نشریه راهبردهای فنی در سامانه های آبی
پیاپی 1 (تابستان 1402)

In drainage and irrigation channels, vertical drop structures are commonly used to transfer water from a higher elevation to a lower one. At the downstream end of these structures, measures are taken to prevent channel bed erosion and reduce the destructive kinetic energy. In the present study, the effect of a nonextended step on the relative energy of the vertical drop structure was investigated using the FLOW-3D software and RNG turbulence model. Two relative heights and three relative widths for the step were considered, and the relative critical depth range was chosen between 0.2 and 0.5. The results indicate that the computed values of downstream relative depth show good agreement with experimental data. Additionally, both extended and non-extended step configurations yielded similar results, with an increase in the relative height of the step resulting in a reduction in the relative remaining energy. In other words, at a constant relative height of the step, for all critical relative depth values, the drop and turbulence generated in the plunge pool are the same for both extended and non-extended step models. Furthermore, employing a tranquility basin downstream reduced the wall height and length of the tranquility basin by more than 12% compared to the model without a step.

The Isfahan water treatment plant, with a final capacity of 12.5 cubic meters per second, is one of the largest water treatment plants in the Middle East. It has 10 sedimentation basins with a retention time ranging from 1.91 to 2.75 hours; each basin has a volume of 9172 cubic meters and a surface load of 14.2 to 2.85 cubic meters per square meter per hour. This research was conducted to investigate the efficiency of the combined use of accelerator sedimentation basins equipped with tube settlers on a full and field scale. The goal was to achieve greater efficiency in improving the quality of output water and managing the reduction of water wastage, backwashing time wastage, as well as reducing the need for repairs and maintenance of treatment plant equipment. In this study, the accelerator sedimentation ponds related to two stream 1 clarifiers from the first phase of the treatment plant were equipped with rapid tubular settlers made of food-grade polypropylene. These settlers are hexagonal in shape with a hydraulic diameter of 50 to 80 mm; placed at a 60-degree angle to the surface, and have a length of 90 cm. Stream 2 was operated without the simultaneous use of rapid tube settlers in the circuit. The amount of backwashing’s of filters, the number of times the aerators and backwashing pumps are engaged in the circuit, the amount of water wastage, and the time required for each wash in streams 1 and 2 were compared with each other. The results of this study showed that the number of times of reverse washing of filters was reduced by an average of 25% compared to stream 2. This action also reduced the amount of water used for backwashing the filters and consequently reduced the number of working hours of the electrical and mechanical equipment of the water treatment plant.

Piano key weirs are a type of long-crested weirs with a light foundation and a high discharge coefficient. Due to the high efficiency of these weirs, it is essential to find ways to increase their energy dissipation and ultimately reduce scour. This study investigated the energy dissipation of piano key weirs with a jump in their outlet keys. A laboratory experiment was conducted using a trapezoidal piano key weir with three discharges of 0.3, 0.35, and 0.4 cubic meters per second. Two jumps with radii of 0.21 and 0.15 meters and jump heights of 0.14 and 0.075 meters were also used. The results showed that the energy dissipation increased with increasing jump radius. The energy dissipation in the weir with a jump radius of 0.21 meters and in the weir with a jump radius of 0.15 meters is approximately 3.8% and 2.5% higher, respectively, than in the weir without a jump. The average energy dissipation in weirs with jump radii of 0, 0.15, and 0.21 meters was 54.1%, 55.4%, and 56.2%, respectively. With increasing jump radius and jump height, the discharge coefficient decreases. The discharge coefficient in piano key weirs with jump radii of 0.21 and 0.15 meters is reduced by 10.9% and 3.9%, respectively, compared to the weir without a jump. The use of a jump in the outlet keys of a weir can throw the flow forward of the weir toe. This can be effective in reducing scour.

Advancements in technology have significantly facilitated fieldwork for engineers and researchers by providing new tools and methods. Utilizing tools and software designed for routing, orientation, and traffic management has proven highly efficient and effective in field surveys, particularly in river engineering. One such software is AlpineQuest. This application is easily installable on both Android and iPhone devices, granting users access to topographic maps, Google Earth imagery, slope maps, and more for any location on Earth. Additionally, AlpineQuest aids in determining the optimal route efficiently in terms of cost and time. This software offers various capabilities, including sketching, data collection in different formats, compatibility with other engineering software, and geometry calculations. In this study, AlpineQuest was used during a field visit to investigate the causes of the July 2022 flood in Rafsanjan. The software was used to register the accident locations, critical intersection structures, and the entrance to the floodway. The flood polygon was mapped and point data were defined within the application. Initial analyses of the field sites were conducted using Google Earth maps, Google Hybrid, and AlpineQuest slope maps. Subsequently, all data collected during the field visit were exported from AlpineQuest in GIS format. The findings indicate that factors such as long-term precipitation, urban development in the downstream alluvial fan, critical intersection structures near accident locations, and the presence of unregulated flood control structures upstream from Rafsanjan airport were responsible for the flood in Rafsanjan City.

In this study, the hydrological processes of Khaveh Watershed located in Markazi province, Iran were simulated and the effect of check dams on floods in this basin was evaluated. To assess the impact of watershed management structures on floods, flood volume and peak discharge with different return periods were calculated. In order to estimate the irrigation rate of Khaveh Watershed, in this study, the method of Justin was studied. Then, flooding situation of Khaveh Watershed was simulated using HEC-HMS model. For this purpose, the flood hydrographs resulting from the design storms with different return periods in the pre- and post-construction states of watershed management structures were compared with each other. The results showed that the constructed dams clearly reduced the peak discharge and flood volume of the region. Based on the results, the construction of corrective structures has reduced the peak flow, increased the base time of the hydrograph and increased the time to the peak of the hydrograph in different return periods. For the 5, 10, 20, 50, and 100-year return periods, the peak is 0.6 to 3.3, 4.9 to 2.7, 9.4 to 1.5, and 6, hours respectively. Discharge decreased to 0.8 and 22.4 to 12.4 cubic meters per second. Also, the base time of the hydrograph for the mentioned return periods increased from 6.8 to 11.2, 9.3 to 0.16, 2/10 to 17.5, 5/10 hours to 18.5 and 10.10 to 29.3 hours. The latency in time-to-peak for hydrographs due to the construction of structures was approximately 3.5 h.

Arched concrete dams are three-dimensional structures that, in terms of their special shape resembling a huge shell, transfer the water pressure from the tank to their stone supports. Besides the forces of weight, hydrostatic pressure and thermal stresses, another significant force that the dam's structural system must withstand is the dynamic forces generated by earthquakes. In such dams, there is a possibility of nonlinear behavior due to the change in the location of the two faces of the contraction joints, cracking, corrosion, or non-linear behavior of the concrete of the dam body depending on the intensity of the earthquake. Dynamic analysis of time history, assuming that the dam body is an integrated structure with elastic behavior, usually leads to the creation of significant tensile arch stresses in the upper levels of the dam, which is not in accordance with reality. Since the arch dams are built as ridge blocks, due to the opening and closing of the contraction joints during the earthquake, the released tensile stresses and internal forces are redistributed from the arch performance mode to the ridge performance. As a result, by reducing the level of tensile stresses and energy consumption as a result of joint closure, the risk of concrete cracking and dam destruction is greatly reduced.

Water loss is a significant issue that leads to substantial damage to water resources, civil infrastructure, the environment, and water distribution companies. Urban water supply networks, particularly in regions with scarce water resources, face challenges related to water loss. Leakage from these networks constitutes a major portion of the overall water loss. Factors contributing to leakage include the aging of water supply systems, pipe damage due to soil stresses and urban traffic, fluctuations in water pressure, improper urban plumbing practices, and inadequate embankments. Examining factors such as pressure, pipe type, soil environment, and temperature can help identify the causes of leakage and effectively manage and mitigate its volume. Laboratory and field investigations have revealed that the leakage power, contrary to the pressure-leakage relationship, falls within the range of 0.5 to 2.79, with values exceeding 0.5 due to variations in pipe types, dimensions, and the type of cracks. Reducing the D50 (median grain size) of the soil and selecting an appropriate soil granulation around the pipes can effectively reduce the leakage flow rate. This article provides an overview of water wastage, its types, and underlying causes, followed by a discussion on the fundamentals of leakage calculation.