جستجوی مقالات مرتبط با کلیدواژه "حوزه آبخیز کجور" در نشریات گروه "آبخیزداری، بیابان، محیط زیست، مرتع"

Soil surface rock fragment is considered as an important factor on runoff and soil erosion. However, few studies have been focused on quantitative evaluation of the effect of soil surface rock fragments on runoff components as an integral part of soil erosion process especially in natural conditions. The present study has been conducted to evaluate the effect of soil surface rock fragments on runoff components in field plots under rainfall simulation on a clay-loam soil generally less than 1 meter depth and the slope of 20%. Runoff components including runoff commencement time, volume, coefficient and end time were measured in 1×1 m field plots with 6 wide range of surface rock fragments (2±2, 10±2, 18±2, 26±2, 34±2 and 42±2 % of soil surface cover) with 3 replications under simulated rainfall with constant intensity of 40 mm h-1. The results showed that increasing surface rock fragments up to a specific soil surface cover (about 34%) led to increase infiltration and runoff commencement time, decrease runoff volume and coefficient and runoff end time. The trend of runoff components has been reversed in the range of 34 to 42% of soil surface rock fragments.

By increasing the intensity of rainfall, runoff, which is considered as a very important factor in soil erosion process, occurs. Climate, geometrical characteristics of watershed, geological formations, soil, vegetation and land use are among factors affecting runoff generation. Although in plots under rainfall simulation, the experiment time is more limited and the effect of rainfall duration on the results is more tangible, this effect has been less considered. The present study was therefore conducted to evaluate the effect of rainfall duration in 6 levels of 5, 10, 15, 20, 25 and 30 minutes with 3 replications under constant rainfall intensity of 40 millimeter per hour on runoff parameters including commencement time, volume, coefficient and end time and sediment concentration. The field plots under rainfall simulation located in an eastern highland slope of Kojour Watershed were selected to achieve the study purposes. The Results indicated that the runoff parameters were significantly increased (p≥0.05) with increasing rainfall duration while the rate of increase was not the same in different rainfall duration levels. In other words, under the present study conditions, the turning point of hydrological response to rainfall duration was occurred between 25-30 minutes, where the gradient of runoff parameters with rainfall duration was considerably increased. The results also showed that the sediment concentration decreased with increasing rainfall duration.

Laboratory plots and rainfall simulators are useful tools for erosion studies, but transferring soil and consequent preparation steps which leads to damage soil structure, are among the disadvantages of laboratorial soil erosion studies yet. In other words, soil preparation steps can cause considerable errors in the results of runoff and erosion in laboratorial conditions. On the other hand, measuring splash erosion, as the first ability to detach and move the soil particles, is very important in soil erosion studies. Knowing the uncertainties of splash results due to soil preparation methods is therefore essential to improve the accuracy of laboratory results. The present study has been therefore conducted to measure and compare the amount of splash in a sandy-clay-loam soil in both undisturbed and disturbed conditions in a hillslope in the southern part of Alborz Mountains under three rainfall intensities of 40, 60 and 80 mm h-1. The results showed that disturbing soil in erosion laboratory studies could significantly increase the upslope, downslope, gross splash (p

Soil erosion will cause nutrients washes out, soil depletion and water pollution. Therefore, information on nutrient loss variations and its transport in surface water is very important. The present study was conducted to analyze phosphorus losses in 5 rainfall events and the relationship between the hydrographs and the phosphorus pollutographs in Kojour watershed. Results showed that maximum and minimum phosphorus loss were 32126 and 6707 g, respectively with an average value of 2620 g. The results of pollutographs were also showed that most of the pollutographs are in advanced and eveloped stages and rating loops also recognized as clockwise type. The results ultimately approved the necessity of further detailed studies in storm scale and different time bases.

Phosphorus (P) is an important nutrient for plants، in other hand P contaminates water resources. The present study aimed to access the applicability of rainfall and runoff variables of seven storm events occurred during 2008 in prediction of storm-wise peak and average P concentration and total P loss in Kojour watershed with the help of bivariate and multivariate regression models. Towards this attempt، seven storm events occurred during study period were analyzed، samples of river were collected for seven events with time intervals of 1 h. The results verified the capability of regression model with relatively high determination and efficiency coefficients of 0. 884، 0. 883 respectively. The results could facilitate the application of given methods obtained in the present study to other areas with similar conditions and leading to the suitable soil and water management.