فصلنامه علوم و مهندسی آبیاری
سال چهل و سوم شماره 2 (تابستان 1399)

Introduction Drought phenomenon is one of the natural and creeping disasters, which occurs in almost every climate and its properties vary spatially. A considerable number of scientific research has been done on drought in Iran and throughout the world. These studies have examined various aspects of drought. Through such research and knowledge effective and efficient solutions could be found to deal with good management of drought. Since Iran is located in an arid region of the world, nowhere in the country is immune from this phenomenon. This research has attempted to present appropriate models to predict drought for the city of Semnan, Iran.

The agricultural sector is the largest consumer of renewable water. Improvement of water consumption pattern in this sector could reduce the pressure on water resources. To monitor water consumption in agriculture, it is necessary to study water productivity indicators in addition to monitoring irrigation efficiency, which determines the performance of irrigation systems. This research was conducted to evaluate the efficiency of two-way, closed-end furrow irrigation and the effect of irrigation management and different levels of nitrogen fertilization on yield, yield components and water productivity of maize. Because of its specific characteristics (the presence of four carbons, and in particular, its heat-soaking character), corn is closely matched to arid and semi-arid regions. Iran has a good climate diversity, including areas susceptible to corn production. Khuzestan province, due to its flat and fertile lands and high sunny hours, is suitable for planting most crops, especially corn. In many Iranian farms, traditional furrow irrigation is used for row plants.

Peak, volume, and duration are the main characteristics of a flood. Therefore, in designing hydraulic structures, the frequency analysis of flood should be done considering the multivariate point of view in order to decrease the flood damage. Since the interaction of dependent variables is not considered in the univariate frequency analysis, it can lead to underestimating or overestimating the magnitude of a certain event. Copula is a powerful tool, which has the capability and efficiency required for concurrent analysis of behavior of the variables and the correlation among them. This research emphasizes the necessity of bivariate analysis of flood in designing the hydrological structures and decreasing the flood damage. Therefore, copula functions were used for bivariate frequency analysis of flood (discharge and volume).

Severity and duration of agricultural droughts have distressed farmers worldwide by triggering hazards for agricultural products. Droughts are a widespread natural threat with tremendous social impact (Alston and Kent, 2004; Glantz, 1987). They are most often caused by a significant drop in precipitation from the normal amount. Agriculture is often the first sector to be affected by the onset of drought due to its dependence on water resources and soil moisture reserves during various stages of crop growth (Narasimhan and Srinivasan, 2005). Recent studies show that the frequency and severity of droughts seems to be increasing in some areas as a result of climate variability and climate change (IPCC, 2007; Patz et al., 2005; Sheffield and Wood, 2008; Lehner et al., 2006). Among various drought indices, Palmer Drought Severity Index (PDSI) (Palmer, 1965), Crop Moisture Index (CMI) (Palmer, 1968), Standardized Precipitation Index (SPI) (McKee et al., 1993), Surface Water Supply Index (SWSI) (Shafer and Dezman, 1982), and The ETDI (Narasimhan and Srinivasan, 2005) are used extensively for water resources management as well as for agricultural drought monitoring and forecasting. In this study, the agricultural droughts during the recent half-century were evaluated by the modified ETDI method and compared with the SPI as well as meteorological drought index in Shahrekord plain. The results show that the estimation of modified ETDI by SPI3 is applicable.

Prediction of plant water consumption in each growth stage plays an important role in soil and water resources management and proper irrigation scheduling. The aim of this study was to determine the amount of water requirement and crop coefficient of pepper in terms of soil coverage with different amounts of Zycosil. This paper used the Kc procedure of FAO No. 56 (Allen et al. 1998) to obtain single and dual crop coefficients of sweet pepper. The dual crop coefficient approach is more complicated and requires more numerical calculations than the single crop coefficient approach. The single crop coefficient is defined as the ratio of ET from crop to some reference ET as defined by weather data. The dual crop coefficient has two fractions, one for crop transpiration, i.e., the basal crop coefficient (Kcb), and one for soil evaporation (Ke). Basal crop coefficients, Kcb, represent primarily the transpiration component of ET and a small evaporation component from soil that is visibly dry at the surface.

As one of the main indicators of soil quality, structure is related to hydraulic parameters which plays a significant role in predicting and estimating them (Pachepsky et al., 2008). Mohawesh et al, (2017) stated that hydraulic properties are key factors in the movement of water and the transport of pollutants, and the soil structure has a significant effect on the storage and movement of water in the soil. Tension infiltrometer is an effective tool to measure infiltration rate and the flow of water into pores using suctions less than 0 cm, where the macro and meso pores have highest rate of hydraulic activities for water and solution transportation. The measurement of hydraulic conductivity in different suctions is important for characterizing different aspects of unsaturated and near-saturated water in the soil. Although the hydraulic properties of the soil have been investigated from different aspects and by different methods, the role of soil structure specifically from comparison viewpoints of different types of structures and their effects on hydraulic properties has not yet been studied. The aim of this study was to measure and evaluate the hydraulic properties and quantitative parameters describing the water conductive active pores using tension infiltrometer in near-saturated condition of different soil structures.

Evaporation is one of the main elements of hydrologic cycle. Accurate estimation of pan evaporation is very important in many water-related activities such as irrigation and drainage projects, water balance studies, reservoir operation, and the like. The class A pan is one of the main pan evaporation instruments, which is used in standard synoptic weather stations in Iran. Direct measurement of evaporation is expensive and time-consuming. Therefore, different empirical models, which use different meteorological variables, can be used to estimate pan evaporation. This is so crucial in arid and semi-arid countries such as Iran, where the climate is mostly hyper-arid and it is not easy to measure evaporation directly. In the recent decades, by the development of computers many data driven models have been created for estimating evaporation. One of the intelligent models widely used to hydrologic processes is Bayesian Network Model, which was introduced by Bentin in 1990, and then applied for neural networks by MacKey (1992). Bayesian networks (BNs), also known as belief networks (or Bayes nets for short), belong to the family of probabilistic graphical models (GMs). These graphical structures are used to represent knowledge about an uncertain domain. In particular, each node in the graph represents a random variable, while the edges between the nodes represent probabilistic dependencies among the corresponding random variables. These conditional dependencies in the graph are often estimated by using known statistical and computational methods. Hence, BNs combine principles from graph theory, probability theory, computer science, and statistics. GMs with undirected edges are generally called Markov random fields or Markov networks. These networks provide a simple definition of independence between any two distinct nodes based on the concept of a Markov blanket. Markov networks are popular in fields such as statistical physics and computer vision. BNs correspond to another GM structure known as a directed acyclic graph (DAG) that is popular in statistics, machine learning, and artificial intelligence societies. They enable an effective representation and computation of the joint probability distribution (JPD) over a set of random variables (Reggiani and Weerts, 2008). In addition, BNs model the quantitative strength of the connections between variables, allowing probabilistic beliefs about them to be updated automatically as new information becomes available. In this model, the unknown relationships between parameters in processes can be shown by a diagram. This diagram is non-circular, and has directions composed of nodes and curves for showing the possible relationships in parameters (Money et al, 2012). Therefore, the main objective of this study is modeling of daily class A pan evaporation using the Bayesian Network model in six stations of East Azerbaijan Province.

One way to increase water use efficiency in the farms is performing pressurized irrigation system projects. Proper choice of the type of pressurized irrigation system in each region is an important step in the optimum use of water and soil resources (Hejazi Jahromi et al, 2011). Operating pressurized systems requires initial costs, operating costs, energy consumption, and special equipment. Therefore, if it is not chosen wisely, it will ultimately prove a non-economical option. Choosing the best irrigation method in each region depends on several parameters, including required surveys with respect to the conditions of the plain (topography and soil properties), region, crop, quantity and quality of irrigation, and cultural and social characteristics of each project. Therefore, assessment of the feasibility of these systems to make higher returns in a sustainable way is necessary (Gharadaghi et al, 2014). Land suitability is studied in different regions of Iran, including Fars and Hamedan provinces (Rezaei et al, 2014; Akhavan and Ghaemizadeh, 2014), and the world (especially China) (Lio et al, 2013). According to the existing instructions, the choice and design of pressurized irrigation systems should be based on climatic conditions, topographic conditions, soil and water characteristics, crop, energy supply conditions, cultural backgrounds, human resources status, operating conditions and maintenance, and finally costs in each region (Alizadeh, 2007). Therefore, this research has taken into account all the factors affecting the design of different irrigation methods to perform optimal zoning for implementation of various irrigation methods in Ardabil plain in ArcGIS environment.

Groundwater plays an important role in the sustainable development of human societies. The rapid growth of population, low level effectiveness, and performance of irrigation in agriculture sector have led to increase in demand for water resources in Iran. Therefore, the regional management of water extraction and the optimal usage of available water resources are highly important. Considering the urgent and intense need for groundwater resources, we used Shannon’s entropy and frequency ratio models to identify the groundwater resources of Sero Plain for agricultural and drinking purposes as well as to detect the factors that affect occurrence of groundwater and zoning.

Drought is one of the most complex and destructive climatic phenomena, which can be perceived as the least understood natural disaster (Kao and Govindaraju, 2010). The most important and challenging characteristics of drought are frequency and return period (Bazrafshan et al., 2014; and Zhang et al. 2015). This complexity is derived from the interdependence of drought characteristics that make the univariate frequency analysis inefficient (Mirakbari et al., 2012). Therefore, instead of using traditional univariate analysis, a better approach is to derive the joint distribution of drought variables (Mishra and Singh 2010). Furthermore, insufficient data at the stations and the existence of ungagged areas necessitate regional analysis. Regional frequency analysis, on the one hand, provides the possibility of analysis for ungagged regions, and, on the other hand, provides better and more comprehensive information for meteorological stations using a combination of points and regional data. The main objective of this research is regional bivariate drought analysis in the semi-arid climate of Fars Province, Iran. In this regard, the index variable based on linear moments is one of the most advanced methods ( Núñez ez et al., 2011).

It is vitally important that rivers reach an equilibrium state (regime). To be more precise, determination of stable hydraulic geometry is one of the most important factors on which designing, planning and training of rivers is based. In this research, an analytical model was proposed initially by using extremal hypotheses and then multivariate hydraulic geometry relationships were applied to the rivers under dominant bed load. Thereafter, field study was carried out on several gravel bed rivers in Khuzestan and Chaharmahal provinces. A total of 24 hydrometeorological stations in 17 river reaches were sampled to characterize bed material gradation curve. With regards to bed structure of gravel bed rivers, samplings were made by surface and volumetric methods. Then, sediment samples were put into two categories of surface and armor layers. The collected field data was originally applied to derive regime relationships by using multivariate regression analysis. The effect of bed structure was directly studied to better understand it in the regime relationships. A reasonable agreement was observed between the developed analytical and empirical exponents of the hydraulic geometry relationships in this study and those by other researchers. Finally, the developed model was calibrated using the field data of Iran and the mean relative error of the bankfull width and depth calculation were 26% and 24%, respectively.

The erosion of the deposited cohesive sediments by flow is a complex phenomenon. In general, hydraulic transmission of fine-grained sediments include depositional processes, consolidation and erosion. Cohesive sediments caused by physical-chemical effects on particle surfaces due to their strong ionic surfaces tend to form masses of low density or flocs. Depending on the conditions of the flow and resistance of the sedimentary masses, the erosion of sediments can occur in three different forms of floc, superficial and massive states (Mehta, 1991; Winterwerp and van Kestern, 2004). This study focuses on the effect of consolidation time on erosion rate of the deposited cohesive sediment in an annular experiment flume.

Embankment weirs are finite crested weirs with various side slopes that can be used for different purposes such as flow measurement and diversion, water level management, aeration or water purification, etc. The hydraulic performance and the characteristics of flow over solid weirs with finite crest length in free and submerged flow conditions have been of interest to many studies (Azimi and David. 2013). Unlike the impermeable weirs, porous weirs contribute to the water purification in the rivers and channels downstream of the structures. Hence, they are structures with positive impact on water treatment. Sargison and Percy (2009) studied the performance of BC weirs with side slopes varying between vertical positions to 1V:2H. Results indicated that by decreasing the slope of upstream face, the discharge coefficient increases and the height of the upstream water surface reduces. Although the characteristics of flow over porous weirs have been studied until now, there are still remaining facts to discover about performance of these kinds of structures in practice. Hence, this study has benefited from extensive experimental data obtained by laboratory tests to develop formulas to estimate hydraulic parameters for discharge reduction factor in the submerged flow conditions. This study investigates the hydraulic performance of flow over the porous embankment (PE) weirs for both free and submerged flow conditions. To do this, the hydraulic behavior of flow over 16 different PE weir models was examined in a rectangular flume. Results showed that the effect of the upstream slope of weirs is negligible on the modular limit index while the downstream slopes of weirs did not affect the free flow parameters. Also, both up- and downstream side slopes have no significant effect on the characteristics of the submerged flow.

The aim of this study was to investigate cloud’s characteristics and some effective physical indices on rainfall in Mashhad. We initially studied cloudy sky in Mashhad by consulting meteorological yearbook of 1986-2010. Density and prevalence for medium and low clouds as well as density, prevalence and average for vertical clouds (type 2 cumulus and cumulonimbus) were calculated for every month. This study shows that in Mashhad the highest frequency of low and medium clouds occurs in cold and rainy months during winter and spring, while most of the clouds with vertical development occur in spring. We also studied freezing level in clouds in both rainfall and no-rainfall cases, using skew-T diagrams and radiosonde data during 1992 to 2011. The condition considered here was overcast sky. We obtained a regression equation in order to specify role of physical indices (CAPE، SI, K، PWT) in precipitation. At first, rainfall days of Mashhad were extracted from Khorasan Razavi meteorological department archive (1992 to 2011). On these days, six hour rainfall (00 to 06 Z) were determined. Then, instability and physical indices were obtained from radiosonde data of Mashhad weather station. A regression equation was estimated by analyzing the relationship between natural logarithm of six-hour rainfall as dependent variable and instability indices as independent variable. This research determines which relationship between some indices with natural logarithm of six-hour rainfall is nonlinear. Analysis of regression variance shows that regression was significant at 99% level. This means that at least one of the indices has a linear relationship with logarithm of six-hour rainfall. In this equation, due to significant level, CAPE and PWT were removed. Most relationships were found between SI and natural logarithm of six-hour rainfall.

The 2D shallow water equations are used in flow simulation of rivers, floodplains, coastal currents, etc. In the research, updating or the so-called numerical integration of temporal terms of two-dimensional equations using first-order methods is more stable but less accurate. In contrast, high-order accuracy methods have numerical stability problems and cause divergence (Brouwer et al., 2014). For this reason, second-order accurate methods with median properties are widely used. Despite much research on how to deal with spatial terms, according to a review by the authors, there is less research on how to deal with the temporal terms of equations. In addition, studies on time integration methods are limited to solving 1D problems. In this research, two different time integration methods of Runge-Kutta third order (RK-3 method) and Strang splitting operator method (Strang method), which have a second-order of accuracy and are commonly used in various research (Huang et al., 2013), have been investigated. Therefore, two models have been obtained in which the applied time integration methods are different, but the ways adopted to deal with spatial and sources terms of equations are same. Then, 1D and 2D reference problems are implemented using these two models and their results are presented in order to recognize the appropriate time integration method for solving 2D shallow water equations.