Iranian Water Research Journal

Abstract Introduction:
Groundwater, as a vital resource for drinking water, agriculture, and industry, plays a crucial role in sustainable development, especially in arid and semi-arid regions. In recent years, factors such as climate change, reduced precipitation, population growth, and over-extraction have led to significant declines in groundwater levels and quality in various parts of the country. In this context, underground dams have emerged as innovative water management structures that reduce surface evaporation, increase water residence time, and enhance artificial recharge, thereby improving both quantity and quality of groundwater. Global studies have demonstrated that underground dams can raise groundwater levels, reduce salinity, and control saltwater intrusion; however, improper design or operation may increase nitrate levels and electrical conductivity (EC), posing risks for drinking and agricultural uses. Chaharmahal and Bakhtiari Province, characterized by semi-arid conditions and over 20 meters decline in groundwater levels during the past three decades, provides a suitable setting for underground dam implementation. The first underground dam in the province was constructed in 2015 in the Yancheshmeh watershed. This study aims to comprehensively evaluate the effects of this dam on groundwater quantity, focusing on water level changes and quality, with special emphasis on EC and nitrate concentrations as key indicators of water suitability and potential health risks.
Material and Methods:
This study was conducted in five main phases: desk studies, field operations, laboratory testing, statistical analysis, and result interpretation. The research focused on an underground dam located on the Zayandehrood watershed, with a reservoir length of approximately 5800 meters and a surface area of 3.5 hectares. (1) Desk Studies: Baseline data related to geology, meteorology, hydrology, hydrogeology, geography, and climate of the study basin were collected. A monitoring plan was developed to define sampling points and measurement locations for groundwater level and quality in wells both upstream (outside the reservoir) and within the reservoir. )2( Field Operations: Groundwater levels were measured monthly and weekly during rainy periods in wells within a one-kilometer radius of the dam from spring 2020 to spring 2024. Measurements were taken using a tape and meter. Water samples were collected seasonally and monthly during rainy periods from two points: a well at the reservoir inlet (furthest from the dam) and a well behind the underground dam. Sampling employed mechanical pumping assisted by a tractor. (3) Laboratory Testing: The collected samples were analyzed at the Agricultural and Natural Resources Research and Education Center laboratory for water quality parameters including pH, salinity, cations (Ca, Mg, Na), anions (Cl, CO3, HCO3, SO4), insoluble salts (lime, gypsum), and nitrate concentrations. This aimed to evaluate suitability for drinking and agricultural use. (4) Statistical Analysis: Data were analyzed using SPSS software and descriptive statistics (mean, standard deviation, range, skewness, coefficient of variation) were calculated. Student’s t-test (with three replicates) assessed significant changes over time, while Duncan’s test compared means at a 95% confidence level. (5) Result Interpretation: Annual groundwater level changes and yield variations in two selected wells were analyzed. Correlations between groundwater level and physical-chemical parameters were evaluated, especially nitrate and salts. The Schuler and Wilcox diagrams were used to assess the underground dam’s impact on water quality for drinking and agricultural purposes.
Results and Discussion:
Groundwater level monitoring was conducted regularly from spring 2020 to spring 2024 with 46 measurement events. These events included post-rainfall sampling . The water level fluctuations in Well 1 (inflow area) and Well 2 (within the underground dam reservoir) showed strong correlation, confirming the direct impact of surface water inflow on the stored groundwater volume. Well 2 had an average water level depth of 6.32 m, with fluctuations between 3.4 and 7.8 m, while Well 1 had an average of 5.81 m with variations from 3.9 to 9 m. The coarse alluvial aquifer of the reservoir was estimated to have the volume of 700,000 m³ and an effective porosity of 20%, yielding a potential water storage capacity of about 140,000 m³. Considering an average saturated thickness of 12 m, the usable groundwater volume was calculated to be approximately 100,000 m³. Despite continuous seasonal withdrawal, the reservoir volume replenished annually, which contrasted with pre-dam conditions, under which water was absent during dry seasons. This stable water supply contributed to a 49.3% increase in cultivated land area between 2019 and 2022. Physicochemical analyses of 47 water samples revealed mostly stable concentrations of chemical parameters, except for bicarbonate, carbonate, and nitrate ions which showed significant seasonal changes. Electrical conductivity (EC) increased during dry periods due to water volume reduction but decreased with recharge, indicating natural dilution effects. Nitrate concentrations peaked during irrigation seasons due to fertilizer use but were diluted during wet periods; nitrate levels were lower inside the reservoir, demonstrating the dam’s mitigating effect on contamination. Water quality classification using Scholler, Wilcox, and Piper diagrams confirmed that the water was suitable for drinking and moderate agricultural use. The water type was predominantly calcium-bicarbonate, consistent with local geology.
Conclusion:
The present study demonstrated that the Yan-Cheshmeh underground dam, strategically located in a suitable geological setting and designed based on hydrogeological principles, has effectively contributed to groundwater storage and management. The impermeable foundation, large volume of coarse alluvial deposits, and considerable reservoir depth enable the storage of approximately 100,000 m³ of usable water. This volume remains sustainably available despite seasonal withdrawals, successfully supporting agricultural demands in the region. Water quality analyses revealed that seasonal water retention in the underground reservoir does not degrade water quality; instead, natural dilution reduces nitrate concentrations. Scholler, Wilcox, and Piper diagrams classified the water quality as ranging from good to acceptable for drinking and from moderate to good for agricultural use. A key strength of this research was the integrated approach combining fieldwork, laboratory analysis, and statistical evaluation over multiple years, which enhanced result reliability. However, limitations included the temporal coverage and sample size, which could be expanded for more detailed seasonal analysis. Overall, the Yan-Cheshmeh underground dam exemplifies a successful nature-based infrastructure for sustainable water resource management in semi-arid areas. It is recommended that similar projects be considered by policymakers and water resource

Abstract Introduction:
Scour around bridge piers is the main reason of bridges destruction. Hydraulic structures act as obstacles to the flow of water near the structure, so that the flow pattern changes and locally causes scour around the bridge pier. Moreover, floating debris are gradually carried by the flow and accumulate around the bridge piers. The shape of the channel as well as the position and the geometry of the bridge pier significantly affect the accumulation of floating debris and tree foliage in front of the bridge pier. The main parameters which affect the scour depth around bridge piers are flow intensity, characteristics of bed sediments, and bridge pier geometry. Previous researches indicated that the maximum scour depth for a sharp nose bridge pier located at the lateral corners of the base, between the nose and the corner. Also, wedge shape debris resulted in a lower scour depth than the rectangular ones due to the less deviation of the flow towards the base.
Materials and Methods:
The experiments were carried out in Shahrekord University laboratory. A rectangular flume was set up with galvanized floor and glass walls. The flume had a length of 20 meters, a width and height of 60 cm, and a constant bed slope of 0.1%. A total number of 52 experiments were conducted under clear water conditions, with and without debris (control sample). A square shape pier with 9 cm side was applied. The bed was covered with 160 mm of sand, with an average sediments particle size of 0.75 mm. The flow depth was kept constant at 20 cm with flow rates of 10, 20, 30 and 40 Lit/s. To simulate wedge-shaped debris, pieces of wood were placed in wedge-shaped net racks in four different sizes (varying in length and width, with a constant height). These debris were installed in front of the square base at three positions: above, below, and at the water surface. Scour depth was measured using a caliper to ensure accuracy. A dimensional analysis was conducted using the Buckingham π theorem to develop a predictive equation for scour depth around a sharp-nose square bridge pier in presence of wedge shape debris.
Results and discussions:
The duration of all experiments in this research was seven hours. To achieve the goals of the research and facilitate better analysis of the results, the initial tests were conducted without floating objects by the flow rates of 10, 20, 30 and 40 Lit/S. Subsequent experiments were carried out in the presence of floating objects in different dimensions and positions (above, below and at the water surface), in front of the square base. It was observed that the floating objects increased the length, width, and depth of the scour hole, and consequently its volume. The level and dimensions of the floating objects in front of the pier had a great impact on the maximum scour depth. Comparison of the three positions of the floating objects in front of the pier indicated that the objects above the water surface created the minimum scour depth, while in cases of the floating objects below the water surface the maximum scour depth occurred. This trend was observed for all the experiments with different debris dimensions. According to the longitudinal and transverse profile of the scour, when the object was positioned under the water surface, the scour hole was formed upstream towards the pier, with a gradually steep slope. For the cases in which debris were located above the water level, the slope was formed more slowly. Also, according to the final changes of the bed profile, for objects with larger dimensions, a larger scour depth was obtained; therefore, more sedimentation happened across the channel. Finally, an equation was extracted to predict scour depth around bridge piers in presence of wedge shape debris, using the results of dimensional analysis and a linear regression with SPSS software. The results of the equation showed the highest R² and the lowest mean square error. Comparing the maximum measured scour depth with the calculated results by the equation confirmed the accuracyof the equation.
Conclusion:
In this study, the scour depth in front of a square pier was investigated without (control sample) and with floating debris in three positions. For different positions of floating objects (below, above and at the water surface level), scour development during time and equilibrium scour depth were measured. The results indicated that 75% of the scouring rate occurred in the first hour, after that the scour depth slowly increased until it stabilized at 420 minutes. Larger debris dimensions resulted in the greater scouring depth around the pier. The transverse dimension had the greatest effect for wedge-shaped objects. The lowest scour depth was observed in the control sample. The accumulation of debris at the three positions of above the surface, at the same level and below the water surface were 1.4, 1.3 and 3.6 times that of the control sample, respectively. The maximum scour depth occurred in the position in which the debris were located below the water surface.

Abstract Introduction:
The velocity distribution in sediment-laden flows is an important and fundamental parameter for calculating the rate of suspended sediment transport. Previous studies have shown that suspended sediments significantly alter the velocity distribution in open channel flows and river systems. Suspended sediments tend to reduce the shear rate near the bed. This occurs because a part of the energy from the flow turbulence is spent on keeping sediment-laden particles in suspension, reducing the energy available for momentum transfer near the boundary. Also, the presence of suspended sediments suppresses the flow turbulence. Therefore, the velocity gradient near the bed shrinks. Consequently, ignoring the presence of these particles in the flow can cause significant errors in the estimation of parameters such as flow discharge and sediment discharge in rivers. Despite efforts to develop relationships for estimating the velocity distribution in sediment-laden flows, the estimation of the parameter is associated with a significant error, and it is essential to use a reliable method that is capable of accurately predicting the velocity distribution while considering the effects of suspended sediments. For this reason, the use of numerical models is a great help to researchers studying the mechanism of suspended sediment transport.

Materials and Methods:
In order to validate and calibrate the results of the numerical model, two laboratory data sets covering a wide range of hydraulic conditions were utilized. The first set of data was from the experiments by Einstein and Chien (1955) which were conducted in a flume 0.307 m wide, 0.357 m high, and 120 m long. These tests were performed on smooth and rough beds with slopes of 0.00185 and 0.0025. Sediment particles with diameters of 1.3, 0.94, and 0.274 mm were used. Sediment concentrations were determined by collecting point samples from the flow using a tube. At each sampling point, three to 15 samples with a volume of one liter were taken. About 16 data sets was chosen from the first set of experiments. The second set of data originated from the experiments of Vanoni (1946) conducted in a rotating flume with 0.305 m deep, 0.845 m wide, and 18.3 m long. The number of measurement points varied from 7 to 17, covering 2% of the flow depth. The flow rate varied from 28.3 to 155.7 L/s. The bottom of the flume was covered with sand particles with an average diameter of 0.47 mm and 0.88 mm. In the current study, Flow-3D software was used as a numerical simulation tool. Flow-3D software is a comprehensive software package in the field of computational fluid dynamics. This software package uses advanced numerical techniques to solve three-dimensional equations of fluid motion for multiphase problems.

Results and discussions:
By examining the experimental data of relative velocity (u/u*) versus relative depth (y/h) at different sediment concentrations on a semi-logarithmic scale, it was observed that the presence of suspended sediments in the flow caused a deviation from the logarithmic distribution observed in the experimental data. The amount of change in the inner region was greater than that in the outer region. After running the numerical model with different mesh sizes, a mesh size of 10 mm was selected as the optimal mesh size for running the numerical model in this study. The K-ε model was selected as the turbulence model for the present study. After ensuring the performance of the FLOW-3D numerical model in estimating the velocity distribution of sediment-laden flows, the effect of parameters such as bed roughness, suspended sediment diameter, and initial flow concentration on the velocity distribution was investigated. The purpose of this section is to simulate conditions that cannot be achieved in the laboratory, and the use of a numerical model provides valuable insights into the sediment-laden flow pattern.

Conclusions:
The results showed that the FLOW-3D numerical model demonstrated acceptable accuracy in estimating velocity values at different depths. The average error rate of the numerical model in estimating velocity distribution values was 12.6% for Vanoni data and 75.3% for Einstein and Shen data. In general, it can be said that the numerical model overestimates velocity values at shallow depths (inner region of velocity distribution) and underestimates them at greater depths (outer region) compared with the measured values. These results indicate that using the FLOW-3D numerical model provides a more accurate estimation of velocity in sediment-laden flow than employing empirical relations.

Abstract Introduction:
Managing municipal sewage sludge has evolved into a critical environmental and economic challenge globally due to its constantly increasing volume and the complex issues surrounding its safe and cost-effective disposal. Conventional methods like landfilling or incineration are often expensive and carry significant environmental risks, including the release of greenhouse gases and potential contamination of soil and groundwater. This situation underscores the urgent need for finding sustainable and circular economy solutions for resource recovery. The utilization of processed sewage sludge (biosolids) as a soil amendment or agricultural fertilizer offers a promising sustainable pathway. This material is rich in essential macronutrients like nitrogen, phosphorus, and potassium, which are vital for plant growth. Furthermore, its high organic matter content effectively enhances the soil's physical structure, improves water retention capacity, and stimulates microbial activity. This practice not only provides a valuable outlet for waste management but also significantly reduces agriculture’s reliance on costly synthetic fertilizers, contributing to greater overall system sustainability. However, potential risks, particularly the presence of heavy metals and pathogens, necessitate careful evaluation of its safety and efficacy before widespread agricultural application.

Material and Methods:
This study evaluates the effectiveness and risks of using sewage sludge from the wastewater treatment plant in the city of Tiran, Isfahan province, for growing summer vegetables. The research was conducted in 2024 using three different mixtures of soil and dried sludge at weight ratios of 0%, 20%, and 40% for the cultivation of tomatoes, eggplants, and peppers in a greenhouse. The Tiran wastewater treatment plant, located at 32°38'21.88" N and 51°11'12.20" E, uses an anoxic-aerobic biological process with an average flow of 864 cubic meters per day to treat the wastewater of its covered population. Plants were grown in pots with a height of 40 cm and a diameter of 30 cm, holding approximately 3.5 kg of soil. Seedlings of each vegetable were surface-sterilized with a 2% (w/v) sodium hypochlorite solution for 10 seconds before planting. For each scenario, four pots were initially cultivated. After one month, one pot with the least similarity to the others was removed, leaving nine pots per product for further research. During the growth period, weeds were manually removed, and no other fertilizers or chemicals were used. The pots were irrigated with municipal drinking water every three days for the first 30 days, and then every four to five days, until the soil reached its field capacity. Key soil characteristics, including pH, electrical conductivity (ECe), organic carbon, total nitrogen, available phosphorus, and heavy metals (lead and cadmium), were analyzed. Standard methods such as the Kjeldahl method for total nitrogen and atomic absorption spectrophotometry (model B1100 Perkin Elmer) for heavy metals were used. Plant growth parameters, including the total number of fruits, total fresh fruit weight, number of branches, main stem diameter, and plant height, were measured during the harvest period, which began 60 days after planting and continued for 30 days. The data were statistically analyzed using SPSS software.

Results and Discussion:
The addition of sludge reduced the soil pH from 6.78 to 6.7 and 6.5 in the 20% and 40% sludge treatments, respectively, although these changes were not statistically significant (p>0.05). The application of 20% and 40% sludge increased organic carbon levels by 128% and 258%, respectively. Total nitrogen content also significantly increased from 0.08 g/kg in the control sample (0% sludge) to 1.82 g/kg in the 40% sludge treatment. The concentration of available phosphorus rose from 13 mg/kg to 3400 mg/kg, highlighting the sludge's potential as a rich source of nutrients. Statistical analysis revealed significant differences (p<0.005) in growth parameters, including plant height and stem diameter, with increasing sludge percentage. Maximum plant height and stem diameter were recorded at 73 cm and 19 mm, respectively, in the 40% sludge treatment. Furthermore, plants grown in the 40% sludge mixture showed an average 70% increase in fruiting compared to the control group. The heavy metal content in the sludge, specifically lead and cadmium, was measured at 2.8 and 1.4 mg/kg, respectively, which were below permissible limits. The processing method involving aeration and sunlight exposure successfully reduced pathogen levels in the sewage sludge

Conclusion:
The findings of this research indicate that applying sludge at concentrations of 20% and 40% not only enriches the soil with essential nutrients like nitrogen, phosphorus, and potassium but also improves its fertility. Higher sludge concentrations positively correlate with improved plant growth metrics, including total fruit production, plant height, and stem diameter, emphasizing its importance as a nutrient-rich organic amendment. This study alleviates concerns about heavy metal accumulation, as the observed levels were within safe limits, ensuring the safety of this agricultural practice. Overall, the processed sewage sludge effectively enhances the growth of the three selected plants and improves soil fertility without increasing heavy metals or pathogens. The study highlights the importance of preventing industrial wastewater and agricultural runoff from entering urban sewage networks and using physical dewatering processes without chemical polymers to produce safe sludge.

Abstract Extended Abstract

Introduction:
Climate change, as one of the main challenges of this century, has significant impacts on the hydrological cycle and water resources management, especially in arid and semi-arid regions. Temperature changes, precipitation fluctuations, and increased occurrence of extreme events such as floods and droughts threaten the sustainability of water systems. In this context, hydrological models such as the Soil and Water Assessment Tool (SWAT) serve as effective tools for simulating watershed responses to various climatic scenarios. At the same time, the new climate scenarios presented in the sixth report of the IPCC and the new generation GCM models have enabled a more accurate assessment of hydrological responses. Numerous studies conducted in regions such as China, India, Iran, and South Korea have demonstrated that climate change can significantly alter surface runoff patterns, typically increasing runoff during wet seasons and reducing flow during drier periods. Therefore, a detailed study of the hydrological response of watershed under different climate change scenarios can play a key role in developing sustainable water resources management strategies in the future.

Material and Methods:
The SWAT model (Soil and Water Assessment Tool) was applied in this study to evaluate the impact of climate change on the hydrologic response of the Golroodbar watershed, Semnan Province, Iran. The input data, which were collected from authoritative sources, included digital elevation models (DEM), land use/land cover maps, soil maps, and climatic and hydrological time series. The SWAT model was calibrated and validated with observed streamflow to simulate surface runoff under the baseline climate conditions. For future climates, outputs of CanESM5 global climate models were used under the Sixth Assessment Report of the IPCC (CMIP6), including three Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, and SSP5-8.5). The Statistical Downscaling Model (SDSM) was used to downscale the GCM daily precipitation and temperature to the basin scale. The downscale future climate data were used as for the inputSWAT model to simulate runoff for different future time periods. Next, seasonal runoff patterns for each climate scenario were viewed and compared with the baseline. This methodological design enables a realistic and holistic hydrological analysis of basin responses to future climate, providing a foundation for adaptive water resource management can be conducted in semi-arid watersheds.

Results and Discussion:
The simulation results demonstrated that the SWAT model performed well in simulating the surface runoff in the Golarudbar watershed. The model accuracy was acceptable with Nash-Sutcliffe Efficiency (NSE) and Coefficient of Determination (R²) values of 0.66 and 0.66 during the calibration period, and 0.55 and 0.79 during the validation period. The p-factor and r-factor values were also within satisfactory ranges in both periods. Future climate scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5) were simulated using the SDSM model with CanESM5 data. These scenarios showed significant changes in monthly average precipitation and temperature compared with the historical baseline. According to the results, in the warm months of the year (May to September), precipitation remains very low and almost similar to historical values; although in some months such as June, a slight increase is seen in the SSP5-8.5 scenario. After that, the precipitation trend increases again from October. Overall, the SSP5-8.5 scenario shows the greatest change in the precipitation pattern, which could indicate an increased likelihood of heavy rainfall and flooding in the future. Also, a decrease in runoff is observed in most months compared with the historical period. The largest decrease in runoff is in January in the SSP1-2.6 scenario, which is -64.05 percent, which indicates a significant effect of the decrease in temperature and precipitation in this scenario. In contrast, the largest percentage increase in runoff is in August, July, and November in the SSP5-8.5 scenario, which is 51.30, 33.98, and 33 percent, respectively. This trend indicates that runoff increases due to more intense short-term precipitation caused by global warming conditions.

Conclusion:
This study demonstrated that the SWAT model effectively simulates the hydrological pattern of the semi-arid Golrudbar basin, capturing runoff variation accurately. Climatic and physiographic parameter optimization and statistical index-based validation ensure maximum credibility of the results. Downscaling climate predictions from the CanESM5 model at different greenhouse gas emission scenarios demonstrates that temperature and precipitation variability has significant impacts on runoff patterns. The SSP5-8.5 high-emission scenario predicts greater peak runoff and increased variability in surface flow, suggesting a potential increase in future flood hazards. Lower-emission scenarios like SSP1-2.6 has more symmetric trends in runoff. The findings highlight the need for wise climate policies and adaptive strategies, especially in arid and semi-arid regions, to ensure sustainable water resource management and flood risk reduction under climate change.

Abstract Extended Abstract

Introduction:
Water scarcity has become one of the most critical challenges to sustainable agricultural production, particularly in semi-arid regions. Efficient irrigation management and soil amendments such as biochar have shown great potential in improving soil structure, enhancing water retention, and increasing crop productivity under limited water supply. Tomato ( Solanum lycopersicum L. ) is one of the most economically important vegetable crops, yet it is highly sensitive to water deficit. The relationship between irrigation levels and crop yield can be analyzed through production functions and water use efficiency (WUE), which provide valuable insights for optimizing water productivity. Moreover, the Relative Growth Rate (RGR) serves as an important indicator to assess plant growth dynamics under different management conditions. This study aimed to evaluate the combined effects of various irrigation levels and biochar application rates on WUE, production function, and RGR of greenhouse-grown tomato. The findings are expected to contribute to improving irrigation strategies and sustainable resource use in protected cultivation systems.

Materials and Methods:
The experiment was conducted as a factorial arrangement in a randomized complete block design with four replications in the greenhouse of Lorestan University during winter and spring for 120 days. The mechanized polycarbonate greenhouse (20 × 9 m; 6 m height) provided controlled conditions, including 18–28 °C temperature, 50–70% relative humidity, and 500–600 µmol m⁻² s⁻¹ light intensity. Experimental factors included seven irrigation regimes—50 (L50), 60 (L60), 70 (L70), 80 (L80), 90 (L90), 100 (L100), and 110 (L110)% of crop water requirement based on soil moisture depletion and three levels of rice bran biochar: 0 (B0), 3 (B3), and 6 (B6) t ha⁻¹. Biochar was produced from agricultural residues using a muffle furnace under nitrogen gas at 500°C to ensure an oxygen-free environment. In total, 21 treatment combinations were applied to 84 pots, with L100 and B0 serving as the control.
Soil physical and chemical characteristics, including bulk density, pH, electrical conductivity (EC), cation exchange capacity (CEC), and organic carbon, were measured following standard .Water use efficiency (WUE) was calculated as the ratio of total fruit yield to the amount of water consumed. The production function between yield and evapotranspiration (ET) was fitted using a second-degree polynomial regression model to determine yield response to irrigation. The crop yield response factor (Ky) was also calculated according to the Stewart model (1977). Relative Growth Rate (RGR) was determined based on changes in plant biomass over. Data were statistically analyzed using ANOVA, and mean comparisons were performed using the least significant difference (LSD) test at the 5% significance level.

Results and Discussions:
The results demonstrated significant effects of both irrigation levels and rice bran biochar application on tomato yield, WUE, and growth parameters. The highest WUE value was recorded with (L90) combined with 6 t ha⁻¹ biochar (B6), indicating improved water productivity with minimal yield reduction compared to L100. The nonlinear (quadratic) relationship between yield and water use was fitted between tomato yield (Y) and cumulative water use (X), with an R² of 0.945, indicating that 94.5% of yield variation was explained by water consumption. In this study, Ky was calculated using the Doorenbos and Kassam (1979) model and was estimated at 0.77, which is lower than the FAO value for tomato (1.05). This lower Ky suggests that, under the experimental conditions, the crop exhibited reduced yield sensitivity and a degree of tolerance to water stress. In fact, the application of biochar reduced this sensitivity by improving soil moisture retention and root environment. Although Relative Growth Rate (RGR) naturally declined after early growth, biochar treatments, particularly B6, mitigated the negative effects of water stress, enhancing RGR by 10–25% and highlighting its role in promoting vegetative growth throughout the growing period.

Conclusion:
The results of this study indicated that the application of biochar combined with appropriate irrigation significantly improved tomato growth, yield, and water-use efficiency (WUE) The highest WUE was observed at 90% crop water requirement (L90) with 6 t ha⁻¹ rice bran biochar (B6), reflecting water savings without reducing yield. Biochar enhanced soil water retention, root environment, and nutrient uptake, while the quadratic production function revealed a nonlinear relationship between yield and water use, with a Ky of 0.77 indicating low yield sensitivity to water deficit. Relative Growth Rate was also increased in biochar-treated plants, particularly under optimal irrigation, highlighting improved vegetative growth and biomass accumulation. Overall, integrating biochar with precise irrigation management can enhance water productivity, maintain yield, and support sustainable agriculture in semi-arid regions.

Abstract Introduction:
Water quality plays a crucial role in sustaining aquatic ecosystems, human health, and socio-economic development. River ecosystems are particularly vulnerable to anthropogenic pressures such as urbanization, agricultural runoff, and industrial discharges, which disrupt their physicochemical balance and ecological integrity. Monitoring key water quality parameters—such as Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Nitrogen (TN), Total Phosphorus (TP), Total Suspended Solids (TSS), and pH—is essential for assessing the health of river systems. Seasonal variations, especially between dry and wet periods, can significantly influence pollutant concentrations due to changes in river discharge, dilution, and runoff intensity. In regions like Kurdistan Province, Iran, where rivers such as Gheshlagh and Gaveroud converge into the Sirvan River, the combined impacts of municipal effluents and agricultural return flows pose serious environmental challenges. This study aims to evaluate the spatial and temporal variations of major physicochemical parameters using the Inverse Distance Weighting (IDW) method within a GIS environment to identify pollution hotspots and provide insights for sustainable watershed management.

Materials and Methods:
Water samples were collected at six selected stations along the Gheshlagh and Gaveroud tributaries and the main Sirvan River during two contrasting seasons—summer (low flow) and winter (high flow) of 2024. Station 1, located downstream of Gheshlagh Dam, served as a reference site with minimal anthropogenic influence, while stations 2–4 were situated upstream and downstream of the Sanandaj wastewater treatment plant to assess the effects of effluent discharge. Station 5 represented the Gavehroud tributary with relatively low pollution, and station 6 was located at the Sirvan outlet near Zhaveh Dam. Three replicate samples were collected per site at a depth of 20–30 cm using pre-cleaned polyethylene bottles, transported on ice at 4°C, and analyzed according to APHA (2017) and WHO (2017) standards. BOD was determined using the five-day incubation method at 20°C, COD by the dichromate oxidation method, TN through persulfate digestion followed by spectrophotometric detection, TP via ammonium molybdate–ascorbic acid reaction, and TSS by gravimetric filtration through 0.42 μm glass-fiber filters. pH was measured in situ using a calibrated WTW portable meter. Spatial interpolation of the measured parameters was conducted using the IDW technique in ArcGIS 10.8, with a power parameter of 2, a search radius including 8–12 neighboring points, and a raster cell size of 30 m. This method assigns weights inversely proportional to the distance between sampled and unsampled locations, enabling the continuous prediction across the study area.

Results and Discussions:
The spatial maps derived from the IDW model revealed distinct seasonal trends in water quality. During summer, BOD exceeded 6 mg/L near stations 2 and 3, indicating the impact of untreated municipal effluents from the Sanandaj wastewater treatment plant. In contrast, the Gaveroud tributary (station 5) exhibited the lowest BOD values. COD values surpassed 25 mg/L in summer and increased to over 50 mg/L in winter, likely due to enhanced surface runoff carrying refractory organic compounds. The lower BOD/COD ratio in winter confirmed the dominance of non-biodegradable organic matter. The persistently high TN values in both seasons indicated sustained nutrient loading from domestic sewage and agricultural fertilizers. TP levels in summer exceeded 3 mg/L at stations 3 and 4—several orders above global thresholds for eutrophication (0.05 mg/L)—and showed a slight decline. This sustained phosphorus enrichment represents a critical eutrophication risk to downstream reservoirs such as Zhaveh Dam. TSS concentrations reached up to 80 mg/L in summer but decreased to 20–60 mg/L in winter due to dilution. Elevated suspended solids reduced water transparency and may impair photosynthetic activity and fish habitats. The pH values remained stable (7.6–8.2) across stations and seasons, staying within the safe range for aquatic life. Overall, spatial interpolation using IDW effectively delineated pollution gradients, particularly downstream of the wastewater discharge, confirming the method’s reliability in riverine water quality assessment.

Conclusion:
This study demonstrated that the Gheshlagh, Gaveroud, and Sirvan River systems are significantly influenced by municipal wastewater and agricultural runoff, particularly during the dry season. The marked increases in BOD, COD, TN, and TP in summer indicate intensified organic and nutrient pollution, leading to potential eutrophication and ecological degradation. Although winter flows partially dilute pollutants, persistent pollutant loads remain a serious concern. The application of the IDW interpolation method in GIS effectively visualized spatial pollution patterns and identified critical hotspots, supporting its use as a practical tool for environmental monitoring and watershed management. To safeguard the ecological integrity of these rivers, stricter wastewater control measures, improved treatment plant efficiency, and the adoption of sustainable agricultural practices are urgently recommended.

Abstract Introduction:
Among the most important structures of water intakes, various types of Neyrpic gates can be highlighted, which are now extensively used in irrigation and drainage networks in our country. These water intake structures are designed to deliver water under non-uniform flow conditions in a way that ensures each branch canal receives its designated flow. These types of modular gates are selected for controllable water intake in canals and some diversion dams and include five types: X, XX, L, C, and CC. They are named with the index 1 or 2, respectively, depending on whether they are single-blade or double-blade, and are used at the installation site according to the required water intake rate and hydraulic conditions. The flow through these modular gates can be varied over the entire upstream level range close to the nominal value and within ±5% to ±10% of the flow. These devices control the flow through the combined weir and orifice method. In assessments conducted in the country's irrigation networks, it has been observed that the discharge from the water intake gates is not equal to the nominal discharge, and in some water intakes it is more and in some water intakes it is less than the design rate. Due to existing restrictions and the lack of specific instructions for producing these gates domestically, the specifications of the manufactured gates are different from standard gates.

Materials and Methods:
When reviewing Iranian and foreign sources to select the geometric dimensions of the structure, it was observed that most of the geometric dimensions presented in scientific sources are in complete agreement with each other, but there is a difference of opinion regarding the opening of the gate (vertical height of the blade relative to the crest of the spillway) by approximately 4 mm (the actual estimated number is 4.4 mm). Laboratory model 1, with an opening height of 90 millimeters, was constructed from the intersection point of the upstream and downstream slopes of the spillway, while laboratory model 2, also with an opening height of 90 millimeters, was prepared from the tangent line of the upper edge of the spillway and placed in testing after adhesive application, positioning the blade of the second model 4 millimeters lower compared to the first model. In fact, the total opening of the gate in the first model is 94 mm, but in the second model, the total opening of the gate is 90 mm. Also, in reviewing the available scientific sources, it was observed that there are three different methods for using the stage-discharge curve. Therefore, in this study, in order to investigate this duality in sources and determine the appropriate model, first, laboratory data were measured and stage-discharge curves were drawn for the two mentioned laboratory models, and then three different data extraction methods were used for both mentioned laboratory models. The first method is consistent with the stage-discharge curve presented by Bos (1989), the second method is a proposed method based on the design discharge point being known at the break point of the stage-discharge curve between the first and third methods, and finally the third method is consistent with the stage-discharge curve presented in other available scientific sources such as Amiri-Tokladany and Siahi (2015). In the present study, two criteria, root mean square error (RMSE) and coefficient of determination R2, were used in the Microsoft Excel software environment.

Results and Discussion:
The general trend of the two stage-discharge curves for the two laboratory models is similar, but due to the larger opening of the first model (94 mm) compared to the second model (90 mm), the water flow head that leads to the onset of interference of the model blade is also different and changes from a higher head in the first model (approximately 16 mm) to a lower head in the second model (approximately 13.5 mm). In general, it is observed that by changing the angle of the gate body from horizontal (zero slope) to slopes of ±5 and ±10 degrees, the gate flow coefficient decreases and the stage-discharge curve shifts towards lower flow rates. The justification for this difference in the curves is that changing the slope angle of the flume bottom from zero to the horizon leads to a change in the slope of the spillway body and the geometric characteristics of the module gate. From comparing the stage-discharge curves of scientific sources with the results of the arranged laboratory data, it can be concluded that the second laboratory model apparently has a very good agreement with the standard curve, but the first model shows a huge difference. In fact, the first model has an opening of 94 mm and has a larger opening (4 mm) and starts the flow interference at a higher head and discharge. Also, a calculation table was created for 5 key points in the stage-discharge curve (Q, 1/1Q, 1/05Q, 0/9Q, 0/95Q) to determine the minimum root mean square error (RMSE) and the maximum coefficient of determination R2 between regression models between the six studied cases with standard data (for two laboratory models and each for three data extraction methods).

Conclusion:
Generally, the Stage-discharge curves in model 2 demonstrated better alignment with the Stage-discharge curve of the standard gate compared to model 1, which had a larger opening. The laboratory data of Model 1 were generally much higher than the design values by comparing the Stage-discharge curve for all three data extraction methods, while the laboratory data of Model 2 were generally slightly lower but close to the design values for all three methods. The result is that geometric model number 2 has been approved for constructing the geometry of the X1 type module gate, and the basis for the gate opening should be the tangent line to the curvature of the spillway. It was also observed that data extraction method 2 showed closer alignment with the experimental results, whereas method 1 indicated a significant deviation. Therefore, determining the important design points in the Stage-discharge curve using the method presented by Bos (1989) shows a significant difference with the experimental results. Additionally, the impact of changes in blade angles and upstream and downstream spillway slopes (due to the presence of slopes in the flow) on the Stage-discharge curve was investigated, and the influencing factors in these differences were discussed.