نشریه آب و توسعه پایدار
سال پنجم شماره 1 (پیاپی 10، بهار و تابستان 1397)

The gully erosion is one of several water erosions which their expansion causes significant changes in terms of land, land degradation, and destruction of the environment. To study the diversity and expansion of gullies and the development of gully erosion from one place to another, remote sensing and geographical information systems were used. To achieve the current research objectives, the spatial and temporal extent of gully erosion and expansion of the eroded areas were investigated using the Landsat 7 and 8 satellite images with a resolution of 30 m in the period of 2001 (1380) and 2014 (1393). The spatial resolution has been enhanced from 30 m to 15 m using the band PAN (15 meters) and technique Resolution merge. This method was applied to all bands and pictures for two different time periods. The results from combining two layers of waterways, in the period of 13 years, applied on the Shordareh basin located in Golestan province, showed an increase in the length of the gully and the drainage density of sub-basins. The erosion rate in the assumed period is estimated at 0.99 meters per year. The gully expansion is directly related to the geological formations, land use, and other human activities such as unprincipled construction of rural and inland roads.

Flood risk management is a comprehensive approach which includes various evaluation indicators in river basins, it is an effective and sustainable but complex method. Flood risk assessment provides valuable information to assess vulnerability and exposure to hazard. For assessing the flood risk in river basins, several models such as RF, DSS, ANN, RFM, SVM, and GA are used to study the effective parameters of flood risk which have been used in different watersheds for the determination of the importance of these indicators. Determining a suitable model for use on the basin scale requires the consideration of the model suitability for the basin local conditions, data requirements, model complexity, accuracy and validity of the model, model hypothesis, spatial and temporal variation of the model, model components, and user target. In general, there is no model suitable for all conditions. Problems related to the inability to identify, the lack of uniqueness of the model, and the physical incomprehensibility of calibration parameters are some of the issues that are caused by the application of distributive and physical models. These issues also exist in complex conceptual models. To meet the growing needs of field administrators, it is necessary to have tools that can be fully used to investigate the spatial distribution of floods and the transport of river materials. As a general and practical rule, the development of distributed models with a relatively low physical complexity is recommended.

Implementing large civil projects such as dam construction can considerably affect geographical areas, and these impacts are not necessarily positive. Therefore, attention to this problem to decrease the negative effects of dam construction and considering these effects in the assessment of benefits and costs in water sector planning is necessary. This study aims to measure the effects of Karun-3 dam's construction on the environment, society, economy, and the body of Izeh city. This investigation is a descriptive-analytical research. The territory of study is the Izeh city located in Khuzestan province. The statistical population of the study consists of experts, specialists, and regional development experts who live in city of Izeh. To measure the effects, a researcher-made questionnaire has been used. The sample volume is calculated as 375 people using the Cochrane method which are questioned by the available random method. Central statistics and bionomial tests were used to describe, analyse, and determine the correlation between independent and dependent variables. The results show that implementing Karun-3 dam had negative effects on the environment, society, and economy with correlation values of 0.77, 0.63, and 0.56, respectively. However, the effects of dam construction on physical component were low, with the value of 0.15.

Control and collection of flood runoffs are one of the most important and fundamental issues in the watershed management which is more important in cities due to urban development and significant changes in the natural pattern of the watershed. In many countries, traditional urban flood management approaches have focused on the collection, transport, and dispose of the flood runoffs. Nowadays, a modern approach in urban flood management is recommended which relies on methods that best fit the natural cycle of surface water processes, namely "low-impact development" methods. Using this method as one of the key strategies in urban flood management, especially in developed countries, is becoming more important. In Iran, due to the growth of urbanisation and the formation of large cities, urban flood management has growing importance. Therefore, large investments have been made on urban flood management with a traditional approach by creating a variety of structures for flood collection and disposal, and less attention has been paid to low-impact development methods. In this study, low-impact development methods are introduced and already implemented procedures and their role in urban flood management are expressed. Moreover, the best management solutions for different regions of Iran are introduced.

Water balance models are generally based on mass continuity and the hydrologic cycle of water in the natural environment. Monthly water balance models evaluate the importance of various hydrological parameters under diverse hydrological conditions. As water balance models are becoming widespread, there is a significant effort devoted to the development of these models towards estimating the hydrological components of the basin. Different models and algorithms consider various parameters which range from relatively complex conceptual models for dry areas to very simple models for areas with temperate climates. Therefore, it is essential that these models be closely and precisely analysed, and ultimately, reviewed. Generally, rainfall data have long been recorded, but discharge data are often scarce. Therefore, the need to estimate the discharge of rivers resulted from rainfalls has motivated a great number of research in this area of study. In this paper, parameter naming in different models has been homogenised, presenting a clearer image of similarities and differences among different models. The overall framework of the models is similar and inspired by the Thornth Waite model. The input parameters are precipitation and temperature, and the output is the monthly runoff of the basin. All models include soil water storage capacity, evapotranspiration, and runoff. However, some of the models consist of water storage capacity layers, separation of rain and snow, groundwater storage, and base discharge. These differences in the number of parameters distinguish the models from each other.

Low rainfall with poor temporal and spatial distribution, scarcity of water resources, and the increasing demand for water are major problems in arid and semiarid regions. The efficient use of water resources and efforts to achieve new water sources are two main solutions to slightly overcome these problems. Among these, rainwater harvesting is one of the most prominent methods for rainwater management to confront the scarcity of water that is rapidly developing in many areas. Due to the variety and extent of rainwater harvesting methods, characteristics such as the amount of rainfall and its distribution, topography, soil type, soil depth, social and economic factors, as well as the water consumption in each area must be considered when selecting the appropriate method. In this paper, firstly, the factors affecting the selection and design of each rainwater harvesting method is studied that includes natural factors such as weather conditions, topography, runoff, and the technical, economic, social, and organisational factors. Then, the different methods of rainwater harvesting systems including microcatchment, macrocatchment, and rooftop rainwater harvesting systems are expressed in detail.

In arid lands where agriculture is dependent on irrigation, water shortage has been one of the main motivations for many innovations, such as Qanats, which play an important role in maintaining and developing civilisation on the Iranian plateau. What is known today as sustainable development, was actually understood and applied by our ancestors. Their method of sustainable use of water resources from these areas can be a good example to solve recent crises. The present research aims to answer the question of how and under what conditions a Qanat was able to cause human adaptation to nature and sustainable balance? To this end, the current research is carried out using qualitative content analysis and the MAXQDA software. The study area is the Zarch Qanat located in a large area of Yazd province. The study population includes 16 specialists in Qanat. The results indicate that all aspects of the indigenous knowledge of Qanat have been established based on natural features in order to achieve economic goals. Through this development, a social system was established which shows the existence of local planning in line with sustainable development.

Undoubtedly, the power of any country to regulate, allocate, and control water resources depends primarily on the existence of a legal framework to manage and protect water resources. The rules and approaches to protect water rights in many countries, including Iran, are often complex and dispersed, and are very far from the modern modes of water management. The criminal protection of water rights has been sporadically observed in the laws of Iran, both before and after the Islamic Revolution. These regulations do not provide the opportunity for the public to have a fair share of water resources. On the other hand, they do not prevent the commission of abusive behaviours against the water resources, and maybe these laws have somehow intensified the water crisis in the country. Iran's comprehensive water legislation, followed within the framework of the constitution and general policies of the system, with regards to the economy, security, and political value of water, aims to solve the existing challenges and is committed to the effective protection of water rights.