مجله ترویج و توسعه آبخیزداری
پیاپی 5 (تابستان 1393)

Scarcity in precipitation along with great variability is the most feature of climate in Iran. Drought as a phenomenon of climate, leaving behind undesirable effects every year in Iran. The purpose of this study was investigation of the spatial characteristics of drought using SPI index in monthly scale in Golestan province. Therefore, the 35-year rainfall data from 23 climate stations were used. Monthly Moving Average chart reviews showed that withincreasing time scales, the severity of the drought is reduced while the drought duration is increased.The highest intensity and frequency of droughts were occured in the northeast stations in Golestan province. Zoning map was also showed the drought prone zone increases while changing time scales from 3-month to 24-month.

Soil erosion and its consequences are major obstacles for development of the country. On the other hand, natural factors underlying erosion in Iran have caused Iran to have a high potential for water erosion. Knowing the erosion conditions are very important for erosion control, but significant differences can be observed in the presented information. Then, in this article it has been tried to present an illustrated image of the water erosion conditions in Iran. Reviews show that professionals have declared specific erosion rate of 16 to 25 t/h/y. In landscape of the country watersheds plan, the mean of specific erosion, total erosion of the country and total sediment of the country have been estimated using EPM model equal to 6.94 t/h/y, 975 and 129 million tons respectively. While, using the rating curves studies, total sediment yield has been estimated equal to 250 million tons per year. The results of erosion and sediment studies in 38 catchments in Qazvin province, indicate the rate of 16.6 t/h/y for the mean of specific erosion. The average sediment production of country is less than 15 t/h/y, based on the sediment measurement in reservoirs of small dams. Therefore, accurate estimation of the sediment yield with proper methods is necessary, since the estimated methods and the achieved values are very different. However, it can be said that the average erosion rate of the country lies between 7 and maximum 16 t/h/y. According to the area of Iran, soil erosion of the country would be 1.15 to 2.64 billion tons annually that is considered a high rate of water erosion.

Soil erosion and sediment yield in the watersheds are the major limitations in achieving the sustainable development. Hence, the stabilizers and soil amendments such as natural, organic and synthetic materials have been used or tested on erodible soil surface in order to increase the soil stability and reduce soil erosion. However, the use of stabilizers and amendment are somewhat challenged due to their limitations such as having instabilities and temporary nature as well as having the destructive effects to the environment. Therefore, the present study has attempted to provide comprehensive information about microorganism’s application as a sustainable and biological strategy for the restoration of degraded soils. According to the results reported in literatures, the effective role of biological soil crust made by microorganisms especially cyanobacteria, bacteria and fungi in aggregate stability, soil particles shear strength, permeability, moisture retention, carbon and nitrogen sequestration has been documented. It increases soil quality for the presence and growth of vegetation and other organisms through secreting polysaccharides and developing aggregate adhesions. Thus, these soil microorganisms with dynamic role create the suitable conditions for stabilization, vegetation present and other organisms. Therefore, the support and richness of soil microorganism through the development of this organism as the first stage of plant ecosystem of soil would cause the suitable conditions for the sustainable restoration and promotion of ecosystems and eventually would lead to runoff and soil loss control. Therefore, it is necessary to examine the role of soil microorganisms especially cyanobacteria and bacteria in soil erosion processes analysis and their application as an alternative to other conventional stabilizers and additives. However, it is initially needed to be examined under laboratory conditions with further attention to environmental aspects.

Soil is a component of each ecosystem and it has more important role in human survival, therefore, there is necessity for soil protection. Soil erosion and sediment are important environmental problems and concerns in sustainable development. Although most erosion and sediment deposition processes have been studied in detail, but modeling and making a link between on-site soil erosion and total sediment yield at the outlet of a catchment are often hard because of the difficulties associated with modeling of a cascading system, and also because of the lack of detailed input data at regional scales. Effective control of sediment transport is important component in management of natural resource. Knowledge on delivery ratio is useful in recognition of the resources and the amount of sediment load; also it’s more important for model developers. Most regional erosion estimation models do not consider the spatial variability of sediment supply to streams. Therefore, we should use an index such as sediment delivery ratio. Since, extensive research has been conducted on the sediment delivery ratio, but different results have been shown. The aim of this paper is to collect and review past studies on SDR since now, because we can choose the best way to estimate sediment load and we can provide more effective actions for management of natural resources. Results showed that each method has advantage and disadvantage, and it’s difficult to choose one way for estimates delivery ratio. But most research in Iran showed that Renfro (1975) method is better than others. Of course, all researches havn’t been conducted on all methods and this subject suggest necessity of planning for the projects on sediment delivery ratio methods.

Rainfall/ precipitation, as one of the most important inputs to hydrological systems, is one of the most significant parameters in many hydrological models. In the recent decades, different types of forecasting methods are employed for forecasting and analyzing monthly precipitation rates. Linear regression is one of the methods are being used for this purpose. Recently, the use of singular spectrum analysis in water resources studies for removing random components of hydrological series has extensively increased. The main objective of this study is to investigate the use of linear regression coupled with singular spectrum analysis for monthly precipitation forecasting. The monthly data of Ponel raingauge station which span the period from 1991 to 2010 (i.e. 20 years) were used to develop the proposed model. The proposed model was compared with regular linear regression and the results indicated the superiority of combined linear regression and singular spectrum analysis models.

Drought and exploitation of groundwater resources are major stresses on the aquifer. Drought and exploitation management is efficient tool for balancing the Aleshtar aquifer. In order to assess groundwater flow MODFLOW model was used. The model response to the scenarios of moderate drought, severe and very severe were measured. The results showed that with increasing drought, water table level and storage are reduced. To control the effects of normal, moderate and severe droughts, exploitation reduction inwater use and new irrigation projects were considered. But for the control of very severe drought stress, in addition to using management system, implementation of artificial recharge design is recommended.

In this study the effects of Miankooh flood spreading on vegetation cover and production is investigated in 2002. for the first step, 9 plots were selected.6 as flood spreading and 3 as observational plots. In second step, 3 transections (100meters) were selected with 5 meter intervals. Then 10 plots (1×2 m ) were used. The vegetation cover percentages and productions were measured with clipping and weighting method, within plots. In the last step data were analysing with Duncan's test using completely random blocks. The result shows that the percentage of vegetation cover and production in the flooded area has significant difference compared to the control area.