Iranian Water Research Journal

Abstract Model complexity is not sufficient for its accuracy. In practice, the models which are designed according to the nature of process and its applicability are more common. The main challenge is not to understand all the details about the process, but to make the problem simple and focus on the most important and effective factors. In this study, the WASMOD software is used to rainfall-runoff modeling. Despite of the simplicity of this model, the obtained results have good consistency with the observed values. It needs only basic meteorological data for a basin such as: precipitation and temperature, so it takes less time and cost for modeling. The model was run on a monthly time scale for two 15-year periods: calibration period (1975-1989) and verification period (1995-2009). The sensitivity analysis of the model’s parameters has performed based on Mean Absolute Error of the model relative to parameters’ changes. In the sensitivity analysis, the consistency between model results and observed runoff has been investigated. In general, it can be concluded that according to the accuracy level and the required input data, the WASMOD model has a good capability in simulating the monthly runoff. The Nash coefficient for model calibration and verification were obtained 0.62 and 0.55, respectively.

Abstract Nowadays, due to human progress in computer science, many models have been produced to simulate hydrodynamic and water quality of the water bodies. Among these models, CE-QUAL-W2, a two-dimensional width-averaged model, has been extensively used as a commercial model all around the world. Since this model included a large number of calibration coefficients and there is no standard guideline for calibration, the model calibration is a time-consuming process. In this paper, an appropriate method has been introduced for model calibration. This method reduces the run time and increases the simulation accuracy. In the proposed method, first, the effective coefficients were identified by sensitivity analysis. Then, the calibration performs after classification of the coefficients. For this purpose, the data of 15-Khordad dam reservoir measured at the end of each month of 1997 were used. The results showed that this method was suitable for making accurate predictions of temperature distribution and reducing run time. As the Absolute Mean Error (AME) for water surface elevation and temperature were obtained 2.5 cm and 0.45 °C, respectively. 

Abstract In this research, the shallow-water equations are described and the governing equations are discretized using Rayleigh–Ritz method in order to assemble the required local and global stiffness matrices. The depths and the velocities of fluid flow throughout the channel and at different times are acquired by solving the governing equations using non-explicit methods. The obtained results from the numerical model with three, five and seven node elements were compared to the pre-existing results of other researchers, and it was observed that they are in a reasonably good agreement. It was concluded that employing the non-linear elements, oscillations induced by using linear models can be efficiently reduced. Subsequently, the model was utilized to investigate Ardak dam-break as a case study. In this study, three equivalent-roughnesses (Horton, Lotter and Paw?owski) were used for the numerical simulation of the flow induced by dam-break and to calculate water depths and velocities at different times and places through the river. The maximum average-depth throughout the river was 24.78m with using Paw?owski roughness, and the maximum average-velocity was calculated 15.05m/s by using Lotter roughness at t=100s.

Abstract Development of cities and the intensification of pollution are two important factors for climate change; on the other hand, changes in land usage and worsening environmental condition lead to the spatial and temporal variation in precipitation, temperature, and evapotranspiration etc., which make the hydrological variables more complex, and the prediction of them is more difficult. Chaos theory is a tool that proposed based on the chaotic and complex behavior and it can be appropriate for rainfall data with a higher variation coefficient. In this study, monthly rainfall of the Bandar Anzali in the historical and climate change condition has been considered by applying chaos theory. For this purpose, the period of 1993-2010 was chosen as historical period and the results of LARS-WG model under three scenarios (A1B), (B1), and (A2), in the period of 2020-2035 were considered as a future period. According to the results, flood and drought will increase with a 14 percent reduction in rainfall in the future period. Moreover, the historical and generated data series showed deterministic chaotic behavior and the A2 scenario with the fractal dimension of 4.13 showed the most complexity in comparison with others.

Abstract Estimating the suspended sediment transfer rate has always been considered as a complicated work for engineers from the past which they were faced with it in doing any water project. Lack of knowledge about the transfer rate of the suspended sediments and particularly an estimate lower than its actual rate can lead to wrong design and consequently destructive effects after the performance in hydraulic structures. Generally, constructing of hydraulic structures such as dams, bridges, power stations and other water supplies is impossible without studying and predicting suspended sediment load. Many relations have been suggested for estimating the suspended sediment load. In this study, six hydrological methods, including single-linear, mean of categories, continuance of flux, the cumulative mean of categories, seasonal and similar hydraulic period have been used for estimating the suspended sediment load in Chamsiah River situated in Kohgiloyeh and Boyerahmad province. These methods are different in using statistics of flow discharge or kind of sediment rating curve. Results indicate a significant difference among considered methods, and finally the cumulative single-linear had been chosen as the optimum method and the continuance of flux method specified as the unsuitable one.

Abstract Precipitation with multiple time scales is considered as one of the most important parameters in water resources studies. Precipitation with different time scales can be expressed with fractal nature. One of the standard tools in the fractal investigation of hydrological processes is the power spectrum method. In this method, the power spectrum is calculated with transmitted observation from time space to frequency space. When all or a part of the spectral follow the power functions, the data in this power range will have fractal properties. In this study, the power spectrum of monthly precipitation of the 33 rain gauge stations in Iran was analyzed and scaling regimes with spectral exponent value are shown for each station. The results indicate that 81 percent of the stations have fractal nature and scaling properties in a period less than one year. In addition to the first scaling regime, 17 stations have second scaling regime and 3 stations have the third scaling regime. None of the stations in its second scaling regime have fractal nature and only one station in the third scaling regime has fractal nature.

Abstract Employment of automatic control systems in irrigation water management and distribution in open channel is essential as a tool to improve the management and efficiency of these systems. The objective of this study is design and evaluation of an automatic downstream controller algorithm with proportional-integral technique (feedback+ feedforward and decoupling) for EPC canal in the Sarakhs irrigation network. Algorithm efficiency was evaluated by simulation of some different operation scenarios using SOBEK hydrodynamic model and calculation of performance indices of control systems as well. Tuning of control algorithm was done by determination of canal reaches characteristics using system identification process. The average of MAE (Maximum Absolute Error), IAE (Integral of Absolute Magnitude of Error) and STE (Steady State Error) indices were calculated 0.042, 0.005 and 0.001 respectively for different reaches. The results show that this algorithm has considerable potential in flow control and dissipating the disturbances. Also, this algorithm can provide the condition of demand – oriented distribution and improving the water distribution system.

Abstract Estimation and allocation of environmental flow are the most effective approach to avoid the negative effects of the regulation of surface flows on the ecosystems. One of the useful approaches in this field is the wetted perimeter method. Determination of critical point in the P-Q curve is an important issue in this method, which is still associated with ambiguity. In this paper, the minimum environmental flow of Kheyr-Abad River, with the average annual flow (AAF) of 34 m3/s, is calculated using the wetted perimeter method based on the slope and curvature techniques for determining the critical point. The results indicated that the slope technique always gives higher values than curvature technique. The calculated values for flow using the slope and curvature techniques were equal to 5.2 and 2.0 m3/s, respectively. By comparing the results of both techniques with the acceptable range of Tennant’s table (10-30 percent's of AAF), it is specified that the results of slope method (15.3% of AAF) are located in this range, while the results of the curvature technique (6.0% of AAF) don’t lie in the acceptable range. The results indicated that the curvature technique cannot be a suitable choice for determining the critical point in the curve and the slope technique presented acceptable results.

Abstract Flow pattern in bends due to changing of hydraulic conditions causes scour and sedimentation. In this study, experiments were done in a 90 degree sharp rectangular bend with R/B=2 and constant flow depth 17 cm at three different flow discharges of 15, 25 and 35 lit/s having Froude numbers of 0.17, 0.28 and 0.40, respectively, and in each Froude number, flume bed was covered by particles with uniform sizes, with three roughness height of 0.5mm, 2mm and 5mm. Results indicate that with increasing roughness, shear stress increases and maximum shear stress in all of the conditions is located at 10-65 degree close to inner bank and from a location of 90 degrees is close to outer bank. Also, changes of strength of vortex along the channel has an absolute maximum and a relative maximum in the location of 50 and 80 degrees, respectively, which increasing the roughness cause the absolute maximum occur in head of bend (50 degree) and moreover hydraulic conditions of the bed (smooth or rough) are effective on the strength of the vortex. On the basis of changing of shear stress and the strength of the vortex, the location of 80-90 degree of bend in outer wall is diagnosed as erodible region.

Abstract Several factors are important to evaluate the potential of karst groundwater resources which can be referred to as hydrogeological (springs), structural (fractures and faults), geological (lithology), topographic (local base level and slope), precipitation and vegetation factors. The aim of this research is to assess the potential of karst groundwater in Dashtak anticline and its effective factors. Accordingly, several thematic maps have been prepared by means of using Geographic Information System (GIS) and Remote Sensing (RS) techniques. The rating has been done in each map by crisp method on a scale from 0 to 9. Weighting of the maps has been performed by using the analytical hierarchical process (paired comparisons), and finally maps have been combined using the index overlay. The final map includes weights from 0 to 9 and the classified map is presented. The results show that karst groundwater potential of the northern part of Dashtak is more than the southern part .The correlation between high groundwater potential areas and high discharge springs indicates that the proposed model can be successfully applied to karstic areas.

Abstract Actual evapotranspiration (ETa) is one of the important factors for agricultural water management. However, its estimation is not easy, especially in vast areas with different land uses. In the recent decades, many studies have been conducted for estimating Eta using remote sensing technology, which are mainly based on the surface energy balance concept. The SEBAL model is one of the well-known methods for this task. Nevertheless, application of such a model needs more insights about its capabilities, advantages and weaknesses. In this study, the SEBAL algorithm was applied to estimate monthly ETa using images of the Terra satellite (MODIS sensor) for the period of 2002 to 2008. The Urmia Lake basin is selected as the study area, which has a variety of land uses, including agriculture lands, water bodies and salty areas. The results revealed an acceptable agreement between estimated values of ETa and observed values in irrigated areas (R2= 0.84) and water bodies (R2= 0.84). But, the performance of SEBAL in the cases of the salty area, dry farming and grasslands was not enough good.

Abstract Dynamic Programing models are appropriate tools for deriving optimal operation policies of reservoirs, especially during the water scarcity situation. In this paper, the performances of a variety of these models including deterministic Dynamic Programming (DP), Stochastic Dynamic Programming with inflow classification (SDP_Class), Stochastic Dynamic Programming based on inflow scenarios (SDP_Scenario) and Sampling Stochastic Dynamic Programming (SSDP) were evaluated and compared for Zayandeh-Rood multi-purpose system. For this aim, beside the complete supply of domestic, industrial and environmental demands, optimal operation policies considering constant agricultural demand and then both agricultural and hydropower ones were derived. Finally the performance of optimization models was evaluated and compared based on simulation models, computational load of optimization models as well as some efficiency criterion such as temporal and volumetric reliability, maximum and average shortage. Results showed that stochastic models like SDP and SSDP performed better than DP models, considerably. This superiority was considerable, especially during extreme water shortage conditions. Despite the SSDP preference its computational load as well as its execution time were higher than others. In order to alleviate this problem, pre-allocation and vectorization techniques were applied and they had a significant effect on the run-time reduction of all models, particularly on SSDP.

Abstract Side weirs are used in drainage systems, flood control, runoff collecting and many water resources and environmental projects. In this study, discharge coefficient in trapezoidal sharp crested side weirs was investigated by designing 18 weirs in subcritical condition and the effective factors on this parameter were studied. Some equations presented for calculating discharge coefficient with 4.3 and 5.4 percent error by using statistical methods and multiple regression. Results demonstrate that considering the side slope of the weir as an effective factor on discharge coefficient, increase accuracy of computations 1.2 up to 2.3 percent. Also, according to the calculations, the most important factor on discharge coefficient in this type of weirs is the ratio of overflow length to the length of the weir and omitting this factor leads to increase the error up to 1.4 percent.

Abstract Due to importance of scouring, numerous researchers have investigated the local scouring and various methods suggested for controlling this phenomenon. These methods can be divided into two general categories, increasing the bed resistance and changing the flow pattern. The collars are plates which installed parallel to the bed on the pier; operate as an obstacle against the down flow and prevent the formation of the scour hole at the upstream side of the pier. The current research investigated the effect of elliptical collar on scouring process. For this purpose, three elliptical collars with the ratio of the collar length at the downstream of the pier to the pier diameter ( ) of 1, 1.5, 2, the 3 mm thickness and cylindrical pier with 21 mm diameter, were examined at 5 different discharges. Also, the Length, width and depth of the laboratory flume were 8, 0.255 and 0.3 meters, respectively, and the mean size of the bed sediment was 0.88 mm. The results showed that utilizing the collar led to reduce the scour volume in comparison with the usage of the pier without collar. The maximum (81.5%) and minimum (13.36%) scour reduction were belonged to the elliptical collars with and , at Froude numbers of 0.246 and 0.294, respectively.

Abstract Trend analysis conducted on stream-flow measured at hydrometric stations across the central part of Karkheh River watershed in monthly, seasonal and annual time scales using statistical methods. The data used were the monthly discharge time series of 11 selected hydrometric stations over a 40 year period (1969 to 2009). The slope of the trend line of discharge time series was estimated using the Theil-Sen approach (TSA) and the effect of the significant autocorrelation coefficient was removed using trend-free pre-whitening (TFPW), pre-whitening (PW) and variance correction approach (VCA) methods, and the discharge time series were pre-whitened. Then, the trend of original and pre-whitened data were analyzed using the Mann–Kendall (MK) test. The ability of TFPW, PW and VCA methods for removing the effect of the autocorrelation coefficient were evaluated. The results showed that the TFPW is the best method for removing the effect of serial correlation from discharge time series. So, trend analysis of monthly, seasonal and annual discharge time series was conducted by using the MK-TFPW method. The results show that at annual time scale, more than 70 percentages of considered stations have experienced a significant decreasing trend at the 5% level.

Abstract In this paper, the characteristics of free and submerged outflow from the sluice and radial gates were studied by using energy and momentum equations, and experimental data of other researchers. An equation has been given to approximate the energy loss of the gate along with its application in improving the accuracy of the discharge coefficient under free flow condition has been demonstrated. A theoretical equation is also developed for estimating the discharge coefficient of sluice gates and three types of radial gates, namely Hard-Rubber, Music Note, and Sharp, under submerged flow condition. It was observed that at a certain condition, the outflow from Hard-Rubber type radial gate is larger than Music Note and Sharp types. It was realized that the mean energy loss of these types of radial gates, under submerged flow condition, is dependent on the ratio of the axial height of the gate to its radius which was used to improve the discharge coefficient. Under a certain condition, it was observed that, the discharge coefficient would decrease if the angle of gate lip is increased. It was also observed that under certain circumstances, the outflow from three types of radial gates, is much larger than sluice gates. It is noteworthy to mention that the application of the developed equation for estimating the discharge coefficient of the Sharp radial gate for Hard-Rubber and Music Note types may cause considerable errors.

Abstract Understanding of the strong transversal flow due to centrifugal force in meanders leads to detecting the location of maximum erosion in outer bank. By identifying the best sites for constructing the intake structures and proper river training techniques, it is possible to prevent destruction of structures and farmlands which located near the rivers. This article focuses on the experimental study of secondary flow strength, its changes in meanders and models predicting the location of the maximum lateral erosion rate. The experiments are carried out at a sharp bend with the central radius-width ratio of 1.31 on a developed topography and discharges of 63, 89 and 104 liter per second. Investigations indicate a complete correlation between secondary flow and transversal bed slope and also between the reduction of the secondary flow strength and increasing discharge. To make it clear, the ratio of transverse to longitudinal kinetic energy has dropped from 43 percent at discharge rate 63 liter per second to 35 percent at discharge rate 104 liter per second. Also, the place of the intake on sharp bend can be in 1/3 from the entrance of the bend. Moreover, evaluation of phase lag models in the secondary flow showed that they lack the ability to correctly predict the location of maximum erosion. It may be the result of disregard for the sharpness of the bend (the ratio of central radius to canal width) which is highly effective for transversal flow pattern.

Abstract The investigation of plants behavior under different flow conditions, because of the interaction between "depth and flow velocity " and also "the amount and type of plant bending and its rupture point", is a complicated phenomena. In this research, a dynamic analytical method is introduced to investigate the bending curve of flexible plants, maximum tensile stress, critical rupture condition and the rupture point in submerged condition. The results indicate that the rupture point locates near the base of flexible plants with uniform diameter, while it shifts upward for the others with a non-nuniform diameter. In this regard, the rupture point will move toward the water surface when the difference between the plant diameter at the top and bottom of which increases. Moreover, when plant's stem diameter increases, the plant experiences more drag force; that is, the amount of bending will increase when other factors remains fixed. Plants with non uniform diameter have larger deflection, and an increase in the plant flexibility will move the position of maximum deflection upward, which in turn influences the flow roughness. Additionally for flexible plants, dimensionless drag force decreases strongly with the increase of the Reynolds number; that can be translated as the presence of a less hydraulic resistance.

Abstract Water and soil conservation activities cannot limit sediment production on watersheds, completely and it seems that the only practical way to remove the sediments from the reservoir is to flush it out by bottom outlets. Because of the importance of turbulence energy in air entrainment to flow and cavitation occurrence, in this paper numerical simulation of sediment transport through the bottom outlet of the dam is performed. For this purpose, first, the air-water mixture in bottom outlet is simulated and the results are compared with experimental measurements. Then, a three phase flow with two sediment concentrations of 300 and 500 gr/lit are simulated to investigate the effect of sediment concentration on flow turbulence and its energy. The results show that the turbulence energy is negligible in flow with high sediment concentration in comparison with clear water and only affects on the flow surface and near the gate. Adding sediment particles to the flow leads to reduce the turbulence intensity of flow through bottom outlet tunnel, so that, increasing its concentration to 300gr/lit reduces the maximum of turbulence energy about 50%.

Abstract To Study river systems different element of eco-system including hydrology, hydraulic, erosion processes sedimentation and river geometry should be taken under consideration. There is a time delay between changes taken place at independent variables and response of dependent variables, that by values and changes ranges and varability of ability is controlled. This research, for review geometric and hydraulic specifications of river, Firooze - shahjoob river in province North Khorasan was chosen. After analyze out put results of hydraulic model HEC-RAS, for discharge with return period 10 year for 37 reach during the river was action .The best equation from among regression relationships that including minimum standard error, minimum probability value and maximum coefficient of determination is selected. Result of research showed that power equations as more appropriate equation for relationships geometry-channel for river under study, that including minimum standard error, maximum coefficient of determination and p-value less than 0.1 than other models.The river systems study of different aspects of the natural environment includes hydrology, hydraulic, erosion processes sedimentation and river geometry, there is always a time delay between changes in the independent variables and response of dependent variables, that is controlled by values and changes ranges in the independent variables and also flexibility in depended variables. In this study, after analyzing the result of HEC-RAS hydraulic model for 10 years discharge in 37 reaches, the geometric and hydraulic characteristics of cross sections of Firooze - Shahjoob River in the province of North Khorasan were studied. The best equation was chosen among all of the regression equations that have the lowest standard deviation and p-value, and also has the highest coefficient of determination. The results showed that the exponential equation was the most appropriate equation for presenting the geometry channel relations of the studied river which had a standard error of 0.010, coefficient of determination of 0.88 and p-value 0.002 compared to other models.

Abstract Among the methods which can be used for preventing the sediment deposition is self-cleansing in the structure. In the first of this research, a general relationship for conditions of self-cleansing in open channel and inverted siphons was developed by applying the dimensional analysis. Then experimental tests were conducted by using two experimental models and 14 non-cohesive sediment with different dimensions of 0.2 to 4.4 mm in three channel bed’s slopes of 0.5, 1 and 1.5 percent and four different bed slopes of 0.0, 8.0, 16, and 24 degrees for horizontal and outlet conduit of inverted siphon. Two graphs were drown that can be used for determining the condition of self-cleansing in open channel and horizontal and outlet conduit of inverted siphon. Then, by using these graphs and suspended load particle size distribution curves of the Karkheh River in Paypol station, the self-cleansing velocity was extracted for preventing the deposition of sediment particles with diameters less than 2 mm that is the largest particle size observed in Paypol channel and their inverted siphons.