انجمن هیدرولیک ایران نشریه علمی هیدرولیک 2345-4237 20 4 2025 12 22 Study of the Effect of Parallel Computing and Various Grid Spacings on Flood Modeling using STE software بررسی تاثیر پردازش موازی و فواصل مختلف شبکه‌بندی در سرعت و دقت مدلسازی سیلاب با استفاده از نرم‌افزار STE 1 21 218254 10.30482/jhyd.2024.432211.1689 FA رضا تیموری گروه مهندسی آب، دانشکده آب و خاک، دانشگاه علوم کشاورزی و منابع طبیعی گرگان، گرگان، ایران 0009-0008-9187-1640 امیر احمد دهقانی گروه مهندسی آب، دانشکده مهندسی آب و خاک، دانشگاه علوم کشاورزی و منابع طبیعی گرگان، گرگان،گلستان، ایران. 0000-0002-5237-8975 مهدی مفتاح هلقی گروه مهندسی آب، دانشکده مهندسی آب و خاک، دانشگاه علوم کشاورزی و منابع طبیعی گرگان، گرگان،گلستان، ایران. 0000-0001-8109-5336 Journal Article 2023 12 25 Introduction In recent decades, as climate change has intensified, flood risks pose a greater threat to countries than ever before. These events have resulted in significant losses, including the tragic loss of thousands of lives and substantial economic damages due to severe and flash floods. Rapid estimation of flood extents is one of the most important and crucial things in emergency management and reducing damages caused by floods. To mitigate risks, damages, and challenges, leveraging available data and meteorological forecasts is crucial for better identifying flood extents and pinpointing the exact locations of impacts. This information empowers us to take prompt and necessary actions to reduce risks and minimize damages effectively. With the advancement of computers, achieving a method for precise and rapid flood mapping is now possible. For this purpose, extensive studies have been conducted in the past, and various hydraulic, hydrological, and empirical models have been proposed and examined. Existing models and methods for delineating flood zones are often hydraulic, involving heavy computational load and consuming significant time for calculations. Alternatively, they may be hydrological or empirical, lacking desirable accuracy and sometimes speed, making it challenging to provide precise and timely information on flood inundation areas. Methodology In this study, the 2D-shallow water equations were solved by developing a new user-friendly module of STE software. The impact of parallel processing and various computational grid spacing on the speed and accuracy of the obtained flood-prone areas has been investigated. The model results were compared with Sentinel-2 satellite and HEC-RAS results for the 2019 flood in the Golestan province, Gorganrood River. In order to model 2D surface water flow, the equations under consideration, based on assumptions derived from the Navier-Stokes equations, are known as the shallow water equations. The key to simplifying these equations is to locally approximate the inertial term based on the assumption of the negligible contribution of the convective acceleration term compared to the other terms of the equations. Therefore, it is possible to neglect the mentioned term, and the simplified equations, named local inertial approximation, can be written as the relations (4) to (6). These equations have been solved in the developed software in this study using the finite difference method in both implicit and semi-implicit schemes. In this study, new user-friendly module of STE software have been undertaken with an extension named STEGIS. This extension is tasked with conducting geographical analyses and performing all GIS operations and two-dimensional calculations, presenting the results, and analyzing them. In the development of this extension, efforts have been made to incorporate all the necessary tools for users in a way that eliminates the need for separate software such as QGIS, Arcmap, HEC-RAS, HEC-HMS, etc., during hydraulic, hydrological, and other modeling and analyses. Therefore, the aim is to make all the necessary tools for working with raster, vector, and geographical files, as well as performing hydraulic, hydrological, and topographic calculations and analyses, readily accessible to the user in this extension and making it easier to use. For more information, please visit www.en.ste.hwstr.ir. Given the binary nature of the observed data (flood zone extracted from satellite imagery) being either zero or one, it is necessary to assess the accuracy of the models using specific parameters designed for evaluating binary data. For this purpose, parameters such as accuracy percentage and point percentage have been employed. Results and Discussion In this study, the 2D module of the STE software was developed to investigate the impact of parallel computing and various computational grid spacing on the speed and accuracy of flood simulations. Flood zones and their extents were estimated using the two-dimensional shallow water equations. The obtained results were compared, discussed, and evaluated against the outcomes of HEC-RAS software and the flood zone recorded by Sentinel-2 satellite for the flood event in the Gorganrood River, Golestan province, in March-April 2019. In summary, the results of this research demonstrated that the developed STE software provides more accurate results compared to HEC-RAS software across all computational grid spacings. Meanwhile, the time required to complete flood simulation in the STE software is nearly 95% less than that in HEC-RAS software. In both software applications, precision and the time required to complete the simulation increased with a reduction in the computational grid spacings. Values ranging from 10 to 15 times the size of reference topographic map cells have proven to be the optimal range for computational grid spacings in both software applications. Utilizing these values, computation can provide sufficient accuracy along with an appropriate time frame for completing the simulations. The time required to complete the simulation using various discretization methods in the STE software is nearly the same, but these methods significantly impact the accuracy of the simulation. The Hybrid method provides higher accuracy at different computational grid spacings. Parallel computing and simultaneous computation of different sections of the two-dimensional solution domain only result in increased computational speed and reduced time needed for completing simulation, especially in shorter computational grid spacings. This approach has no impact on the accuracy of the simulation and other considerations. The algorithm implemented in the STE software for adjusting the time step has successfully, maximized the time step in order to minimize the overall simulation time and prevented computational errors in water volume estimation which makes the computations more stable. Conclusion Results indicate that the developed software in this study, apart from better accuracy, demonstrates significantly higher speed in flood simulations and delineation of flood zones. It has the capability to reduce the time required to complete simulation and provide precise flood extents by up to 95% compared to the HEC-RAS software. Parallel computing proves highly effective in reducing the necessary time for modeling completion. Moreover, increasing the computational grid spacings up to 15 times the cell sizes of the reference topographic map results in both satisfactory simulation speed and good accuracy. پهنه‌بندی سریع سیلاب یکی از مهمترین و اساسی ترین موارد در مدیریت بحران و کاهش خسارات ناشی از سیل است. تحلیل و نمایش دقیق پهنه سیل به مراجع ذی‌ربط کمک می‌کند تا متوجه شرایط سیل، خطرات و تهدیدات آن قرار گرفته و به موقع اقدامات لازم را انجام دهند. به منظور کاهش خطرات، خسارات و مواجهه به موقع، نیاز است تا بتوان پهنه سیلاب و نواحی از منطقه مورد تهدید که دچار آبگرفتگی و خسارت خواهد شد را به سرعت شناسایی کرده و اقدامات لازم انجام شود. در این تحقیق، با توسعه بخش دوبعدی نرم‌افزار کاربر پسند STE اقدام به حل سریع تر معادلات آب کم عمق شده است و تاثیر پردازش موازی و افزایش فواصل مکانی بین گره‌های محاسباتی بر سرعت و دقت پهنه های بدست آمده، با استفاده از پهنه‌ ثبت شده توسط ماهواره سنتینل 2 و نتایج نرم‌افزار HEC-RAS برای سیل سال 1398 استان گلستان رودخانه گرگان‌رود مورد بحث و بررسی قرار گرفته است. نتایج نشان داد نرم‌افزار توسعه یافته در این تحقیق علاوه بر برتری در دقت، از سرعت بسیار بیشتری در مدلسازی سیلاب و مشخص سازی پهنه سیل برخوردار است و می‌تواند زمان لازم جهت اتمام مدلسازی و ارائه پهنه دقیق را تا 95% نسبت به نرم‌افزار HEC-RAS کاهش دهد. پردازش موازی بسیار موثر در کاهش زمان لازم، جهت اتمام مدلسازی بوده و افزایش فاصله مکانی بین گره‌های محاسباتی تا 15 برابر دقت نقشه توپوگرافی مورد استفاده، ضمن ارائه سرعت مناسب در مدلسازی از دقت خوبی نیز برخوردار می‌باشد.

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انجمن هیدرولیک ایران نشریه علمی هیدرولیک 2345-4237 20 4 2025 12 22 Sensitivity analysis of the Stage-discharge parameters using the concept of isovel contours بررسی حساسیت پارامترهای رابطه دبی-اشل مبتنی بر کنتورهای هم سرعت 23 38 220492 10.30482/jhyd.2024.478211.1719 FA فرید جامی فر گروه مهندسی عمران، دانشکده مهندسی شهید نیکبخت، دانشگاه سیستان و بلوچستان، زاهدان بهاره پیرزاده گروه مهندسی عمران، دانشکده مهندسی شهید نیکبخت، دانشگاه سیستان و بلوچستان 0000-0002-5728-3481 محمود فغفور مغربی گروه عمران، دانشکده مهندسی، دانشگاه فردوسی مشهد Journal Article 2024 09 13 Introduction In recent years, numerous studies have been conducted to evaluate discharge. A practical approach in this regard is to evaluate the discharge at different water levels using the available information on a reference water level. Using the stage-discharge curve, the discharge rate at other levels can be predicted and evaluated if the discharge is known at one surface level. Maghrebi et al. presented a method to determine the stage-discharge relationship.This relationship compares the discharge at two different levels of a cross-section. Therefore, using the discharge collected at level i as reference point, the discharge values at other levels can be evaluated. Therefore, the current study investigated the effect of changing these powers on the discharge evaluation error. Methodology A reasonable value for the powers must first be considered to investigate the effect of changing the stage-discharge relationship’s powers on the amount of discharge evaluation error. Then, in different examples, coding should be done so that the powers are changed and for each power, the discharge evaluation error is calculated and reported separately. Then, it is checked whether the error has been reduced or not. The error relations and the Maghrebi relation are coded in MATLAB software for the cross-section of Figure 2. The discharge Flow evaluation error values for FCF-Series 10 were calculated separately for the levels specified in Figure 3 by considering the interval [-2,2] for each power of the Maghrebi relationship and its changes are shown in Figures 5 to 10. In these figures, the horizontal dashed line shows the error value in Maghrebi relation to evaluate discharge. Results and Discussion In Figures 5 to 10, the reduction of the discharge evaluation error can be seen in some ranges of the power change interval. The maximum error reduction can be seen in Figure 10, Case C, which shows a reduction of about 4%. The error reduction ranges are given in Table 3. Figures 5 to 10 and the results presented in Table 3 show that it is possible to improve the performance of the Maghrebi relation by changing the relationship powers within the suggested range. On the other hand, it was stated earlier that up to a 4% reduction in discharge evaluation error can be achieved. Conclusion Finally, this study provides a suggested range for each power. The most important result of the present article is that changing the powers of the stage-discharge relation can reduce the discharge evaluation error. The results show that changing the powers reduce the discharge evaluation error by more than 5%. رابطه دبی-اشل که توسط مغربی و همکاران (2017) ارائه گردید، یکی از دقیق‌ترین روابطی است که برای تخمین منحنی دبی-اشل هم در مقاطع آزمایشگاهی ساده و مرکب و هم در رودخانه‌های طبیعی پیشنهاد شده است. در این رابطه، دبی در دو تراز مختلف با یکدیگر مرتبط می‌شود. بعبارتی به کمک دبی برداشت شده در یک تراز، مقادیر دبی در سایر ترازها محاسبه می‌گردد. رابطه مزبور از چند پارامتر بدون بعد تشکیل شده که هر پارامتر دارای توان مخصوص به خود است. از طرفی با توجه به اینکه ارزیابی دبی سایر ترازها همواره با مقداری خطا همراه است، بررسی این نکته که آیا تغییر توان‌های پیشنهادی مغربی و همکاران (2017) می‌تواند خطای محاسبات را کاهش دهد، موضوعی است که دانش پاسخ به آن می‌تواند مورد توجه محققین مختلف باشد. لذا در مقاله حاضر، محدوده‌ای منطقی برای توان‌های رابطه مذکور در نظر گرفته شد و بررسی گردید که تغییرات توان‌ها در محدوده تعریف شده چه تاثیری بر خطای ارزیابی دبی دارد. برای این منظور، از سه رابطه متداول محاسبه خطا بهره‌گیری شد و مقادیری برای هر یک از توان‌ها پیشنهاد گردید. مهم‌ترین نتیجه آن بود که تغییر توان‌های رابطه دبی-اشل توانست خطای ارزیابی دبی را کاهش دهد بطوریکه تغییر توان‌ها کاهش بیش از 5 درصدی خطای ارزیابی دبی را نتیجه داد.

https://jhyd.iha.ir/article_220492_eb6cd24d729360af2236b354b564aa00.pdf

انجمن هیدرولیک ایران نشریه علمی هیدرولیک 2345-4237 20 4 2025 12 22 Investigation of the Entropy Methods for Determining Velocity Distribution in Meandering Compound Channels ارزیابی روش‌های آنتروپی درتخمین توزیع سرعت جریان در آبراهه‌های سیلاب‌دشتی پیچانی 39 55 220494 10.30482/jhyd.2025.500845.1727 FA وحیده, مرتضوی امیری گروه علوم و مهندسی آب دانشکاه فردوسی مشهد 0000-0002-6035-1780 کاظم اسماعیلی هیات علمی 0000-0001-5354-0949 Journal Article 2025 01 19 Introduction Hydraulic modeling in natural channels encompasses sediment transport, pollutant dispersion, channel design, and velocity distribution (Singh, 2013). In meandering channels, the distribution of velocity and its interaction with momentum are crucial for understanding flow dynamics. Various methods exist to model velocity distribution, with the concept of entropy being a key approach. The entropy principle maximizes the entropy function, minimizing errors by considering probabilistic distributions linked to the problem's nature. The application of entropy in open-channel flow began with Chiu (1987), who established a linear relationship between mean and maximum velocities. Ksia (1997) extended this for the Mississippi River, showing its reliability even in meanders. Recent studies have focused on Shannon entropy for velocity distribution, with findings indicating its effectiveness in both laboratory and natural channels (Moramarco & Termini, 2017; Gholami et al., 2019). While entropy methods have been widely used for velocity distribution, their application in meandering floodplain channels has received limited attention. This study aims to evaluate the effectiveness of entropy-based methods in meandering rivers with complex three-dimensional flow patterns, addressing the challenge of accurately simulating velocity distribution in such channels. Methodology Experimental Setup The experimental data were collected from the Hydraulic and Physical Modeling Laboratory at Ferdowsi University of Mashhad. A physical model of a meandering floodplain channel with a rigid bed was constructed, measuring 10 meters in length and 120 cm in width. Flow conditions were steady and uniform, with a constant discharge of 22.3 L/s. Flow depth in the main channel was 25 cm, while in the floodplain, it was 10 cm. The Froude number of the flow was 0.2. Velocity Measurement Velocity profiles were measured using a 3D ultrasonic velocimeter (Sontek2001), capturing flow velocities along the longitudinal, lateral, and vertical axes. Measurements were taken at multiple cross-sections along the channel, and the data were processed using Vectrino and WinADV software to determine velocity distributions. Entropy Methods Two entropy methods were used to model the velocity distribution: • Shannon Entropy: Maximizes entropy subject to physical constraints like mass conservation, providing a statistical model of velocity distributions. • Tsallis Entropy: A generalized entropy approach that is more suited for complex, non-extensive flow systems, such as meandering channels. Error Analysis The accuracy of the entropy models was evaluated using three error metrics: Root Mean Square Error (RMSE), Mean Absolute Error (MAE), and Mean Absolute Percentage Error (MAPE), which compared the observed and predicted velocity profiles. Results and Discussion Longitudinal Velocity Distribution In meandering channels, maximum flow velocity is typically observed near the inner bend. As the flow enters the bend, secondary currents and increased pressure gradients in the outer bend led to a reduction in velocity. Conversely, the inner bend experiences an increase in velocity. After exiting the bend, the maximum velocity shifts toward the channel center and eventually to the outer bend downstream (Shiono & Moto, 1998). At CS1, CS2, and CS3, maximum velocities occur at the deepest point in the channel, which is influenced by momentum transfer at the transition between straight and meandering sections. Secondary flow effects and the pressure gradient changes near the bends likely contribute to this velocity distribution, consistent with findings by Pan et al. (2019). Velocity Distribution Using Entropy Methods The velocity distributions were modeled using Shannon and Tsallis entropy methods. Parameter values ϕ and M were determined for each cross-section using the respective entropy equations. The calculated values of M for CS1, CS3, and CS5 were 4.77, 5.02, and 5.92, respectively, which are within the range for rivers in the U.S. (Lü & Singh, 2011). Figure 5 compares the velocity profiles predicted by Shannon and Tsallis entropy methods with measured velocities at the three cross-sections. The Shannon entropy method provided more accurate predictions, especially toward the center of the channel, with errors increasing near the channel walls due to the unaccounted effects of proximity to the bends. Error Analysis Error metrics, including RMSE, MAE, and MAPE, were used to evaluate the accuracy of both entropy methods. Shannon entropy achieved the lowest RMSE (0.01) at CS3, while the Tsallis method had larger errors, particularly at the bends. The minimum MAPE for Shannon entropy was 8.59% at CS3, compared to 26.81% for Tsallis entropy. Conclusion The results show that both methods perform well, with Shannon entropy providing better accuracy, especially at the channel center. Despite its limitations in accounting for the influence of channel walls, entropy methods, particularly Shannon entropy, offer a simple, cost-effective, and relatively accurate approach for determining velocity distribution in natural river channels. Keywords Shannon entropy, Tsallis, velocity distribution and meandering floodplain. چکیده: یکی از پارامتر‌هایی که نقش اساسی در فهم هیدرودینامیک جریان درکانال‌های باز ایفا می‌کند، سرعت جریان است. درآبراهه‌های سیلاب‌دشتی پیچانی، به‌علت جریان سه‌بعدی پیچیده‌ی ناشی از انتقال مومنتم میان مجرای اصلی و سیلاب‌دشت‌ها، توزیع سرعت جریان درمقایسه با کانال‌های مستقیم متفاوت است. به‌کار‌گیری مفهوم آنتروپی به‌عنوان روشی مناسب در رابطه با تخمین توزیع سرعت در کانال‌های باز مستقیم معرفی شده است. در این پژوهش، به‌منظور ارزیابی آنتروپی شانون و تسالیس درشبیه‌سازی توزیع سرعت جریان در مجرا‌های سیلاب‌دشتی پیچانی، از داده‌های آزمایشگاهی در یک مدل فیزیکی پیچان‌رودی استفاده شد. تابع چگالی احتمال با در‌نظر‌گرفتن محدودیت‌های مرتبط با مساله، در دو روش مورد نظر برای تعیین مقادیر پارامتر M و G در سه مقطع کانال تعیین شد. نتایج نشان داد این روش‌ها می‌توانند انتخاب مناسبی برای تعیین توزیع سرعت در پیچان‌رود‌ها باشند. کمینه مقدار خطاها در بین مقطع‌های بررسی‌شده در روش‌های شانون و تسالیس، به‌ترتیب مربوط به قوس سوم(مقطع CS3)و قوس اول (مقطع CS1)، با مقادیر RMSE برابر 01/0 و 06/0 می‌باشد. همچنین با‌توجه به نتایج مطلوب در روش شانون در عمق کمتر از مجرای اصلی، به نظرمی‌رسد برای کاربرد روش آنتروپی در تعیین سرعت آبراهه‌های پیچان‌رودی، نیازمند اصلاح ضرایب در تراز‌های بالاتر از عمق ورودی به سیلاب‌دشت می‌باشد.

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انجمن هیدرولیک ایران نشریه علمی هیدرولیک 2345-4237 20 4 2025 12 22 Evaluation of the effects of Anzali Port Development on Sedimentation at Anzali Wetland by Numerical Simulations ارزیابی اثرات طرح توسعه بندر انزلی بر رسوبگذاری در تالاب انزلی با استفاده از شبیه سازی ریاضی 57 70 233944 10.30482/jhyd.2025.519157.1730 FA حسن حیدرنژاد فارغ التحصیل کارشناسی ارشد مهندسی آب و سازه های هیدرولیکی، دانشکده عمران، دانشکدگان فنی دانشگاه تهران پیمان بدیعی دانشکده عمران پردیس فنی دانشگاه تهران 0000-0001-6636-7612 Journal Article 2025 04 26 Introduction: Coastal wetlands, such as the Anzali Wetland in Iran, are ecologically sensitive areas that play crucial roles in environmental health, climate regulation, and biodiversity conservation. However, human activities and climate change threaten these ecosystems, leading to habitat loss and reduced ecological services. The Anzali Wetland, designated as a Ramsar Site, faces challenges like sedimentation and overgrowth of invasive species. Understanding hydrodynamics and sediment transport in these areas is vital for effective environmental management. Numerical models offer valuable tools for simulating water flow, sediment dynamics, and morphological changes in coastal wetlands. Previous studies have focused specifically and individually on the Port or Wetland but to the knowledge of Authors, none have addressed the entire wetland-port system. This study aims to fill this gap by incorporating newly acquired field data to enhance the accuracy of simulations and exploring the effects of port development on wetland sedimentation. Methodology: In this study, numerical simulations were conducted using Delft3D software to analyze the flow patterns and sediment exchange in the Anzali Wetland-Port (AWP) system. The simulations utilized the two-dimensional coupled flow, sediment, and morphology modules in the curvilinear version of Delft3D. The computational domain consisted of nine subdomains with 10,963 elements and 17,531 nodes, with a higher resolution grid in the northern port channel where calibration data were available. The model was calibrated for the period from October 31 to December 11, 2019, using measured data on daily water and sediment discharge into the system. The hydrodynamic module was calibrated by adjusting the bed roughness and turbulence viscosity coefficients, with results showing good agreement with measured velocities, especially during flood periods. For the morphology module, sediment transport parameters were calibrated based on sediment concentration and erosion/sedimentation patterns observed during the same period. The model predicted 45,000 m³ of sedimentation, which closely matched the measured 49,000 m³. Simulations were validated against measured bed level changes, showing good agreement during the calibration period. The calibrated model was applied to evaluate the impact of port development on wetland sedimentation. The results highlight the natural sediment flushing during floods, which may help reduce sediment accumulation at the piers, and provide insights into managing sediment transport in the AWP system. Results and Discussion: The calibrated Delft3D model was applied to assess two key issues: the sediment balance of the Anzali Wetland-Port (AWP) system and the impact of port development on wetland sedimentation dynamics. 1. Sediment Balance of the AWP System Simulation results reveal that the AWP system is experiencing critical sedimentation, especially within the Wetland’s floodplains. Analysis of sediment transport from incoming rivers showed a total annual inflow of approximately 661,000 m³ of sediment. Of this, 286,000 m³ is transported from the Wetland to the Port, and 237,000 m³ eventually reaches the sea. This implies a net annual sedimentation of 375,000 m³ (57%) within the Wetland and 49,000 m³ (7%) within the Port, while the remaining 36% is flushed out to the sea. The spatial pattern of sedimentation suggests that the Wetland acts as a sediment trap, with most deposition occurring in broader floodplain areas, while localized erosion is observed at the Wetland-Port boundary and within the Port itself. 2. Impact of Port Development on Sedimentation To evaluate the influence of recent Port development, especially the construction of the western breakwater, a scenario with modified geometry, facilitating flood outflow into the sea, was simulated. The new configuration involved shortening the breakwater and closing the west wing of the eastern basin to form a more direct outflow channel. This simulated results of this scenario was compared to current conditions. The results indicate that while the modification does not significantly change sedimentation within the Wetland, it substantially reduces sedimentation within the Port area—by nearly 90%. This suggests that these modifications in port layout can significantly improve sediment management and reduce dredging needs. Conclusion: A depth-averaged coupled hydrodynamic and sediment transport model was developed and validated for the AWP system using Delft3D. The model reliably simulates flow and sediment dynamics, with sediment transport being highly sensitive to physical parameters and primarily driven by flood events. Results indicate that approximately 57% of riverine sediments deposit in the Wetland, 7% in the Port, and 36% are discharged into the sea. While port geometry modifications do not impact Wetland sedimentation, they can reduce Port sedimentation by up to 90%, highlighting the effectiveness of structural interventions in sediment management. Acknowledgment This article is derived from the first Author's M.Sc. thesis and further, based on the project "Research Studies to Examine the Sedimentation Status in the Iran Commercial Ports," which was commissioned by the Ports and Maritime Organization of Iran and carried out by Khakbaft Consulting Engineers. The above is expressed as a means of acknowledgement and appreciation. تالاب انزلی، واقع در سواحل شمالی ایران، یکی از تالاب‌های بین المللی است که از سال ۱۹۷۵ در کنوانسیون رامسر به ثبت رسیده است. این تالاب بخشی از یک سامانه هیدرولیکی گسترده است که از جنوب توسط چندین رودخانه‌ تغذیه شده و از شمال، از طریق یک دهانه رودخانه‌ای به دریای خزر متصل می‌شود. یکی از چالش‌های پیش‌روی این منطقه، بررسی تأثیر توسعه‌های جدید بندری بر رسوب‌گذاری در تالاب انزلی است. برای پاسخ به این مسئله، یک شبیه‌سازی عددی با استفاده از مدلسازی دوبعدی جریان و انتقال رسوب به کمک بسته نرم افزاری Delft3D انجام شد تا الگوی جریان، انتقال رسوب و تغییرات بستر در سامانه تالاب–بندر انزلی بررسی شود. در این مدل، داده‌های هیدرولوژیکی و اندازه‌گیری سرعت جریان برای واسنجی و صحت‌سنجی مدل استفاده شد. اطلاعات به‌دست‌آمده از عملیات لایروبی و پایش‌های هیدروگرافی پیاپی نیز برای تعیین الگوهای رسوب‌گذاری و فرسایش در ناحیه بندر و تنظیم مدل مورفولوژی به‌کار رفت. نتایج نشان می‌دهد که حدود ۵۷٪ از رسوبات ورودی به سامانه تالاب –بندر انزلی در تالاب ته نشین شده، ۷٪ در حوضچه‌های بندر رسوب می‌کند، و ۳۶٪ به وارد دریای خزر می‌شود. همچنین، تغییر هندسه موج‌شکن بندر تاثیر قابل‌توجهی بر افزایش رسوب‌گذاری در تالاب نداشته‌، اما می‌تواند رسوب‌گذاری در محدوده بندر را تا ۹۰٪ کاهش دهد.

https://jhyd.iha.ir/article_233944_93b99c04fcfd363eeef983172fb4032a.pdf

انجمن هیدرولیک ایران نشریه علمی هیدرولیک 2345-4237 20 4 2025 12 22 A Review of the Performance of Inclined and Vertical Drops on Effective Hydraulic Parameters and Energy Dissipation Mechanism مروری بر عملکرد شیب‌شکن‌های مایل و قائم بر پارامترهای هیدرولیکی موثر و مکانیزم استهلاک انرژی 71 93 233943 10.30482/jhyd.2025.518770.1729 FA فرهود کلاته گروه آب و سازه های هیدرولیکی، دانشکده مهندسی عمران، دانشگاه تبریز، تبریز ، ایران 0000-0001-5192-9408 احسان امین وش دانشجوی دکتری آب و سازه های هیدرولیکی، دانشکده مهندسی عمران، دانشگاه تبریز، تبریز، ایران. 0000-0001-8901-2232 رسول دانشفراز استاد گروه مهندسی عمران، دانشکده فنی و مهندسی، دانشگاه مراغه، مراغه، ایران. 0000-0003-1012-8342 Journal Article 2025 04 28 Introduction Drop structures are widely used hydraulic constructions in water supply networks, irrigation and drainage channels, sewage treatment systems, and erosion control infrastructures. These structures dissipate the flow energy primarily via a hydraulic jump occurring downstream, with substantial energy dissipation also occurring when the flow plunges from the structure's edge before reaching the hydraulic jump. Inclined drops, specifically, are implemented in drainage and irrigation canals, as well as mountainous areas where the constructed channel slope is milder than the natural terrain slope. They are effectively employed to transfer flow from higher elevations to lower levels, simultaneously dissipating excess kinetic energy. Considering the engineering importance of energy dissipation in hydraulic infrastructures, this study aims to provide researchers with a comprehensive overview of inclined and vertical drop structures, highlighting their effectiveness in dissipating kinetic energy through supplementary structural arrangements. Pagliara and Chiavaccini (2006a, b) investigated the effects of base materials and reinforced block ramps on flow energy dissipation, while Pagliara et al. (2008) explored submerged flow conditions over reinforced slopes constructed with rigid blocks. Methodology This review systematically followed these stages: 1. Identification and review of literature on inclined drop structures. 2. Identification and review of literature on vertical drop structures. 3. Investigation of previous studies focused on energy dissipation mechanisms. 4. Analysis and synthesis of findings from steps (1), (2), and (3). 5. Examination of various stilling basin designs associated with drop structures. 6. Evaluation of auxiliary structures and their role in energy dissipation within drop structures. Despite the limited number of studies explicitly targeting drop structures, substantial research exists on spillways. Although spillways and drops share similar functional objectives, their hydraulic and geometric characteristics are notably different. Generally, drop structures are restricted to heights that do not exceed roughly 4 meters, while spillways can greatly exceed this height limitation. Literature review revealed that comprehensive research on drop structures mainly emerged after 2012, with a notable concentration of studies conducted between 2018 and 2023. The literature reviewed in this research was sourced from recognized academic databases, including Google Scholar, Science Direct, CAS, and various esteemed publishers such as Elsevier, Springer, Taylor & Francis, and MDPI. In total, 49 articles spanning the years 1932 to 2023 were critically assessed, with the majority reflecting recent research advances. Results and Discussion Analysis of inclined, vertical, and stepped drops revealed critical insights into their hydraulic performance and energy dissipation capabilities. Results indicated that relative energy dissipation generally decreases with increasing relative critical depth and decreasing channel slope angles for flow rates ranging between 3.31 and 3.5 liters per second. Comparative analysis demonstrated that under identical geometric and hydraulic conditions, vertical drops exhibited the highest relative energy dissipation, followed by stepped and inclined drops. The relatively lower energy dissipation observed in inclined drops is primarily attributed to the absence of a substantial plunge pool and jet formation, resulting in diminished structural energy dissipation. An essential factor influencing energy dissipation efficiency is the relative height of drop structures. Lower heights in stepped drops inhibit the formation of fully developed two-phase (air-water) flows, reducing their energy dissipation capacity compared to vertical drops. In vertical drops, substantial energy dissipation occurs due to significant drop heights, the formation of plunge pools, and pronounced two-phase flows. The inclined drop configurations examined typically involved slopes of 26.56° and 33.7°, highlighting their sensitivity to structural angle variations in terms of energy dissipation. Conclusion Drop structures are vital components in systems designed to transfer water flow from higher to lower elevations, serving key roles in flood control and water supply management. Among the various drop configurations, vertical drops with adequately designed stilling basins demonstrate superior energy dissipation capabilities. As such, vertical drops remain highly desirable within hydraulic engineering practice. Conversely, inclined drops transfer flows downstream more rapidly due to their structural geometry, relying heavily on hydraulic jumps to dissipate energy. However, critical areas such as cavitation risks, pressure, and velocity distribution remain largely understudied for both inclined and vertical drop structures. Future research is required to address these knowledge gaps comprehensively, ultimately contributing to safer, more efficient hydraulic structure designs. Keywords: Inclined drop, vertical drop, stepped drop, energy dissipation, stilling basins, hydraulic structures. References Pagliara, S., & Chiavaccini, P. (2006a). Energy dissipation on block ramps. Journal of Hydraulic Engineering, 132(1), 41-48. Pagliara, S., & Chiavaccini, P. (2006b). Flow resistance of rock chutes with protruding boulders. Journal of Hydraulic Engineering, 132(6), 545-552. Pagliara, S., Das, R., & Palermo, M. (2008). Energy dissipation on submerged block ramps. Journal of irrigation and drainage engineering, 134(4), 527-532. Results and Discussion By examining different types of drops with common geometries, including inclined, vertical and stepped drops has been conducted. The results obtained show a decrease in relative energy dissipation with an increase in relative critical depth and a decrease in the channel angle in the flow rate range of 3.5-3.31 liters per second. A comparison of the anodic dissipation in the range of variables of the present study shows that under equal geometric and hydraulic conditions, the maximum amount of relative energy dissipation is allocated to the vertical drop, with stepped and inclined drops in the second and third place, respectively. The reason for this is that in inclined drops, due to the lack of formation of a pool and a falling jet, the energy dissipation caused by the structure itself is much lower than that of other drops. One of the most important parameters that increases energy dissipation is the relative height of the structure. The low height of stepped drops prevents two-phase flow of water and air from occurring on the steps, which is a factor in the low depreciation compared to vertical drops. While in vertical drop, due to the flow falling from a high height and the formation of pools and two-phase flows, more energy will be taken from the flow. For the inclined drop used in the research, they are from two angles with values of 26.56 and 33.7 degrees. Conclusion در کانال‌های آبیاری و زهکشی عموما برای انتقال آب از تراز ارتفاعی بالاتر به تراز پایین‌تر از شیب‌شکن‌ها استفاده می‌گردد. شیب‌شکن‌های قائم و مایل به‌عنوان سازه‌های هیدرولیکی مؤثر در مهار انرژی جنبشی جریان، نقشی کلیدی در کنترل فرسایش بستر و کاهش خسارات پایین‌دست دارند. این مقاله مروری به بررسی مقایسه‌ای عملکرد این دو نوع شیب‌شکن در استهلاک انرژی جریان پرداخته و مکانیزم اصلی اتلاف انرژی یعنی برخورد جت ریزشی جریان با بستر پایین‌دست و تشکیل پرش هیدرولیکی را تبیین می‌نماید. نتایج تحقیقات نشان می‌دهد که شیب‌شکن‌های قائم در شرایط مشابه نسبت به شیب‌شکن‌های مایل، به‌طور متوسط ۲۰ تا ۳۵ درصد استهلاک انرژی بیشتری ایجاد می‌کنند. نتایج نشان داد که مدل ترکیبی با ایجاد اغتشاشات مؤثر در بستر جریان، موجب افزایش میانگین استهلاک انرژی به میزان 3/74٪ در شیب‌شکن قائم و 6/49٪ در شیب‌شکن مایل در مقایسه با مدل پایه شد. همچنین، استفاده از المان‌هایی مانند زبری و صفحات مشبک به ترتیب باعث کاهش طول پرش هیدرولیکی به میزان 22٪ و 31٪ گردید. در تحلیل نهایی، علاوه بر کاویتاسیون، به خلأهایی چون عدم پایداری جریان، کمبود داده‌های میدانی و فرسایش موضعی در شیب‌شکن‌ها نیز اشاره شده است.. اگرچه تمرکز اصلی این مطالعه بر مرور مطالعات شیب‌شکن‌های مایل و قائم است، اما در جریان تحلیل‌ها، برخی زمینه‌های مغفول‌مانده نظیر پدیده‌ی کاویتاسیون، کمبود داده‌های میدانی در خصوص رفتار جریان در دبی‌های بالا، تاثیر بلند مدت پارامترهای هندسی بر پدیده‌های هیدرولیکی نیز به‌عنوان خلأهای تحقیقاتی قابل‌توجه نمایان شدند که می‌توانند در مطالعات آینده مورد توجه بیشتری قرار گیرند.

https://jhyd.iha.ir/article_233943_ce385f8d25ec2d6100c486c7e4ea3689.pdf

انجمن هیدرولیک ایران نشریه علمی هیدرولیک 2345-4237 20 4 2025 12 22 Mathematical and laboratory model investigation of linear proportional sharp edge spillways بررسی مدل ریاضی و آزمایشگاهی سرریزهای لبه تیز متناسب خطی 95 108 233945 10.30482/jhyd.2025.524113.1736 FA سهراب نظری استادیار گروه مهندسی عمران، واحد اقلید، دانشگاه آزاد اسلامی، اقلید، ایران 0000-0002-9446-5057 محمد کریمی چهارطاقی گروه مهندسی عمران 0000-0001-8337-1752 Journal Article 2025 05 17 Introduction Weirs are simple devices used to measure flow in open canals and ducts. Generally, the geometric cross section of the weirs is rectangular, trapezoidal and triangular. The discharge - height relationship in this type of weirs is nonlinear. The geometry of sharp weirs generally follows a mathematical equation. The governing mathematical equation can also be expanded based on the Gamma function and the Abel integral. The first idea to design the body shape of the weir was proportionally and linearly completed by Stout, 1897 and later by Sutro, 1908. Sutro weir (proportional) consists of a combination of a rectangular section and a special curve. The discharge-height relationship in the Sutro weir is linear and proportional. Sutro type weirs are used to measure discharge in various industries, including chemical industries, wastewater transmission and treatment, and water transfer channels in irrigation and water supply. The geometric dimensions of the base rectangle affect the shape of the curve and the flow rate. Methodology In this study, by examining the governing equations and using the expansion of gamma and Abel integral functions, the design equations of sharp overflow body were extracted. The amount of flow through this type of overflow is also a function of hydraulic conditions and geometry of the weir shape body. In this regard, the flow rate passing through these types of weir is important. Dimensional analysis of dimensional factors affecting the Cd discharge coefficient was identified and tested in the laboratory by making 12 different samples of Sutro weir with different dimensions. To make Sutro weir, first using Excel software and placement in the extracted equation, the coordinates of the overflow body are extracted and then using AutoCAD software, the body of the weir is drawn and using a laser cutting machine on aluminum plates perforate with a thickness of 2 mm with precision. Suitable for engraving and cutting. For experiments in the hydraulic laboratory of Eghlid Islamic Azad University, a laboratory channel with a length of 6 meters, width and height of 100 and 60 cm, respectively, with a water circulation system was used. The weirs were installed at the end of the canal and a level gauge with an accuracy of 0.10 millimeter was used to measure the depth above the weir where the water level was completely horizontal. To measure the flow, a Megap magnetic flowmeter with an accuracy of 0.001 liter per second installed in the main transmission pipeline and a standard trapezoidal weir calibrated and installed on a reservoir at the end of the system were used. By establishing the flow, flow and water depth on the weir were measured and finally in all conditions, using the governing relations, the experimental coefficient of flow of each of the weir was extracted. Results and Discussion This study conducted to determine the discharge coefficient in the Sutro weir. Dimensional analysis of dimensionless factors affecting the Cd discharge coefficient was identified. Flow rate (Q) diagrams were plotted against the parameter [H-1/3 a] for all experiments. In all graphs, a linear relationship with a correlation coefficient of R2 was observed to be appropriate and near one. The results of dimensional analysis of the parameters affecting the discharge coefficient are as follows equation. C_d=Q/(2√2g Wa^(1/2) )=f_2 (h/W,h/P,h/a,h/((2W+a)),h/(h+P),R_e,W_b,F_r ) The above dimensionless parameters were calculated for all experiments. In order to evaluate the priority of the effect of dimensionless parameters using SPSS-21 software, this was done first. The results showed that the most effect is related to the dimensionless parameter H / w. Of course, the parameters H / (P + H) and Fr are also in the next priority. Therefore, in the next step, regression model analysis was performed between these three parameters and Cd coefficient. Finally, using multivariate regression, the relationship between flow coefficient and dimensionless parameters was extracted. All tests were performed under turbulent flow conditions. Weber number was also calculated, this number is the measure of the effect of surface tension. The effect of this parameter can be ignored in situations where the water depth is more than about 2 to 3 cm. In addition, the Approach velocity and velocity head were calculated. The results showed that the effect of approaching velocity could also be ignored. Conclusion In this research, using the Abel integral function and the expansion of the gamma function in the design of the body shape of the weirs were studied. The first idea to design the body of the overflow was proportionally and linearly completed by Stout, 1897 and later by Sutro, 1908. Various studies have been performed by different researchers in this field, each of which provided equations according to the basic constraints of the weirs. This amount can be determined in the laboratory by making the desired weir and performing the test. In this research, a linear proportional type overflow was made and tested. The analysis of the experiments showed that the value of the weir coefficient discharge in these conditions is equal to 0.620 on average. Keywords Linear Proportional Weir, Discharge Coefficient, Abel Integral Function, Gamma Function. سرریزهای متناسب خطی(ساترو) دسته ای از سرریزهای لبه تیز هستند که به دلیل حساسیت کم نسبت به تغییر عمق بالادست از دقت نسبتا بالایی برخوردار میباشند و رابطه میان دبی و عمق آب خطی است، در این پژوهش بر اساس مبانی نظری موجود ابتدا معادلات ریاضی حاکم بر سرریزها توسط بسط تابع گاما و انتگرال ابل استخراج گردید. در شرایط کاربردی مقطع تئوری با ترکیب یک مقطع مستطیلی پایه اصلاح گردید. به منظور بررسی تجربی و آزمایشگاهی حساسیت هیدرولیکی مقطع اصلاح شده تعدا 12 مدل با عرض و ارتفاع مستطیل پایه مختلف طراحی وساخته شد. در آزمایشگاه هیدرولیک برای بررسی تناسب رابطه عمق و جریان عبوری تعداد حدود 450 آزمایش با دبی 2.5 الی 35 لیتر در ثانیه و اندازه گیری عمق انجام گرفت. نتایح حاصل نشان داد که در تمام مدلهای مورد مطالعه رابطه دبی – عمق به صورت خطی و ضریب جریان عبوری تابعی از نسبت های بدون بعد عمق آب به ارتفاع تاج سرریز و عدد فرود می باشد. با استفاده از بخش عمده ای از داده های آزمایش و پارامترهای بی بعد رابطه ای جهت ضریب حریان عبوری استخراج گردید. مقایسه نتایج حاصل از رابطه بدست آمده با نتایج آزمایشگاهی نشان داد که میزان خطای نسبی موجود در حد فاصله ∓5%می باشد.

https://jhyd.iha.ir/article_233945_8ac6201e360fe2250ecef7331a450905.pdf

انجمن هیدرولیک ایران نشریه علمی هیدرولیک 2345-4237 20 4 2025 12 22 Evaluation of LRR Model in Numerical Simulation of Wall-Jet with Circular Nozzle ارزیابی مدل LRR در شبیه‌سازی عددی جت دیواره با مقطع دایروی 109 121 233947 10.30482/jhyd.2025.523942.1737 FA مهدی عزیزی‌پور دانشکده مهندسی عمران و محیط زیست، دانشگاه صنعتی امیرکبیر، تهران، ایران. 0009-0007-7881-8805 بابک خورسندی دانشکده مهندسی عمران و محیط زیست، دانشگاه صنعتی امیرکبیر، تهران، ایران. میثم بالی دانشکده مهندسی عمران و محیط زیست، دانشگاه صنعتی امیرکبیر، تهران، ایران. 0009-0004-8602-6953 Journal Article 2025 05 24 Introduction Three-dimensional wall-jets have received attention due to their wide range of applications, such as film cooling or effluent discharges into hydrosphere. One of the main characteristics of these type of jets is high lateral to vertical spread ratio. Viets and Sforza (1966) showed potential core will be dissipated as stream-wise distance increase. Sforza and Herbst (1970) found that at far enough distances, the expansion rate and velocity decay are independent of nozzle geometry. Rajaratnam and Pani (1974) showed that nozzle caused no major influence on jet behavior at far region, whereas, Davis and Winarto (1980) found that nozzle-to-wall distance affects the rate of velocity decay and the rate of velocity development in lateral plan. Launder and Rodi (1983) results showed stream-wise vortices are the primary contributors to secondary flows. Later, Eriksson et al. (1998) and Padmanabham and Lakshmana Gowda (1991), investigated the influence of presence of confining walls. Moreover, Agelin-Chaab and Tachie (2011) demonstrated the independency of expansion rate and decay rate of velocity from the Reynolds number. In this research, application of LRR turbulence model have been studied. By calculating velocity field, results compared to experimental data, such as maximum velocity decay, velocity profiles and spread rates. Methodology The governing equations for three-dimensional wall-jet consist of the conservation of mass and momentum equations, as presented in Equations (1) and (2). The Launder–Reece–Rodi (LRR) turbulence model was employed in this study to address a research gap in the literature. Unlike two-equation models such as k-ϵ, this turbulence model is not based on the Boussinesq hypothesis. The numerical simulations were conducted using OpenFOAM, an open-source software, with appropriate boundary conditions and numerical algorithms, which are briefly discussed in Sections 2.2 and 2.3, respectively. Furthermore, additional details regarding the simulation configuration in OpenFOAM, including the discretization methods for different parameters, are also provided. It should be noted that a schematic representation of the computational domain is depicted in Figure 1. Results and Discussion In this research, the assessment of the LRR turbulence model in simulating a three-dimensional wall jet is discussed in Section 3. The jet discharges fluid from a circular nozzle into a rectangular domain with a quiescent ambient. Earlier studies has demonstrated that the presence of an impermeable wall near the nozzle exit affects the flow structure, causing it to develop asymmetrically which is shown in Figure 4. To evaluate the accuracy of the LRR turbulence model in predicting the characteristics of the jet, some important parameters which computed numerically, compared with experimental data. These parameters are the decay rate of maximum velocity along the nozzle axis, the velocity distribution profiles in both vertical and lateral directions, and the half-width variations in the horizontal and vertical planes, which shows how much velocity spreads. As depicted in Figure 3, maximum velocity decay rate, which can be approximated by Equation (3), was found to be higher than the values reported in literature. However, despite this discrepancy, the general trend remains consistent with experimental data. Figures 5 and 6, exhibit a strong correlation between the vertical and horizontal velocity profiles with measured data, indicating that the numerical model provides sufficient accuracy in prediction of velocity filed. To further analyzing of the spreading characteristics of the velocity field, the vertical and horizontal half-widths were plotted against the stream-wise distance from the nozzle exit. The results showed that the vertical spread rate agreed with the range of experimental data only for x/d > 20, whereas the lateral velocity spread, particularly in the range 10 < x/d < 40, demonstrates excellent agreement with experimental measurements data. Overall, these findings confirm that the LRR turbulence model is a reliable model for predicting the flow behavior of three-dimensional wall jets discharged from a circular nozzle in a quiescent ambient. Conclusion In present research, three-dimensional wall-jet was simulated numerically. The LRR turbulence model was employed. To evaluate its performance in predicting the velocity flow field numerical results compared to experimental data. Results indicated rate of velocity decay was higher than the experimental measurements but qualitatively acceptable. The lateral and vertical velocity profiles were computed with high accuracy. Som. Moreover, lateral spreading rate, which is one of the most important parameters in studying three-dimensional wall jets, was predicted well within the range of previous studies. جت‌های دیواره‌ آشفته دایروی به دلیل کاربردهای گسترده‌ای که در پدیده‌های مهندسی دارند، بسیار مورد توجه قرار گرفته‌اند. یکی از مدل‌های آشفتگی که کم‎‌تر مورد توجه پژوهشگران علاقه‌مند به این دسته از جت‌های آشفته قرار گرفته، مدل آشفتگی LRR است که دقت بالاتری نسبت به دیگر مدل‌های آشفتگی در محاسبه میدان جریان‌های ثانویه و چرخشی دارد. با این وجود، به دلیل دشواری در رسیدن به راه حل پایدار و حساسیت بالا به شرایط مرزی و شبکه بندی، توجه کم‌تری به خود جلب کرده است. در مطالعه حاضر با استفاده از مدل آشفتگی LRR، مدل‌سازی عددی میدان جریان در اطراف جت دیواره‌ آشفته دایروی به صورت سه بعدی مورد بررسی قرار گرفته است و نرخ تغییرات سرعت حداکثر، پروفیل‌های قائم و عرضی و نرخ توسعه جت درناحیه خود متشابه یا کاملا توسعه یافته در هر دو راستا مطالعه شد. نتایج محاسبات نشان می‌دهد که مدل LRR در مقایسه با نتایج آزمایشات تجربی در پیش‌بینی ساختار جریان در اطراف جت دیواره دقت قابل قبولی دارد.

https://jhyd.iha.ir/article_233947_a4dc95c2181008bef3f0d2a2c028555b.pdf

انجمن هیدرولیک ایران نشریه علمی هیدرولیک 2345-4237 20 4 2025 12 22 Assessment of Legal Riverbed Boundary Delineation for Natural Streams Branched from Rivers in Floodplains Using a Hydraulic Analysis Approach: A Case Study of the Shahrstan Stream بررسی نحوه تعیین حد بستر قانونی نهرهای طبیعی منشعب از رودخانه در سیلاب‌دشت‌ها با رویکرد تحلیل هیدرولیکی - مطالعه موردی نهر شهرستان 123 136 233948 10.30482/jhyd.2025.524426.1738 FA سوران عزتی دانشکده مهندسی عمران/ دانشگاه تربیت مدرس 0009-0003-3539-0571 ضیا ایدی دفتر مهندسی رودخانه/ شرکت آب منطقه‌ای البرز سید حسین مهاجری استادیار، دانشگاه خوارزمی 0000-0002-8056-293X Journal Article 2025 05 20 Introduction Determining legal riverbed boundaries in low-gradient floodplain environments is a persistent challenge, particularly in regions where traditional delineation relies on administrative or geomorphological approximations rather than hydraulic criteria. The Shahrstan Stream, a natural distributary of the Jajrood River in Tehran Province, exemplifies such a case. The Eastern Regional Water Authority designated a 600-meter-wide legal bed for the Shahrstan Stream near Abasabad village, an estimate that has sparked controversy due to its excessive breadth and apparent disconnect with hydraulic realities. To address this discrepancy, the current study investigates the hydraulic validity of various bed width scenarios for the Shahrstan Stream using a simple but robust analytical method. Instead of relying on conventional width estimation, the study adopts a performance-based approach focused on hydraulic behavior, specifically the ability of each width to sustain flood flows with sufficient flow energy. The Australian flood energy criterion (velocity × depth ≥ 0.3 m²/s) is used as the threshold for identifying active flood-conveying sections. The objective is to develop a scientifically grounded, technically defensible estimate for the legal riverbed width of a disturbed floodplain stream, an approach that promotes more accurate and replicable outcomes in future river management decisions. Methodology This study applies Manning’s hydraulic equation to evaluate the flood-carrying capacity of the Natural Shahrstan Stream under five proposed riverbed widths: 100, 200, 300, 400, and 600 meters. Given the extensive morphological changes and insufficient elevation precision in the study area, two-dimensional modeling was deemed impractical. Instead, a simplified analytical approach was adopted to assess stream hydraulics. The 25-year design flood discharge of the Jajrood River was estimated at 389 m³/s. Based on satellite imagery and relative inundation areas, this value was proportionally reduced to approximately 39 m³/s for the Shahrstan Stream. SPOT satellite data from 1986 and legal documentation from the Iran Water Resources Management Company and Sazeh Pardazi Iran Consulting Engineers supported the spatial and hydrological assessment. For each width scenario, Manning’s formula was used to calculate average flow velocity, depth, and discharge. The hydraulic validity of each scenario was evaluated against the Australian standard flood energy threshold (velocity × depth ≥ 0.3 m²/s), a widely accepted criterion for determining active flood channels. The approach emphasizes practicality and replicability in similar floodplain contexts lacking high-resolution data. It integrates both hydrological theory and regulatory frameworks to yield a rational estimate for the legal riverbed boundary, as stipulated by Bulletin No. 307. Results and Discussion The hydraulic analysis demonstrated that the 600-meter bed width, as designated by the water authority, is a substantial overestimate. At a flow depth of 1 meter, this width would produce a discharge of approximately 1330 m³/s—more than 34 times the estimated 25-year design discharge of 39 m³/s. Adjusting the flow depth to align with the target discharge requires a depth of just 12 cm, which yields a velocity–depth product of 0.065 m²/s. This value falls far below the minimum energy criterion, indicating insufficient hydraulic function. The intermediate widths—400, 300, and 200 meters—likewise failed to meet both the design discharge and the minimum energy threshold. Although deeper flows improved energy levels, they also produced excessive discharges inconsistent with the natural capacity of the stream, and shallower flows remained under-energized. In contrast, the 100-meter width demonstrated ideal hydraulic behavior. At a depth of 0.3 meters, the stream reached a velocity of 0.99 m/s and a discharge of 29.76 m³/s. This configuration achieved the target velocity–depth threshold of 0.3 m²/s while approaching the design discharge, offering a balanced and defensible estimate of the stream's legal riverbed. Higher flow depths further confirmed the flexibility of the 100-meter configuration, yielding discharges up to 219 m³/s, without violating hydraulic constraints. These findings align with international practices in floodplain delineation and emphasize the importance of integrating flow energy criteria into legal and technical assessments. Unlike the traditional approach based solely on width extrapolation, this method offers a rational and replicable solution for disturbed floodplain systems. It also validates the use of simplified hydraulic models in settings where complex simulation is not feasible but regulatory compliance is essential. Conclusion This study confirms that the 100-meter riverbed width is the only configuration that satisfies both the hydraulic energy threshold (velocity × depth ≥ 0.3 m²/s) and the 25-year design discharge (~39 m³/s). Wider widths (200 to 600 meters) either generate unrealistically high discharges or insufficient flow energy, making them incompatible with the hydraulic behavior of the Shahrstan Stream. Therefore, the 100-meter width stands out as the most technically and legally appropriate boundary, offering a model approach for future delineation efforts under Bulletin No. 307 in similar disturbed floodplain environments. یکی از چالش‌های تعیین حد بستر قانونی نهرها در کشور، مربوط به نهرهایی است که بستر آنها به شکل سنتی و بدون مدل‌سازی هیدرولیکی تعیین شده است. در پژوهش حاضر، با تمرکز به حد بستر قانونی نهر شهرستان (یکی از انشعابات رودخانه جاجرود) تفاوت بستر تعیین شده به شکل سنتی با رویکرد هیدرولیکی و بر اساس راهنمای پهنه‌بندی سیل و تعیین حد بستر و حریم رودخانه (نشریه شماره 307) بررسی می‌گردد. به منظور مدل‌سازی و برآورد دبی سیلاب نهر شهرستان و پهنه‌های سیلگیر رودخانه در حالت طبیعی، از تصاویر ماهواره SPOT مربوط به سال 1365 استفاده شد. پنج عرض بستر (600، 400، 300، 200، و 100 متر) بررسی و پارامترهای هیدرولیکی شامل سرعت، دبی و حاصل‌ضرب سرعت و عمق محاسبه شدند. مطابق توصیه نشریه 307 معیار استاندارد استرالیا با آستانه سرعت × عمق ≥ 0.3 مترمربع بر ثانیه برای شناسایی عرض بستر به‌کار رفت. نتایج مدل‌سازی نشان داد که دبی عبوری از نهر حدود 10 درصد کل دبی سیلاب رودخانه جاجرود است. به علاوه مشاهده شد که عرض بستر 100 متری، با دبی نزدیک به دبی سیلاب 25 ساله و انطباق با معیار انرژی جریان، عرض مناسب بستر نهر شهرستان می باشد. این مطالعه نشان داد که روشی عملی پیشنهاد شده در نشریه شماره 307 برای تعیین عرض بستر رودخانه های سیلابدشتی و کم شیب در شرایط بستر دستخورده از دقت مناسبی برخوردار است و می توان آن را در پروژه های مشاوره ای به کار برد.

https://jhyd.iha.ir/article_233948_c3b25b52cd61d38328108605a54d0955.pdf