unsteady flow

Weirs are a type of water structures that are used to pass floods, control water levels and measure flow rates. The accurate and appropriate design of the weir is of particular importance, and the existence of weirs with inappropriate discharge capacity is one of the most important factors of channel inefficiency. Circular crest weirs are reliable weirs for use in channels that are built perpendicular to the flow or at an angle (oblique) to the direction of the flow. Oblique weirs are used to increase the effective length of the weir and increase the water-passing capacity and hydraulic parameters such as the discharge coefficient. On the other hand, the study of the flow in the unsteady state, in which the flow variables in the channel vary with time, is of special importance in hydraulic science. In this research, the calibration of the discharge coefficient of the oblique circular crest weir under unsteady flow condition has been discussed. Also, the effect of changing the height of the weir and changing the flow pattern on the discharge coefficient of the unsteady flow in this type of weir has been investigated.

In this research, three oblique circular crest weirs with a height of 15, 10 and 20 cm and other identical geometric parameters under free and unsteady flow conditions in the flow range of 25 to 51 liters per second under the range of flow rate changes of 1, 3 and 5 liters per second and the range of time changes of 5, 10 and 15 seconds have been tested. Therefore, the total number of tests was equal to 27. Experiments were carried out in the research flume of Islamic Azad University, Isfahan (Khorasgan) branch with a rectangular cross-section of 10 meters in length and 0.6 meters in width, and weirs were installed at 2.5 meters from the entrance of the channel The flume has no slope of the floor and the height of the flume is the same without change and its walls are made of tempered glass and completely sealed. The mentioned flume is equipped with a closed water circulation system and can provide a maximum flow rate of up to 55 liters per second. The tank of this flume is made of fiberglass and has a cylindrical shape with a volume of 10 cubic meters and is placed underground at a height of about 2 meters. Flow can be regulated by PLC device. The depth gauge of the device without contacting the free surface of the flow, by sending and receiving ultrasonic waves, measures the distance with very high speed and accuracy, and in this way the depth of the flow is recorded in the PLC device. In fact, the most important part of this test set is the PLC device connected to the flume, which controls all flow settings, including the flow rate, maximum flow rate, relevant hydrographs, and records the flow depth data. In this study, the governing relations were first extracted and then the genetic algorithm was used for optimization. The optimization process in the genetic algorithm is based on a guided random process. This method is based on the theory of gradual evolution and Darwin's fundamental ideas. Genetic Algorithm is a non-algebraic optimization method that is suitable for functions whose optimization with algebraic methods is exhausting. This algorithm and other evolutionary algorithms examine the response space in parallel and cluster by cluster and not member by member and for this reason, the possibility of occurrence of local maxima or minima is eliminated. Also, these methods do not need information about the derivatives of the target function and only the main form of the function is required. In this research, the solver available in Excel software was used for optimization with evolutionary algorithm method. After specifying the target variable, which is the discharge coefficient in this research, the evolutionary algorithm option is selected, and the software performs its analysis to calculate the best discharge coefficient with the lowest value for total errors.

The results obtained in this research show that in all patterns of flow changes, increasing the ratio of water height relative to the weir crest to the weir height (H/P) causes a decrease in the discharge coefficient of unsteady flow. Also, in all patterns of flow rate change, increasing the height of the weir causes a decrease in the discharge coefficient of the unsteady flow, that is, the discharge coefficient of the unsteady flow in the oblique circular crest weir is a function of the upstream flow conditions and the height of the weir. Also, the unsteady flow rate coefficient in this type of weir is a function of the flow rate change pattern. As can be seen from the graphs obtained in this research, the flow rate change pattern does not have much effect on the slope of the flow coefficient changes compared to the H/P changes, but it is effective on the degree of influence of the weir height changes for a fixed H/P value. On the other hand, the graphs show that the discharge coefficient of unsteady flow for oblique circular crest weir varies between 0.5 and 1.5, which previous researchers had also concluded that the discharge coefficient of unsteady flow for other weirs is not constant and is a function of the geometry of the weir and the pattern of changes in flow rate.

Gibson et al. (2010) modeled the COWLITZ river considering the moving bed and used the HEC-RAS model for simulation. They did the modeling for the last 20 miles of the river because the possibility of flooding due to sedimentation was higher in this area. The purpose of this study was to evaluate the effects of sedimentation on the increase of flood risk in the long term. The Laursen-Copeland relationship was used in the sediment calculations because the sediments ranged from very fine sand to large rubble. They also stated that the ability to add bed particle size in 20 different classes has been added to the HEC-RAS model in version 4.1. The geographic location of this research is based on the UTM geographic system, around 33'22'32' to 32'45'17 north latitude and 40'22'48' to 48'57'19 east longitude. According to Figure 1, the total length of the studied route is about 75 km between Zargan and Farsiat and includes 155 cross sections, and the approximate length of the meander is 13.4 km. In order to simulate the hydraulic flow and sedimentation of the river by HEC-RAS model, geometric information (cross sections, distance of sections from the downstream control section, Manning's roughness coefficient and opening and narrowing coefficients), hydraulic information (flow information and water level level at the lower station) meteorological (water temperature) and sedimentary (related to flow-sediment discharge and bed sediments granularity) is necessary. In general, it can be said that after the formation of the loop, the upstream interval (R1) of its sedimentation decreases from upstream to downstream until it undergoes erosion at the bifurcation of the river, and the middle interval (R2) changes from erodible to sedimentary and the interval Downstream of the ring (R3) remains almost unchanged and shows very little tendency to erode. HEC-RAS model is used in this research. When using this software, the continuous flow series is divided into continuous flow segments based on flow and time variables. In general, it can be said that after creating the ring of the upstream interval (R1), its sedimentation decreases from upstream to downstream until it undergoes erosion at the bifurcation of the river, and the middle interval (R2) turns from erodible to sedimentary and the base ring interval (R3) remains almost unchanged and has a very little tendency to be erodible. The middle section of the Karun River (R2) turns from erodible to sedimentary with the creation of a loop, which is the reason for the tendency of the river to deposit sediments in this section after the creation of the loop, reducing the amount of incoming flow and, as a result, reducing the speed The flow in this section is caused by the division of the flow due to the two branches of the river upstream of this section.

Floods are one of the natural events that cause significant morphological changes in riverbeds and adjacent lands, which result in financial, human, and other losses. When a flood occurs, the interference of the flow in the main channel and the flood plain causes the transfer of movement and complexity in the flow pattern from the main channel to the flood plain. Due to the dynamic nature of these events, statistical, experimental, and semi-experimental criteria are used to determine the dimensions of stable regime channels. Nowadays, the use of two-dimensional models to study the behavior of the regime channels has a superior advantage over the empirical and theoretical approaches, which are based on one-dimensional. There haven't been many numerical studies done on the flow pattern and sediment transport in alluvial channels, but there have been a lot of experimental studies. In this study, the behavior and hydraulic geometry of the trapezoidal compound channel have been investigated using MIKE21software for type of steady and unsteady overbank flow and Finally, the results of modeling in steady flow conditions showed less difference with real values than in unsteady flow conditions.In order to study the behavior of the main channel in the flood flow, the flow has been selected in such a way that the flood plain are in the state before the movement threshold. First, the compound trapezoidal channel section with fully losses boundaries/ with fully mobile boundaries was developed under bankfull flow, and then the behavior and geometry of the developed trapezoidal channel (regime channel) were evaluated under type of steady and unsteady flows. In the first step of permanent steady flow modeling, the flow conditions in the channel at a certain point are constant with respect to time, which means that the speed along the flow and the average depth of the flow are the same. In the second step of the modeling, the unsteady flow along the channel was checked with the same conditions as the first step, with the difference that the input discharge is variable in time.The results showed that when the cross-section of the main channel is full of water, there was no significant change in the width of the main channel, but the width of the main channel in overbank flows is higher than the full section and increases rapidly. The mean relative differences obtained at upstream and downstream width trapezoidal section, and flow depth in steady flow conditions are0.96, 0.88, and0.98,respectively, and in unsteady flow conditions, the average relative difference obtained at parameters upstream and downstream width trapezoidal section, and flow depth in steady flow conditions are1.12, 1.15and1.05,respectively. According to the sediment transport equations available in the software, the England-Hansen sediment transport relationship chosen as the appropriate relationship for the parameters of the channel dimensions, which can be more predictable to laboratory values.An stable alluvial channel with a bankfull, when subjected to flooding, tilts towards a new stable channel.Under steady flow conditions, estimating the results of the depth and width of a stable alluvial channel in the MIKE21model is more accurate than the results obtained from unsteady flow. Also, the values of width, depth and sediment concentration predicted by the above software are better estimated than the sustainable channel design methods such as brownlie, vanrajin and WBP. In all models, the width of the channel increases rapidly over the first 3hours, and then approaches the balance stage and the channel erosion rate decreases. As the discharge increases up to 15liters per second, the depth and width of the channel is more severe and then these changes are almost constant.

In recent decades, several factors such as population growth, limited surface water resources due to reduced rainfall, and over-withdrawal of aquifers have caused a sharp drop in groundwater levels (GWLs) in many plains of Iran, including Salmas plain located in the province of West Azerbaijan. In this study, the numerical model of the Salmas plain aquifer was prepared using MODFLOW model in GMS software in both states of steady flow (September 2015) and non-steady flow (from September 2016 to August 2017). The input parameters of the model were calibrated for the measured values of GWL at the location of observation wells and validated from August 2016 to July 2018. Finally, the GWL was investigated applying 6 scenarios including a 10% to 30% decrease in pumping wells and a 5% to 15% increase in rainfall. The results of studied scenarios showed that reducing the pumping rate of the wells significantly improves the condition of groundwater resources. By reducing the pumping rate of the wells up to 30%, the volume of groundwater will increase by 13.66 mcm and shortage of the aquifer reservoir will be compensated. However, 15% increase in annual rainfall will improve the condition of the aquifer by only 0.5 mcm. Results show that reducing the rate of withdrawal from wells reduced the amount of groundwater flow entering the aquifer from 41.98 mcm in the calibration state of the model to 38.7 mcm in terms of 30% reduction of discharge rate in the wells. However, the increase in rainfall did not cause significant changes in the amount of groundwater inflow and outflow. The results of this study indicate that management scenarios such as preventing over-withdrawal from authorized wells and blocking unauthorized wells have more significant effects on improving the GWL than possible climatic scenarios.

Analysis of the unsteady flow on the weir end sill is fundamental to determining the passing flow's exact flow discharge and height. Due to the difference between the steady and unsteady flows and the effect of different terms of the Saint-Venant equation, the weirs' stage-discharge curves under the two types of flows are different. In the present study, 3D free-surface flow on the Ogee and the Piano-key weirs under steady and unsteady flows was modeled using the FLOW-3D numerical model, and the effect of different input hydrographs for multiple time bases was investigated. Based on the obtained results, the steady flow condition's unit stage-discharge curve turned into a circular curve in the case of the unsteady flow condition. In both types of the weirs, by increasing the hydrograph time base, the stage-discharge curve changed from a circular curve into a unit curve and finally conformed to the steady-state's stage-discharge curve. In both types of studied weirs, for a constant flow discharge, the water head difference was more considerable for the hydrograph with smaller base-time, i.e. the hydrograph with steeper ascending and descending branches. The amount of head difference in the ogee weir due to your hydrographs with time steps of 4, 10, and 40 seconds is 0.023, 0.013, and 0.008, respectively, and for the piano key weir is 0.024, 0.019, and 0.009. In other words, for steeper input hydrographs on the end-sill of the weirs located on the channels or the weirs used as a diversion, an unsteady flow analysis should be performed. For a fixed weir height and a fixed input hydrograph, water head changes of the Piano key weir were greater than the Ogee weir.

Unsteady flow analysis is performed using the equations of St. Venant. Calculating the slope of the energy line (Sf) is of great importance in the analysis of unsteady flow. Since Sf is equal to the hydraulic gradient (i) in a coarse porous media, the calculation of i is of great importance. In the present study, using experimental data recorded in a steel cylinder with a diameter of 16 cm and a length of 70 cm, 40 cm of which is filled with rockfill with three small, medium, and large grains, investigated the unsteady flow in a confined porous media. The particle swarm optimization (PSO) algorithm is used to optimize the Forchheimer binomial relation coefficients used in steady flow (a, b) and the triplet relation used in unsteady flow (a, b, c). The results of the present study indicate that the values related to the mean relative error (MRE) in the case of using a triple relation to the binomial relation to calculate the hydraulic gradient of unsteady flow, in small materials 14.5, in medium materials 14.7 and in large material, it has improved by 12.2%. The value of the third sentence is a triple relation to the hydraulic gradient ((cdv/dt)/i) in 7.23% in small materials, 14.79% in medium materials, and 17.01% in large materials. In other words, since with increasing the diameter of the material, the efficiency of the nonlinear (non-Darcy) relation increases compared to the linear (Darcy) relation, the third sentence of the triple relation also has a greater effect on the hydraulic gradient calculations.

The inverse transport problem is very difficult and challenging to solve due to some special characteristics, including the lack of solution, non-uniqueness and instability. Regarding to these complexities, usually some simplifications are made in solution process, which ultimately leads to identification methods that cannot be extended for real-world applications. This study aims to develop a practical method for pollution source identification in rivers under realistic conditions, which considers irregular cross-sections, unsteady flow and both physical and chemical transport processes. The stochastic framework of proposed method provides the possibility of estimation of source characteristics in greater time instances than available observation data as well as consideration of uncertainty due to error in those data. Considering that direct solution is also required in the solution of inverse transport problem, at first flow and transport equations is solved by finite difference numerical scheme. Then, inverse transport equation is solved to identify active pollution sources using the geostatistical method. Results of application of the method to three hypothetical examples and two sets of real data indicated the great accuracy and numerical stability of proposed method in reconstruction of source characteristics even in complicated real-world condition and using sparse and erroneous observation data. Furthermore, the identification uncertainty was considered through 95 percent confidence interval.

In this study with respect to the sensitivity analysis of transmissibility coefficient, storage coefficient and specific leakage of infinite and finite leakage aquifers in the unsteady flow state of groundwater, which was carried out using an analytical method, these results were obtained: 1. Withincreasing the coefficients of transmissibility, storage and specific leakage of infinite and finite leakage aquifer, the drawdownreduces. 2. In all of the examined sensitivity analysis, it was observed that the drawdown of infinite leakage aquifer is more than the finite leakage aquifer and the drawdown of finite leakage aquifer 2 is more than the finite leakage aquifer 1. 3. With increasing the transmissibility coefficient and specific leakage of infinite and finite leakage aquifer, the groundwater flow reaches earlier to steady state. 4. With increasing the storage coefficient of infinite and finite leakage aquifer, the groundwater flow reaches later to steady state. 5. Infinite leakage aquifer reaches the steady state later than the finite leakage aquifer and finite leakage aquifer 1 reaches the steady state earlier than the finite leakage aquifer 2.

Creation and propagation of unsteady flow in irrigation canals causes changes in water delivery to canal intakes. Unsteady flow in irrigation canals usually form by operation of check structures. Up to now simulation of unsteady gradually varied flow in irrigation canals has been considered in various researches. Simulation of unsteady gradually varied flow mostly done using available hydrodynamic models, but these models can’t simulate unsteady rapidly varied flow. In this research, using MacCormack numerical method, a numerical model was developed to solve the governing equations for rapidly unsteady varied flows, and the TVD method was used to control unrealistic and non-physical oscillations. The model was developed in MATLAB programming environment to simulate positive waves caused by the suddenly closure of a gate at the end of the E1R1 canal in Dez irrigation network and a hypothetical channel. The results showed that the higher flow in the gate at the moment of gate closure causes the higher numerical solution errors. Also, the results showed that the simulation using MacCormack method would have a large error, but the simultaneous application of the TVD and MacCormack method could reduce the numerical solution errors and simulate the water surface fluctuations according to the reality.

One of the major topics in river engineering, is design and construction of the bridges with sustainability considerations; estimating the maximum depth of scour in the vicinity of the pier also has a lot of importance. Scour is one of the most important reasons for instability and ultimately the defeat of the bridges. While most of previous researches on Bridge Piers scour are mainly focused on steady flows; in rivers and especially during flood, the flow is unsteady and the changes in flow rate based on the time, could be really fast and rapid. On the other hand and based on the author’s literature reviews, considering unsteady flow would cause more economic and realistic prediction about the maximum depth of scour around the piers. Many different methods have been used till now to protect piers of the bridges. In this research, a non-structural and environmental friendly solution has been used to reduce the depth of the scour of bridge piers in unsteady condition.

Based on author’s knowledge, so far Nano materials just used to correct the behavior of concrete resistance and also used in dusty rural roads. For this reason, this experimental study attempts to test a new method to reduce the scouring around the bridge pier in river in unsteady flow condition. To achieve this, in flume bed around the piers, the combination of nanostructured materials, called Nano-clay had been used. Experiments for both steady and unsteady conditions, were conducted on cylindrical pier with a diameter of 35 mm, in a channel with a 9.5 m length and the equal height and width of 40 cm, and a slope of 0.001. In this study, experiments have been done in two different cases, with and without the existence of Nano clay materials in the bed of the channel. For simulating unsteady flow, stepped triangular hydrographs with a peak time of 7.5 minutes and flow peak of 8, 12, 16 and 20 liters per second were used in two different modes of Nanostructure mixture with and without materials.

The timing development of scour phenomenon at the piers of the bridge has been studied and compared in both cases, with and without presence of nano-materials. In the presence of nano-materials and at all maximum discharges, it has been seen that the scouring process at initial time steps is almost as same as the condition without nano-materials with sharper trend. The trend in later time steps has experienced lighter changes and finally has reached to a constant value.

The results of experiments in unsteady flows indicated that with the presence of Nano materials in the bed sediment, the maximum scouring depth at the adjacent of the bridge piers has been deducted while discharge rate increased. It has also been shown that the maximum reduction of scour depth, 62.86%, happened at maximum discharge of 20 lit/sec. In this discharge, the maximum scour depth has been reduced from 47.4 millimeter to 18 millimeter. The minimum reduction of scour depth with 56.15% happened at the discrge of 8 lit/sec.

Levees are man-made embankments built to prevent rivers from overflowing their banks. A levee is a naturally elongated ridge or artificially constructed fill or wall that regulates the water level. It is usually earthen and often parallel to the course of a river in its floodplain or along low-lying coastlines. The levee construction is a common and very old method of river flood control recently used considerably as an engineering operation to reduce or prevent the detrimental effects of floodwaters. It can be used either alone or together with other methods to minimize the floodwater damage. Engineered earthen levees are of three general types: compact, semi-compact, and uncompact; the former are usually and traditionally used in areas of high property values, high populations, high land use, or in controlled compaction, steep-sloped embankments utilized on good foundation conditions during construction. The semi-compact or uncompact levees are generally used in low value, poor foundation areas or those with high rainfall during the construction season. Compared to other floodwater control methods, levees are more efficient because they are not only quite cost-effective, but also provide more factor of safety for slope stability. Artificial levees are aimed at preventing the adjoining countryside flooding and slowing the waterways' natural course changes to provide reliable shipping lanes for maritime commerce over time; they also confine the river flow causing higher and faster water flow. Levee construction materials should be coarse enough to withstand the erosion caused by the flowing water, their shear strength should be enough to satisfy the levee's slope stability, and they should be adequately impermeable meaning that they should also contain fine aggregates to prevent the extra seepage that has undesirable effects on the levee's slope stability; therefore, making specific arrangements to reduce repercussions deems necessary. Massive constructions that require large amounts of materials need to use the available on-site materials to reduce the transportation distance and hence the project construction cost; using on-site materials is a significant advantage the levee construction enjoys. As mentioned before, since the levee construction needs both coarse- and fine-grained materials to reduce permeability, the best choice can be the coarse-grained soil containing clay; therefore, both GC (clayey gravel) and SC (clayey sand) soil types take priority over any other types. Hence, evaluating the amount of the soil fine aggregates and the effects of compaction percentage on the permeability coefficient and on other strength parameters to meet the economic, speed, and time requirements of the levee construction is quite important. This research studies the effects of compaction percentage and the amount of fine aggregates on the SC soil permeability and on the steady and unsteady seepage flow through levees. Accordingly, three levee samples A, B, and C (from Mehran River borrow area) with respectively 12.8, 20, and 28.4% fine aggregates and 60, 70, 85, and 100% compaction have been selected to carry out the permeability tests. Results of tests with different compaction and fine aggregate percentages showed that an increase in the percent compaction of each sample (from 60 to 100, 70 to 100, and 85 to 100) decreased the permeability coefficient 25, 14.3, and 8.91 times, respectively. At every compaction percentage, sample A's permeability coefficient was 1.2 times that of sample B and 1.69 times that of sample C and that of sample B was 1.41 times that of sample C. Next, using the numerical modeling, both the flow rate (in the steady state) and phreatic line (in the unsteady state) through the levee were studied with different compaction percentages and the results showed that in simulating the unsteady seepage through the levee the phreatic line did not intersect the downstream slope and was significantly far from it. The results of this research can be used to either design or construction of the levee; furthermore, it can used to analyze the effect of the soil compaction percent on permeability parameter during construction of levees.

To evaluate a pipe network performance, both steady and unsteady flow conditions are required to be accurately analyzed in the system. For this purpose, mathematical models are developed and utilized. Calibration of parameters with dynamic effects like the steady and unsteady friction loss factors as well as pipe wave speed is crucial to the simulation models. A common approach for calibration of pipe networks under unsteady flow is the Inverse Transient Analysis (ITA) method. This study introduces a model for hydraulic analysis of unsteady flow in pressurized pipes using the numerical Method of Characteristics (MOC). To each calibration parameter a correction factor is specified. Then, a nonlinear optimization problem is developed with the aim of minimizing the discrepancy between the calculated and measured transient pressure heads at the measurement sites. The decision variables are the correction factors multiplied by the pipe wave speeds, steady friction factors and unsteady friction loss components. In this Article, the proposed model applied to an experimental system set up in the Technical University of Lisbon. By defining the genetic algorithm to minimize the objective function, after 30 generations error rate was reduced from 140 m to 92.15 meters. The results, increasing the accuracy of modeling showed as much as 33%.

Building homogeneous rock-fill dams is certainly one of the most effective methods of controlling floods. In flood situations, the in-flow to these dams typically contains a considerable amount of sediments. This underscores the need to study the flow behavior and sediment concentrations so that one could identify the amount of passed and trapped sediments, and decide on their management. Thus, first, on the basis of numerical solution of Saint-Venant equations, the flow characteristics (e.g. depth and velocity) were calculated, using finite volume method, with a completely implicit approach, and then the concentration of the sediments at different points of the reservoir were determined, using discretization of the convection diffusion equation based on upwind hybrid. For this purpose, first mathematical model of mentioned equations prepared in Matlab and then in order to evaluate the performance of this model used the results of conducted experiments in the hydraulic laboratory of Agriculture faculty of Bu-Ali Sina University of Hamadan on the Rockfill dams. On the basis of the comparison drawn between the data yielded by measurement of sediment concentration and the calculations conducted in eight sections and three layers of 5, 10 and 15cm high in the reservoir of rock-fill dams, mean value of the relative error of sediment concentration was found to be 5.1, 7.1 and 8.2 percent, indicating a good correlation between the output of mathematical simulator and measured sediments in the experimental model. Results also revealed a decrease in the relative error of the simulator with an increase in the diameter of aggregates used in the body of dam due to the better structure of hypotheses of one-dimensional flow.

Poor performance of irrigation networks due to improper management and operation of irrigation canal structures has attracted the attention of managers to improve operational management of these structures. Regulating in-line reservoirs can have significant impacts on performance improvements of operational management of irrigation systems. To this end, good coordination between inlet and outlet structures as well as downstream demands should be provided. Under the condition that control and management of the reservoir is done with good coordination with other sectors, the flow in the canal would be more stable. This leads to decrease in the water level fluctuations and better services to water users. Reservoir operation and management investigation requires applying hydrodynamic models. In this study, hydrodynamic model of ICSS was adopted for modelling the flow in the regulating reservoir of Moghan Irrigation Network. Eight operational scenarios for entrance hydrograph to the canal system were considered, which consisted of gradual and sudden decreasing of inflow for two status of (i) non operation and (ii) with reservoir operation. Similar scenarios were assessed for the increasing mode as well. The results indicate that response time of the system and stability of water delivery improve by applying reservoir operation. In the decreasing scenarios, the adequacy indicator improves, while in the increasing ones, the efficiency indicator of water delivery increases when the reservoir is operated. According to the results, the latter improvement for the main off-take was obtained as 0.45% and 6.75% for, respectively, adequacy and stability.

Sharp-crested weirs are common measuring devices in rivers and irrigation networks. Their installation and operation are simple yet very practical. The hydraulic performance of sharp-crested weirs and their head-discharge equations in unsteady flow condition are of great interest, however, very limited studies are available in the literature. In the present study, the hydraulic performance of 90° V-notch weir, located at the end of a storage, was investigated in unsteady flow condition and the differences between steady and unsteady overflow were observed and evaluated. The results indicate that the difference between steady and unsteady discharges are significant whereas the difference value of investigated scenarios arise up to 40 percent, sometimes. Therefore, the previous head-discharge equations are no longer valid.

For accurate simulation of transport in natural rivers, some revisions have to perform in classical advection dispersion equation and some terms for considering of transient storage zones added to this equation. In this study a new and comprehensive model that merges numerical schemes with higher order accuracy (QUICK scheme) for solution of advection dispersion equation with transient storage zones in rivers with irregular cross sections at unsteady flow regime is presented. The presented method is verified by analytical solution, hypothetical example and two sets of real data. The results of verification implied that presented model have reasonable accuracy in simulation of contaminant transport in this condition. Also with implementation of model in the case of pure advection and comparing the results with two other numerical model results that use from centered difference method in spatial discretization of equations the ability of presented model in more accurate simulation in this case is shown. Results show that presented model in this study, is an applicable model and could be suggested as alternative for common present models at contaminant transport studies in natural rivers and streams.

In this study the unsteady flow in AMC canal of irrigation network of Tabriz plain was simulated using CanalMan model. The aim was to evaluate different settings of canal control structures and turnout in passing from months with low to high water requirements and choose the most appropriate operational program among the considered options. For this purpose 10 operational options for an increasing discharge rate were considered and compared with each other for a 10-hour water delivery duration. The criteria for comparing different options included shortage of water delivery, absolute rate error of discharges and the average root-mean-square of error. The results showed that the tenth option with the least values in all three criteria, was the best option. The temporal changes of discharges for control structures and turnouts in the tenth option were presented. According to the results the disturbance travel time from canal inlet to the control structure and its damping time periods were the least in the chosen option.

Implementation of subsurface drainage in Northern Iran paddy fields is crucial to achieve the feasibility of round-cropping and improve sustainable use of limited soil and water resources. One of the subsurface drainage systems is bi-level system that can be installed because of lower costs than conventional and better control in drains discharge. Installation of this system needs suitable knowledge of designing of subsurface drainage systems due to layered soil of paddy fields. In this study¡ an analytical solution of two dimensional transient saturated flow of Bear equation to subsurface drainage in a paddy field is presented to investigate the bi-level drainage systems operation. Also¡ due to importance of vertical head in clay and layered soils¡ a modified procedure was performed to separately involve vertical head. Validity of the solution has been evaluated by comparing with the field data collected at paddy fields of Northern Iran. The two dimensional solution was not able to reasonably predict the water table profile. But the obtained results indicated that considering the vertical resistance in the media improved the simulated data in the bi-level subsurface drainage systems and provided good representation of water table dynamics. The differences between field data and results were only 21% for modified procedure in comparison with 61% for two dimensional solution. Totally¡ it would be mentioned that in future work for designing bi-level drainage systems in paddy fields¡ the vertical head loss should be considered.

Poor performance of irrigation and drainage networks causes to reduce the transfer and distribution throughputs and in result comes useless water and makes too much consumption in forming. A significant portion of water losses in irrigation and drainage networksis related to transmission and distribution. Therefor more consideration in thrirrigation network management, improve irrigation efficiency and also the exploitation of water resources, especially in the agricultural sector is necessary. Controlling and adjusting structures of water level in the direction of drainage and irrigation canals can influence on increasing of throughput and decrease the use of water. So, right choosing and recognition of the deficiencies of these structures helps carry up the throughput of the networks and prevents to waste water. It is hard to solve equations of water flow in canals and related institutions by using analytic methods. For this reason, this research was done with HEC-RAS hydraulical model in the main channelof irrigation and drainage network of Sistan plain.
Sistan plain is located in southeastern of Iran with good potential for agricultural production because of the alluvial sediments from Hirmand River. 23820 ha of the Sistan plain is covered by 5 blocksof the Shibab irrigation and drainage network. While Sistan’sShibab irrigation network efficiency is low, HEC-RAS Hydraulics model in unsteady condition was performed to control and adjust this network’s main canal in approximately 19 Km length. In this research, the evaluation model in the canal was performed for more suitable intakingwater in the quadruple order 2 canals . So, the existing structure’s operation was analyzed on controlling structures in management and lack of management situations.This research was assessed during a 15-day impounding period using hydraulic model of HEC-RAS with the aim of performance and operation evaluation of existing structures on the Shibab main canal. HEC-RAS model was prepared by United States army corps of engineers which is developed by the hydrologicengineering center.HEC-RAS analyzes river system and runs under the Windows operating system. This software package is of hydraulic analysis program series, where the user communicates with the system via a graphical user interface (GUI). The system is capable of performing steady and unsteady flow water surfaceprofile calculations. HEC-RAS software is designed to perform one dimensional hydraulic calculation for a full network of natural and synthetic channels. Visits were made before and after the beginning of irrigation, and during the Operation, in order to record the data of the flow and observe the way of utilization of canal, and existing structures. Then, the model was calibrated on the basis of depth and discharge measurement and simulation data in real condition of operation for 10 days impoundment during 21 to 30 April, and the Statistical parameter values:RMSE, EF, MBEand R2 were calculated. Then the objective functionwas evaluatedusingoperational performance indexes of adequacy, efficiency, equity and reliability of Molden and Gates regarding to HEC-RAS simulation results in unsteady condition.
According to the simulation results in existing condition,theerror of delivery dischargeis equal to 0.54 while applying the management onthe adjustment structure of irrigation networkdeclined theerror to 0.42. By the canal routstructuremanagement in HEC-RAS model, on the basis of proposed operation option, according to existing operation condition, delivery discharge loss in comparison to the total discharge of the network 0.12 value decreases.Based on the simulation results, the mean percentage of improvementin performance indexes of adequacy,efficiency, equity and reliability, as well as objective functionofdelivery discharge are equal to 19.7, 20.90, 66.07, 65.24and54.81. Therefore based on simulation results of different scenarios and investigation of the effective factors onto the flow, onthe forms of charts and tables show that without management on controlling structures, it isn`t possible to appropriate of flow rate onto second class canals and traditional streams branched out main canal and also streams branched out second class canals, properly.
The results show that the model of HEC-RAS is proper for hydraulic simulation of main canal in the irrigation and drainage network of Sistan plain. Based on the simulation results of different scenarios of this research, the mostimprovements intheobjective functionare allocated toequity and reliability indexes in the Shibab main canal with the proposed management method.