| The flood in the Yellow River is the biggest threat to the lives and properties of the people living in the lower reaches. Because of the severe soil and water loss in middle reaches of the Yellow River, a large amount of sediment deposited in the bed of the lower reaches, which make the river the famous perched river. After liberation, our governments at all levels pay high attention to the-flood control of the Yellow River. Thus the Yellow River has no break in the past 50 years. The solidity dykes is the basic guarantee. With the heightening of the Dykes of the Yellow River every year, it became higher and steeper. There are many rills and puddles on the dyke slopes. According to the investigation of the dykes in Xinxiang reach of the Yellow River, the annual volume of soil erosion caused by storm runoff amounted to 0.07 million cubic kilometres. In order to eliminate the hidden trouble caused by storm runoff erosion, the mechanism of the storm runoff erosion on the slope surface of the Yellow River dykes has been studied in this thesis. Through the simulation rainfall experiments and field observations, the formation mechanism of storm runoff scouring, rills and sockets have been opened up. Meanwhile the possible control measures have been suggested.Based on the analysis of the data and information from the field observations and lab experiments, the results were as follows:(1) The results of the simulated rainfall and runoff erosion experiments in lab. Under the design experiment conditions including the constant rainfall intensities of 1.0, 2.0, 3.0mm/min and the rainfall durations of 30, 70 minutes and with soil moisture content 9.5% or 10.0% for dry situation, as well as with the soil moisture content 19.0% or 20.0% for wet situation, the soil erosion increased nonlinearly withthe rainfall intensity, and the rainfall duration. The results of the experiments indicated that the amount of soil erosion caused by the simulated rainfall and runoff on the dry-soil slope was more than that on the wet-soil slope. With the same slope gradient and slope length, the soil erosion on the dyke slope caused by the runoff mainly depended on the factors such as the runoff, flow velocity, rainfall intensity, rainfall duration, as well as the up-slope drainage area of dyke slope.(2) The results of the rainfall-affected runoff scouring experiments in lab. When the rainfall intensity was less than l.Omm/min, the soil erosion caused by the combination of rainfall and the upslope runoff was more than that caused by only the simulated rainfall. When the rainfall intensity was more than 2.0mm/min, the upslope runoff strengthened the effect of the runoff yielded in the local area on the dyke slope surface, and the effect increased with an increase of rainfall intensity.(3) The formation mechanism of the rills and sockets. The rills and sockets were both the results of rainfall runoff erosion. According to the analysis of the data of field observation and the simulated rainfall erosion experiment in lab, the results showed that there were many differences in the formation mechanism and development processes between the rills and sockets. On the formation mechanism, the rills were mainly formed by the concentrated action of the runoff on dyke slope, while the formation of socket mainly depended on surface runoff, subsurface flow and the existing defects within the dykes such as crack, mouse hole, fox and brocks dens. On the development process, the rills were influenced by rainfall runoff on slope, but the sockets were the result of the long-term repetitious action of rainfall and runoff and subsurface flow. As for a given rainfall experiment, the soil erosion in the rill was more than that in the socket. The rill only existed on the slope surface of the dyke could be rapidly infilled by the soil after rainfall. On the contrary, because the sockets were connected with the holes within the dykes, they were uneasy to be found in time. Therefore, the sockets had been developed up to a dangerous degree...
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