فصلنامه پژوهش های فرسایش محیطی
سال پنجم شماره 1 (پیاپی 17، بهار 1394)

Gully erosion is one of the most significant erosion types. This type of erosion is one of the most important sources of sediment in different regions of the world. Gullies often have different dimensions and complex characteristics and these characteristics may affect the distribution of vegetation. Topographic characteristics of gullies provide complex ecosystem for vegetation establishment. In this study was examined the relationship between morphometric characteristics of gullies and vegetation in Lamerd saline lands. Also according to the Hydrogeomorphic classification, along almost homogeneous gullies was measured valley width, valley depth, channel width, channel depth, channel slope, valley width / valley depth, channel width / channel depth, valley width / channel width, valley depth / channel depth, (valley width / valley depth) / (channel width / channel depth) and vegetation characteristics. Relationship between vegetation distribution and morphometric characteristic were evaluated by statistical tests. The results show that there is most vegetation cover (%) in medium size streams and small size streams have sparse vegetation cover in study area. Ta.spp plant type is associated with large width and depth gullies, Sa.ri-At.le plant type is correlated with medium size width and At.le-Al.ca-Pr.fr plant type is associated with small size width and depth gullies. There is a significant correlation between morphometric characteristics and vegetation cover. The results show that the gullies characteristics determine the percentage of vegetation cover. Differences in the distribution of plant type and plant species studied by multivariate statistical techniques. In conclusion, results of this study show that morphometric characteristics of gullies in saline lands determines vegetation types and plant distribution.

The goal of this study is determination of erosion rate and sediment production and exploring sensitive areas of erosion in Zemkan basin, located in the West of Kermanshah Province.To achieve these objectives, the erosion potential method (EPM) was used.Geographical information system also was used to reduce the errors and increase the relative accuracy in the analysis of the model. Required data in this study were obtained through fieldwork, existing maps, data from meteorological and hydrometric stations and library resources. The nessesary data layers were digitized and georeferenced and finally database were created. Using standard tables provided in the EPM model, accordant values for the basin extracted and incorporated into the layers according to the relations given in EPM model, the erosion intensity map, erosion and sediment ratio were calculated for the basin. Results revealed that the ratesof especial erosion (WSP) and especial sediment are (GSP), 2742.02 and 1005.55 m3/km2/yrespectively. The intensity of erodibleity of the basinwas also classified as very intensive (V).However the intensity of the erosion in the basin suggests that, different policies of erosion control in the basinare necessary.

Different factors affect the runoff and sediment production during storm conditions. Among different soil properties, clay content is one of the most important bonding agents for aggregation and infiltration. Rock fragments also affect hydrological and erosional processes, but these relationships in various soil clay contents or surface rock fragments may be positive or negative, thus examination of these effects is of importance in erosion process. Besides, runoff and sediment modeling is essential, because of the difficulties associated with measurements, for any sediment and flood remediation efforts. In this study, in order to have control on levels of variables for each treatment, a set of rainfall simulation system at experimental plots was utilized. In the next step, factorial design including 6 groups of clay treatments (0, 10, 20, 30, 40 and 50 percent) and 6 groups of impermeable surface treatments (0, 5, 10, 15, 20 and 25 percent), each in 3 replicates, (totally 108 experimental plots) was used. To study temporal variations of runoff and sediment, 30-minute rainfall simulations were run with sampling in 2.5-min intervals. Trend analysis showed that in all mentioned treatments, runoff volume increased significantly (p<0.01) but sediment production trend decreased when soil clay content increase. Also, in runoff and sediment production, clay content had the main role when compared to surface rock fragments. Finally, Inverse and S-curve models had best fits on runoff trends. However, sediment production trend and regression models between runoff and sediment mainly both had cubic patterns.

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.

Suspended sediment transport by rivers is important in water quality of cities and villages fed by certain drainage basins. On the other hand, the effective discharge refers to discharge that transports the most sediment over long time and controls the shape of river bed. Therefore, determination of effective discharge for suspended sediment transport and analysis the variation of effective discharge at temporal scale is very important. The aim of this study is evaluating the effective discharge for sediment transport using flow discharge and sediment discharge for a thirty one year period (1983-2013) in Korkorsar watershed, Mazandaran Province. For this purpose at first, sediment rating curve was provided based on monthly, seasonally and total period time scale by using USBR and clusters average limit methods. Flow discharge was clustered into several equal clusters and mean flow discharge was calculated for each cluster. Then, for each mean flow discharge, amount of suspended sediment was determined based on flow discharge and sediment rating curves. Finally, the histogram of flow discharge and total sediment was plotted and effective discharge was determined. Results indicate monthly effective discharge and seasonally effective discharge vary from 0.24-25.42 m3 s-1 and 4.37-25, respectively. The effective discharge in whole studied period was equal to 24.36 with return period of 100-year. In addition, the comparison of effective discharge in different time scale demonstrated that effective discharge amount could have high variability in monthly and seasonal time scale. Determining the effective discharge and its temporal variation in watersheds plays the effective role on decreasing sediment transport via. appropriate rive reach and land management specially at the time of occurrence of effective discharge.

Landform is a complication of land or landscape the establishment of which is formed by natural processes that can be described and defined by diagnosis index and if detected, the Landform information about their structure and composition, texture or its integrated offers. Landform variety and diversity of participants, mainly by changing the shape and position of the controls placed. So, classify and identify different areas according to their morphologic characteristics is essential. This study attempts to classify different Landform in the Hakan Watershed, Jahrom City. This research is Descriptive - analysis based on quantitative methods, field and modeling software Where the TPI method were used for the identification and classification of Landforms the study area. The model input data, including slope, curvature width, curvature minimum and maximum curvatures. The results of the study showed that the morphological classification of the study area includes 10 Landform (stream, mid-stream valleys, drainage, high, u-shaped valleys, plains, small, open slopes, steep upper edge high, middle edge of the slope, the high ridge, mountain).