Iranian Water Research Journal

Abstract Interaction between water flow characteristics and bed erodibility plays an important role in sediment transport process. In order to reach stability, rivers with deposition or bottom erosion make different forms in the bed .The bed forms create extra resistance, which is called the bed resistance. The mutual interaction between the flow and the erodible bed through sediment transport phenomena in a sand-bed channel causes a variety of bed forms. Starting with ripples and gradually increasing in shear stress or water velocity, dunes, washed out dunes, flat bed, anti-dunes, and standing waves are formed. The most common boundary conditions in alluvial rivers are the mobile beds covered with Ripple and Dune. These forms, in many alluvial systems, play a critical role in contrast between the flow, discharge of sediment and morphology of bed. One way to identify the behavior of the rivers is to study the structure and the formation of bed forms within them. Ripples are among the smallest of the bed forms. The longitudinal cross-sections of ripples are usually asymmetrical. The upstream face of ripple is long and has a gentle slope, and the downstream face is short and steep. The height of ripples is usually between ۰.۵ cm and ۲ cm, but not more than ۵ cm. The wave lengths normally do not exceed to ۳۰cm, and they are usually within the range of ۱ cm to ۱۵ cm. Some ripples that form in deep-water regions are symmetrical. Ripples are the smallest of the bed configurations. They are related to physical parameters near the river bed and have little correlation with the water depth. Their occurrence is the result of the unstable viscous layer near the boundary. They can form in both shallow and deep water. In plan, they either are parallel to each other or have a shape like fish scales. With increasing the flow velocity, the plan form of the ripples gradually develops form straight line to curves and then to a pattern like fish scales, symmetrical or unsymmetrical Resistance is a function of the geometrical dimensions of the bed forms and depth of water. Estimating of the flow resistance is one of the most important matters in planning, designing and operating of water resources projects, including water transfer and river system management. In this research, the effects of two different types of ripples (parallel and flake shape) on the hydraulic characteristics of flow were experimentally studied. The experiments flume located at the hydraulic laboratory of Shahrekord University, Iran. The flume used in this study was a Straight type that had the dimensions of ۰.۴ m wide and depth and ۱۲ m long. This flume has vertical PVC sidewalls. Generally ۴۸ tests in variety slopes of ۰.۰۰۰۵ to ۰.۰۰۳ and variety discharges of ۱۰ to ۴۰ lit/s were conducted. Velocity and the shear stress were measured by using an Acoustic Doppler Velocimeter (ADV). Velocity measurements were performed with a frequency of ۲۰۰ Hz, which provided accurate statistics on the mean flow and turbulence characteristics. Detailed velocity measurements were performed in ۹ cross-sections in the Straight flume. The cross-sections were determined at: before crest, crest and after crest. Generally, in each section velocity was measured in ۱۲ point (۵, ۲۰ and ۳۵ cm from flume side and ۴ points from bed). For All tests, flow depth was kept constant. In this study generally ۴۸ test were tested under different hydraulic conditions. It was observed that the peak value of the bed shear stress appeared on the midpoint of upstream surface (before crest ripple) and the crest of the ripples had the lowest value of the bed shear stress. From the crest to trough (after crest) of the ripples, the general bed shear stress was in an increasing trend. It was generally found that with increasing Froude number and the bed shear stress increased. Also, in the case of parallel ripple bed form, the shear stress was about ۲۶% more than that of plane bed and in the case of flake ripple bed form the increasing rate was ۲۳%. It indicated that the shear stress was much affected by the parallel shape of ripple bed form compared with the flake shape, as it was ۲۷% more than the flake shape.

Abstract Diverting flow from rivers and channels is one of the methods of transfer water for agricultural and industrial purposes. Dividing channels are also used in urban wastewater in collecting system. Intakes are amongst hydraulic structures which are used for the purposes of controlling and deviating flow in agricultural irrigation and drainage networks and also in sewer systems. In some cases, energy is produced through intakes. Determining the model of the flow, which is entering the branch channels from the main channel, is of utmost important in these hydraulic structures.
A part of flow in the main channel is deviated and enters the branch channel when impounding the river due to the suction force applied to it; as a result, flow separation zone and flow compression zone are formed near the entrance of the intake channel. The flow deviated into the intake has complex properties. The flow particles rotate in the separation zone, near the entrance wall of the intake channel, and the longitudinal velocity of the flow decreases and it increases in the opposite direction of the flow. The longitudinal velocity intensely increases in the compression zone, due to the density of the flow lines, and reaches its maximum levels. Therefore measuring the flow velocity in the flow separation zone and the flow compression zone is difficult and accompanied with error. Normally, flowmeters are installed in intakes in order to compute the flow discharge. A very complex flow is formed as the flow diverts from the main channel into the branch. As the flow approaches the branch channel, it undergoes lateral acceleration and is divided into two sections due to the suction pressure from the diversion. Entering the intake, the flow loses balance because of lateral pressure gradient and shear force and the centripetal force and this leads to the formation of secondary flow. A large number of experimental and numerical studies have been conducted on the flow within the intakes. Simulating the flow field, using numerical methods, reduces experimental costs and saves time therefore numerous studies have been conducted on the flow hydraulics in the diversion channels. The flow hydraulics in diversion channels have been three- dimensionally simulated in liquid and gas phases. In these studies finite volume method was widely used. Ramamurthy et al. (2007) conducted a numerical research in an intake with a 90 degree diversion and calculated the velocity of the flow within the channel through numerical calculations and compared the results with experimental data. They studied the separation zone in the intake channel and came to the conclusion that increase in dewatering ratio leads to an increase in the vortex’s strength. Mignot et al. (2012) used 3D numerical model to simulate flow patterns through junctions. In their study, in order to evaluate errors flow rate measurements were done by installing sensors in various locations, at the downstream of the junction. They showed that the measured discharge performed by sensors can produce the error more than 60% from real discharge. When fluid is flowing within a main channel with an intake, it enters the branch channel due to the suction force from the branch channel which causes lateral acceleration in the flow. When the flow enters the branch channel, separation area is formed on one side of the branch channel and flow contraction forms at the other side, due to the development of the flow. These phenomena lead to the flow having a thoroughly three- dimensional behavior.
The flow’s behavior has been three- dimensionally modeled in the deviation location through using ANSYS-CFX software, in this study. The results of the numerical model with a 90- degree contact angle have been compared to the experimental results, for the purposes of verification and then effects of the bed elevation difference of the meeting channels on the flow pattern structure were studied. The obtained results indicated that increase in the bed level of the main channel (0.05m higher than the branch channel bed) leads to: (1) moving high-speed lines of the flow upwards, from the bottom to the water surface; (2) disappearing of the separation area in the entrance of the branch channel; (3) increasing the intake ratio in the branch channel; (4) transferring the secondary flow from the bottom to the middle and therefore reducing of erosion intensity in the bed and floor of the branch channel.

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Abstract The spillway is one of the most important elements of dam building. So studying and designing of the spillway hydraulic should be considered in dams and other similar projects. The ogee spillway, because of its superb hydraulic characteristics, has been widely studied. Its ability to pass flow efficiently and safely, when has been properly designed, with relatively good flow measuring capabilities, has enabled engineers to use it in a wide variety of situations. In the last two decades, there has been an increasing interest in the stepped spillways in various laboratory experiments around the world. This is partly because of technical advances in the construction of Roller Compacted Concrete (RCC) dams and considerable amount of energy dissipation along the chute, leading to reduction in the size of the stilling basin. Flow analysis using laboratory experiments usually involves considerable time and cost requirements .Nowadays, availability of computational fluid dynamic (CFD) programs and powerful computers has resulted in increasing usage of numerical methods of flow analysis. Free surface flows are encountered in hydraulic engineering problems including water jets, weirs and around gates. For the numerical modelling of a steady flow, the area of calculation and therefore the position of the free surface have to be known. The main object of this study is numerical analysis of free surface profiles on ogee and stepped spillways by finite volume and finite element methods and comparison of the two methods.
The physical laws governing a fluid flow problem are represented by a system of partial differential equations regrouping the continuity equation, the Navier-Stokes equations and any additional conservation equations. The numerical analysis resolves these equations by accurate and complex numerical schemes. A program or code, where the numerical algorithm is implemented, is then solved on a computer. In recent study experimental results offered by Tabara and CHatila (2005) have been used to investigate stepped spillway physics models of Tabara and Chatara (2004) for studying ogee spillway. FLUENT and ADINA software have been used to simulate flow field of types of stepped and ogee spillways. It should be noted that k-£ model has been applied in order to modeling turbulence. Gambit preprocessor software is a tool for networking flow field. In recent study we have used PRESTO scheme for discretization of pressure, quick plan for discretization of terms of displacement of momentum equations, turbulence formulas and PISO algorithm for coupling velocity and pressure. In finite element method, Galerkin relation has the second order accuracy. SUPG method is used in momentum equations and turbulence for discretization of term advection which is effective in problem convergence. Meshing type has been selected as triangle form in ADINA code, but quadrilateral in FLUENT code regarding the spillway geometry. In some area structured mesh and in some other ones non-structured mesh have been chosen. Due to existence of rotatory flows over the steps, more fine meshes have been used in both codes near to body of stepped spillway as well as ogee spillway, because of the velocity gradient nearby wall, where flow enters spillway channel from reservoir.
In recent study, water surface profile has been simulated in four types of stepped spillways and 3 types of ogee spillways on the basis of finite element method using FLUENT code and finite volume method using ADINA code. Relatively close consistency has been observed between water surface profiles in both codes by comparing experimental results. Note that free surface profile simulated over the ogee spillway was closer to water surface profile evaluated in laboratory than the profile by finite element method. There were observed better consistency in results from free surface profile over stepped spillway with finite volume method. Maximum differences between results of water surface profile in numerical model of FLUENT and ADINA were nearly 1.2 cm and 1.6 cm, comparing with laboratory results respectively. This value in numerical simulation is acceptable regarding to different meshing in model networking. On this basis, numerical methods of FLUENT and ADINA are proper in order to simulate similar structures for saving costs due to construction of physical model. Flow surface can be determined considering the lower error of FLUENT model in measuring free surface flow; thereby, designing lateral walls of spillway is realized with more precise.

Abstract

Abstract Snow cover, as an important component of land cover, is one of the most active natural and plays an important role in hydrological processes and climate. Variability in snow covered area has a significant influence on water and energy cycles, as well as socioeconomic and environmental repercussions. Frequent and long-term snow observation, accurate snow cover (SC) mapping and snow water equivalent (SWE) estimation are crucial for operational flood control, water delay planning, and resource management in snowmelt-dominated basins. Today, satellite-derived snow products obtained from visible and infrared imagery, as well as passive microwaves are available on the Internet, with few recently availability in near-real time . Optical sensors (e.g., Landsat, Advanced Very High Resolution Radiometer-AVHRR, Moderate Resolution Imaging Spectroradiometer-MODIS, Systeme Probatoire d’Observation de la Tarre-SPOT) have been well developed to provide snow information with good temporal and/or spatial resolution. But, cloud cover is a major factor in optical remote sensing that limits our capability to map the Earth’s surface. It is often not an easy task to collect a time-series cloud-free images for a particular area of interest, using optical remote sensing, which limits their wider applications for SC monitoring. Space-borne passive-microwave radiometers (e.g., Scanning Multichannel Microwave Radiometer-SMMR, Special Sensor Microwave/Imager-SSM/I, Advanced Microwave Scanning Radiometer-Earth Observing System-AMSR-E), can penetrate cloud to detect microwave energy emitted by snow and ice and provide information on SC and SWE. These passive microwave data are well suited to snow cover monitoring because of the characteristics such as all-weather imaging, large swath width with frequent overpass times. But, the coarse spatial resolution (e.g., ۲۵ km of AMSR-E daily SWE product) hinders their applications in operational hydrological modeling. It seems that the combination of MODIS and AMSR-E can take advantage of both high spatial resolution of optical data and cloud transparency of passive microwave data. In this study, daily cloud-free SC and SWE maps at the ۵۰۰-m resolution were produced for Karun watershed, Ahwaz, Iran (January ۲۵–۳۲, ۲۰۰۴). The daily MODIS-Terra, MODIS-Aqua, and AMSR-E snow data products were used via a fusion-disaggregation algorithm. The developed SC and SWE maps were evaluated, using total accuracy of snow mapping in clear-sky (Os) and all-sky (Oa) conditions, underestimation (UEc) and Overestimation (OEc) of snow covered area in clear-sky condition, snow accuracy in clear-sky (Sc) or in all-sky (Sa) conditions, and no snow accuracy in clear-sky (NSc) or in all-sky (NSa) conditions. The results of this study showed that the combination of MODIS-Terra and MODIS-Aqua considerably reduced the cloud coverage in such high resolution optical data. Although MAC-SC and MAC-SWE products have been developed to have ۵۰۰ m spatial resolution, the massive and continuous cloud cover (larger than ۲۵ km in size) in the MODIS-Terra and MODIS-Aqua and, hence, TAC products were simply replaced by the coarse AMSR-E pixels. In this case, although those cloud coverages were removed in the MAC-SC and MAC-SWE products, the actual resolution of the snow or no-snow pixels kept ۲۵ km and such pixels had the false spatial resolution of ۵۰۰ m. The SWE redistribution of AMSR-E based on MAC-SC products enhanced (to some extent) the spatial resolution of the AMSR-E SWE products. However, there was no measured data to evaluate the accuracy of the enhanced SWE products. It can be concluded that for pixels with scattered cloud cover (less than ۲۵ km in size) in the TAC products, the MAC-SC and MAC-SWE products indeed improve the spatial resolution of those pixels to ۵۰۰ m, while for massive cloud cover (larger than ۲۵ km in size), the actual resolution of those pixels in the MAC-SC and MAC-SWE products are ۲۵ km, even in ۵۰۰ m pixel size. Despite of these limitations, the MAC-SC and MAC-SWE maps are suitable for hydrological, meteorological modeling on a daily basis in the study area.

Abstract Shortage of water resources and successive droughts are one of the most important types of problems caused by climate changes and governmental activities that will undoubtedly cause great disputes in the future. Global water crisis, drought and famine and their effects have made governments to make their utmost effort to control and use groundwater resources. Groundwater, as one of the main and most important water resources in Iran, is a major supplier of drinking, agricultural, and industrial water and has an important role in economic growth. Historical changes of water laws from ۱۹۲۸ so far, not only have not been in conformity with modern circumstances, but also have increased violations and reduced power and authority of sovereignty over the water. The process began and strengthened with the law of equitable distribution of water and subsequent laws. The laws has led to a situation that despite the legal decisions, a large number of illegal wells was made during the period of ۱۹۹۴ to ۲۰۰۵. There are still more than ۲۵۰ thousand illegal wells in the current situation (Mazaheri and Abdulmanafi, ۲۰۱۵) and there is an incentive to continue these activities and increasing violations. In spite of the weaknesses in the legislation, the capacity and powers of the existing laws are not used properly and a remarkable part of the intentions of the legislator is not met. In the law of equitable distribution of water, no new decree has been issued regarding to the private ownership of water resources, except groundwater. Whether beneath a private land or public land, water is absolutely a joint asset that people can own by obtaining permission from the government. In fact, what has changed with the adoption of new rules is the issue of water resource allocationand private ownership of water resources still remains. However, the assumption of ownership of the water in the law of equitable distribution of water does not mean absolute ownership of holders. Since the fluid nature of groundwater prevents the physical possession of the underground source by the holder, it can be said that traditional rules of use of groundwater do not generally provide any right of ownership that the holder can appeal to the legal system. Based on the studies of ministry of energy, different regions of the country have been divided into two forbidden and free zones in terms of the possibility of exploiting underground water. In free zones, individuals can submit a written request to the regional water companies in each province to get a license for digging wells or constructing subterranean and exploiting underground water resources for any purposes. The use of groundwater resources up to ۲۵ cubic meters per day for domestic, drinking, sanitation, and watering use does not need a permit in these areas and people can only use up to the abovementioned figure by informing the Ministry of Energy. In the forbidden zone, licensing well digging for industrial and civil projects of government with the approval of the Ministry of Energy and drinking water supply for cities, towns and villages with the offer of relevant ministries or their affiliated organizations. Industrial and drinking water, livestock and poultry health water supply with the certificate issued by the competent authorities will be possible based on the water facilities and the approval of the Ministry of Energy. Obvious point about the law is that tens of thousands of different beneficiaries didn’t see it necessary to make use of law for getting legal license. Because offenders, within three decades of experience, have found that regulated well digging leads to government’s supervision over their destiny and endless harassment upon them. This is the process that began and strengthened with the equitable distribution of water and subsequent laws. One of the opportunities created in forbidden areas for well digging licensing is related to livestock and greenhouse units. Experience has proven that these licenses are solely a certificate to permit legal well digging and investigations show an overdraft of more than ۶۰ to ۷۰ percent of these units. It can be asserted that more than ۶۰% of these units have virtually no greenhouse or livestock activities and just tremendously extract water and continue traditional agriculture and high-consuming activities (in term of water). In many cases, the owners have used the value added of converting rain-fed land around wells to water-fed lands and try to sell with high prices.

Abstract Drought is a temporary and recurring meteorological event, originating from a lack of precipitation over an extended period of time. The success of drought preparedness and mitigation depends on timely information about drought onset and forecasting. This information may be obtained through continuous drought monitoring, which is normally performed using drought indices. Drought is an unpleasant, naturally occurring event caused by climate change that directly affects societies through changing their access to water resources. Among the numerous indices for drought intensity rating, the EDI and SPI have widespread applications. The SPI was computed by fitting a probability density function to the frequency distribution of the monthly precipitation records of each station. A drought event is considered to occur at a time when the value of the SPI is continuously negative and ends when the SPI becomes positive. The computation of the SPI drought index for any location is based on the long-term precipitation record (at least ۳۰ years) cumulated over a selected time scale. This long-term precipitation time series is then fitted to a gamma distribution, which is then transformed through an equal probability transformation into a normal distribution. Positive and negative SPI values respectively indicate wet conditions (greater than median precipitation), and dry (lower than median precipitation). In most cases, the probability distribution that best models observational precipitation data is the Gamma distribution. Unlike most other drought indices, the EDI in its original form is calculated with the daily. The resulting EDI value represents standardized value for currently utilizable water resources, considering the continued dry period. If a negative DEP continues for more than ۱day, the addition period of EDI will increase as long as the continued days. This variable addition period is limitless. The nature of genetic programming allows the user to gain additional information on how the system performs, i.e., gives insight into the relationship between input and output data. The GP is similar to genetic algorithm (GA) but unlike the latter, its solution is a computer program or an equation as against a set of numbers in the genetic algorithm. So, GP is more attractive than traditional GA for problems that require the construction of explicit models. The GP thus transforms one population of individuals into another one, in an iterative manner by applying operators. In evolutionary computation, it can distinguish between three different types of operators which are named crossover, reproduction, and mutation. M۵ model tree approach is based on the principle of information theory that makes it possible to split the multi-dimensional parameter space and generate the models automatically according to the overall quality criterion. It allows for variation in the number of models created. The splitting in the M۵ modal tree approach follows the idea of decision tree, but instead of the class labels, it has linear regression functions at the leaves, which can predict continuous numerical attributes. Model trees generalize the concepts of regression trees, which have constant values at their leaves. Therefore, they are analogous to piece-wise linear functions (and hence nonlinear). Computational requirements for model trees grow rapidly with increase in the dimensionality of the data set. Model trees learn efficiently and can tackle tasks with very high dimensionality. The major advantage of model trees over regression trees is that model trees are much smaller than regression trees and regression functions do not normally involve many variables. This research used precipitation data on two basins in Hamedan and Lorestan Provinces to calculate the SPI and EDI indices for monitoring drought. The genetic programming model and M۵ model trees were used to predict the occurrence of drought in these two basins. It was found these models had good capability in predicting drought and enjoyed high accuracy in solving prediction problems. Another advantage of these models is that they use simple equations for predicting the phenomena under study. In the best-case scenario, the coefficients of determination for the EDI index in the M۵ model trees and in the genetic programming model were ۰.۹۷ and ۰.۹۵, respectively. Moreover, the coefficients of determination for the SPI index in the M۵ model trees and in the genetic programming model, in the best-case scenario, were ۰.۹۳ and ۰.۸۳, respectively. This suggests the M۵ model trees are more accurate compared to the genetic programming model and enjoy relative superiority because they are simpler and more understandable than the genetic programming model.

Abstract The aquifers are about four percent of the water on the earth, but they are considered as the best and most accessible source of fresh water. In recent years, they have been faced with severe water withdrawal, therefore some plains was considered as forbidden plains that it means the water withdrawal from these aquifers is unauthorized. At some point, plains have been faced with land subsidence that showed the severity of the disaster. Given such a critical situation in aquifers, management of groundwater resources in the form of tools such as monitoring the level of the aquifers is essential. One of the plains in Iran that has a critical groundwater resource is Birjand plain which requires management measures to be protected from future water resources crisis. Prediction of groundwater level in future periods is a useful tool to enforce management measures before a crisis occurs. Thus, in this study, groundwater level was predicted in Birjand aquifer taking ۱۰ monthly forecasting scenarios in a period of ۵ years and in both crisp (continues) and clustering approaches using probabilistic Dynamic Bayesian Networks (DBNs). Nowadays, various tools are used to predict the aquifer level including mathematical models, artificial neural network, neuro-fuzzy, Bayesian networks, and time series and so on. In recent years, due to the flexible and simple structure, Bayesian networks have been used for predictions of different parameters, especially in forecasting of hydrological parameters. Bayesian network as a modern forecasting probabilistic method shows probabilistic relationships between a set of variables by graphical model. It represents the dependence structure among several factors, that affecting on each other, and is based on Bayesian theory. Dynamic Bayesian Networks have been extended from Bayesian Networks which are created for two purposes: first, as the cycle of dependency detector over the time, quite similar to Markov model; second, as the fixed process which is repeated in fixed-time interval. Another feature of Dynamic Bayesian network is their willingness to approximately structured changing. In this study, the input data (predictor parameters) of the model includes: temperature, rain, evaporation, monthly aquifer recharge in each Thiessen Polygon (Recharge), monthly withdrawals of groundwater in each aquifer Thiessen Polygon (discharge), groundwater levels in the current month and the groundwater level in the next month (predicted parameter). The first step in modeling by the dynamic Bayesian network is determining the dependent and independent data for calibration and validation. Model calibration data in both crisp and clustering approach include a ۱۲-year period (۱۹۹۸ to ۲۰۰۹) and data validation include ۵-year period (۲۰۱۰ to ۲۰۱۴), in monthly time step. Depending on the type of input data, both crisp and clustering approach was used. In the crisp approach, the probability functions were used and the predicted data were obtained by using the training data. In the clustering approach, by assigning each of the numbers to the right cluster, the modeling was done. A cluster is collection of objects that their relative distance to each other is low and relative to other members is high. In the first approach by using crisp data and NPC training structure in confidence level of ۵%, the training was applied. In the second approach, the Silhouette index was calculated by using MATLAB software and by using the validation Silhouette index, and then, the number of clusters was determined. Finally, the clustering was performed by using k average method. Then, training was done in the second approach, using clustered data and NPC training structure in confidence level of ۵%. Considering ۱۰ different scenarios to predict groundwater level in the next month, the uncertainty of predicted parameters in both crisp and clustering approach were assessed. In fact, using these scenarios, sensitivity analysis was performed to check the accuracy of the model with respect to the existence or absence of different predictor parameters. In addition, the uncertainty of the model output is evaluated using dynamic Bayesian network probabilistic analysis. The results of the selected scenario in crisp approach showed the high prediction accuracy of Bayesian networks. For example, in piezometers ۴ and ۹, the coefficient of determination was estimated about ۰.۹۸. According to the results, crisp dynamic Bayesian networks approach predicted hydrograph aquifer more accurate than clustering approach. Due to the low efficiency of clustering approach in predicting groundwater hydrograph, to obtain the accuracy of ۱۰ scenarios predictions in this approach, instead of coefficient of determination (R^۲) and root-mean-square error (RMSE), the percentage of correct predicted clusters was determined. According to the results, the clustering approach predicts clusters with high accuracy for different piezometers. The scenario ۶ had the best prediction which all predictor parameters except evaporation were used for the prediction. In this scenario, R^۲ and RMSE were showed good accuracy as ۰.۹۹۴۶ and ۰.۱۲۷۵, respectively. The other scenarios had also the accuracy in their predictions very close to scenario ۶, except scenario ۹ which the groundwater levels were not used as input. Thus, in the crisp approach, the groundwater levels have a substantial impact on the accuracy of the prediction. Generally, in crisp approach, all predictor scenarios have acceptable accuracy of over than ۹۰% except scenario ۹. In clustering approach, by examining the accuracy of the scenarios in predicting clusters, most scenarios were accurate except scenario ۹. Dynamic Bayesian Network model in clustering approach correctly predicted clusters but, unlike the crisp approach in predicting hydrograph, it was not able to present acceptable results. The results showed the ability of the proposed model in planning and management of groundwater resources, reducing the risk of aquifer level declining by applying short term management scenarios and predict its effects on rehabilitation. Moreover, this model can be used in the similar plains for aquifer management.

Abstract

Abstract Estimation of flood discharge and return period of extreme events is one of the most important factors in design of hydraulic structures. Therefore, conducting researches for improving the accuracy of estimation methods is very important. Nowadays, the fractal behavior of all earth science phenomena, including precipitation and runoff has been accepted. This method is used for modeling of natural phenomena because of its strong physical background. As power law is derived from fractal theory, it can be a suitable method for estimation of design flood. In the annual maxima method, a maximum value is extracted among all the recorded discharge occurred during a year. Therefore, in this method, out of a number of extreme events happened at the end of the year, only one value is chosen and other values are eliminated. The positive point of this method is that the extracted data are independent of each other. However, this method has its own limitations. For example, in years with high flood occurrences, the values that stand in the second and third places in terms of magnitude lose the chance to participate in the annual maxima series. On the other hand, in dry years, the occurred maximum values are far lower than the second or third ranked discharge of wet years. Thus, correspondence of the annual maximum time series with reality is not suitable, and such a selection may result in neglecting the real pattern in the recorded values. In another method, partial time series (the time series greater than a given threshold) is employed. In this sampling method, a certain threshold of flow rate is considered and all flow rates that are above the threshold, are taken into consideration. In this study, power law has been employed to select the flood partial series. Therefore, the main objective of this study is to use power law in a) selection of partial series of flood in Dez Basin, and b) flood frequency analysis. In this study, flood frequency analysis of Dez watershed during the period of ۱۹۵۶- ۲۰۱۲ was performed using two approaches of power law (PL) and ordinary statistical distributions. At first, the partial-duration flood series were extracted using power law with the intervals of ۷, ۱۴, ۳۰, and ۶۰ days, and then compared with the annual maxima series. The results indicated that the annual maxima series were not suitable for frequency analysis of the flood in Dez Basin, and the ۳۰-day partial duration series obtained from the power law has a better correspondence with the flow and properties of the Dez Basin. Examining of the independence and stationarity of the ۳۰-d partial duration series by Wald-Wolfowitz (W-W) test, confirmed the independence of the considered series. In the next step, the power distribution and ordinary statistical distributions were fitted onto the flood data of the Dez Basin, and performance of each distribution was investigated using Normalized Root Mean Square Error (NRMSE) and Nash-Sutcliffe (NS) criteria. The results showed that in the Tange Panj Bakhtiari station (TPB), power distribution had a better performance than other considered distributions, and in the Tange Panj Sezar (TPS) and Tale Zang (TZ) stations the power distribution stood in the second rank in terms of the best distribution with a slight difference. The results indicated that the annual maxima within shorter return periods estimate lower values for the flood of the studied stations. However, the partial series extracted using power law solved the problem in the annual maxima, and are in full correspondence with the physics of Dez Basin. Following selection of suitable statistical distributions, flood quintiles were calculated for return periods of ۲, ۵, ۱۰, ۲۰, ۵۰, and ۱۰۰ years in each station. Based on the calculated quintiles, it was observed that TPB station is more vulnerable to the flood occurrence, where the amount of flood increases in it with the prolongation of return period. In other words, in basins culminating in TPB station, development of warning systems and implementation of flood control programs are more needed. Since the performance of power distribution in estimating the flood in Dez Basin has been very satisfactory and calculation of its parameters and its application is easier than ordinary probability distributions, it can be suggested as the superior distribution for flood frequency analysis in Dez Basin.

Abstract