Iranian Water Research Journal

Abstract The Area-Reduction method is one of the experimental methods to estimate sediment distribution in dam reservoirs. In this method, the reservoirs classify based on the geometry into four types. Then the sediment distribution in each type of reservoir specify based on the related parameters. Results of previous researches were shown that in most of the cases; determining the type of reservoir with the Borland and Miller method didn’t lead to an accurate estimation. So, determining the optimized coefficient for the Area-Reduction method can increase the accuracy of sediment distribution prediction in this method. In this study, initially a computer model was provided based on the Area-Reduction method by using MATLAB software, then the optimization model was prepared based on the Ant Colony algorithm and these two models were combined. Best coefficients of the Area-Reduction method for Karaj Dam were obtained from developed model. The results showed that there was a significant increase in accuracy of predicting the sediment distribution using optimal parameters. Using the optimal parameters decreased the error values up to 68.41%.

Abstract Design of a minimum cost canal section involves minimization of the sum of costs per unit length of the canal, subject to uniform flow condition. These costs are included with the costs related to covering every meter of channel length, the cost per cubic meter earthworks and costs associated with water loss (including seepage and evaporation losses) which is considered as the objective function in this study. Seepage and evaporation are forms of water loss in an irrigation canal, while the seepage loss depends on the canal geometry and the evaporation loss is proportional to the area of water free surface. In this study, the Manning’s Formula is considered as the main constraint equation. In addition, the minimum permissible velocity and Froud number are used for optimizing design canal as subsidiary constraints. The optimization algorithm based on directly search is used for optimizing the canal section. Presenting the results of optimization model in the form of the dimensionless curves, provides the possibility of easy design of optimized canal section in order to minimize costs per unit of length of canal. By analyzing the results of this study, it can be found that the trapezoidal canal with a given discharge have the maximum and minimum normal depth in side slopes of 0.75 and 1.5, respectively. Also, by increasing side slope in optimal design of triangular canals, the normal depth decreases and the width of water surface increases.

Abstract Cylindrical weirs are a kind of flow measurement structures in open channels whose crest length is affected by the channel cross section and economical expenses. The current experimental research investigates the effect of side contracting on flow characteristics such as discharge coefficient of cylindrical weirs. The experiments were done on a laboratory flume with dimensions of 7500*300*460 mm, using various diameters of cylindrical weir models in the range of 75≤P≤160 mm, contraction ratios of 0.2≤b/B≤1, and various combinations of discharge and flow depth for free flow. The results show that an increase in the ratio of upstream water depth to the weir height (H/P), leads to an increase in the discharge coefficient for all weirs, but when b/B decreases, the gradient of Cd vs. H/P, will decrease too. On the other hand, for any given P and H, the discharge coefficient will increase with increasing the b/B ratio. The contraction coefficient (Cc) for such weirs, determined by using weir theory and experimental data, varies in the range of 0.71 to 0.98 for 1.2≤H/P≤2.4. These results also show when H/P increases, Cc will increase for all weirs too. Besides, for any given H/P ratio, the flow contraction coefficient over the weir crest will decrease with a decrease in the b/B ratio.

Abstract Cylindrical weirs- gates are one of the combined structure types which have advantages such as low cost, simple design, easy construction and the high discharge coefficient. In this study, the cylindrical weir- gate location in perpendicular orientation to flow direction on discharge coefficient have been investigated experimentally. The experiments were conducted in a flume with the length of 7.5 m and width of 40 cm, using the cylindrical models were made up of plastic pipes with diameters of 50, 75, 110 and 125 mm. Experiments were conducted with different gate opening heights from 0 to 60 mm (reaching to the cylindrical gate by considering the available diameter and discharge). The results show that the maximum and the minimum discharge coefficient has been observed in the cylindrical weir and cylindrical gate, respectively. Moreover, by substituting the cylindrical weir- gate with cylindrical gate, the curves depicted amount of against the ratio of upstream flow depth to the cylinder diameter ( ) and the ratio of difference between upstream and downstream flow depth to the cylinder diameter ( ) has reduced suddenly, which this progress was due to decreasing the amount of backwater and remarkable decreasing in upstream depth. Furthermore, increasing in amount of cylindrical structure diameter leads to decrease in discharge coefficient. The best correlated relations for quantifying the behavior of discharge coefficient , were proposed.

Abstract In this study, the combined effects of different structural parameters such as berth and draft of Pontoon-type floating breakwater on the variation of wave transmission coefficient is examined. To find the combined effect of the width and draft of floating breakwater on the wave transmission coefficient, three drafts of 0.8, 1 and 1.2 m and five widths of 2.4, 4.8, 7.2, 9.6 and 12 m were examined. The analysis was performed for average periods of 2, 2.5, 3, 3.5 and 4 seconds, and the wave height range of 0.2 to 1.2 m. According to analysis done by the ANSYS AQWA software, the results showed that by increasing the width and draft of floating breakwater, the wave transmission coefficient dramatically reduced, so that the wave transmission coefficient increased from 0.88 for a breakwater width of 2.4 m, draft 0.8 m to 0.34 for a breakwater width of 12 m and draft of 1.2 m.

Abstract The paper describes the evolution of local scour hole downstream of an adverse stilling basin. The research was conducted using a wide range of the Froude number, sediment size, tailwater depth, length and slope of stilling basin. The results showed that 87.5% of maximum depth of scour and 86.3% of its distance from the stilling basin were occurred in the first 24 hours when the experiment was continued for 54 hours. A power equation was adopted to describe the characteristic dimensions of the scour-hole, time scale as well as the geometry of stilling basin and sluice gate. The effects of different parameters on the dimension of the scour-hole were investigated and some equations were presented for estimating the variation of scour-hole dimensions with time under relative equilibrium condition. The results also showed a certain similarity among the scour profiles developed at different times. However, the shape of the holes was influenced by the change in length and slope of stilling basin. As the slope of stilling basin increased by 15%, the volume of sediment removed from the unit width of the hole, was increased by 30%.

Abstract This paper investigates the effects of roughness of the flood plain on hydraulic overbank flow in a compound channel with non-prismatic floodplains. Experiments are done using three depth ratio, three divergence angles and three-roughness size of the floodplain. The flow velocity was measured using a three dimensional Acoustic Doppler Velocimeter (ADV) and directional current meter in a lattice along the divergence channel in three sections of the flume (entrance, middle and end of the divergence) with a different depth ratio. Using the experimental data, the values of the shear stress, depth–averaged velocity, local and zonal roughness coefficients, turbulence parameters and divided discharge between the main channel and floodplain were calculated. The results show that with increasing the floodplain roughness, in non-prismatic section, the ratio of the velocity at floodplain to main channel decreased about 31% and turbulence flow increased about 25%. Also under these conditions, the shear stress at interface zone was increased from 26 to 48%. As well as with increasing depth ratio, the above mentioned values are markedly reduced.

Abstract The discharge and suspended sediment concentration are measured only in a few days of the year in most Iranian rivers. Therefore, application of methods which can estimate and forecast the sediment load with the short term or interrupted data is inevitable. The present research was conducted to compare the performance of some data grouping methods for sediment rating curve preparation and another 6 hydrological methods for estimation suspended sediment load in two hydrometric stations located in two different climatic zones of Iran (Ghorbaghestan station located on Gharasoo River and Kordkheil station located on Tajan River). Results showed that in Ghorbaghestan station, the estimated suspended sediment resulted from the sediment rating curve, Smearing and LQMLE methods (in total mode, wet and dry year) were underestimated, while, in the FC1, FC2, FAO, and LQMLE methods (in hydro-climatic and main seasons and composite modes), were overestimated.In Kordkheil station, except FAO method, the estimated suspended sediment resulted from all studied methods were underestimated.

Abstract The aim of this research was to apply a two-dimensional hydrodynamic model to predict and investigate governing phenomena on flow, sediment transport and bank erosion in a natural meandering river. The study area is a meander of Karun River with the length of approximately 5 km between Ahvaz and Farsiat hydrometric stations. Bank protection of the considered meander is so important because the Khuzestan Water and Energy company structures and agricultural farms are located in the vicinity. In this study, mesh generation was performed by CCHE-MESH model. The validated CCHE2D model was applied for flow pattern simulation, and bed and bank change prediction in a 20 years period of time. Results showed the meander Thalweg elevation was decreased between 4 to 8 m and 5.7 m in average (in compare with initial bed level) and secondary flow caused a higher decrease in outer bank elevation. Since the Spur dike is an important structure in the river bank protection, 14 number of Spure dikes were designed in the CCHE-2D model for studied meander. After 20 years of simulation, dikes caused to increase the elevation of outer bank between 1 to 9 m and 4.7 m in average (in compare with 20 years of simulation without dikes), But in some sections the Thalweg became approximately 4m deeper.

Abstract Side weirs are structures that are installed along a channel and when the height of water is exceeding the crest, extra flow inters to the subsidiary channel. In this research, a solution for differential equation of water surface profile over trapezoidal broad-crested side weir in rectangular channels based on the Haar wavelet transform method is reported. Also, the water surface profiles for different width, height and side slope of the weir were measured and compared to those calculated by using the Haar wavelet method. The Lowest error percentage in calculating y1 (maximum error) was observed in the side slop of side weir of 1.5, width of 8 and height of 10 cm. When height and side slope of the side weir were increased, the accuracy of water surface profile estimations using the Haar wavelet method was decreased. The Haar wavelet method is also compared with Runge-Kutta Method. The correlation coefficient of Haar wavelet method and experimental data was more than 0.979 which was greater than the calculated one for the Runge-Kutta method. This result indicates that the Haar wavelet method can estimate the water depths with higher accuracy than the Runge-Kutta method.

Abstract In this study, water resources Decision Support System (DSS), which estimates quantitative indicators based on environmental, social and economical criteria under climate scenarios was investigated in the Aras river basin. The DSS analyzes the effects of management alternatives on balance of water supply and demand with simulating the water allocation between agricultural, domestic, and industrial demands. The Mike Basin water allocation model linked to Excel spreadsheet is used to evaluate the performance of 9 proposed indicators of management options and the Multi Criteria Decision Making analysis 'TOPSIS' is used to determine the best management options. The results indicated that the option of 'Reducing losses and Increasing efficiency' in the optimistic scenario and the option of 'Reducing losses and Reducing cultivated area in the scenario of continuation of current condition and pessimistic scenario are in the first rank. The individually alternatives of 'Don't water transfer to Urmia Lake basin' and 'Decrease cultivated area ' lied in the last rank.

Abstract Estimating reference crop evapotranspiration (ETo) is necessary for designing irrigation systems, water resources management, yield production and environmental assessments. Different models and methods have been developed in order to predict ETo using time series, including AR, MA and ARIMA. However, Chaos Theory has not been utilized to estimate the ETo till now. In this study, the performance of the mentioned time series models was evaluated for estimating daily ETo in Torbat-e-Heydarieh synoptic station, Khorasan Razavi, during 1991-2000. Results showed that the ARIMA and Chaos Theory estimate the ETo with the same accuracy, so that the correlation coefficients between observed and estimated values for ARIMA and Chaos Theory were 0.895 and 0.894, and RMSE values were 0.585 and 0.611 mm day-1, respectively.

Abstract Natural characteristics of each area, especially the climate, plays a major role in planning and development. Chaharmahal and Bakhtiari is a province that located in the south-west mountainous region of Iran. Due to topography diversities, this region has a different distribution of climatic elements (especially, rainfall and temperature). In this study, the multivariate statistical methods such as factor analysis and cluster analysis were used to detect sub-climatic regions of this province. For this purpose, 26 climatic variables were collected from 6 meteorological stations in the province. For overcoming the lack of climate control stations throughout the area the IDW Interpolation technique was used to produce a data matrix with dimensions of 26 × 46 (variables× nods) and it considered as a database for factor analysis. The results of factor analysis on the produced data set showed that four major factors which affect the climate of the province in order of importance are: the precipitation, the clear sky, the temperature and the humidity. Finally, cluster analysis on the matrix of factor scores recognized the four climate zones throughout the province.

Abstract Agricultural, urban and industrial demands for water can be supplied by withdrawing water through reservoirs or conveying channels using vertical intakes. This method usually faces with some problems such as vortex flow formation in the inlet. This causes entrainment of air and swirling flow into the intake, which followed by some other difficulties such as reduction of intake capacity and stimulation of vibrations and cavitation inception. In this study, the effect of dimensions and position of the horizontal stationary rafts on the required submergence to suppress surface vortex (with air core) were examined, experimentally. At first some tests were carried out to determine discharge-critical submergence relationship for the condition wihtout any anti-vortex device is used. Then, a dimensionless equation was fitted between relative submergence and intake Froude number. After that, the effect of each raft with a specified dimension and position were examined for five different flow rates. The performance of rafts to reduce required submergence is calculated for each setup. Based on the results, the 2d×2d raft at the position of 1d has the best performance of 29.85%. Finally, a regression equation is fitted to predict relative submergence in the presence of the anti-vortex rafts, with respect to dimensionless parameters of the Froude number, relative plate dimensions and relative installation position.

Abstract Artificial recharging of aquifers by retreated wastewater is one of the most important and practical methods for reusing wastewater. In order to simulate the physical conditions of artificial recharge basins, three cylindrical PVC columns with 30 cm in diameter and 250 cm in height were used. The columns filled with sandy-loam soil, and urban wastewater of Mahdasht in Alborz province were applied through the columns. Different covering materials such as geotextile and constructed coarse materials were utilized on top of the soil surface to evaluate the performance of the materials in terms of infiltration during permanently pounded condition. The values of total suspended solids, BOD5, COD, pH, EC in inflow and outflow of the column were measured in depth of 1m and 2m; the amounts of soil pH and soil EC used in the columns were measured before and after the experiments. The obtained results indicated a high efficiency in the soil columns covered by Geotextile in reducing suspended solids, BOD5, and COD by 67.7, 84.7, and 77 percent, respectively. These values for covering material were 51.1, 77.5, and 72.1 and for the control treatment 55.3, 70.4, and 57.3 percent, respectively. Providing the Geotextile and covering material’s debris are easy and cheap. In addition, these materials reduce pollutant transformation and can be changed or modified for improving the permeability of soil.

Abstract The goal of this paper is, considering the effects of creating the surface waves in a uniform flow on the bed load transport rate of deposited sediment in a primal rigid rectangular channel. Experiments were carried out in a rectangular flume of 10m length, 0.2m width and 0.3m height. The experiments were conducted for two gradations of sediments with median diameters of 0.34 and 0.48 mm, specific weight of 2.67, for five bed shear stresses (initiation of motion and it’s multiplies of 1.16, 1.25, 1.39 and 1.43 for median diameter of 0.34 mm and initiation of motion and it’s multiplies of 1.15, 1.25, 1.33 and 1.41 for median diameter of 0.48 mm), two wave heights (1 and 1.6 cm) and four different wave velocities. The results showed that creating surface waves generally increases the bed load transport rate. Furthermore, it was observed that for a given experimental parameters, the bed load transport rate increases with Strouhal number, dimensionless wave height and bed shear stress. It can be concluded that creating artificial waves can increase the bed load transport rate in a rigid rectangular channel up to 280% compared to the no wave conditions.

Abstract In this study, the effect of Bendway weir length on bed topography of a sharp 90 degree bend was investigated, experimentally. Tests are conducted at the hydraulic lab of Shahid-Chamran university in a 90 degree sharp bend (R/B=2). Seven Bendway weirs were placed at the outer bank with a height of 5 cm (one-third of flow depth), angel of 30 degrees and three different weir lengths (L/B= 0.15, 0.2 and 0.25), each under four different flow conditions (Froude number ranged from 0.137 to 0.3). At the end of each test, bed topography of bend were taken by a laser bed profiler and plotted by surfer. Comparison of scour and deposition patterns for different weir length shows that weir with the length to width ratio equal 0.2 provides the lowest volume of eroded bed material.

Abstract Accurate estimation of suspended sediment in rivers is very important for designing and operation of water resources projects. Sediment estimation by conventional methods like rating curves don’t provide accurate results. In this paper, gene expression programming (GEP) model which is an extension of genetic programming (GP) technique, was used to estimate suspended sediment in the river. The GEP results were compared with those of the adaptive neuro-fuzzy, neural networks and rating curve models. In this regard, the streamflow and suspended sediment data from Vanyar station that located on Aji-chay river in East- Azarbaijan province are used. The root mean square errors (RMSE) and determination coefficient (R2) statistics were used to evaluate the accuracy of the models. The results showed that the GEP model had better performance than other considered models in estimating suspended sediment. The relative RMSE difference for the test period between GEP and ANFIS-Grid Partitioning, ANFIS-Sub Clustering, ANN and rating curve methods were 8, 10, 13 and 21%, respectively. The R2 values for GEP, ANFIS-Grid Partitioning, ANFIS-Sub Clustering, ANN and rating curve methods were 0.93, 0.84, 0.88, 0.86 and 0.81, respectively.

Abstract Regional flood frequency analysis is one of the most important methods for estimating flood in poorly gauged or ungauged catchments. In this study, a regional flood frequency analysis has been carried out, using cluster analysis approach in Great Karun watershed. After considering the stations in the area, 44 stations which had good data were selected. The watershed was firstly divided into 3 regions based on the physiographic characteristics and then by using the Hosking & Wallis homogeneity criterion and removing or displacing the stations, the watershed was finally divided into 4 homogeneous regions. In order to find the most suitable regional distributions for homogeneous regions, L-moment ratio diagram and Hosking & Wallis goodness of fit test has been used. The distribution parameters were estimated using the method of probability weighted moments (PWMs). Therefore, by calculating the average discharge, the maximum flood discharge for a given return period can be estimated for ungauged area. By applying this method, the regional flood frequency estimation will be possible for every zone, even ungauged area of the great Karun watershed.

Abstract Useful and extensive use of crop models depends on understanding their behavior in response to probable errors in input parameters. The aim of this study was to assess the sensitivity of the simulated silage-corn yield by the most commonly used crop model, CERES – Maize, to physical soil parameters under two nitrogen fertilizer levels. In this study, by using one year field data of silage-corn in Varamin, the model-output sensitivity to field capacity, saturated water content, curve number, root growth factor, drainage coefficient and albedo was analyzed for two N-fertilizer levels (0 and 150 kg N/ha). To determine the model response to changes of input parameters, the model was run 80 times. After collecting data, the normalized sensitivity of each parameter was calculated using the program written in MATLAB environment. The results showed that the highest model sensitivity in the simulation of the yield in both treatments was shown to field capacity. But the response of the model to changes in input parameters was strongly influenced by the amount of fertilizer. Finally, by using the calculated relative sensitivity values, the relationship between probable error in estimating yield for both fertilizer treatments and error in estimation input data was presented.