Showing 43 results for Ahmadi
A. Ahmadi, T. Honar,
Volume 18, Issue 70 (winter 2015)
Abstract
One of the most important problems in the design of a stilling basin is determination of the exact location of the hydraulic jump or stabilization of the hydraulic jump. In the present study, the effects of different forms of end sills on hydraulic jump characteristics were studied. The experiments were carried out for three different forms of end sills, rectangular, square and stepped, with three heights in two distances and for Froude numbers in the range of 4.7-8.23. The results showed that the end sill with larger cross section (square and stepped) will have a greater effect on reducing sequent depths of hydraulic jump and increasing energy loss than narrow end sills. However, in this type of end sills, water fall and the risk of erosion at downstream is greater.
Sh. Ahmadi Doabi, M. Afyuni, H. Khademi, M. Karami,
Volume 20, Issue 76 (Summer 2016)
Abstract
Heavy metals in dust can directly enter to the human body through ingestion and inhalation. They can pollute the water and soil resources via atmospheric precipitation and accumulate in the plant tissues and then enter human body through water and food. This research aimed to study the heavy metals concentration in dust in Kermanshah province and to identify their sources. 49 samples of dust were collected in the cities of Kermanshah, Songhor, Gilangharb, Ghasre-Shirin, Sahneh, Sarpolzahab, Kangavar, Paveh and Javanrood during the spring 2013. The concentration of Zn, Cu, Ni, Cr, Mn and Fe were determined using an atomic absorption spectrometer following the sample extraction with a mixture of HCL and HNO3 (3:1 ratio). The average concentrations of Zn, Cu, Ni, Cr, Mn and Fe were 182.3, 48.6, 115.3, 73.9, 428.1 and 23161 mg kg-1, respectively. Correlation, cluster and principal component analyses were used to identify probable natural and anthropogenic sources of contaminants, and the enrichment factor was used to identify probable effects of human activity on the concentration of heavy metals. The results indicated that metal concentrations, except for Fe and Mn, were higher in comparison with the world soils. Zn, Cu, Ni and Cr are mainly of anthropogenic origin, while Fe and Mn are mainly of natural origin. Zn and Cu are mainly of traffic sources and partly of industrial sources, and Ni and Cr are mainly derived from industrial sources, combustion processes, combined with traffic sources. The analysis of EF revealed moderate enrichment for Mn and Cr, and significant enrichment for Zn, Cu and Ni. Based on the results of this study, more attention should be paid to identifying and controlling the sources of contaminants such as heavy metals in dust in order to prevent their associated pollution.
V. Rezaverdinejad, H. Ahmadi, M. Hemmati, H. Ebrahimian,
Volume 20, Issue 76 (Summer 2016)
Abstract
In this study, two different approaches of infiltration parameters estimation in traditional, variable and fixed alternate furrow irrigation, with and without cutback inflow, were performed and compared. Four usual methods including two-point (Elliott and Walker), Valiantzas one-point, Mailapalli one-point and Rodriguez and Martos optimization methods, as approaches based on advance data, and multilevel optimization method as an approach based on the advance, storage and recession data, were considered. Surface irrigation model: WinSRFR was used to simulate irrigation phases and infiltration value in each method. 13 furrow irrigation field experiments, from two case studies: Karaj and Urmia, were used to perform different methods. Based on the results, the multilevel optimization method predicted the advance and recession phases and runoff-infiltration with high accuracy for traditional, variable and fixed alternate furrow irrigation. The multilevel optimization method for traditional furrow irrigation, showed more accuracy than variable and fixed alternate furrow irrigation in advance and recession phases and the average root mean square error (RMSE) for predicting advance phase for the three furrow irrigation methods was 1.37, 1.8, and 1.57 minutes and for the recession phase was 3.76, 5.0, and 3.03 minutes, respectively. Also the multilevel optimization method for cutback options indicated high performance to advance and recession prediction and the average RMSE of advance and recession prediction were obtained 3.57 and 2.13 minutes for cutback option and 3.8 and 1.3 minutes for no cutback option, respectively. The multilevel optimization method indicated high performance in storage phase, too. The average of relative error (RE) of runoff estimation for traditional, variable and fixed alternate furrow irrigation was calculated 0.5, 0.4 and 0.4 percent, respectively. The runoff average RE of multilevel optimization method with cutback and no cutback option were obtained 1.85 and 0.85 percent, respectively; that showed high performance of this method for no cutback option in comparison with the cutback option. Therefore, the use of data of all irrigation phases to estimate infiltration parameters shows better performance in the prediction of irrigation and water balance components. (run-off and infiltration).
M. Bater, H. Ahmadi, R. Emadi,
Volume 21, Issue 1 (Spring 2017)
Abstract
Kahgel is one of the oldest traditional mortars in Iran capabilities and performance of which in the past to conserve earthen buildings show that it can be used as a covering for conservation and preservation of earthen architectural structures. The ancient waterproof covering is very efficient at keeping the building dry during the heavy rain showers, but low durability and the need for renewal the plaster due to erosion of rainfall suggest that Kahgel plaster is weak and unstable. So, it is very essential and necessary to find appropriate scientific methods to enhance durability and lifespan of Kahgel plaster. In this research, the effect of silicates micronized additives (including Microsilica, Feldspar, Zeolite, Bentonite and Kaolin) on the stabilization and improvement of the physical and mechanical properties of Kahgel plaster with experimental study by hydraulic conductivity and water erosion Kahgel plaster indicated that using the micronized silicates additives can significantly improve physical and mechanical properties of earth and earthen materials such as Kahgel. Experimental results showed that application of Kaolin 150 microns at 3 wt% (by weight of Kahgel) reduced hydraulic conductivity of the Kahgel plaster at 65% level and Zeolite 45 microns at 3 wt% (by weight of Kahgel) decreased by 85%. In addition evaluation of water erosion of the samples during rainfall by rainfall simulator showed that use of 3 wt% micronized Microsilica, Feldspar, Zeolite and Kaolin decreased sample’s total dry material loss of the Kahgel plaster at least10/5% and maximum up to 37/7% and increased their durability against erosion from rainfall. In addition, results from studies indicate that by reducing the particle size of the additive, their positive effect on physical and mechanical properties of Kahgel mortar increases. On the other hand, 3 wt% is the optimized percentage of micronized silicate additives to improve Kahgel coating and increased amount of additives seems to have no significant impact on the improvement of physical and mechanical properties.
A. R. Vaezi, M. Ahmadi,
Volume 21, Issue 3 (Fall 2017)
Abstract
Modified Universal Soil Loss Equation (MUSLE) is one of soil loss estimation models which has been developed based on the runoff characteristics in the event scale. However, it needs to be evaluated in the plot scale for the semi-arid rainfall events. With this aim, a field study was designed using twenty one plots. Runoff and soil loss were measured using 5-min samples under seven rainfall intensities consisted of 10, 20, 30, 40, 50 60, and 70 mm h-1 for 60 min. Soil loss was estimated using the MUSLE based on the runoff volume (Q) and runoff peak discharge (qp) and the values were compared with the observed values. The estimated soil loss was about 3.89 times bigger than the observed value on average. In order to improve model estimations, the power of rainfall erosivity index was modified from 0.56 to 0.62, (Q qp)0.62. The modification of the MUSLE model improved model efficiency (ME) from -5.5 to 0.47 and decreased the root mean square error from 0.000137 to 0.000031. This study revealed that the MUSLE overestimates soil loss from the small plots in the semi -arid regions. Therefore it is essential to calibrate runoff erosivity index using the data observed in the area. The modified MUSLE can be reliably used to predict soil loss in the small plot scale in semi-arid regions.
A. Shabani, A. Jahanbazi, S. H. Ahmadi, M. M. Moghimi, M. Bahrami,
Volume 22, Issue 1 (Spring 2018)
Abstract
In this study, five infiltration models including Kostiakov, Kostiakov-Lewis, Philip, Soil Conservation Service (SCS) and Horton were fitted to the experimental data using the double rings, and the empirical coefficients of these models were determined. Infiltration experiments were conducted in the gravelly sandy loam soil under and between the olive and orange trees in Fasa city, Fars Province, Iran. The results showed that all five models were fitted accurately to the measured data. The accumulated infiltration under the trees was higher than those measured between two trees. Higher infiltration under the tree canopies was probably due to the higher soil organic matter, the lower soil bulk density, and the tree root channeling, which were more pronounced when compared to the small pores in these soils. Despite the positive effect of sand particles on soil infiltration, the big gravel occurrence in soil would decrease the cross section area of water flow path, thereby reducing the infiltration. Therefore, changing the land use and planting olive and orange trees in the gravel soils would increase the infiltration rate and consequently, decrease runoff and erosion rates in such soils.
A. Mansouri, B. Aminnejad, H. Ahmadi,
Volume 22, Issue 2 (Summer 2018)
Abstract
In the present paper, fluctuations of inflow into the Karun-4 Dam under different scenarios of the climate change for the future period of 2021-2050 were investigated. For this purpose, the outputs of the HadCM3 model under the scenarios of B1 (optimistic) and A2 (pessimistic) were utilized for the fourth report; additionally, the outputs of the ensemble model under RCP 2.6 (optimistic) and RCP 8.5 (pessimistic) scenarios were used for the fifth report. Moreover, in order to estimate runoff in the future period, the artificial neural network was considered as a rainfall-runoff model. The results indicated that the average annual precipitation in the five study stations under B1 and RCP 2.6 scenarios was increased by 15 and 5%, respectively, while it showed a decrease equal to 8 and 6%, respectively under the scenarios A2 and RCP 8.5. Furthermore, the average annual temperature in all scenarios showed increase, which was at least 1.06 ⁰C under the scenario B1 and 1.89 ⁰C under scenario RCP 8.5. Examining the input inflow into the Karun-4 dam showed that under both B1 and RCP 2.6 scenarios, the annual inflow will be increased by 1.8 and 1.5%, respectively; under the two scenarios A2 and RCP of 8.5, the annual inflow will be decreased to 10.4 and 9.8%, respectively.
A. Haghizadeh, H. Yousefi, P. Nourmohammadi, Y. Yarahmadi,
Volume 22, Issue 3 (Fall 2018)
Abstract
To determine the potential for groundwater contamination, vulnerability should be evaluated in different areas susceptible to contamination should be investigated. Aquifer (carbonate) karst or part of it is karst aquifer in the western region of Iran; due to the natural conditions of the region and human activities, they are susceptible to contamination by carbonate aquifer through holes devourer and feeding point leading to pollution. The aim of this study was to analyze aquifer vulnerability zoning map karst plain elster by using COP. This model uses three parameters including lining (O) the concentra flow(C) and precipitation regime (P) to assess the vulnerability of groundwater against pollution GIS software. The results showed that the plain with an area 7.8 km2 was dominated in terms of vulnerability, being in the middle class. Other classes, respectively, were low with the area 18.69 km2, high with the area 0.65 km2 as part of the northeast plain, and much less with the area of 0.6 km2 , The results of the sensitivity analysis also showed that at the factorization (P) due to appropriate rainfall area, the maximum impact was in determining the vulnerability of the area. And the factor (C) minimum has impact on determining the vulnerability of the area. Due to the small size of the mature karst area, the wide extent of non-karst region was shown for the verification of results related to electrical conductivity data (EC) against discharge wells in the region with the high vulnerability and moderate. A comparison was made too.
A. Shahbaee Kotenaee, M. Foroumadi, O. Ahmadi,
Volume 22, Issue 3 (Fall 2018)
Abstract
One of the major issues in the contemporary world is climate change. The behavior and characteristics of parameters affecting climate change can cause them to be seen and hidden. As one of the effective ways to detect overt and covert behaviors for periodic climatic data series, Spectral analysis can be used. It is the analysis of each of the wavelengths series, making this behavior clear. Accordingly, the present study was an attempt to use the method of spectral analysis, data cycles in the minimum temperature, maximum temperature and precipitation in Ramsar station (located in the western regions of Mazandaran province) an nd Babolsar (located in the central parts of this province) in a period from1961 to 2014. For this purpose, temperature and precipitation data were obtained from these stations; MATLAB software environment and the environment for the software were logged for each of the variable in the stations. The results revealed that the minimum temperature at both stations had significant cycles, with the return period being 2 to 5 years; Remote Link could be fit into the cycle parameters such as NAO, AO and ENSO. Analysis of the period gram showed cycles 8 and 5/13-year-old and 5-year-old period in Ramsar and Babolsar. During the rainy cycles, the difference between the two stations and the difference in the geographical position affected systems, and rain accounted for the difference in speed dual-zone climate indicator for Remote Link.
O. Ahmadi, P. Alamdari, M. Servati, T. Khoshzaman, A. Shahbaee Kootenaee,
Volume 23, Issue 1 (Spring 2019)
Abstract
Changes in Climate parameters have been accelerated in the coming age, which can affect agricultural activities directly and indirectly. Temperature and precipitation are the most complex climatic factors. Spectral analysis is a scientific and efficient technique used to recognize and detect the hidden behaviors of these variables. In this research, in order to study and analyze the temperature and precipitation return periods using spectral analysis, the statistics of climate parameters (precipitation, mean, maximum and minimum temperature) for a period of 27 years (1989-2015) were used for the sustainable land management. For this purpose, the climatic data of temperature and precipitation entered the MATLAB software environment and Periodogram of each of the climatic parameters was drawn in a separate way. The results of each Periodogram study showed that the absolute minimum of temperature had significant cycles with the return periods of 3.8 and 2.4 years; the absolute maximum of temperature had a significant cycle with a return period of 2.1 years and the mean temperature was significant with a return period of 2.7 years. Also, the review of the Periodogram related to precipitation showed a significant cycle with a return period of 3.4 years. The Results from studying cycles indicated the existence of short-term return periods for climate variables in the region. Given this issue and the need to protect agricultural products, especially garden products, it should be done by applying water and soil resources management methods, including creating terraces and increasing soil roughness; Also, cultivation of appropriate plant species for the suitable regional climatic conditions, Drought resistant and low water requirement, the most optimal conditions could be created for the cultivation of horticultural and agricultural products.
Z. Eshkou, A. Dehghani, A. Ahmadi,
Volume 23, Issue 3 (Fall 2019)
Abstract
Stilling basins have been used as an energy dissipater downstream of hydraulic structures. Dimensions of the stilling basins depends on hydraulic jump characteristics. In this research diverging hydraulic jump with an adverse slope using baffle blocks and an end sill have been studied experimentally and effect of diverging angle of the walls, adverse bed slope and baffle blocks on the hydraulic jump characteristics have been evaluated. Tests have been done for rectangular stilling basin with different bed slopes (0.025-0.05-0.075) and different diverging angle (3-5-9) degree and using baffle blocks. Discharge and Froude numbers considered to range from 39 to 81.7 lit/s and 4.44 to 8.56 respectively. Results have been indicated that the baffle blocks have been reduced sequent depth ratio and relative length of the jump 12% and 18% respectively (in comparison to diverging stilling basin with adverse slope without block). It was also found that baffle blocks and end sill could considerably improve the general condition and features of an expanding hydraulic jump with an adverse slope and could stabilize the position of this type and bi-stable situation of the flow.
N. Alian, M. M. Ahmadi, B. Bakhtiari,
Volume 23, Issue 4 (Special Issue of Flood and Soil Erosion, Winter 2019)
Abstract
One of the most important problems in flood manegment is the damages induced by this phenomenon. Expected annual damage (EAD) is an important index for basin vulnerability against flood. Prediction of flood damages requires the analysis of spatial and temporal risk and must be calculated by the combination of hydrologic, hydraulic and economic models. In this research, the uncertainty was considered in the flood risk analysis. The probability of flood occurrence was calculated by the parabolistic model. By using the river analysis systems software (HEC-RAS) and the geographic information system (GIS) and utilizing the Google-Earth software, the floodplains of Zayande Roud river in Esfahan province were investigated with the return period of 25, 50, 100, 200 and 500 years. The Monte Carlo method was also sed to perform the uncertainty analysis in the proposed method. The logarithmic persion type III was selected as the best distribution of flood. The damage-stage relationship was calculated as well. Based on the uncertinity analysis, the river discharge could be regarded as the major parameter in the uncertainty of EAD.
Sh. Ahmadi-Qolidaraq, A. Abbasi-Kalo, A. Esmali-0uri,
Volume 23, Issue 4 (Special Issue of Flood and Soil Erosion, Winter 2019)
Abstract
Soil is one of the most important natural resources of countries in which erosion occurs. In this research, the effect of soil characteristics on the amount of erosion at the suborder level was studied. For this purpose, 77 soil samples (0-30 cm) were prepared and the parameters were determined in the laboratory. The semi-variograms of soil parameters and their spatial distribution maps were prepared with GS+ and GIS, respectively. The study area was divided into work units by combining land use and geology maps and water erosion was estimated at each unit by the EPM method. By drilling profiles in different parts of study area, soil suborders were determined by Soil Taxonomy and the average values of parameters in each suborder was estimated. The principle components analysis (PCA) was then used for data analysis. The results showed that three parameters of silt, organic carbon and electrical conductivity could account for 30.384% as the first main component; clay, sand and vegetation could explain 11.189% as the second main component; and slope and height covered 15.330% as the third main component; in total, 63.805% percent of erosion variation could be justified by three main components. The lowest and highest amounts of erosion (69.12 and 343.57 m3/km2, respectively) were estimated in Xeralfs and Fluvents suborders. The erosion class of suborders at the study area was determined to be “few” and “medium”.
M. Servati, H. Beyrami, O. Ahmadi,
Volume 24, Issue 1 (Spring 2020)
Abstract
The soil engineering evaluation can be useful for construction and soil use. Aljarafe model has been used to evaluate the soil engineering properties by multiple regression techniques. In this research, Aljarafe model was used to predict the optimum moisture and plasticity index based on 184 series soils data of the Miandoab region. Based on all correlations between clay percentage and plasticity index, the optimum moisture proved to be highly significant (0.88 & 0.72). Also, Cation Exchange Capacity was significantly correlated (0.84 & 0.70) with the engineering properties. However, the correlation coefficients for the organic matter with optimum moisture and plasticity index were very low in the absolute amount. Application of the aljarafe model revealed that 50.3, 5.7, 0 and 44 % of the total extension could be classified as low, moderate and very high, respectively; on the other hand, based on the experiment data, 46, 13, 6 and 35 % could be classified as low, moderate, high and very high plasticity index classes, respectively. So, there was an overall agreement between the aljarafe model and Analytical Plasticity index maps, which was 80.4. Also, the coefficient of Determination, Root Mean Square Error (RMSE), Nash-Sutcliffe index (NES) and Geometric Mean Error Ratio (GMER) between calculated and experiment engendering properties was calculated to be 0.767, 9.3, 0.671 and 0.86 for the plasticity index and 0.739, 14.5, 0.543 and 0.73 for optimum moisture, respectively, were significant (P>5%). Finally, the aljarafe model provided a reliable estimate of engineering properties.
A. H. Nasrollahi, H. Ahmadi, Y. Sabzevari, S. Nouri,
Volume 24, Issue 2 (Summer 2020)
Abstract
The Plant Water Resistance Index (CWSI) is a tool that can be used for the rapid monitoring of plant water status, which is a key requirement for the accurate product irrigation management.The purpose of this study was to calculate the CWSI index for bean hares in the Khorramabad region for two methods of surface irrigation and drip tape irrigation. For this purpose, a design was implemented in the form of randomized complete block design and split plot experiment. The main factors included drip tape irrigation (T) and surface irrigation (F), and the cultivars of Chibi cultivars including COS16 (C), Sadri (S) and diluted (K) served as sub-plots. By using the field measurements, the position of the upper and lower base lines was estimated for each treatment in different months and used to calculate the CWSI index. The results showed that CWSI values calculated in the surface irrigation during plant growth period were always higher than those in the drip tape irrigation. The highest value of CWSI index was obtained for the Sadri variety, which was equal to 0.20 and 0.26, for the type and surface method, respectively. Statistical analysis showed that the effect of irrigation method on the amount of water stress index was significant at 5% level, but there was no significant difference between different cultivars. According to the results of this study, the threshold values for CWSI were considered to be 0.19 and 0.24 for surface and drip tape irrigation respectively, and relationships were presented based on the differences in vegetation and air temperature to determine the irrigation time.
A. Donyaii, A. Sarraf, H. Ahmadi,
Volume 24, Issue 4 (Winter 2021)
Abstract
Optimizing the water resources operation, especially in the agricultural sector, which has the largest share in the water resources operation, is extremely important. Therefore, in this research, while introducing Whale, Gray Wolf and Crow Search Optimization Algorithms, their performance in the optimum operation of Golestan single-reservoir system Dam was evaluated with the aim of providing water demand for the downstream lands based on reliability, Reversibility, and vulnerability indices. In this optimization problem, the objective function was defined as the minimization of the total deficiency during the operation period. Meanwhile, the constraints of continuity equation, overflow, storage and reservoir release volume were applied to the objective function of the problem. Then, the results were compared with the absolute optimal value based on the nonlinear programming method obtained from GAMS software; finally, a multi-criteria decision-making model was developed to rank the optimization algorithms in terms of performance. The absolute optimal response obtained by the GAMS software based on the nonlinear programming method was 19.41. The results showed that the Gray Wolf algorithm performed better than the other algorithms in optimizing the objective function, so that the average responses in Gray Wolf, Crow Search and Whale algorithms were 92, 84 and 67% of the absolute optimal response, respectively. Furthermore, the Gray Wolf optimization algorithm performs better than the Whale and Crow Search algorithms in all parameters. In addition, the coefficient of variation of the responses obtained by the Gray Wolf algorithm is 2 and 1.43 times smaller than that in the Whale and Crow Search Algorithms, respectively. Finally, the results of the multi-criteria decision-making model showed that the gray wolf algorithm had the first rank, as compared to the other two algorithms studied in solving the problem of the optimal operation of the Golestan dam reservoir.
M. Heydari, M. Bahrami Yarahmadi, M. Shafai Bejestan,
Volume 26, Issue 2 (ُSummer 2022)
Abstract
Bed shear stress is one of the most important hydraulic parameters to determine the amount of bed and suspended load and the bed and bank scouring in rivers. Bed shear stress depends on bedforms (ripples, dunes, and anti-dunes) in alluvial rivers. In this study, the effect of artificial ripple bedforms on bed shear stress has been investigated. Two types of uniform granulation with average sizes (d50) of 0.51 and 2.18 mm were used to roughen the surface of the artificial ripples. The bedform length and height were 20 and 4 cm, respectively. The angles of its upstream and downstream to the horizon were selected equal to 16.4 and 32 degrees, respectively. Different flow rates (Q= 10, 15, 20, 25, and 30 l/s) and different bed slopes (S= 0, 0.0001, 0.0005, 0.001, and 0.0015) were examined. The results showed that by increasing the particle size on the bed surface, total shear stress (tb ), grain-related bed-shear stress (t¢b ), and form-related bed-shear stress ( t²b ) increase. The value of tb , t¢b , and t²b in bed form roughened by sediment size of 2.18 mm were, on average, 22.38, 30.86, and 22.3% more than the bed form roughened by sediment size of 0.51 mm, respectively.
M. Ahmadi, H. Ramezani Etedali, A. Kaviai, A.r. Tavakkoli,
Volume 27, Issue 1 (Spring 2023)
Abstract
Studying the effects of drought in mountainous areas is facing problems due to the inappropriate distribution of stations, the lack of long-term data, and areas lacking statistics. Therefore, the main objective of this research was to investigate the drought indices of Kurdistan province using TRMM satellite data and ECMWF dataset, as well as to evaluate their accuracy against the data of land stations in Kurdistan province. First, ECMWF precipitation data for the 2000-2020 period and TRMM precipitation data for the 2000-2019 period were obtained and evaluated using RMSE, MBE, and correlation coefficient statistics. Spearman's correlation coefficient showed a significant relationship between the TRMM satellite precipitation data and the ECMWF dataset with ground stations at the 5% level, and the value of this coefficient was between 0.95-0.85. According to the results, it can be acknowledged that the TRMM satellite rainfall and ECMWF dataset in the monthly time scale had proper accuracy at the Kurdistan province level. Therefore, these two sources were used to examine the drought indices. SPI, SPEI, and ZSI drought indices were calculated in different monthly periods (1-48), PNI in different monthly, seasonal, and annual periods in Kurdistan province (Saqqez, Qorveh, Bijar, Sanandaj stations). Spearman's correlation coefficient indicated a significant relationship at the 5% level between the SPI, ZSI, PNI, and SPEI index of the ECMWF dataset with ground stations. The results of the SPI index showed that the lowest RMSE value for the TRMM satellite at the Saqqez station and the three months was equal to 0.45, and for the ECMWF dataset at the Sanandaj station and the 24 months was equal to 0.35.
M. Badzanchin, M. Bahrami Yarahmadi, M. Shafai Bejestan,
Volume 27, Issue 1 (Spring 2023)
Abstract
The formation of bed form in alluvial rivers due to sediment transport has a significant effect on the hydraulic parameters of the flow such as bed shear stress. The formation of the bed form and its shape and geometry depends on the bed shear stress. Therefore, the relationship between bed form and flow parameters (such as bed shear stress) is complicated. In the present study; the effect of dune bed forms with different heights on bed shear stress has been investigated. Artificial dunes made by sand-cement mortar with a length of 25 cm and heights of 1, 2, 3, and 4 cm were used. In the tests of this research, flow discharge of 10, 15, 20, 25, and 30 l/s and bed slopes of 0, 0.0001, 0.0005, 0.001, and 0.0015 were used. The results showed that with increasing the relative submergence and Δ/λ, the bed shear stress increased in dune-covered beds. The formation of the dune bed form and the increase in its height leads to an increase in the bed shear stress. The bed shear stress in dunes with a height of 1, 2, 3, and 4 cm was, on average, 39, 80, 141, and 146% more than in plane beds, respectively. Moreover, form shear stress for dunes with a height of 1, 2, 3, and 4 cm was, on average, 27.37, 43, 57.11, and 58.74% of the total shear stress, respectively.
L. Hashemi, S. M. Kashefipour, M. Ghomeshi, M. Bahrami Yarahmadi,
Volume 28, Issue 2 (Summer 2024)
Abstract
Local scour around bridge piers is one of the most significant factors for the bridges’ destruction. Therefore, it is necessary to investigate the scour depth around the bridge piers. The effect of the skew angle of the single-column pier group related to the flow direction in two different arrangements including 1×2 and 1×3 piers on the maximum scour depth around the pile group was investigated in this study. The experiments were carried out under steady flow conditions. The pier group was placed in the 1×2 arrangement at the skew angles of 0 to 90 degrees and in the 1×3 arrangement at the skew angles of 0 to 45 degrees. The results showed that increasing the skew angle of the pier group is almost ineffective on the maximum scour depth around the first pier. However, it has a great effect on the maximum scour depth, its temporal development, and the expansion of the scour hole around the second and third piers in different arrangements of the pier groups. The maximum scour depth of the pier group in both different arrangements occurred at a skew angle of 30 degrees, in the arrangement of 1×2 around the second pier and by 13.33% more than the first pier and in the arrangement of 1×3 around the third pier and by 21.57% more than the first pier.
