Iranian Water Research Journal

Abstract Introduction:
Bridge local scour which is responsible for structural failures in river-crossing bridges, occurs as a result of the interaction between the flow field and the bridge pier, leading to the removal of bed material and the formation of a scour hole around the foundation. Most existing research on the geometry of bridge piers focus on circular or rectangular piers aligned with the flow. However, real-world bridge piers often deviate from the flow direction due to hydraulic constraints or structural alignment. The alignment angle (α), defined as the deviation of the pier’s longitudinal axis from the flow direction, alters the symmetry of the horseshoe vortex and significantly affects the magnitude and position of the maximum scour depth. Moreover, the ratio of pier length (in the direction of flow) to its width (L/B) modifies the distribution of flow velocities and shear stresses around the pier. Despite numerous experimental studies, the simultaneous effect of these two parameters on local scour depth around non-circular piers, particularly rounded-nosed rectangular piers, has received limited attention. The present study aims to investigate the combined influence of L/B and α on the local scour depth under clear-water conditions.

Materials and Methods:
The experiments were conducted in the hydraulic laboratory of Isfahan University of Technology (IUT), Iran. The flume used for this study is a 12-meter-long, 0.6-meter-wide, and 0.5-meter-deep rectangular open channel with a water circulation system. The bed material consisted of uniform sand with a median particle size of d_50=0.78" " mmand a geometric standard deviation σ_g=1.29. Flow depth and discharge were controlled using a tailgate and calibrated pump system. Two pier models were fabricated from transparent Plexiglas to allow clear observation of flow structures. The reference circular pier had a diameter =3" " cm, while the rounded-nosed rectangular pier had a constant width B=3" " cm(equal to the circular pier’s diameter) and variable lengths L=6,9 and 12" " cm, corresponding to aspect ratios L/B=2,3 and 4. The piers were tested at three different alignment angles relative to the flow direction: α=5°,10° and 20°. Thus, a total of 13 experiments were conducted, including the reference circular pier case. The flow velocity was adjusted to achieve clear-water conditions at U/U_c=0.86, where U_c is the critical velocity for the initiation of sediment motion, determined using the Shields criterion. The steady discharge was set at 50 liters per second, corresponding to a flow depth of 18.8 cm. Before each run, the sand bed was leveled and compacted to ensure uniform initial conditions. Each test continued until the scour hole reached equilibrium. After completion, the final bed profile was measured using a digital point gauge with 0.1 mm precision. Longitudinal and transverse profiles were recorded at multiple sections to obtain the maximum local scour depth d_s. All experiments were repeated twice to ensure reproducibility, and the mean values were reported. Flow fluctuations were maintained within ±2% of the set discharge. The experimental data were analyzed using dimensional analysis and regression techniques.

Results and Discussion:
The scour process followed the formation of a strong downflow on the upstream face, followed by the development of a horseshoe vortex that transported sediment away from the pier base. The equilibrium scour depth was achieved within 5–6 hours. Effect of Aspect Ratio: At α ≤ 5°, increasing the aspect ratio from 2 to 4 led to a reduction in maximum scour depth which can be attributed to the redistribution of flow momentum along the elongated pier. At α ≥ 10°, the opposite trend was observed. Quantitatively, increasing L/Bfrom 2 to 4 resulted in a 20% decrease in scour depth at α=5°, but a 35% increase at α=20°. Effect of Alignment Angle: Increasing α from 5° to 20° caused the scour hole to deepen and shift laterally toward the upstream corner of the pier. This behavior results from the asymmetric horseshoe vortex system generated under oblique flow conditions. The rounded-nosed rectangular pier produced 15–20% less scour depth at α ≤ 5°, confirming its hydraulic efficiency in near-aligned conditions. However, for α ≥ 10°, the scour depth for rectangular piers exceeded that of the circular pier, indicating the negative impact of larger misalignment angles. Combined Effect of L/B and α: The combined influence of aspect ratio and alignment angle was found to be nonlinear and interactive. For moderate aspect ratios (L/B = 3), the influence of α dominated the scour behavior, while at extreme aspect ratios, both parameters interacted to amplify scour depth. Bed Morphology: Topographic surveys revealed that for α ≤ 5°, the scour hole was nearly symmetrical and shallow, while at α ≥ 10°, the hole became elongated and skewed toward the upstream corner. The deposition zone downstream expanded with increasing α, reflecting stronger wake vortices.

Conclusion:
The present experimental investigation demonstrated that both pier aspect ratio and alignment angle play crucial and interdependent roles in determining local scour depth around bridge piers. The major conclusions are summarized as follows:
For alignment angles below 5°, increasing the pier aspect ratio (L/B) decreases local scour depth by distributing flow energy along the pier face.
For α ≥ 10°, larger aspect ratios intensify scour by promoting asymmetric vortex formation and higher local shear stresses.
Rounded-nosed rectangular piers perform better than circular piers under small alignment angles (α ≤ 5°), but their performance deteriorates at higher angles.
A modified empirical relationship was proposed to estimate the alignment coefficient K_α, which accurately predicts scour depth with R^2=0.94.
From a practical perspective, pier alignment angles greater than 10° should be avoided in bridge design to minimize local scour risks.
Future work is recommended to examine the effects of surface roughness, pier spacing (group effects), and unsteady flow conditions such as floods using both experimental and computational fluid dynamics (CFD) modeling approaches.

Abstract Introduction
Piano key weirs (PKWs) are increasingly used as efficient spillway structures due to their ability to significantly increase discharge capacity without requiring an increase in dam crest width. This advantage makes them particularly suitable for dam rehabilitation and for sites where spillway expansion is constrained by topographic or structural limitations. Among different PKW configurations, Type‑A piano key weirs have received considerable attention because of their favorable hydraulic performance and structural simplicity. Despite extensive research on PKWs, the influence of geometric modifications—especially the inclination of side walls and their orientation relative to the flow direction—has not been sufficiently investigated. Side‑wall geometry can affect the flow pattern entering the inlet keys, the formation of separation zones, and the overall hydraulic efficiency of the spillway. Understanding these effects is essential for optimizing PKW performance. Therefore, the present study experimentally investigates the hydraulic behavior of Type‑A piano key weirs with different side‑wall inclinations and orientations. In addition, data‑driven models are employed to predict the discharge coefficient and evaluate the capability of machine‑learning techniques in modeling complex nonlinear hydraulic relationships.

Materials and Methods
The present study was conducted using a laboratory experimental setup designed to investigate the hydraulic performance of Type A piano key weirs under controlled flow conditions. The experiments were carried out in a rectangular flume with a constant width and adjustable discharge system that allowed accurate control of flow rates. Two geometric configurations of piano key weirs were tested: rectangular and trapezoidal inlet–outlet key shapes. The main objective was to evaluate how the inclination and orientation of the side walls influence the hydraulic efficiency and discharge coefficient of the structure. Side wall inclination angles of 5°, 7.5°, and 10° were selected based on common ranges used in hydraulic structures and previous studies on PKW optimization. For each inclination angle, two orientations were considered: inclination with the flow direction and inclination against the flow direction. These configurations allowed the evaluation of how flow alignment and entrance conditions affect discharge characteristics. During the experiments, the upstream water head was carefully measured using precise point gauges, while the flow discharge was controlled and monitored using calibrated flow measurement devices.
The discharge coefficient (C_d) was calculated for each experimental condition to quantify the hydraulic performance of the tested configurations. The collected dataset was then used for developing predictive data driven models. Several machine learning algorithms were employed, including Artificial Neural Networks (ANN), Extreme Gradient Boosting (XGBoost), Random Forest, and Support Vector Regression (SVR). The input parameters consisted of hydraulic and geometric variables such as upstream head and side wall inclination characteristics, while the output variable was the discharge coefficient. Model performance was evaluated using common statistical indicators including the coefficient of determination (R^2), root mean square error (RMSE), and mean absolute error (MAE). These indicators were used to assess the accuracy and reliability of each model and to determine the most suitable approach for predicting PKW discharge performance

Results and Discussion
The experimental results clearly demonstrate that the inclination and orientation of side walls significantly influence the hydraulic performance of Type A piano key weirs. Flow observations indicated that the side wall geometry directly affects the way water enters the inlet keys and how the flow is distributed along the crest. When the side walls were inclined against the flow direction, the incoming water was guided more effectively toward the inlet openings. This configuration improved the alignment of streamlines and reduced the formation of recirculation zones near the inlet edges. As a result, flow contraction and energy losses were reduced, leading to an increase in the discharge coefficient. In contrast, when the side walls were inclined with the flow direction, the inflow pattern tended to produce local separation zones near the entrance of the inlet keys. These separation regions reduced the effective flow area and caused additional energy dissipation. Consequently, the discharge coefficient obtained in these cases was generally lower than that of the opposite orientation.
The influence of the inclination angle was also evident in the experimental data. Increasing the side wall inclination from 5° to 7.5° and 10° generally improved hydraulic performance, particularly when the inclination was directed against the flow. Among the tested configurations, the best hydraulic behavior was observed for trapezoidal models with side wall inclinations between 7.5° and 10° oriented against the flow direction. These configurations provided the most favorable flow guidance and minimized hydraulic disturbances near the inlet region. A comparison between the two tested geometries showed that trapezoidal PKWs consistently produced higher discharge coefficients than rectangular ones under similar hydraulic conditions. The trapezoidal configuration appears to facilitate smoother flow transitions and better distribution of water across the inlet keys, which enhances the overall discharge efficiency. In some cases, the improvement in discharge coefficient reached approximately 15% compared with the corresponding rectangular configurations. The data driven modeling results further confirmed the experimental findings. Among the applied machine learning techniques, Artificial Neural Networks (ANN) and Extreme Gradient Boosting (XGBoost) showed the best predictive capability. These models successfully captured the nonlinear relationships between geometric parameters and hydraulic performance. The predictive accuracy of these models exceeded 98%, while the associated prediction errors remained below 2%, indicating excellent agreement with the experimental measurements. The results highlight the effectiveness of combining experimental investigations with modern machine learning techniques to better understand and predict the hydraulic performance of complex spillway structures such as piano key weirs.

Conclusions
This study investigated the effects of side wall inclination and orientation on the hydraulic performance of Type A piano key weirs using laboratory experiments and data driven modeling. The results showed that inclining the side walls against the flow direction significantly improves flow alignment and reduces energy losses, resulting in higher discharge coefficients. Trapezoidal configurations demonstrated superior performance compared with rectangular geometries, with improvements reaching approximately 15%. Machine learning models, particularly ANN and XGBoost, provided highly accurate predictions of the discharge coefficient. The findings provide useful guidance for optimizing PKW design and demonstrate the value of integrating experimental data with advanced predictive modeling techniques. The study contributes a validated experimental dataset and robust machine learning formulations that can assist designers in optimizing PKW configurations for enhanced hydraulic efficiency and safer spillway design.

Abstract Introduction:
Food security in the community and a negative water balance in most plains have necessitated the optimal and sustainable use of water resources. Wheat is one of the most important and strategic products in ensuring food security, having been cultivated and produced in all parts of the world for a long time. Ensuring food security in society and the negative water balance in most plains have made the optimal and sustainable use of water resources essential. However, the rate of growth of production per unit area and its productivity, especially the productivity of wheat irrigation water in Iran, has not yet reached its optimal level. The need to increase production and physical water productivity in this strategic product through the use of different techniques and methods is evident. The area under wheat cultivation in Chaharmahal and Bakhtiari Province accounts for 44 percent of the province's cultivable land, with a net irrigation requirement of 400 mm and a water requirement of approximately 5,000 to 8,500 cubic meters per hectare.

Materials and Methods:
To increase productivity and production indices, a split-plot experimental design in the form of a randomized complete block statistical design was used, with the main factor of irrigation systems (sprinkler, tape and subsurface tape), the sub-factor of wheat cultivars (Heidari, Pishgam, Mihan and Orum) conducted with three replications in Chahartakhteh research station, Shahrekord, Iran. In this project, the amounts of water for irrigation (according to FAO Publication No. 56 and the soil characteristics of the root zone) were applied to surface and subsurface tape irrigation systems using a volumetric flow meter, and to sprinkler irrigation systems by measuring and calibrating the sprinklers. The yield of the product under different irrigation systems, along with the amount of irrigation water, was measured and calculated. To calculate plant evapotranspiration (ETo), the FAO-Penman-Monteith equation (No. 56) is used, taking into account the characteristics of the reference plant. In this method, the reference plant is assumed to be a grass cover with a height of 0.12 m, a constant surface resistance of 70 s/m, and a reflectance coefficient (albedo) of 0.23, representing evaporation from a large surface of green grass with uniform height, active growth and access to sufficient water. This relationship is independent of the type of plant and cultivation environment management issues, and is only affected by the climatic data of the region. Cropwatt software calculates the water requirement (CWR) of the wheat crop based on the (CWR = ETO×Kc) equation. The plant coefficient (Kc) for wheat is considered to be from 0.25 to 1.15 during the growth stages (initial, development, intermediate, and final). The amount of irrigation requirement (ICWR) is obtained from the ratio of the net requirement (wheat water requirement- CWR) to the efficiency or effectiveness of the irrigation system in percentage (Ea). The water productivity index is a function of the amount of water used (applied water, cubic meters per hectare) and grain yield (kilograms per hectare).

Results and Discussions:
The results showed that the effect of irrigation systems on 1000-seed weight, biological yield, grain yield and water productivity index at 1% at the 1% significance level was significantly different. Water productivity index in tape, subsurface tape, and sprinkler irrigation systems with values of 1.57, 1.24, and 0.93 kg/m3, respectively, and in Heidari, Pishgam, Mihan, and Orum wheat cultivars, 1.33, respectively, were 1.29, 1.28, and 1.09 kg/m3. Based on the results Heidari cultivarwas suggested as the best among the cultivated wheat cultivars to continue projects. Among the three irrigation systems (sprinkler, surface tape, and subsurface tape) in wheat cultivation, the surface tape irrigation system was superior to the other two. Subsurface tape irrigation systems were damaged due to the location of all pipes and fittings underground, and sometimes due to pressure changes or rodent damage. Their repair and maintenance caused damage, wasted time, and imposed costs on the project. Moreover, the placement of the tapes at a depth of about thirty centimeters below the ground combined with the effect of gravity on the upward transfer of moisture sometimes required additional irrigation to provide the necessary moisture. This issue reduced the efficiency and productivity of this method. As a result, water consumption in the surface tape irrigation method was lower than in other methods (rain and subsurface tape). Wheat crop yield (grain production) in surface tape irrigation systems was higher than in other irrigation methods. The Heidari cultivar had a significantly higher yield than the other tested cultivars (Mihan, Orum, and Pishgam). The highest and lowest water productivity index values among the irrigation systems were surface tape irrigation (1.556 kg/m3) and rain irrigation (0.925 kg/m3). However, among the wheat cultivars, Heidari, Pishgam, Mihan, and Orum had the highest water productivity, respectively. The highest harvest index value was obtained from the surface tape irrigation systems. Among the cultivars, the Heidari cultivar had the highest thousand-grain weight.

Conclusion:
The minimum volume of irrigation water used in surface tape irrigation and the maximum amount of water used in sprinkler irrigation, and the amount of water used in the subsurface tape irrigation system were between the latter two systems. This result is also due to the efficiency and performance of surface tape systems, and in the subsurface tape system, due to the transfer of moisture from a depth of thirty centimeters to the ground surface, the distribution of moisture and the direction of a significant portion of moisture towards the force of natural gravity, the consumption in this system is slightly higher than in the surface tape irrigation system.

Abstract Introduction:
A compound channel is a channel that its cross-section has several sub-sections with different flow profiles and distinct characteristics such as roughness, depth, etc. A natural river that flows over the land on its banks during a flood is a simple example of a compound channel. Flooding accounts for approximately one-third of the financial losses associated with natural disasters worldwide and more than half of the fatalities from these disasters. This research was conducted to physically simulate rigid vegetation (made of PVC) in the floodplain of a compound channel and to investigate its effects on the drag coefficient, friction factor, and flow force ratio. The direct measurements carried out in this research were much more accurate than energy methods and conventional methods of force investigation which were discussed in previous researches. In energy methods, the force value usually differs from the actual values, due to existing errors. The errors were partially compensated by using direct measurement.This research led to development of experimental relationships through which the drag coefficient and friction factor were directly calculated based on the vegetation parameter.

Materials and Methods:
This research investigated the effect of vegetation cover on the flow force ratio, drag coefficient, and friction factor using physical modeling of the flow in a knife-edge hydraulic flume with a length of 14 meters, a width of 107 centimeters, and a longitudinal slope of 10-3The experimental setup was located in the Hydraulic and Sediment Laboratory of the Basic Studies Center for Khuzestan Water and Power Authority, Iran. Five diameters of vegetation cover (20, 25, 30, 40 and 50 mm) made of PVC were considered as rigid non-submerged vegetation covers. The height of this cover was determined to be non-submerged in all cases. In order to use these covers, plexiglass sheets with a length of 1 meter (the length of the knife edge part) and the width equal to that of the floodplain were installed in the flume, , according to different arrangement of vegetation cover and its placement within the flow. Five longitudinal distances (8, 10, 12, 15 and 20 cm), three transverse distances (6, 8 and 10 cm, and two types of arrangement (regular and irregular) were implemented to investigate different cases. Due to the different variables, the total number of runs in this study was 151 different experiments. In this study, for data analysis, a dimensionless parameter that included variables such as distances and number of vegetation, cross-section changes and depth difference between the main channel and floodplain (relative depth) was used as the vegetation parameter.

Results and Discussions:
The results of the experiments were presented in the form of various graphs which illustrated the changes in the flow force ratio, friction coefficient, and friction factor based on the vegetation parameter. The ratio of flow force in the case of vegetated conditions to the flow force without vegetation in all experimental conditions was graphed with respect to the vegetation parameter. An equation with a suitable correlation coefficient (R2=0.9198) was fitted to the data trend. According the results of this study, the decreasing trend of the drag coefficient with increasing vegetation parameter was clear. The main difference between the two arrengment types (regular and irregular) was the range of the drag coefficient. The changes in the drag coefficient in the range of 0-0.5 of the vegetation parameter were between 2 and 10, which was relatively higher compared with the regular vegetation arrangement. The drag coefficient obtained in this study was also compared with the results of research conducted by Tanino and Neff (2008) and Tinoco and Cowen (2013) and their equilibrium equations. It was revealed that the drag coefficient values in the current study had a relatively similar trend to the drag coefficient obtained from the force equilibrium equation, which indicated the suitability of the proposed method and equations for calculating the drag coefficient in the studied area. To investigate the effect of vegetation on changes in the total friction factor calculated based on presented equation, two graphs were presented for regular and irregular vegetation arrangements. Trend lines with relatively good correlation coefficients were also obtained. Accordingly, related equations were presented to calculate these parameters. Considering the change in the type of arrangement, a ratio between the drag coefficient and the vegetation parameter was also defined.

Conclusion:
In this study, the flow force was measured using the direct measurement method and the drag coefficient, and total friction factor were calculated through the provided equations and presented in different diagrams based on the vegetation parameter in the compound channel with the presence of vegetation in the floodplain. According to the results of the diagrams, it was determined that the flow force ratio had a decreasing trend with increasing vegetation parameter, which was consistent with the drag coefficient regardless of the type of arrangement. It is suggested that the investigation of non-rigid (flexible) vegetation cover in compound channels be conducted using this type of flume and measurement method, and the results be compared with other researches.

Abstract Introduction:
Surface water reservoirs are among the most critical infrastructures for water supply, particularly in arid and semi-arid regions where water security is increasingly threatened by climate variability, prolonged drought, and intensified human pressure. In such environments, monitoring reservoir storage dynamics is essential for understanding hydrological drought and for supporting sustainable water resources management. The Chah-Nimeh reservoir system, located in the Sistan region of southeastern Iran, is a vital source of drinking and agricultural water. However, this system has experienced substantial storage decline in recent years, raising serious concerns about regional water security and environmental sustainability. Because Chah-Nimeh is strongly dependent on inflow from the transboundary Helmand River, its hydrological regime is influenced not only by local climatic conditions but also by upstream water regulation and cross-border management. Recent developments in remote sensing and cloud-based geospatial analysis have greatly improved the capacity to monitor reservoir surface area and storage variations with high temporal and spatial resolution. Therefore, this study aimed to investigate the temporal dynamics of reservoir storage and hydrological drought in the Chah-Nimeh reservoir during 2017-2025 using Sentinel-2 imagery and multi-source climatic datasets within the Google Earth Engine platform. It also examined the extent to which local climatic indicators explain the observed storage variations.

Materials and Methods:
This study was designed to evaluate the temporal dynamics of water storage and hydrological drought in the Chah-Nimeh reservoir using an integrated remote sensing and multi-source climate data framework. All analyses were conducted in the Google Earth Engine (GEE) cloud-computing platform, which enabled efficient processing of long-term geospatial datasets. Four main data sources were employed based on their open accessibility, scientific reliability, and appropriate spatial and temporal resolution. Sentinel-2 Level-2A imagery was used as the primary optical dataset for water surface extraction. A total of 345 atmospherically corrected images acquired between March 2017 and December 2025 were processed. Cloud and cloud-shadow contamination were removed using the Scene Classification Layer (SCL), and only images with less than 15% cloud cover were retained. Monthly composites were then generated using the median spectral values, yielding 83 valid monthly observations. To delineate the water body, three spectral water indices, namely NDWI, MNDWI, and AWEI, were calculated for each monthly composite. The use of multiple indices allowed both robust water detection and uncertainty estimation in the derived surface area. Reservoir volume was subsequently estimated from the extracted water surface area using the stage-area-storage relationship of the reservoir. A second-order polynomial regression was fitted between water surface area and storage volume, providing a reliable basis for monthly volume estimation. Water level was also derived through inverse interpolation from the stage-area curve. To assess climatic conditions, CHIRPS daily precipitation data, ERA5-Land monthly temperature and potential evapotranspiration data, and TerraClimate monthly products were incorporated. These datasets were used to compute climatic and hydrological indicators, including SPI, SPEI, PDSI, SRI, SSI, and SWLI. Among them, SWLI, derived directly from reservoir storage anomalies, was considered the principal indicator of hydrological drought, whereas SPI, SPEI, and PDSI were used only for comparative interpretation. The reliability of CHIRPS and ERA5-Land was evaluated against observations from the Zabol meteorological station using correlation coefficient, coefficient of determination, bias, and normalized root mean square error. Trend analysis was performed using the non-parametric Mann-Kendall test and Sen’s slope estimator. Pearson correlation, coefficient of determination, normalized root mean square error, and mean absolute error were applied to examine the relationships between climatic variables and reservoir storage. In addition, lag-time analysis was conducted to identify the temporal response of reservoir storage to precipitation variability.

Results and Discussions:
The results revealed a pronounced decline in the storage status of the Chah-Nimeh reservoir during the study period, confirming the occurrence of significant hydrological stress. Analysis of the monthly time series showed that both reservoir volume and water surface area followed a statistically significant downward trend. Reservoir storage decreased at an average rate of 5.38 million m³ per year, while water surface area declined by 0.63 km² per year, indicating a persistent reduction in the effective capacity of the reservoir. These findings demonstrate that the reservoir experienced not merely short-term fluctuations, but a sustained long-term depletion trend. The temporal pattern of storage dynamics further showed that the reservoir passed through several distinct phases. A relatively stable and wetter phase was observed during 2019-2020, followed by a gradual decline during 2021-2022, and then a severe depletion phase extending through 2023 to early 2024. The lowest storage value was recorded in February 2024, when reservoir volume dropped to approximately 26.27 million m³, representing the most critical hydrological condition during the study period. In contrast, a sharp recovery occurred in May 2024, when storage increased abruptly from 36.56 to 99.05 million m³ within a single month. Given that local precipitation during this period was negligible, this sudden increase cannot be attributed to local rainfall and is more plausibly associated with changes in upstream inflow conditions or transboundary water release. Hydrological drought analysis provided further evidence of this pattern. Based on the SWLI index, which was adopted as the principal indicator of reservoir hydrological drought, 12 out of 82 analyzed months were classified as drought periods, of which 83% fell into the severe or extreme drought categories. The year 2023 represented the most critical hydrological drought condition, with an average SWLI of -1.35, indicating severe drought. However, a key finding of the study was the clear mismatch between reservoir-based hydrological drought and locally derived climatic drought indicators. During periods when SWLI indicated severe depletion, the meteorological indices SPI and SPEI often remained close to normal. This divergence was especially evident in 2023, when hydrological drought intensified despite the absence of a comparable meteorological drought signal. Correlation analysis supported this interpretation. None of the examined local climatic variables or drought indices showed sufficient explanatory power for reservoir storage variations. Even the relatively better-performing indicators, such as SPEI-6 and SPEI-12, exhibited limited agreement with observed storage dynamics, as confirmed by low R² values and relatively high NRMSE. These results suggest that the Chah-Nimeh reservoir is not governed primarily by local climatic forcing. Rather, its storage behavior is strongly influenced by upstream inflow from the Helmand River and by transboundary and managerial controls. Therefore, the hydrological drought observed in the reservoir should be interpreted as a process driven by these factors.

Conclusion:
The findings of this study demonstrated that hydrological drought in the Chah-Nimeh reservoir cannot be adequately interpreted using local meteorological indicators alone. Reservoir storage showed a significant declining trend during 2017-2025, while the SWLI index identified severe hydrological drought conditions, particularly in 2023 and early 2024. In contrast, the SPI, SPEI, and PDSI did not show consistent agreement with the observed storage depletion. This mismatch indicates that reservoir behavior is primarily controlled by regulated inflow from the Helmand River and transboundary management factors. The integrated Google Earth Engine-based framework proved effective for continuous monitoring of reservoir dynamics in data-scarce and transboundary dryland systems.

Abstract Introduction:
The limited water resources of Hamedan Province and the decline in groundwater levels will lead to the risk of drying up of the wells that supply water as a source of irrigation for the province's important crops, including garlic and potatoes. This issue, in turn, can seriously threaten the sustainability and durability of their cultivation and work in the suburbs of Hamedan. Therefore, the possibility of using treated urban wastewater in a legal and healthy manner, in addition to providing part of the water needs of these products, will help maintain and sustain the cultivation, especially two important crops of garlic and potatoes, in the suburbs of Hamedan.However , wastewater is considered an unconventional source of water, and its use in agriculture requires careful and necessary management in controlling and purifying it to ensure the health of soil, plants and humans while avoiding environmental hazards. Therefore, the present study was conducted to use treated wastewater from Hamedan city to irrigate two crops, garlic and potato, by investigating its effect on soil chemical properties, distribution, and soil contamination with heavy metals such as copper, cadmium, chromium, lead, nickel, and arsenic.

Materials and Methods:
Initially, before planting the crops, samples were taken from the soil, treated wastewater, and water extracted from a well that was used to irrigate the two crops of garlic and potato. In order to enable the practical application of treated wastewater for the irrigation of garlic and potato cultivation, a suitable land parcel was identified, and a farm with convenient access to the treated wastewater supply was chosen. In the next step, soil samples, treated wastewater samples, and water extracted from the well were transferred to the laboratory and various tests were performed on them. Twenty soil samples from the designated cultivation area for both crops, along with twenty samples each of well water and treated wastewater, were collected randomly and in equal quantities. Irrigation was applied by driple tape irrigation system, using 16 mm diameter tubes with dripper spacing of 33 cm and a discharge rate of 1.6 liters per hour, placed on the ridges. The amount of water consumed was measured using calibrated flowmeters. In these tests, the amount of nitrogen and nitrate, EC value, acidity level, exchangeable sodium percentage (SARadj), saturation index, amount of B^-, Cl^-, Na⁺ and So4^2- ions, and levels of heavy metals such as chromium, arsenic, cadmium, copper, nickel, zinc and lead were determined. At the end of the growing season and after harvesting the crops, soil samples were taken from the studied farm and the physical and chemical properties of the soil were also determined. Other chemical properties of the soil, such as salinity levels, pH changes, nitrate nitrogen levels, and heavy metal levels of chromium, cadmium, arsenic, copper, nickel, zinc, and lead, were also measured.

Results and Discussions:
By evaluating the results of the chemical characteristics of well water and treated wastewater, it was determined that well water and treated wastewater were close in terms of electrical conductivity (EC) and pH, and based on the standards proposed by the Food and Agriculture Organization of the United Nations (FAO, 2004) and the World Health Organization (WHO), there are no restrictions for irrigation and growth of the studied crops. The amount of bicarbonate in well water and treated wastewater was found to be 5.25 and 1.75 milliequivalents per liter, respectively. The much lower bicarbonate content of treated wastewater compared with well water is an important advantage, especially in this regard, in the soil of the area in question, which also has a relatively high pH, it has a positive effect on reducing the fixation of cations such as calcium and magnesium, and there is less inhibition of phosphorus absorption in irrigation with treated wastewater water. The amount of sulfate ion in treated wastewater was significantly higher at 3.6 milliequivalents per liter than in well water (average 0.9 milliequivalents per liter). This amount of sulfate is considered an important advantage, especially since it can also be useful in the absorption and transport of elements such as iron, manganese, and zinc by helping to lower the pH of the root environment. The concentrations of calcium and magnesium, as well as the trace elements iron, zinc, and manganese, were significantly lower in well water than in treated wastewater. The high levels of all these elements in treated wastewater also contribute to its value as a source of essential plant nutrients and can be very useful in providing part of the nutritional needs of crops, especially garlic and potatoes. By examining the results of measuring the amount of heavy metals in treated wastewater, it was determined that all five heavy metals that are considered sources of contamination of wastewater are, fortunately, present in very small amounts in the treated wastewater. There was no significant increase in EC, saturated soil reaction, and bicarbonate in the soil in both garlic and potato crops after harvest in the plot where treated wastewater was used. In contrast, the amount of chlorine, sulfate, and copper ions in the soil, in two stages before planting and after harvest, showed a different situation compared with other nutrients, so that after harvest, their amount in the soil increased relatively. The amount of phosphorus, potassium, and nitrogen in the soil, as well as micronutrients, decreased relatively after harvesting of the both crops. The concentration of heavy metal pollutants in the soil in both plots dedicated to garlic and potato cultivation, especially nickel and arsenic, was higher than copper, chromium, and cadmium. However, in terms of pollution and necessary standards, they were lower than the maximum permissible and harmful levels and were of less concern.

Conclusion:
The findings of this experiment collectively demonstrate that the treated wastewater effluent from the Hamadan Province treatment plant is of a satisfactory quality. It meets acceptable standards for EC, sodic salinity, bicarbonate, and chloride. Crucially, levels of heavy metal contaminants, specifically arsenic, nickel, chromium, and cadmium, were below the established maximum limits, indicating no adverse impact on soil pollution or the accumulation of harmful residues. Thus, this treated effluent can serve as a viable alternative water source for irrigating both garlic and potato crops, complementing existing groundwater resources.

Abstract Introduction
In many parts of Iran, excessive groundwater extraction and insufficient recharge have caused significant decline in groundwater levels. The Shahrekord Plain watershed is among the regions experiencing groundwater depletion and negative water balance conditions. Managed Aquifer Recharge (MAR) is widely recognized as an effective approach for improving groundwater resources. Among MAR techniques, underground dams are particularly suitable for dry regions because they store water below the ground surface, reducing evaporation losses and enhancing groundwater availability. Unlike surface dams, underground dams intercept subsurface flow and increase groundwater storage within alluvial deposits upstream of the dam axis. These structures can improve water security, support agricultural production, and increase resilience to drought. The effectiveness of underground dams strongly depends on appropriate site selection. Hydrological, hydrogeological, geological, geomorphological, environmental, and socio-economic factors must all be considered during the planning process. Geographic Information Systems (GIS) have become valuable tools for integrating spatial datasets and supporting water-resource management decisions. GIS-based approaches enable the simultaneous evaluation of multiple criteria and facilitate the identification of suitable sites. Therefore, this study aimed to identify suitable underground dam axes within the Shahrekord Plain watershed using GIS-based spatial analysis as the first stage of a broader groundwater recharge planning framework.
Materials and Methods
This study was conducted in the Shahrekord Plain watershed, southwestern Iran, where increasing groundwater exploitation and recurrent droughts have intensified the need for sustainable groundwater management. A GIS-based spatial analysis framework was developed to identify suitable locations for underground dam construction. Spatial datasets, including digital elevation models (DEM), topographic maps, drainage networks, geological and hydrogeological maps, land-use data, and groundwater information, were integrated within the GIS environment. In the first stage, drainage channels were extracted and analyzed to identify narrow valley sections capable of intercepting subsurface flow with minimum construction cost. This process identified 51 potential underground dam axes. Subsequently, a series of exclusion criteria was applied to remove unsuitable locations. Areas with reservoir slopes greater than 5%, inappropriate land use (urban areas, exposed bedrock, and infrastructure), and unfavorable geological conditions were excluded. Geological investigations focused on identifying impermeable foundations and stable abutments while eliminating zones with fractured formations or high seepage potential. Environmental and socio-economic constraints were also incorporated by mapping qanat systems and defining protective buffer zones to avoid adverse impacts on existing groundwater resources. Finally, reservoir characteristics, including alluvial thickness, potential storage capacity, and groundwater recharge potential, were evaluated using borehole records and available geophysical data. The integration of these spatial criteria within a GIS framework provided a systematic and reproducible procedure for screening and selecting the most suitable underground dam locations in the study area.
Results and Discussion
The GIS-based screening procedure effectively reduced the number of potential underground dam locations by integrating topographic, geological, hydrogeological, environmental, and socio-economic criteria. From the initial 51 candidate axes identified along drainage channels, only 12 sites satisfied all selection requirements. Topographic analysis excluded areas with reservoir slopes exceeding 5%, while land-use evaluation eliminated urban areas, exposed bedrock, and incompatible land-cover classes. Geological investigations further reduced the candidate sites by removing locations with fractured bedrock, unfavorable lithology, or high seepage potential. Hydrogeological evaluation showed that thicker alluvial deposits and higher groundwater storage capacity significantly improved site suitability by increasing recharge potential and subsurface water storage. Incorporating qanat protection buffers ensured that selected sites would not cause adverse affect on traditional groundwater-dependentsystems or downstream water users, thereby improving the environmental and social sustainability of the proposed framework. The final 12 locations exhibited favorable reservoir geometry, suitable impermeable foundations, adequate alluvial thickness, low leakage risk, and minimal conflicts with existing infrastructure. These findings demonstrate that GIS-based multi-criteria evaluation provides a reliable and reproducible approach for identifying suitable underground dam sites while substantially reducing the need for costly field investigations. The results also confirm that successful underground dam planning requires the simultaneous consideration of hydrogeological, geological, environmental, and socio-economic factors rather than relying solely on engineering criteria. Overall, the proposed methodology offers an effective decision-support framework for sustainable groundwater management in semi-arid regions.
Conclusion
This study applied a GIS-based spatial analysis framework to identify suitable underground dam axes within the Shahrekord Plain watershed. By integrating topographic, geological, hydrogeological, land-use, environmental, and socio-economic criteria, the methodology successfully reduced 51 preliminary candidate sites to 12 suitable locations. The results confirm that GIS is a reliable and efficient tool for underground dam site selection and can significantly improve decision-making in groundwater recharge projects. Geological suitability, leakage potential, reservoir slope, alluvial thickness, and protection of existing qanat systems were identified as the most important factors influencing site suitability. The selected sites provide promising opportunities for enhancing groundwater storage, increasing drought resilience, and supporting sustainable water-resource management in the Shahrekord Plain watershed. As the first phase of a broader research program, this study establishes a foundation for future investigations involving multi-criteria ranking, engineering feasibility analysis, economic evaluation, and detailed hydrogeological modeling of the selected underground dam sites.

Abstract Extended Abstract
Introduction:
The Shahrekord plain faces chronic water scarcity, especially during dry seasons, and increasing dependence on groundwater resources to meet domestic, agricultural, and industrial demands. However, uncontrolled groundwater extraction has resulted in declining water tables and reduced aquifer sustainability, highlighting the urgent need for alternative water management strategies. Among the available solutions, subsurface dams have gained attention as an effective and environmentally friendly technique for controlling subsurface flow, enhancing groundwater recharge, and improving water storage capacity in alluvial aquifers. The successful implementation of subsurface dams critically depends on the proper selection of suitable locations, which requires a comprehensive evaluation of multiple hydrogeological, environmental, and socio-economic factors. Accordingly, the main objective of this study is to identify suitable sites and prioritize potential locations for subsurface dam construction within the Shahrekord Plain watershed using an integrated GIS and Multi-Criteria Decision-Making (MCDM) framework.

Materials and Methods
This research adopted a structured two-stage methodological framework. In the first stage, a GIS-based suitability analysis was conducted to identify potential locations suitable for subsurface dam construction. As a result of this process, 12 candidate dam axes were identified as suitable for further analysis. Detailed information regarding this stage is presented in the previous paper. In the second stage, the Analytical Hierarchy Process (AHP) was employed as the MCDM tool to prioritize the selected axes. The decision hierarchy was structured into main criteria, including groundwater quantity/quality, reservoir characteristics, axis conditions, and socio-economic factors, each further subdivided into relevant sub-criteria. Pairwise comparison matrices were developed based on expert judgment, field observations, and a literature review, and consistency ratios were checked to ensure the logical reliability of the comparisons. The weights of criteria were calculated using the geometric mean method. To address uncertainty and potential bias in expert weighting, five different decision scenarios were defined. In Scenario 1, all main criteria were assigned equal importance, representing a neutral decision perspective. In Scenarios 2 to 5, each scenario emphasized one dominant criterion by assigning it a higher relative weight compared to the other criteria, allowing for sensitivity analysis of the decision model. For each scenario, a composite suitability index was calculated for all 12 candidate axes by aggregating standardized criterion values using weighted linear combination methods. Hydrogeological parameters, surface runoff, recharge conditions, soil permeability, and socio-economic indicators were collected and analyzed.

Results and Discussion
The results of the multi-scenario AHP-GIS analysis revealed that although some variations occurred in rankings across different weighting scenarios, the overall prioritization pattern remained relatively stable, indicating the robustness of the decision model. Among the 12 candidate axes, Axis 54 consistently ranked as the most suitable site for subsurface dam construction in all scenarios. This high ranking was mainly attributed to its favorable hydrogeological and geomorphological characteristics, including relatively thick alluvial deposits, substantial subsurface flow availability, moderate slopes, and minimal environmental constraints. Furthermore, its limited negative impact on downstream water users strengthened its environmental and socio-economic acceptability. In contrast, Axis 65 consistently ranked as the least suitable option across all scenarios. The main limiting factors for this site included relatively steep topographic gradients, insufficient aquifer thickness, lower permeability of subsurface materials, and reduced groundwater storage capacity. Sensitivity analysis of the five scenarios indicated that groundwater quantity-related criteria had the greatest influence on site prioritization outcomes, followed by reservoir characteristics such as sediment thickness, permeability, and storage capacity. Socio-economic criteria, including accessibility, agricultural water demand, and proximity to settlements, also played a significant role in refining the final rankings. Water quality parameters were particularly important in excluding areas potentially affected by salinity sources, evaporitic formations, or anthropogenic contamination. The integration of GIS with AHP proved to be a powerful approach for managing complex spatial decision problems. The scenario-based approach further enhanced model reliability by demonstrating that the final ranking was not overly sensitive to minor changes in weighting assumptions.

Conclusion:
This study demonstrated that integrating GIS-based spatial analysis with the AHP provides an effective and reliable framework for identifying and prioritizing subsurface dam sites in complex hydrogeological environments. Applying this methodology in the Shahrekord watershed led to the identification of 12 suitable candidate axes and their evaluation under five different decision-making scenarios. The results consistently identified Axis 54 as the most suitable location, while Axis 65 was determined to be the least suitable due to its unfavorable structural and hydraulic characteristics. Overall, the findings indicated that hydrogeological parameters, particularly groundwater availability and aquifer storage characteristics, were the dominant factors influencing site suitability for subsurface dams. The proposed approach offers a transferable decision-support framework that can be applied to other arid and semi-arid regions.