جستجوی مقالات مرتبط با کلیدواژه "پوشش سطح خاک" در نشریات گروه "آب و خاک"

The effect of surface rock fragments on soil erosion processes has been an important challenge in erosion studies during the last two decades. Rock fragment characteristics including size, position and coverage may affect soil erosion and cause a complication in predicting their effects on soil loss. The aim of this study was to model the effects of rock fragment coverage, size and the flow rate on soil loss and surface flow velocity employing response surface method and central composite design. Two sets of run-on simulation experiments were carried out in a laboratory flume (6×0.5m). The range of the independent variables were 0-45 percent for rock fragment coverage, 3-9cm for rock fragments diameter (size) and 1.67-5 cm3cm-1s-1 for flow rate. The second set of experiments used to develop the predictive model based on the central composite design and the results of the first set of experiments were applied to validate the predictive model. Results indicated that the central composite design models have high performance in predicting flow velocity (R2=0.993) and soil loss (R2=0.994). Models validation with the first data set also indicated a good agreement between the predictive values of flow velocity (R2=0.887) and soil loss (R2=0.851) with the experimental values of these two variables. Rock fragments coverage, flow rate and the size of the rock fragments have the highest influence on soil loss and flow velocity, respectively. There was a significant interaction between the flow rate and rock fragment coverage, which should be considered in modeling of their effects. A linear relationship was also observed between the flow velocity and soil loss.

Studying hydrological processes is important for effective management of soil and water resources. However، it has received less attention. Therefore، the present study was conducted to analyze temporal variations of hydrological processes in each of experimental plots in a forest watershed. Experiments were carried out with simulated rainfall intensity of 1. 6 mm min-1 and experimental plots of 30×30 cm in downstream of Educational and Research Forest Watershed of Tarbiat Modares University. The temporal variations of runoff depth، runoff commencement time and sediment yield were investigated for eight months from September 2008 to April 2009. Results indicated that the aforementioned variables have been changing over the time. Runoff depth was measured in March and November with respective value of 12. 5 and 10. 2 mm with the highest antecedent soil moisture of 25 and 23%، and the lowest surface litter cover. Sediment yield was at the maximum rate in April and May with rate of 21. 1 and 18. 9 mg due to reduction in soil surface cover. In addition، runoff commencement time was highly dependent on antecedent soil moisture if the soil surface was not covered well. October with low antecedent soil moisture of 9% had the maximum time of runoff generation of about 67 seconds. Runoff generation had the minimum time of about 32 seconds with the maximum soil moisture in early March. In other months، it was hard to find a reasonable relation in this way، whereby، it could be deduced that runoff beginning time was sensitive to environmental conditions.