Environmental Erosion Research Journal

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One of the types of water erosion and land degradation which causes imbalance in the area of natural resources and agricultural land and gives heavy losses, is the gully erosion phenomenon. To control this phenomenon, It is important to understand the influence factors on the geometry specification. Land degradation, a broken ecological balance of the land and landscape and risk of falling at biological resources in these areas, among other things, the study of the gully, is inevitable and necessary especially in the Darrehshahr township. In this regard, Gully 36 number were selected in Darrehshahr area in the Ilam province. To this end, were identified environmental factors, Physical - Chemical Soil properties, cover and hydrological properties of gullies tested using aerial photography, the digital maps and field operations. Results of statistical analysis using multiple regression (stepwise method) revealed that length of gully with upstream area of the gully, top and bottom width and cross section of the Gully with basin elongation, deep gully with basin elongation and slope curvature, high of head Gully with local slope of the gully and steep walls of gully with percentage cover have a significant relationship. So could be concluded that characteristics of geometry gully in the study area would be a function of the upstream, basin elongation, curvature slope, and local slope of the gully head and the percentage of canopy cover catchment area of gully.

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Gully erosion is the most important water erosion which causes land degradation and imbalance in lands. Land degradation, broken ecological balance of landscapes and sensitive condition of biological resources are among reasons of gully erosion study. This study performed with the goal of determining the topographical threshold of gully erosion and expansion and also predicting sensitive areas to this kind of erosion. Therefore, 36 gully in the study area selected and after data separation, impact of land use factors, various active mechanisms for gully expansion and method of data extraction of area and slop using aerial photographs, field measurement and GIS were investigated. Results showed that R2 coefficient has increased from 0.162 to 0.214 for agricultural land use data. But for abandoned land use, this value was equal to 0.043 and non-significant (P=0.54). R2 coefficient of 0.267 for the field measurements data and 0.162 for the GIS derived data, show that in spite of the significant relationship for both method (at significant level of 5%), use of field methods and direct measurement will lead to better results. In addition, the ability of model about sensitive areas predicting to gully erosion was studied using ROC curve. Area under the ROC curve was equal to 0.748 and indicated that this model is suitable for prediction of sensitive area for gully erosion.

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Coastal and inland dune sands in desert environments are compositionally and texturally controlled by physical and chemical processes such as the wind action, marine/fluvial processes, weathering, air temperature and precipitation. The objectives of this research are study of sedimentological characteristics, calculation of CIA in the Aeolian sediments and classification of sand dunes in the Yazd-Ardakan plain. For study of sedimentological characteristics and calculation of the CIA were analyzed 88 and 20 samples, respectively. Major element component measured using XRF. Results showed that, sorting and mean grain size is weak and coarse to medium respectively, which it indicates sources of Aeolian sediments is local. According to classification of Besler (2008) sand dunes classified to strongly saline class. Amount of CIA in the all sample is less than 55, which it indicate there weren’t any weathering in the case study and the maximum of CIA is related to Kalot facies with 50.7.

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Extended abstract
1- Introduction
Soil erosion by water is a dominant geomorphic process which threatens food security in most parts of the world .The geomorphic characteristics of a watershed play an important role in watershed hydrology, soil erosion processes and sediment yield. Geomorphic characteristics can be an indicator of soil erosion and sedimentation of a watershed. Geomorphic characteristics of watersheds are classified into linear, relief, and areal categories. Linear characteristics include stream number, bifurcation ratio, stream length and streams order. Relief characteristics include three-dimensional features of the watershed such as hypsometric integral, ruggedness number, and relative relief. Areal characteristics encompass morphological characteristics such as drainage density, stream frequency and watershed shape parameters. Accessibility to Digital Elevation Models and remote sensing data as sediment yield predictors simplify the calculation of the watershed geomorphic characteristics. The purpose of this study was to use the latest capabilities of geographic information system to extract the watershed geomorphic characteristics and determine their relationship with sedimentation in the subwatersheds of Khorasan Razavi province.
2- Methodology
This study was conducted in 22 subwatersheds in Mashhad, Neyshabour and Fariman watersheds in Khorasan Razavi province. In order to select appropriate subwatersheds, the hydrometric and rainfall data for hydrometric and meteorological stations were obtained from Khorasan Razavi Regional Water authority for the selected watersheds. Annual sediment load was calculated using sediment rating curve method. Physiographic and geomorphic characteristics including 30 geomorphic parameters were calculated for each subwatershed using Digital Elevation Model with spatial resolution of 30 m. In order to determine the relationship between geomorphic characteristics and sediment yield of the subwatersheds, a multivariate regression stepwise analysis was used. In the multivariate regression, the important geomorphic characteristics which affected watershed sedimentation were identified and based on those parameters, the best annual sediment yield and geomorphic characteristics equation were presented.
3- Results
The subwatershed areas under study vary from 40 square kilometers for the Chakaneh Olya to 9339 square kilometers for the Hossein Abad subwatershed. The average annual sediment yield for the studied subwatersheds during the period of 30 years varied from 1026 tons per year in the Jang subwatershed to 274572 tons per year at Hossein Abad watershed. The subwatersheds of Kalateh Rahman and Jang had the highest and lowest sediment yield, respectively, with 317 and 5 tons per square kilometers. The relationship between geomorphic characteristics and sediment yield of subwatersheds showed that the annual sediment yield had a positive correlation at the 5% confidence level with form factor and annual rainfall. The results of this study showed that the watershed shape parameters including form factor, elongation ratio and shape index had high correlations with sediment yield with the pertaining coefficients of 76.8, 76.5 and 72 percent, respectively. Also, the correlation coefficient of annual rainfall with annual sediment yield was 73.9 percent. After rainfall and form factor, elongation ratio was the third parameter that had a high correlation coefficient (76%) with sediment yield. In addition, watershed shape index which was a function of form factor was correlated with sediment yield at 72%.  Among these characteristics, the annual rainfall and watershed form factor were used in the stepwise regression in the final model and were selected as predictor variables for sediment yield. Study results showed that the annual rainfall and watershed form factor variables could predict 64% of the annual sediment yield of the studied watersheds.
4- Discussion & Conclusions
The results of this study indicated that there was a significant relationship between the geomorphic characteristics of the studied watersheds and annual sediment yield. Watershed form factor was a dimensionless index for flood flow and movement, erosion severity and sediment transport capacity of watersheds. This factor was a function of watershed area and length. The runoff and the amount of flood peak in bigger watersheds will increase the sediment yield. Many researches have reported a high correlation between rainfall and sediment yield. Arid climate and poor vegetation coverage in the selected watersheds were the main reasons for the high correlation of rainfall and sediment yield. Soil erosion and sediment yield would increase due to the high intensity and low duration of rainfall along with the scarcity of vegetation coverage and erodible soils in this region. Overall, the study results indicated that with the development of new technologies and the possibility of extracting different physiographic and geomorphic parameters of watersheds from a Digital Elevation Model, it is possible to present regional equations for the prediction of sediment yield using geomorphic characteristics that can be used in sediment control and Watershed Management Programs.

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Extended abstract
1- Introduction
Evaluation is a process of assessing the degree of achievement to determined goals. In the meantime, choosing the right method for evaluating the effects will have a significant role on the results and management strategies. Therefore, considering the importance of check dams in watershed management programs in Iran, in this study, performance of check dams in Kond watershed in Tehran province is evaluated with a new economic approach named Cost-Effectiveness Analysis.
2- Methodology
At first, the cost associated with check dams is Actualized based on 2019. Then, their effectiveness in controlling sediment load is determined by calculating the volume of stored sediment in their reservoir by Nakhjavani method. Next, Economic evaluation of check dams done using Cost-Effectiveness approach and their spatial distribution is obtained. Finally, the most cost-effectiveness and optimal type and height of check dams in the Kond watershed is determined.
3- Results
Obtained results showed that the effectiveness of check dams in the Kond watershed was equal to the control of 131782 t of sediment load, which is a high value. Overall cost-effectiveness of these check dams is equal to 317180 IRR per each ton of controlled sediment load. Their effectiveness-cost is also equal to 0.00000315 ton of controlled sediment load per each IRR, which is a small amount. The results show that the cost-effectiveness criterion increases as the height of check dams up to 4.5 m in the study area. After height of 4.5 m, the cost effectiveness decreases due to the change of the type of check dams from gabion to Masonry. In fact, the cost of sediment load control in check dams with a height of 4.5 meters is about nine times less than that of the check dams with a height of one meter. Accordingly, it is found that sediment load control in this case study has been done with high cost. One of the main reasons of high cost-effectiveness is the large number of check dams in the height range of 1 to 1.5 m (43%) where the cost of sediment load control with them is very high. Obtained results by considering the type of check dams also showed that Gabion check dams with 4.5 m height and cost-effectiveness equal to 134615 IRR per each ton of sediment load have the lowest cost-effectiveness and are the most economical and optimal types of check dams for sediment load control. In contrast, masonry and gabion check dams with heights of 1 and1.5 m also have highest cost-effectiveness and the cost of sediment load control in this type of dams is very high.
4- Discussion & Conclusions
This result indicates that the choice of right type of check dams in the management plans will have a significant impact on the efficiency of cost of sediment load control. Also these results show that watershed management approach in Iran needs to change its attitude. In fact, if it is necessary to control the sediment load on the stream, the choice of a less number of check dams with optimal height and type, will load better results than choosing a large number of small check dams.
 

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1- Introduction
Gully erosion is one of the linear and progressive forms of water erosion that has an expanding role in land degradation. A gully is a channel with a steep side slope and head cut that is formed by surface or subsurface soil erosion processes though heavy rains, soil disturbance or landuse changes. Upon once the gully initiation head cut retreating is the main effective erosion process influencing land degradation and soil loess. The development of the head cuts have caused the removal of fertile soil, the aggravation of flooding by wild land and production of sediment from agricultural lands. Therefore, it is necessary to monitor the growth and expansion of gullies in order to identify the factors involved in soil loss and effectiv implimentation of soil conservation projects. In the same regard, besides paying attention to the special climatic conditions and the high sensitivity of the soil in the study area, the main aim of this research is to compare the growth of the gullies by aerial photographs and field operations to determaine the most important factors on gully head development over the short and long time spans. Also, other geometric of gullies including length, volume and surface growth were estimated and modelled by regression analysis procedure to find out the most important variables.
2- Methodology
The present research was conducted by selecting 30 permanent gullies using a survey based on field sampling, and conducting experiments to extract data and performing statistical analysis in two areas of Ismail Abad and Najm Abad villages in Alborz province. Identification of the gullies’ location and mapping of gullies distribution were performed by using the google earth database, interpretation of aerial orthophotos of the 1980s and 1990s, digital topographic maps (25,000). Also the present location of head cuts were determined by field survay in 2017 with a GPS device. The length, width and depth of gullies, the slope of the upstream channel leading to the gully and the slope of the gully channel bed and the landuse condition were recorded during field surveying. At the end soil samples were taken from the gulleis’ walls to determine the physicochemical attributes of the soil. Using geographic information system (GIS), the longitudinal, surface and volume growth of the gullies over the three time periods of 1988-99, 1999-2017 and 1988-2017 in two study areas estimated directly. By multiplying the surface of each gully by the average depth obtained from the field surviving, the volumetric growth was also determined. Multiple regression analysis was applied into the data to determine the significant factors (soil and topography and upland contribution area and road density).
3- Results
The growth estimation results showed that the average annual longitudinal growth over the 1988-1999, 1999-2017 and 1988-2017 in Ismailabad and Najmabad were 1.24, 1.18, 1.2 m/Y and 75.03, 30.78, 3.75, respectively. The average surface growths are 4.96, 4.46 and 4.65 m²/Y in Ismailabad region and 464.2, 18.73, and 187.7 m²/Y in Najmabad region. Also, the average volume growths are 4.59, 3.38, and 3.84 m³/Y in Ismailabad region and 513.86, 20.70 and 207.76 m³/Y in Najmabad region. The gully volumetric growths of Ismail Abad and Najmabad during the period of 11 years (88-99) are 45.31% and 93.82%, respectively. Also, the volume growths during the period of 99-2017 (18 years) are 54.69%, 6.18% respectively in the two regions of Ismailabad and Najmabad, and the average gully growth over the 29-year period is more than the 18-year period.
4- Discussion & Conclusions
The volume growth in both regions is higher in the first phase, the average gully development in the long-term time span (1988-2017) is more than the short-term period (1988-1999), which can be due to the greater growth of the head cuts in the initial phase of formation, landuse changes, and heavy low-frequency rainfalls. Also, due to factors such as slope, type of land use, soil, and humane construction activities, the average gully growth in Najmabad region is higher than Ismailabad one. The growth (longitudinal and surface) of gullies in Najmabad region has been much higher than in Ismailabad region. In Ismailabad region, due to the conditions of hilly rugged land, the contribution upstream area of the head cuts were less than Najmabad region (alluvial plain) and ttherefore, the amount of runoff will be less and consequently the gully head development is more in Najmabad. Comparing the results of this research with other researches shows that the reason for the high growth of headcuts in this research can be related to the sensitivity of the soil, the dry climate and the human developing constarctions such as roads construction.