emphasize the necessity of watershed planning and management by considering the changes in hydrological connectivity caused by structural changes in the river network.
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