عطاله کاویان

In severely eroded areas, especially steep slopes, establishment of vegetation cover is not possible. The application of organic and inorganic amendments can therefore improve the conditions leading to establish vegetation cover through playing an effective role in runoff control. Accordingly, in the present study, woodchips as a soil organic amendment was applied to control runoff variables including time to runoff, runoff volume and coefficient. For this purpose, three levels of woodchips treatment of 0.5, 1.0 and 1.5 kgm-2 were used in three replications at in 1 m2- plot scale. The plots were located in 30% slope in accordance with field conditions under simulated rainfall of 60 mmh-1 and duration of 15 min. The results showed that application of woodchips in 0.5, 1.0 and 1.5 kgm-2, time to runoff increased 97.50, 192.38 and 203.31%, respectively. The runoff volume decreased 35.23, 55.11 and 60.43% and runoff coefficient also decreased 42.43, 67.40 and 72.14% in three levels of woodchips treatments, respectively. The results of GLM showed that woodchips treatment had a significant increasing effect on time to runoff (p≤0.01) as well as a significant decreasing effect on runoff volume and coefficient (p≤0.05). The application of woodchips as a conservation treatment on the soil surface showed that this amendment can be used for runoff control especially where large quantities of woodchips are simply available.

Nowadays, soil and water conservation is one of important methods for the natural resources management. There are several ways to do this. One of these methods is the use of organic mulches. In this research, the effect of Agropyron elongatum residueon runoff and soil loss were examined in three cover percentages (0, 30 and 70%) with diameters 4 cm in length and 0.35 cm width in the laboratory conditions using rainfall simulator. The experiments were carried out in a plot with 2 meters length, 1 meter width and 0.2 meter depth, where 0.2 m of the depth of plots was filled with silty loam soil. Then plants residue was covered soil surface and simulated rainfall intensity was 50 mm per hour for 20 minutes. After experimental rainfall simulations, the amount of runoff and sediment were measured. LSD test results in cover percentages of (0, 30 and 70%) for 4cm size showed there are significant differences in runoff volume, sediment load, sediment concentration and runoff coefficient at 95% level of confidence (sig ≤0.05) between the percent cover (0, 30 and 70%) of this size.

Rainfall intensity and duration are one of the most important factors in the occurrence of landslides; therefore, nowadays rainfall is recognized as the most common and triggering factor in the occurrence of landslides. Since raw data of landslide displacement is very important to researchers in order to study the deformation process and laws of landslide displacement, the Global Positioning System (GPS) and computer sciences can be used as a tool to measure the landslide displacement. So monitoring and determining the relations between the amount of landslide movement and characteristics of precipitation (such as type, intensity, duration) and the direction of the sliding mass using GPS can be a turning point in the sustainable management of this natural disaster.
Study Area :The study area refers to the Tavan landslide which occurred in 2010 covering an area of 40 ha in Qazvin Province in Iran.
Material and After identifying the sliding mass, a network of fixed points on the inside (17 points) and outside of it (3 points) was created in order to monitor the movement, and the exact position of the points was determined using a dual-frequency GPS at 5timescales. The precipitation data and their characteristics such as the amount of precipitation, maximum intensity of 10, 20, 30, 60 minutes, average of precipitation, height of snow, average and total duration of precipitation were also calculated for each timescale. Finally, the relationship and correlation between the amount of displacement and the characteristics of precipitation was investigated by determining the vertical and horizontal displacement at the 5 timescales and the characteristics of precipitation for each period of time.
In the total period of the study, 64 precipitation events happened in which the total of precipitation was more than 2 mm in 52 cases. Drawing displacement vectors of the points on the topographic map revealed that the direction of mass movement is consistent with the general slope of the region. The correlation between rainfall characteristics and the amount of horizontal and vertical displacement of the monitoring points at the five timescales are provided in Table 7. The results showed that among all the characteristics of precipitation, rainfall intensity features have more solidarity with the average of horizontal and vertical displacement of points at the five timescales. Moreover, no significant correlation was found between other characteristics of precipitation and the amount of displacement.
The analyses of displacement at the five timescales showed that the relative displacement has occurred at some points of the network. Although there have been slow vertical and horizontal displacement at all points in the network but the amount of movement is clearly visible at the points of 1, 2, 6 and 8. The total amount of horizontal displacement of moving points at the five timescales (511 days) was 1876mm with the monthly rate of 110 mm. The total amount of vertical displacement of moving points was also 898 mm with the monthly rate of 56 mm. The results also showed that among the different characteristics of precipitation, only the intensity of precipitation has a good correlation with the amount of landslide displacement. Previous studies have also achieved similar conclusions about the triggering role of precipitation and the relationship between the intensity of rainfall and the landslide occurrence. The highest coefficient of correlation was found between the average intensity of precipitation and the maximum rainfall of 30 minutes with the horizontal movement of the sliding mass. Generally, it can be concluded that several factors such as topography, soil, geology, land use and intensity of precipitation caused favorable conditions for the occurrence of Tavan sliding; however, in this landslide, rainfall intensity has played the role of a trigger.

The runoff and soil erosion is most basic of environmental, agricultural and food production problems in the world, that these had adverse effects on the natural ecosystems and man-managed. One of the most important factors of runoff and soil erosion control is using organic and inorganic mulches, that they have most role in runoff and soil erosion control. Therefore in this study, for studying time to runoff and runoff coefficient changes used from an organic mulch (wheat straw mulch) in laboratory conditions. The experiments was done using rainfall simulation, in slope of 30% and plot scale of 0.5 m2 with 3 replications, with two cover percent of 50 and 90% and rainfall intensities of 50 and 100 mm h-1 for 10 min and then the time to runoff and runoff coefficient rates measured. The results showed that in rainfall intensities of 50 and 90 mm h-1, the conservation treatment could increase and decrease time to runoff and runoff coefficient, respectively and the cover of 90% had more effect in increasing time to runoff and decreasing runoff coefficient. The enhancement percent of time to runoff in rainfall intensities of 50 and 100 mm h-1 (cover of 90%) was 102.37 and 70.80%, respectively. The reduction percent of runoff coefficient in rainfall intensities of 50 and 100 mm h-1 (cover of 90%) also was 36.58 and 27.31%, respectively. The effect of conservation treatment and rainfall intensity variables evaluated significant expect in the effect of rainfall intensity × conservation treatment.