Iranian Water Research Journal

Abstract Bridges are critical structures in river engineering, requiring robust protection against scour, a significant hydraulic concern. Scour around bridge piers, exacerbated by flood events of varying intensity and duration, poses a substantial risk of structural failure. Furthermore, the accumulation of floating debris around piers can significantly alter local flow dynamics and scour patterns. Understanding these phenomena under diverse conditions is paramount for accurate scour depth estimation and the development of effective bridge protection strategies.
One of the primary factors contributing to scour is the accumulation of floating debris around bridges, particularly near the piers. This debris reduces the flow cross-sectional area, thereby increasing the flow velocity beyond design thresholds. Consequently, especially in regions characterized by high-velocity water currents—such as mountainous and forested areas—the accumulation of floating debris causes a compounded increase in flow velocity, leading to severe scour. Thus, it is imperative to identify bridges susceptible to debris accumulation and implement mitigation measures, such as installing debris traps upstream of the bridge piers, to prevent excessive debris buildup.
This research investigates laboratory-scale scour around bridge pier groups under live-bed conditions, specifically examining the influence of pier arrangement and the presence of accumulated floating debris.
Methods The study analyzed pier groups consisting of 3, 5, and 6 piers, with a relative pier width (pier diameter to channel width ratio) of 1/10. A total of 18 experiments were conducted across two scenarios: with floating debris and without floating debris (control).
To eliminate the influence of channel walls on scour depth, the pier diameter should not exceed 10 percent of the channel width. Therefore, piers with a diameter of 6 cm (exactly 10 percent of the channel width) were utilized in these experiments. Tests were performed in a mobile-bed flume to evaluate how varying discharge rates (24, 39, and 54 L/s) affect scour dynamics. The experimental design aimed to demonstrate that increasing the relative flow velocity leads to greater scour depth and volume, and to quantify the significant exacerbation of scour caused by floating debris accumulation.
To prevent the influence of bed particle size on scour depth, the ratio of pier diameter to the mean sediment particle diameter was maintained at 50, in accordance with Chiew and Melville (1987). Furthermore, to eliminate the effect of sediment non-uniformity on scour reduction, the geometric standard deviation of the sediment was kept below 1.3. Consequently, a mean particle diameter of 0.96 mm was selected for this study.
Prior to initiating each experiment, the sediment bed surface was leveled using a trowel, and the area around the piers was precisely leveled using a laser level and a spirit level. The tailgate at the downstream end of the flume was fully raised to prevent initial scour and the formation of bed forms. Subsequently, the pump was started at a low discharge rate. After a few minutes, once the sediment was fully saturated, the discharge was gradually increased to the target flow rate. The previously closed tailgate was then slowly adjusted to establish the required water depth. After allowing several hours for the scour around the piers to reach an equilibrium state, the pump was shut down, and the water in theFlume was slowly drained. Following the cessation of flow, the topography around the pier group was measured using a non-contact Bed Profiler (Figure 5) to ensure accurate assessment. The 3D profile of the bed was acquired without any physical contact, achieving a measurement accuracy of 0.1 mm.
Results In the absence of floating debris, the maximum scour depths for the 3-, 5-, and 6-pier groups were recorded as 11.5 cm, 12.1 cm, and 14.8 cm, respectively. The 6-pier group exhibited a 22.31% increase in scour depth compared to the 5-pier group, and a 28.70% increase compared to the 3-pier group. Furthermore, the presence of floating debris resulted in a 35.14% increase in scour depth for the 6-pier group relative to the no-debris condition.
Conclusion Based on the conducted experiments and the obtained results, an empirical relationship for predicting scour depth was derived using dimensional analysis for the three investigated groups of cylindrical piers. Statistical validation, performed with the aid of SPSS software, confirmed the high accuracy of this relationship in predicting scour depth.

Abstract Introduction:
This study investigates, through laboratory experiments, the effects of a central baffle structure on the hydraulic characteristics of flow within a rectangular compound channel under two distinct hydraulic regimes: subcritical and supercritical. The primary objective is to analyze and evaluate the influence of flow obstruction caused by the central baffle on the flow pattern and its key parameters. Unlike previous research, which has predominantly focused on channels with simple cross sections, this study employs a rectangular compound channel equipped with a central baffle, thereby simulating more realistic conditions typically encountered in hydraulic engineering systems such as water conveyance channels, rivers, and water resources management structures. A deeper understanding of flow behavior in these more complex environments provides the scientific basis necessary for the optimal design of baffled structures, leading to improved hydraulic performance, reduced erosion, and enhanced efficiency of water systems. Focusing on both subcritical and supercritical regimes enables a comprehensive investigation of flow pattern variations and hydraulic parameters under different discharge and energy conditions.

Materials and Methods:
Experiments were conducted in the hydraulic laboratory of Shahrekord University using a rectangular compound channel equipped with a central baffle at a 1:50 scale. The flume measured 20 meters in length, 60 centimeters in width, and 60 centimeters in height, featuring transparent fiberglass walls and a metal bed. The experimental channel and central baffle were constructed with precise dimensions and carefully installed in the flume. The total length of the channel and the characteristics of its compound cross section complied with the experimental design. The central baffle, with specified geometric dimensions, glass material, and accurately defined installation location along the channel, was fixed using clamps and connectors to ensure stability without vibration or displacement. The water supply system and return pathway to the reservoir were configured to maintain steady selected discharges. The experimental program included five subcritical and five supercritical discharges. Three water depth measurement points were designated for each test: the beginning of the baffle, the center of the baffle, and the end of the baffle. For each discharge, water depths at these three points were recorded to examine depth distribution along the channel and the effect of the baffle on the water surface profile. In this research, parameters such as discharge, flow depth, average velocity, Froude number, and energy loss were accurately measured and recorded in the presence of the central baffle across different discharge ranges for both subcritical and supercritical regimes. The experiments were organized into two distinct categories based on flow regime: the subcritical regime (Froude number Fr < 1) with discharges ranging from 0.01057 to 0.025496 m³/s, and the supercritical regime (Fr > 1) with higher discharges ranging from 0.04896 to 0.108 m³/s. The central baffle, designed with standard geometric dimensions, was installed at a designated location within the channel. Measurements were performed using precise hydrometric instruments, including an Acoustic Doppler Velocimeter (ADV) for velocity measurements and water surface level sensors.

Results and Discussions:
The results of this study revealed the significant impact of the central baffle structure on the flow pattern within the rectangular compound channel across both hydraulic regimes. In the subcritical regime, as the discharge increased from 0.01057 to 0.025496 m³/s, the flow depth increased proportionally, indicating an increase in the total flow energy with higher discharge. The most significant depth increase occurred in the upstream regions due to backwater effects, while this trend was attenuated in shallower or lateral regions (at the outlet and the throat). In this regime, the baffle induced a backwater effect (h_1>h_3) and substantial hydraulic resistance, resulting in significant energy losses ranging from 74.2% to 77.9%. This energy dissipation was primarily attributed to form drag, intense turbulence, and local friction around the baffle, demonstrating its effectiveness in dissipating energy in low-velocity flows. The Froude number in this regime ranged from 0.140014 to 0.255311 (Fr< 1), and its mild increase with discharge indicated flow stability in the presence of the baffle. In contrast, in the supercritical regime, as the discharge increased from 0.04896 to 0.108 m³/s, despite the increase in depth and velocity, energy dissipation by the baffle decreased significantly (25.73% to 35.08%), and the flow tended toward more stable conditions. Phenomena such as standing waves and flow separation were observed in this regime. The Froude number ranged from 1.098702 to 1.25347 (Fr > 1) and decreased with increasing discharge. Velocity profile analysis indicated an intensification of the three-dimensional nature of the flow, increased velocity around the baffle, vortex formation downstream, and, ultimately, increased energy dissipation. In the supercritical regime, the channel was capable of passing much higher discharges, and the accelerating effect of the throat was less pronounced than in the subcritical regime. Behind the baffle (downstream zone), flow separation induced recirculating regions or “dead zones” characterized by low velocities or even reverse flow (vortices), which are evident in velocity profiles as significant velocity reductions or vector reversals at the structure’s exit. These zones play a crucial role in energy dissipation and increased turbulence. Overall, changes in the velocity gradient and increased turbulence led to the transformation of velocity profiles and an increase in the system’s total energy loss.

Conclusion:
This research clearly demonstrated that the central baffle structure exerts significant hydraulic effects on flow in rectangular compound channels. In the subcritical regime, the structure induces increased flow depth and high energy dissipation, whereas in the supercritical regime, it acts as a moderator and stabilizer, resulting in lower energy losses. Collectively, these effects contribute to increased depth, reduced average velocity, and a lower Froude number, proving effective in controlling high velocities and mitigating downstream erosion. The findings of this study provide a deeper understanding of energy dissipation mechanisms and flow behavior in the presence of hydraulic obstructions, offering a scientific basis for the optimal design of structures aimed at flow control and erosion reduction.

Abstract Introduction:
Given the increasing population, the annual decrease in precipitation, and the limited water supply resources, optimal use of existing water resources is one of the best options for creating sustainable agriculture. Maximizing irrigation water productivity has been one of the most important policies of managers and planners of the country's agricultural sector in recent years. Among the appropriate techniques for improving productivity and efficiency of water use are modern irrigation systems and the application of management scenarios such as deficit irrigation. One of the most important advances in the drip irrigation system is the invention of the subsurface drip irrigation system. Cotton is one of the most important agricultural products that, in addition to providing raw materials for the textile and oil industries, plays an important role in creating jobs in the agricultural, industrial, and commercial sectors; However, the occurrence of continuous and severe droughts in Kerman province, especially in the Orzoueyeh agricultural region, and the lack of comprehensive and citation-worthy studies and research on this issue and doubts about the economic justification of implementing these systems require that surface and subsurface drip irrigation systems for cotton crops in Orzoueyeh County be evaluated from a technical and economic perspective.

Materials and Methods:
The present study was conducted at the Orzoueyeh Research Farm affiliated with the Kerman Agricultural and Natural Resources Research and Education Center during 2024 and 2025. In order to evaluate surface and subsurface drip irrigation systems on cotton yield in Orzoueyeh County, an experiment was conducted in the form of split strip plots in a randomized complete block design with three replications. This experiment was conducted in the form of 12 treatments, three irrigation levels: I1=125, I2=100, and I3=75 percent of water requirement, and two irrigation systems including surface drip irrigation (S1) and subsurface drip irrigation (S2), as well as two drip pipe installation patterns (in all rows=L1 and one in between=L2). The factors I and S were conducted in strip and cross (factor I levels vertically and factor S levels horizontally) in each replication, and the factor L was divided into the plots resulting from the intersection of the two factors I and S. To measure and calculate the studied traits after removing the margins, the two middle lines of each plot were used. Finally, the yield of the plant per hectare, the number of bolls per plant and the water use efficiency (WUE) were measured and calculated as the amount of product per volume of water used. The studied traits were subjected to a combined analysis of variance for two years using SAS.9.2 software and the least significant difference (LSD) test was used at a probability level of 5% to compare the means. After collecting farm data to select the best treatment economically, the results were first examined using the partial budgeting method and investment priority analysis. It should be noted that sometimes, in order to determine the investment priority in the treatments under study, it is inevitable to conduct an analysis of the final rate of return on investment. In this study, too, the decision-making in the investment priority analysis was dependent on the analysis of the final rate of return on investment, which was carried out.

Results and Discussions:
Based on the results, the crop yield at the irrigation level of 100 percent of water requirement was obtained in surface and subsurface drip irrigation systems, respectively, equal to 2292 and 2555 kg/ha, and the planting pattern in all rows and in between at this irrigation level yielded 2565 and 2282 kg/ha, respectively.
The study of various indicators of crop yield, water consumption, water use efficiency, number of bolls per plant, boll weight, and the results of economic analysis of the treatments indicate the superiority of the subsurface drip irrigation system over the surface irrigation system and the superiority of the planting pattern in all rows over the planting pattern of water pipes in one between in cotton cultivation for the following reasons. The cotton crop yield in the subsurface drip irrigation system treatment is 234 kg/ha higher than that in the surface drip irrigation system. The number of bolls per plant and boll weight in the subsurface drip irrigation system are 16 and 3 percent higher, respectively, than in the surface irrigation system. The cotton yield in the all-row irrigation pattern is 254 kg/ha higher than in the one between irrigation pattern. Despite the same amount of water consumption, the water use efficiency in the all-row irrigation pattern is about 8 percent higher than in the one between irrigation pattern. The number of bolls per plant and boll weight in the all-row irrigation pattern are 12 and 3 percent higher, respectively, than in the in the one between irrigation pattern. From an economic point of view, investing in the I2S2L1 treatment (subsurface drip irrigation at 100 percent of water requirement and in a planting pattern in all rows) is preferable to investing in other treatments.

Conclusion
Investment in the I2S2L1 treatment (subsurface drip irrigation at 100 percent water requirement and in the planting pattern in all rows) is preferable to investment in other treatments. The results of the technical analysis of the project also showed that the (I2S2L1) treatment has the best statistical position (A). Considering that cotton is a water-intensive crop and the amount of irrigation has a great impact on yield, all the studied traits have a better position in the 100 percent water requirement treatment compared to the other two treatments. Therefore, it can be said that this treatment has a better ability to justify. In addition, the selection of the 100 percent water requirement treatment was made based on economic evaluation and profit for the farmer, and the low-irrigation treatment is useful for maintaining water in the field, which is not done by farmers because farmers are always looking for profit.

Abstract Introduction:
Water distribution networks in arid regions face persistent challenges including pressure standard maintenance, infrastructure cost reduction, and water loss management. Iran, with annual precipitation of 240–250 mm, confronts severe water scarcity, making efficient network management critically important. Leakage — an unavoidable phenomenon in distribution systems — is directly governed by network pressure, rendering pressure management a primary strategy for loss reduction (Lambert, 2001). Recent advances in multi-objective evolutionary algorithms have expanded optimization capabilities for water distribution networks. While NSGA-II and MOEA/D have been extensively applied in hydraulic engineering, AGE-MOEA — developed by Panichella (2022) based on non-Euclidean Pareto front geometry approximation — has not previously been evaluated in water distribution optimization contexts, as confirmed through systematic searches of Scopus and Web of Science databases. Furthermore, existing studies predominantly assess Pareto front quality metrics while neglecting the operational implementability of optimization outputs, particularly the stability of pressure-reducing valve (PRV) hourly scheduling patterns under real operating conditions. This study presents a comprehensive two-phase framework integrating hydraulic simulation (WaterGEMS/EPANET) and evolutionary optimization (Python/DEAP/WNTR) to evaluate NSGA-II, MOEA/D, and AGE-MOEA across benchmark networks (Hanoi, Balerma) and the real Poldokhtar western zone network, assessing both Pareto front quality and practical operational feasibility
Materials and Methods:
This study developed an integrated framework combining hydraulic simulation and multi-objective evolutionary optimization across three water distribution networks of increasing complexity: the Hanoi benchmark (34 pipes, 32 nodes, single gravity reservoir), the Balerma irrigation network (454 pipes, 443 nodes, four reservoirs), and the real Poldokhtar western zone network (261 pipes, 206 consumption nodes, one 5,000 m³ gravity reservoir, two pressure-reducing valves). Hydraulic models were initially constructed in WaterGEMS and converted to EPANET 2.2 standard format, with pressure-driven analysis (PDA) implemented through the WNTR library in Python, where nodal demand follows q_i^actual=q_i^demand⋅((P_i-P_i^min)/(P_i^req-P_i^min ))^0.5for P_i^min≤P_i≤P_i^req. The Poldokhtar model was calibrated against field measurements of reservoir outflow and PRV discharge rates, achieving acceptable agreement between simulated and observed values; full nodal pressure calibration was constrained by limited field sensor deployment. Three multi-objective evolutionary algorithms — NSGA-II (dominance-based), MOEA/D (decomposition-based), and AGE-MOEA (geometry approximation-based) — were implemented using the DEAP library with identical computational budgets of 200,000 function evaluations (population N=200, generations=1,000), SBX crossover (pc=0.9, ηc=20), polynomial mutation (pm=1/n, ηm=20), and 30 independent runs with random seeds 1–30. For Hanoi and Balerma, decision variables comprised all pipe diameters selected from discrete commercial sizes, with objectives of minimizing total network cost (Z₁) and pressure deviation from permissible ranges. For Poldokhtar, 53 decision variables encompassed hourly scheduling coefficients of two PRVs (48 variables) and diameters of five selected pipes (5 variables), with three objectives: minimizing total hydraulic penalty from pressure and velocity violations (Z₁), minimizing excess pressure (Z₂), and minimizing the sum of selected pipe diameters (Z₃). Algorithm performance was evaluated using Hypervolume (HV) with reference point r=1.1×fmax and Inverted Generational Distance (IGD) computed against a reference front constructed from all non-dominated solutions across 30 runs of all three algorithms, where higher HV and lower IGD indicate superior performance.
Results and Discussions:
Performance evaluation across three networks revealed distinct algorithmic behaviors reflecting fundamental differences in search mechanisms. On the Hanoi network, NSGA-II achieved the only fully feasible solution with zero pressure deviation at a network cost of $77,551, demonstrating superior capability in navigating tight hydraulic constraints, while AGE-MOEA recorded the highest overall Pareto front quality metrics (HV=4.7, IGD=1.87) and MOEA/D performed weakest (HV=3.6, IGD=3.75) due to its inherent sensitivity to objective scale differences — the Tchebycheff scalarization function becomes dominated by the larger-magnitude cost objective, disrupting convergence toward feasible pressure-compliant solutions. On the large-scale Balerma network (454 pipes, 10⁴⁵⁴ search space), AGE-MOEA maintained its quantitative superiority (HV=0.85, IGD=0.019), followed closely by NSGA-II (HV=0.82, IGD=0.024), while MOEA/D exhibited significant diversity loss (HV=0.61, IGD=0.041), confirming that decomposition-based approaches struggle with high-dimensional design spaces where neighborhood assumptions break down. The Poldokhtar three-objective case produced the most operationally informative results. Pareto front comparison (Z₁: total hydraulic penalty vs. Z₂: excess pressure) revealed that AGE-MOEA dominated NSGA-II across the majority of the objective space in the Z₁ range of 5,750–6,000, delivering lower excess pressure for equivalent hydraulic penalty values, while both algorithms provided substantially wider solution diversity than MOEA/D, which concentrated exclusively in the high-penalty low-excess-pressure region (Z₁>6,050, Z₂≈28,800–29,600) — a computationally significant weakness for multi-objective optimization. Hypervolume convergence analysis (Figure 15) revealed an important distinction: MOEA/D achieved the highest final cumulative HV (4,603,078) compared to NSGA-II (4,089,945) and AGE-MOEA (3,369,721), which does not contradict its weaker Pareto front coverage but reflects its deep convergence within a narrow objective region — a fundamentally different metric capturing exploration history rather than final solution quality. PRV hourly scheduling analysis exposed a critical operational dimension absent from purely quantitative assessments: despite their Pareto front superiority, NSGA-II and AGE-MOEA generated highly oscillatory valve settings fluctuating between 18–23 m within single-hour intervals, with quantitative indicators confirming significantly higher variance, directional change frequency, and oscillation amplitude compared to MOEA/D, which produced conservative near-constant patterns with only minor adjustments — most notably a smooth transition at hour 7 for PRV-1. This operational contrast, supported by the equal-weight MCDM compromise solution extracted from each algorithm's Pareto front, demonstrates that Pareto front quality metrics alone provide an incomplete basis for algorithm selection in real operational contexts: AGE-MOEA is recommended for large-scale design optimization where Pareto coverage is paramount, NSGA-II excels when strictly feasible solutions under tight hydraulic constraints are required, and MOEA/D — despite its quantitative limitations — produces the most operationally stable PRV scheduling patterns suitable for direct field implementation, highlighting a fundamental trade-off between mathematical optimality and engineering practicability that warrants explicit consideration in future water network optimization frameworks.
Conclusion:
This study presented a comprehensive evaluation of NSGA-II, MOEA/D, and AGE-MOEA for water distribution network optimization through an integrated WaterGEMS-EPANET-Python framework. AGE-MOEA demonstrated superior Pareto front coverage in large-scale networks, while NSGA-II proved most effective for constraint-intensive design problems requiring fully feasible solutions. Despite weaker Pareto front diversity, MOEA/D generated operationally implementable PRV scheduling patterns with minimal oscillations, revealing a fundamental trade-off between algorithmic optimality and practical deployability. Algorithm selection should therefore be governed by decision-maker priorities: AGE-MOEA for Pareto quality, NSGA-II for constraint satisfaction, and MOEA/D for operational stability. Quantified leakage reduction requires dedicated pressure-leakage modeling in future research.

Abstract Introduction:
Water scarcity, declining soil organic matter, and deterioration of soil structure are important constraints to agricultural production in dry and semi-arid regions. Improving soil water retention and physical quality is therefore essential for increasing water-use efficiency and sustaining crop production. Biochar, a carbon-rich and porous material produced through pyrolysis of biomass under limited oxygen, has been proposed as a soil amendment capable of modifying soil structure, pore characteristics, and water retention. However, its effects depend on feedstock type, pyrolysis temperature, application rate, soil texture, and duration of application. Moreover, limited information is available on the effects of biochar produced from locally available poplar pruning residues and wheat straw on the simultaneous physical and hydraulic properties of soils in northwestern Iran. Therefore, this study evaluated the effects of different application rates of a 1:1 mixture of poplar wood and wheat straw biochars on selected physical and hydraulic properties of a loamy sand soil under greenhouse conditions. The study particularly focused on changes in bulk density, porosity, water retention, total available water, electrical conductivity, and saturated hydraulic conductivity.

Materials and Methods:
The experiment was conducted in the greenhouse and soil laboratory of the Faculty of Agriculture, University of Tabriz, using a completely randomized design with three replications. Surface soil was collected from the 0–30 cm layer of an agricultural field at the university research station. The soil had a loamy sand texture, containing 62% sand, 24% silt, and 14% clay, with a pH of 7.65 and organic carbon content of 0.48%. Biochars were produced separately from poplar pruning wood and wheat straw under oxygen-limited conditions. Wheat straw and poplar wood were pyrolyzed at 350 and 400 °C, respectively, using a heating rate of 15 °C min−1 and a residence time of 120 min at the final temperature. The resulting biochars were mixed at a 1:1 mass ratio. Four application rates were evaluated: 0% (control), 1%, 3%, and 5% biochar by soil mass. After complete mixing, treated soils were transferred to plastic pots and maintained under greenhouse conditions for four months. Soil moisture was regularly adjusted to approximately field capacity using distilled water to maintain comparable moisture conditions among treatments. After incubation, electrical conductivity (EC), bulk density, total porosity, saturated water content, field capacity (FC), permanent wilting point (PWP), total available water (TAW), and saturated hydraulic conductivity (Ks) were measured using standard laboratory methods. FC and PWP were determined at matric potentials of 33 and 1500 kPa, respectively, using pressure plates. Bulk density was measured using sampling cylinders, total porosity using a gas pycnometer, and Ks using the constant-head method. Data normality and homogeneity of variances were assessed using the Shapiro–Wilk and Levene tests, respectively. Following confirmation of the assumptions of parametric analysis, one-way analysis of variance was performed using SPSS version 26. When treatment effects were significant, means were separated using Duncan’s multiple range test at the 5% probability level.

Results and Discussions
The statistical analyses showed that biochar application significantly affected physical and hydraulic properties of the soil. The treatment effect was highly significant for bulk density, field capacity, and total available water (P<0.01), while electrical conductivity, saturated water content, and total porosity were affected significantly at P<0.05. In contrast, the effects on permanent wilting point and saturated hydraulic conductivity were not statistically significant. Bulk density decreased progressively with increasing biochar rate, from 1.53 g cm−3 in the control to 1.44, 1.33, and 1.18 g cm−3 at 1%, 3%, and 5% biochar, respectively. Thus, the 5% treatment reduced bulk density by 22.80% relative to the control. Total porosity increased from 44.00% in the control to 44.61%, 48.68%, and 55.90%, corresponding to increases of 1.38%, 10.64%, and 27.04%, respectively. Saturated water content also increased markedly, from 26.43% in the control to 29.96%, 34.69%, and 41.02% at the three biochar levels. The increase at 5% reached 55.20% relative to the control. Field capacity increased significantly from 14.72% in the control to 16.95%, 18.68%, and 21.22%, representing increases of 15.15%, 33.69%, and 44.16%, respectively. Total available water increased from 12.31 mm to 15.13, 16.83, and 18.70 mm, with the 5% treatment showing a 51.90% increase compared with the control. Permanent wilting point increased numerically from 6.51% to 6.87%, 7.46%, and 8.75% as biochar rate increased, but these differences were not significant. Saturated hydraulic conductivity similarly increased from 11.45 cm h−1 in the control to 12.28, 13.34, and 15.87 cm h−1, respectively, but the variation was not statistically significant. Electrical conductivity increased significantly from 1.11 dS m−1 in the control to 1.36, 1.42, and 1.40 dS m−1 under 1%, 3%, and 5% biochar, respectively; however, the three biochar treatments were statistically similar. The increases in porosity, saturated water content, and field capacity can be attributed to the low density and porous structure of biochar, together with changes in soil pore volume and arrangement. The stronger response of field capacity than permanent wilting point suggests that biochar preferentially increased water retention within pores contributing to plant-available water. Consequently, the increase in total available water resulted mainly from the substantial improvement in field capacity rather than from changes in the lower water-retention limit. Although saturated hydraulic conductivity showed an increasing trend, the lack of statistical significance indicates that greater total porosity did not necessarily produce proportionally greater water flow. This may reflect the importance of pore size distribution, continuity, and connectivity in controlling saturated hydraulic conductivity. The increase in electrical conductivity was likely related to the release of soluble salts and basic cations from biochar, although the measured values remained within a non-saline range. Overall, the 5% treatment produced the greatest improvement in most measured soil properties, particularly bulk density, water retention, and total available water.

Conclusion:
Application of the mixed poplar pruning and wheat straw biochar improved the physical condition and water-retention capacity of the loamy sand soil, with the 5% rate producing the greatest overall improvement. This treatment reduced bulk density and increased porosity, saturated water content, field capacity, and total available water. The results indicate that biochar can enhance soil water storage and potentially support more efficient irrigation management in dry and semi-arid environments. However, because the experiment was conducted under greenhouse conditions for only four months, the results should not be interpreted as establishing a universal optimum application rate. Long-term field studies are required to evaluate persistence, crop response, and economic feasibility.

Abstract Extended Abstract

Introduction:
Urban rivers are important components of surface water resources, and their quality can be affected by urban development, land-use changes, increased impervious surfaces, human activities, and surface runoff. These factors can introduce various pollutants into surface water systems and consequently alter water quality along the river course. In addition, changes in hydrological conditions between dry and wet periods can affect the transport and distribution of pollutants and, ultimately, water quality. Therefore, assessing water quality during different periods and investigating its spatial and temporal variations are essential for understanding surface water conditions and supporting appropriate pollution management and control strategies. The West Tehran watershed is an important area for surface runoff generation and transport due to extensive urban development, intensive human activities, and the presence of the main Kan, Hesarak, Farahzad, and Darakeh rivers. These rivers pass through mountainous and urban areas and eventually enter the surface runoff collection and conveyance network and the Western Tehran flood diversion channel. Therefore, assessing their water quality under dry and wet conditions can provide an appropriate representation of surface water quality in the watershed. This study aimed to assess the water quality of the main rivers in the West Tehran watershed using the Iranian Surface Water Quality Index (IRWQIsc), compare water quality between dry and wet periods, and investigate dominant patterns of co-variation among water quality parameters using Principal Component Analysis (PCA).
Materials and Methods:
The study area included the main rivers of the West Tehran watershed, namely the Kan, Hesarak, Farahzad, and Darakeh rivers, as well as the Western Tehran flood diversion channel. Ten sampling stations were established within the study area. Sampling was conducted during two periods: August 2025, representing the dry period, and February 2026, representing the wet period. Due to the absence of flow in the Hesarak River at stations 3S and 4S, these stations had no samples available for analysis during either period. Consequently, data from eight active sampling stations were analyzed. Water quality parameters were selected based on the requirements of the IRWQIsc and included BOD₅, COD, pH, electrical conductivity (EC), turbidity, dissolved oxygen (DO), nitrate, total ammonium, phosphate, total hardness, and fecal coliforms. Samples were collected using the grab sampling method, transferred to the laboratory, and analyzed using the designated analytical methods and laboratory equipment. The IRWQIsc was then calculated for each station, and water quality was classified according to the descriptive categories of the index. This index integrates 11 physical, chemical, and microbiological parameters into a single numerical value representing the overall status of surface water quality. For statistical analysis, the normality of the index data was assessed using the Shapiro–Wilk test. Because the data followed a normal distribution, a paired t-test was used to compare the mean IRWQIsc between the dry and wet periods. In addition, PCA was performed to identify dominant patterns of co-variation among water quality parameters and reduce the dimensionality of the dataset.
Results and Discussions:
The IRWQIsc results indicated a considerable difference in water quality between the dry and wet periods. During the dry period, IRWQIsc values ranged from 12.09 to 50.81; the highest value was observed at station 1S (50.81), while the lowest was recorded at station 10S (12.09). The mean IRWQIsc was 38.55, and water quality was predominantly classified as “moderate to relatively poor.” During the wet period, IRWQIsc values ranged from 10.64 to 40.96; the highest value was observed at station 2S (40.96), while the lowest was recorded at station 10S (10.64). The mean IRWQIsc was 29.46, and water quality was predominantly classified as “relatively poor to very poor.” Comparison of the two periods showed that the mean IRWQIsc was 38.55 during the dry period and 29.46 during the wet period, and the difference was statistically significant (p = 0.0207). Therefore, water quality during the wet period was poorer than during the dry period. Station 10S showed the lowest index value in both periods, indicating poorer water quality in the downstream section of the flow system after passing through urban areas. PCA results also revealed differences in the co-variation structure of water quality parameters between the two periods. During the dry period, the first three principal components collectively explained 85.9% of the total variance, with the first, second, and third components accounting for 38.2%, 26.5%, and 21.2%, respectively. During the wet period, the first three principal components collectively explained 84.8% of the total variance, while the contribution of the first component increased to 47.3%. In this component, COD, BOD₅, NH₄⁺, PO₄³⁻, and turbidity showed more prominent contributions. This change indicated that, during the wet period, a greater proportion of the variability in water quality parameters was organized along a common component. Overall, the decrease in mean IRWQIsc during the wet period and the increased contribution of the first PCA component indicated that the change in water quality between the two periods was accompanied by a change in the contribution pattern of water quality parameters. However, because of the limited number of samples and the lack of direct data on meteorological conditions, discharge, and pollutant sources, interpretation of the factors responsible for these variations should be considered exploratory. Therefore, the observed variations cannot be attributed to a specific pollutant source.
Conclusion:
The results demonstrated that the combined application of IRWQIsc and PCA provided an integrated assessment of surface water quality and revealed both seasonal water quality status and dominant patterns of variation among water quality parameters in the West Tehran watershed. Nevertheless, because of the limited number of samples and the absence of direct meteorological, hydrological, and pollutant-source data, the factors influencing these variations should be interpreted as exploratory and probable. Future studies involving more sampling events, simultaneous discharge and rainfall measurements, and direct identification of pollutant sources are recommended to improve understanding of water quality variations in the rivers of West Tehran.

Abstract This article evaluates and compares flood resilience using two indices: the Urban Flood Risk Index (UFRI) and the Improved Urban Flood Risk Index (IUFRI). The UFRI was introduced in 2019 as a multidimensional and relatively comprehensive index. The IUFRI was proposed in 2026 to address the weaknesses and limitations of the UFRI. While UFRI focuses on four components (hazard, exposure, vulnerability, and coping capacity), IUFRI adds the component of “coexistence capacity with floods.” By doing so, it also considers the environmental, social, and behavioral dimensions of residents, and therefore represents an index more aligned with the concepts of sustainable development. In this study, the two indices are evaluated in a practical and technical application, and the differences in their analytical results are examined. Based on the obtained results: 1) Overall, IUFRI indicates higher and better levels of resilience across different areas compared with UFRI; and 2) The spatial distribution and variation of the two indices across different areas are not identical and do not change proportionally. This means that the influence of the coexistence capacity component varies significantly among different areas. In general, the IUFRI provides a more comprehensive representation of resilience with an emphasis on sustainable development and can be considered a suitable option for assessing urban resilience. The findings of this research can support more informed decision making in urban management and broader policy development aimed at reducing flood risk and enhancing the resilience of urban areas.