فصلنامه علوم و مهندسی آبیاری
سال چهل و ششم شماره 3 (پاییز 1402)

Hysteresis during supercritical flow is an issue that is not well understood. It occurs near structures in water supply systems, water transmission lines, and channels. The hysteretic behavior of a flow causes different states in the flow for otherwise identical conditions. (Defina and Viero, 2018) investigated the behavior of supercritical flow near a vertical gate. They proposed a theory for predicting hysteresis in the vicinity of a gate based on the Froude numbers upstream and downstream of the gate as well as on the gate opening ratio. Their results also confirm the existence of hysteretic behavior of the flow. The experiments also confirmed the validity of the theory on the effect of upstream and downstream Froude numbers on hysteretic behavior. (Defina and Viero, 2010) examined the various states created by the flow in a gradual narrowing. They showed that the friction and slope of the channel floor affect the stability of the flow and can create different hysteretic loops.The main purpose of this study was to investigate the contradictory behavior of supercritical flow with a sill located in the flow path and with different geometries. The existence of such contradictory behavior occurs due to hysteresis, for which there are relatively limited studies. Generally, the occurrence of hysteresis at the collision of the flow with the obstacle is expected. As for the same input current, two different behaviors are observed that behavior depend on the flow cycle. The flow cycle means increasing the discharge to a certain value and then decreasing it to the initial discharge.

Water scarcity is the most important factor limiting the production of agricultural products, especially in arid and semi-arid regions. Application of some materials such as superabsorbent polymers in soil increases water retention in soil and thus reduces water consumption and fertilizer leaching. These materials can reduce the effects of dehydration on the plant and lead to increased yield in arid and semi-arid regions. In order to investigate the effect of superabsorbent under water stress conditions on yield, yield components and some physiological characteristics of corn, experimental plots were conducted in the form of split plots in a randomized complete block design in Gotvand region in Khuzestan province. Three treatments of Aquasorb 3005 (600,300,0 kg / ha) A1, A2 and A3 and four irrigation strategies (50,75,100,125) percent of water requirement I1, I2, I3 and I4 in three replications for two growing seasons, respectively Summer 2019 and spring planting 2020) were considered. Irrigation planning, biological yield, harvest index and canopy cover were measured at different stages of growth seasons, based on which a growth simulation model was presented using AquaCrop software. The results of this test showed that the use of Aquasorb 3005 increased product performance by one percent. In addition, the results show the effect of superabsorbent application and irrigation planning on improving water efficiency. The highest grain yield in spring and summer cultivation was related to I2A3 treatment equal to 9055 and 9255 kg / ha, respectively, and the lowest yield in both crops was related to I4A0 treatment equal to 5977 kg / ha in spring cultivation and 6344 kg / ha in summer cultivation.

Climate change means any specific change in the long-term average weather state that occurs for a given location or for the entire globe (Goudarzi and Koupaei, 2020). Climate change is one of the most critical factors threatening food security, and it is expected to make food and nutrition security more challenging in the future (Carpena et al., 2019). It will affect the agricultural sector by changing the irrigation water requirements, crop yield, and water productivity (Boonwichai et al., 2018; Liu et al., 2019). Rice is the third most important crop in the world, following wheat and maize (Kapela et al., 2020). The occurrence of water shortages and droughts have raised concerns about the sustainability of rice production, including the main rice cultivation production region of Mazandaran in Iran (Yosefian 2018). Most studies have reported that rice production will decrease in the future due to a projected increase in temperature and a projected decrease in precipitation) Basak et al. 2010; Boonwichai et al. 2018; Nasir et al. 2020; Nicolas et al. 2020). Although many farmers, particularly in Iran, feel that permanent flooding conditions for rice farming are inevitable, climate change forces the use of water-saving technologies to ensure the long-term viability of irrigated rice production in paddy fields (Yosefian 2018; Mirfenderski 2022). Accordingly, it is necessary to find new methods for rice cultivation that reduce water use and make optimal use of the available water for irrigation while maintaining yield under climate change. The goal of this study was to examine the water requirement, water productivity, and risk of rice yield for different irrigation levels under various climate change scenarios using a crop simulation model.

In this research, the sediment washing operation of the Sefidrood Dam reservoir has been simulated using a Numerical Flow 3D model along with two turbulence models, RNG and LES. The results of case studies performed on the Sefidrood Dam reservoir in 2004 have been validated. To simulate, an area of ​​the reservoir with an approximate length of 700 meters and also the dam wall meshed in the form of 2 mesh blocks 1 and 2. Mesh block 1 was considered to include the dam wall, the area close to the dam wall, and the lower Gates. The dam was considered to be a solid type, which is unchangeable. Still, the geometry of the reservoir bed was defined as sediment because it changes with the movement of the flow.The results show that near the lower dischargers of the dam, the maximum amount of sediment washing up to the reservoir bed is conical. The high values ​​of the explanation coefficient (R2) and the low values ​​of the percentage of predictive error of the numerical model indicate the acceptable results of the Flow 3D model with the LES simulator in the flushing modeling of Sefidrood Dam. A comparison of the results suggests that the LES turbulence model has a better performance in estimating the maximum scour depth than the RNG turbulence model, and the results are closer to the flushing results performed in 2004.

Drought is one of the most complex natural hazards that affect natural and human systems (Wilhite et al., 2005, Wilhite et al., 2007). Greenhouse gas emission has contributed to climate change in the last century (Van Pelt and Swart, 2011). Climate change has a significant impact on the hydrological cycle and consequently on water resources, and the frequency and severity of droughts and floods. The most reliable tool available for future climate simulation is the output of coupled atmosphere-ocean patterns of atmospheric general circulation (Shakarami and Massahbavani, 2007). The reports of the Intergovernmental Panel on Climate Change show that if the current trend of greenhouse gas production due to the consumption of fossil fuels continues, the concentration of these gases can reach more than 600 ppm before the end of the 21st century (IPCC, 2007). The downscale model, which is a downscale statistical method, uses semi-empirical distributions for simulation and downscale and can generate future climate parameters at the station level. A major application of these data is to monitor and evaluate future droughts (Hosseinabadi et al, 2020). In the occurrence of drought, there are many factors such as changing the course of rivers and draining reservoirs, climate change and warming of the earth. Nowadays, the increasing occurrence of drought has caused the attention of many meteorologists and climatologists around the world. Drought indicators are used to diagnose and classify drought conditions. These indicators include the possibility of evaluating the standardized precipitation evaporation and transpiration index SPEI, the Palmer drought intensity index PDSI, the standard runoff index SRI and the identification drought index RDI. SPI and SPEI are the most common drought indicators.

Hydraulic jump is used as an important energy dissipator phenomenon downstream of hydraulic structures such as spillways, gates, and chutes. The US Bureau of Reclamation (USBR) surveyed the state of knowledge in this field and presented practical guidelines for the design of different types of stilling basins (Peterka 1958). However, it is always preferable to achieve maximum energy loss with a minimum length and cost in the stilling basin. Experimental studies on the effect of gradually diverging stilling basin walls on the hydraulic jump parameters have shown that diverging walls cause a reduction of the sequent depth by up to 30%, a reduction of the length of the hydraulic jump by up to 22%, and an increase in the energy loss compared with the classic hydraulic jump (Kouluseus and Ahmad 1969; Khalifa and McCorquodale 1979; Omid et al. 2007). Hassanpour et al. (2017) studied the characteristics of the hydraulic jump in a gradually expanding rectangular stilling basin. They showed that the sequent depth ratio and relative length of the jump decrease with decreasing divergence ratio. Arabhaabhirama and Abela (1971) studied radial hydraulic jumps in a gradually expanding rectangular channel with divergence angles from 0 to 13◦. The results showed that the divergence of the walls causes reductions in the sequent depth and length of the jump and an increase in energy loss as compared to the hydraulic jump in a straight rectangular channel.Since the hydraulic jump changes the flow from the supercritical to the subcritical, on the other hand, the flow depth is decreased in the expanding and diverging stilling basins in the supercritical and subcritical conditions, respectively. The innovation of this research is the use of divergent-convergent stilling basins to increase the performance of the stilling basins.  The results of the divergent-convergent stilling basin were compared with the classic and divergent basins as well as previous research.

Drought refers to the lack of rainfall in the long trun, which is one of the most important natural disasters due to its spatial extent and short-term and long-term economic, social and environmental consequences (Nikbakht and Moradi, 2019). Factors affecting the physical, chemical and microbial properties of surface waters: precipitation, geographical location, climate, geology, industrial activities, domestic wastewater, agriculture, mineral pollutants, etc. can be mentioned (Mishra et al., 2017). In addition to drought, land use changes change the hydrological cycle of the basin and upset the balance between rainfall, evaporation, soil permeability and runoff (Farokhzadeh et al., 2016). Land use is one of the most important factors affecting the quality of surface water resources, especially rivers, as land population changes, land use patterns change. Therefore, runoff from rainfall as well as urban wastewater discharge leads to an increase in the amount of nutrients and other pollutants into rivers and surface water sources (Moradi et al., 2012). Tahiru et al. (2020) investigated the impact of land use change and land cover on water quality in a catchment area in the northern region of Ghana. Their results showed that there is a positive relationship between land use change and land cover and water quality parameters. Soltani-Gerdefaramarzi et al., (2021) investigated the effect of land use on surface water quality under both wet and dry periods in the Godarkhosh watershed. The results showed that barren and residential lands had the greatest impact on surface water quality and rangeland and forest land use showed a negative correlation with water quality parameters. Also, a strong significant relationship was found between water quality parameters and land use in dry years. Lei et al. (2021) investigated the effects of land cover, topography, and soil on water flow quality at multiple and seasonal spatial scales in a German lowland catchment. Overall changes in water quality on larger scales were estimated better in the summer. Due to the location of Iran in the dry land belt, most of its area will experience drought during most days of the year, which will cause changes in water and environmental resources. Biology, economic growth and development, agricultural activities, etc. are essential; on the other hands, land use changes have a significant impact on surface water quality. This effect can improve or reduce the quality of surface water. These changes have a great adverse effect on the environment and water resources, so the control and monitoring of surface water for various uses is necessary to make water of good quality available to the public. One of the main sources of drinking water, agriculture and industry in Isfahan province is the Eskandari watershed and the Plasjan river. Therefore, paying attention to water resources is one of the appropriate and necessary management measures at the level of the entire basin. Therefore, in the current research, land use changes during two periods of drought and drought have been investigated on the quantitative and qualitative parameters of the Plasjan River.

Vortex shedding behind the obstacles is one of the factors affecting the transfer of sediments to the downstream of the structures. The flow entering the intake has a lot of momentum in the direction of the main channel, and because of this, flow separation occurs inside the intake. This area reduces the effective cross section of the flow at the beginning of the intake. On the other hand, increasing the flow pressure of the downstream mouth of the intake, the complex flow pattern in the mouth of the intake causes changes in the alluvial bed of the open channels. Haghbin and Ghomeshi (2014) by investigating the effect of the vortex caused by the cylindrical obstacles located in the intake with diameters of 24 and 34 mm and with two discharge ratios (the ratio of flow rate per unit width of the intake to flow rate per unit width of the main channel) 0.63 and 0.83 for  flow rate of 21.17 liters per second and two intake ratios of 0.43 and 1.07 for the flow rate of 17.82 liters per second, they reached these results that in the case of using obstacles with a larger diameter, the amount of bed sediments entering the water intake, in comparison it is less by using obstacles with a smaller diameter.  Also, the amount of sediment entering the intake in the case of a smaller intake is less than that of a larger intake.  In another paper, Khanarmuei et al (2016) discussed the effect of vortex formation on sediment transport in two-pipe intake. The intended research was investigated using a scaled physical model.  Experiments were performed on the inlets of two pipes in three common inlet directions (vertical, horizontal, and at an angle of 45 degrees).  In each experiment, the category of the vortex was determined according to its strength. Particle tracking velocity (PTV) was used to measure the tangential velocity of vortices. The results showed that the speed of sediment transport is significantly affected by the strength of the formed eddies. With the increase in the strength of the eddies, the rate of transfer sedimentation increased.  Also, the amount of sediment transfer was affected by the inlet angle of the pipe.  It can be concluded that the minimum and maximum sediment transfer rates occur for inclined and horizontal intakes, respectively.  In the past researches, understanding the pattern of sedimentation in the entrance and inside the intake, in the presence of obstacles and vortex formation, has received less attention.  In this research, by using cubic obstacles in the case of the flow hitting the top of the obstacles, which has a greater vortex strength after the obstacles compared to the case of hitting the side, an attempt was made to investigate the effect of the vortex on the dimensions of the separation area at the beginning of the intake according to the sediment pattern.