مجله ترویج و توسعه آبخیزداری
پیاپی 31 (زمستان 1399)

In recent years, human activities such as removing bushes, deforestation, degradation of grasslands, inappropriate methods of irrigation, overgrazing, land use change, road and building construction on vulnerable geologic formations and mining have had impact on the increase of soil erosion. On the other hand, sedimentation from erosion has caused environmental damages, financial losses and casualties. To solve these problems, there are numerous methods for declining sedimentation and soil and water conservation. The use of natural and artificial geotextiles at river conservation, roadsides, soil walls and mines is one of these methods at erosion management which helps vegetation growth and establishment by producing sufficient humidity and the fertilizer derived from their biodegradation. However, this method is partially recognized for researchers, planners and organizers of soil and water conservation plans. Therefore, in this study, different types of geotexiles, their functions and features have been broadly explained so that they could be used at sustainable water and soil resources management plans at different scales with the aim of soil conservation. The literature review showed us that geotextiles have played a significant role on soil erosion control and slopes stabilization by high performance and efficiency. On the other hand, the application of geotextiles is more economical and effective similar to the other biological and agricultural methods in terms of availability, its use at small businesses in poor local communities, employment of women at production and the decline of poverty. In addition, the most studies about geotextiles are based on natural geotextiles in Europe. Based on different climatic zones of Iran, it can be concluded that natural geotextiles like rice and corn fibers at the north of Iran as well as coir, palm and sugarcane fibers at the south of Iran are usable to manage soil erosion.

Dry and semi-dry climate and lack of coordination between the time of discharge basins and expenses have been caused that managers try to control and maintenance of surface water resources through fun dams, so in way, they can meet various water needs by management and planning. But always sedimentation in reservoirs shortens the useful life of the dam. Viscous flows are the main factors of sediment transport tanks, it has been disrupted the performance of dams such as the dose, Minab and Sefidrud, so far. In addition to reducing the volume of the reservoir, viscous flows increase the speed of attrition’s turbines and decrease their efficiency and increases maintenance costs. Also, it can be followed by risk of clog ponds, bottom outlet structures or damaging to valves, has been designed for sedimentation. At the moment, the rate of loss of reservoir volume due to sedimentation in reservoirs more quickly builds new reservoirs. Hence, increasing the useful life of dams and maintaining storage volumes in water resources engineering is a vital issue for the continued operation of water control. Knowledge about the turbidity currents properties can help to manage and release these currents from dam reservoirs. In this paper, a comprehensive investigation on the studies of various methods against turbidity currents, combination methods in experimental conditions and limitations in filed applications were carried out. Also, suggestions were presented for further research on selecting methods for controlling turbidity currents.

Knowing the temporal and spatial distribution of rainfall is one of the most important factors in implementing soil and water conservation, flood control, and drought management projects and one of the most important parameters for water resource planning. Given the significant variation in rainfall on the one hand and the shortage of rain gauge stations to record rainfall, on the other hand, the requirement of correlating the rainfall estimation model to the spatial is inevitable. In this regard, geostatistics is one of the most important methods for estimating the spatial distribution of rainfall. The purpose of this study was to evaluate the geostatistical methods in annual, monthly and maximum 24-h rainfall estimations in the Haraz Watershed in Mazandaran province and to study their spatial variations in the time period of the water year 1976-1977 to 2013-2014. In this research, 40 meteorological stations with 38-year statistical period into and around the mentioned watershed were used to compare the geostatistical methods including Kriging, Co-kriging, inverse distance weighting and radial basis function in the isohyetal map for the Haraz Watershed. For this purpose, using the cross-validation method, by removing the individual stations, their precipitation values were determined and compared with the observed values. The results showed that radial basis function for annual rainfall and simple Kriging for maximum 24-hour rainfall, and simple and ordinary Kriging, Co-kriging, inverse distance weighting and radial basis function for different monthly rainfall is the most appropriate method. There is the spatial rainfall dependency on a monthly scale from 11.6 to 99.2 km, annual scale with 35.9 km and maximum 24 hour rainfall with 21.3 km. These results can be used to design distance among meteorological stations for rainfall measurement.

Nowadays, the environmental structure has been changing and natural disasters, including sudden floods increasing. Due to the crossing of Gorganrood River in the city of Aq’qala, it has always been in the risk of flood in the spring and summer. In this study for time series flood zones and flood’s map area calculating which occurred in 23rd March 2019, we used Sentinel-2 and Landsat-8 data because of high spatial resolution and free accessibility. For removing noise and clouds applied the atmospheric and radiometric correction on images and then used MNDWI and NDWI indexes for identifying of water and high moisture soil. The results shown the MNDWI index was better than the NDWI index for identify the moody water and high moisture zones. Flood zones maps produced by MNDWI index are shown more flooding area than NDWI index map. The area of flood maps for Aq’qala county and Aq’qala city were 262.453 and 51.091 Km2, respectively. The maximum flow rate discharge with 50 years returns period was 739 m3/s that the northern and eastern of Aq’qala city were flooded. When the flood is muddy, using MNDWI index is 50 percent better than NDWI index.

Soil erosion is a very serious problem and its assessment in planning and conservation operation in the watershed is very useful. To estimate soil erosion and to establish soil erosion management plans, many computer models have been developed and used. The information needed to control soil erosion is possible by applying the revised universal soil loss equation. The aim of this study, prediction of annual soil loss and sediment load using RUSLE in geographic information system and remote sensing environment. RUSLE factors map including rainfall erosivity (R), soli erodibility (K), slope length (L), slope steepness (S), cover management (C) and support practice factor (P) were prepared using geographic information system and remote sensing. Finally, the erosion risk map was prepared using the integration of the geographic information system and weights obtained from the Analytical Hierarchy Process (AHP) process. The results showed that the mean values of R, K, LS, C and P indices were 207.443 (MJ / mmha-1hr-1 / year-1), 0.63 (t / ha, MJ.mm), 382.997, 0.364, 0.8 (t/year) in the studied basin and the most important factors in the amount of soil erosion were topography and precipitation factors. Also, the results showed that the annual erosion and sediment load in the study area was 7461.69 tons per year and the annual erosion had the highest weight (0.308) and the soil erodibility factor had the lowest weight (0.04). The final erosion risk map also showed that the large area of the studied area is eroded in a high-risk class (285.5 km2) and very high (47.9 km2), indicating that a serious management decision to be taken in the region. According to the results of this research, it is necessary to carry out appropriate protection in the area and these sites can be selected from the output of the RUSLE model.

Estimation of the amount of sediment material (carried by a specific stream) is one of the main topics of sediment research. Sediment research is important in many engineering projects such as planning and design of water storage resources, morphology and changes in river bed, annual sediment estimation for reservoirs, sustainable irrigation, coastal protection, channel dredging, and etc.The evaluation of the sediment occurrences, and estimation of the sediment carried by rivers has a special importance and it is necessary to develop new methods with easy application for estimating the sediment transport. This study seeks to develop a method to be able to predict the amount of bedload with classification and regression trees and compare with some well-known empirical formulas such as Meyer Petter Muller, Shields, Einstein Brown, and Shoklitch. Measured data from Yazdakan station, located in Qotour River in Azarbayjan Gharbi, northwest of Iran, has been used in this research. It is a mountainous river with gravel bed that carries a high volume of sedimentation. A set of 76 field measurements over 8 years was used in modeling after verification and refinement. The model was trained on 80 percent of data and tested on the remained 20 percent. The best input contained whole four variables; flow discharge, suspended sediment discharge, flow depth and velocity, and the output was bedload discharge. The quantitative results of the best Decision Tree include MAE = 2134, RMSE = 2668 and % R = 89. The results of Regression Trees demonstrate more accuracy in the prediction of bedload compared with empirical formulas.

Nowadays, natural disasters and human interventions are the main causes of problems at the watershed scale, hence, the management of such challenges is considered as one of the major problems. However, the present approaches for the management of the watershed resource do not appropriately handle the current issues. So that the scope and type of environmental issues are ever increasing and stand beyond the ecosystem tolerance. As communities strive for recover from disasters and move forward, resilient watersheds facilitate better management of natural systems against future hazards. Towards this, the resilience assessment approach has been proposed as a novel approach using existing potentials and pertinent definitions, indicators, and measurement patterns to strengthen multidimensional systems such as watersheds. Since the application of resilience analysis approach in dynamic and complex, it has not been conceptualized and reported until now in watershed systems. Accordingly, the present endeavor is an attempt to conceptualize the resilience of watersheds in order to provide a useful perspective for understanding management decisions and changes related to natural resources in the context of comprehensive watershed management.