Document Type : Research Paper
Authors
Department of Water Engineering, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran.
Abstract
Keywords
Main Subjects
The geometry and morphological evolution of river cross-sections are among the most critical and influential aspects of water and river engineering. They have a direct impact on river management, planning, and overall ecological health. Achieving the optimal river cross-section is a key structural intervention for sustainable river management and plays a significant role in flood control and the reduction of life and property losses. Cross-sectional geometry and hydraulic flow characteristics must be regularly assessed under different flow conditions for scientific, engineering, and management purposes. Therefore, hydraulic modeling is indispensable to acquire precise geometric and hydraulic data and serves as a foundational step toward achieving optimal river conditions.
In this study, hydraulic modeling was performed using the HEC-RAS software for a section of the Zayandehrud River in Iran. This river originates from the Zagros Mountains in the north of Chaharmahal and Bakhtiari Province, flows westward into Isfahan Province, passes through the city of Isfahan, and eventually empties into the Gavkhouni Wetland. The simulation was conducted as a one-dimensional, unsteady flow model for a flood event with a 25-year return period and a discharge of 521 m³/s, aimed at evaluating floodplain inundation and its impacts on surrounding lands. Subsequently, using a defined objective function and relevant constraints, the Secretary Bird Optimization Algorithm (SBOA) was employed to optimize dredging volumes while maintaining hydraulic stability. A novel metric, the Optimum Cross-Section Index (OCI), was applied to evaluate the degree of deviation of each cross-section from its ideal state. The OCI provides a numerical value reflecting how close each section is to optimal hydraulic performance.
The flood simulation results highlighted significant inundation in floodplains across the study area, underscoring the necessity of channel modification. The hydraulic model provided key geometric parameters such as cross-sectional area, depth, width, wetted perimeter, and hydraulic radius. The trends in these geometric parameters were analyzed using correlation coefficients. Notably, river depth and width did not change uniformly from upstream to downstream. A comparison between the first and last stations showed a 441.56% increase in width and a 55.02% decrease in depth. Based on the analysis of 12 stations, including 120 cross-sections (10 cross-sections per station) of the Zayandehrud River, the final optimized dredging volume after 1,000 iterations was calculated to be 59765160 cubic meters. The correlation coefficient of the OCI index along the river length was 0.71, indicating a weak but increasing trend downstream. The OCI values ranged from 1.01 to 1.53 from upstream to downstream, highlighting a growing deviation from optimal geometry in the lower reaches of the river.
An assessment of depth and width trends revealed a significant decrease in depth and an increase in width downstream, likely due to the river's high sediment transport capacity. The total pre-dredging volume of the stations was 46,369,050 m³, while after dredging, the average total volume in the cross-sections reached 59,765,160 cubic meters. This improvement enhanced the flow capacity of the Zayandehrud River by 28.89%. Furthermore, the OCI index was closer to the optimal value in the upstream regions. As the river progressed downstream, optimal cross-sectional area requirements increased, as did the need for dredging. The OCI value rose by 1% to 53%, indicating a significantly growing deviation from optimal hydraulic geometry in the lower segments of the river.
“Conceptualization, Mohammad Mahdi Malekpour, Mohammad Mehdi Ahmadi, Kourosh Qaderi, and Yousef Rajabizadeh.; methodology, Mohammad Mahdi Malekpour, Mohammad Mehdi Ahmadi, and Kourosh Qaderi.; software, Mohammad Mahdi Malekpour.; validation, Mohammad Mahdi Malekpour and Mohammad Mehdi Ahmadi.; formal analysis, Mohammad Mahdi Malekpour.; investigation, Mohammad Mehdi Ahmadi and Kourosh Qaderi.; resources, Yousef Rajabizadeh.; data curation, Mohammad Mahdi Malekpour and Yousef Rajabizadeh.; writing—original draft preparation, Mohammad Mahdi Malekpour.; writing—review and editing, Mohammad Mehdi Ahmadi and Kourosh Qaderi.; visualization, Mohammad Mahdi Malekpour.; supervision, Mohammad Mehdi Ahmadi.; project administration, Mohammad Mehdi Ahmadi and Kourosh Qaderi.; funding acquisition, not applicable. All authors have read and agreed to the published version of the manuscript.”
All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.
Not applicable.
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The authors declare no conflict of interest.
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