Study On Mechanism Of Storm Runoff Erosion And Design Method Of Drainage Ditch Of The Dikes In The Lower Reaches Of Yellow River

The storm runoff erosion has been one of the problems facing the engineering management of the dikes in the lower reaches of Yellow River for a long time. Some control measures have been taken to solve the problem, but there have been no concerned reports that study systemically the formation mechanism and development process of rill erosion and drop pit on the dike slope so far. Based on the detailed analysis of the data from field and laboratory simulated rainfall experiments, some preliminary results of storm runoff erosion on the dike slope of Yellow River, especially the formation mechanism of rills and drop pit were obtained in the paper, by using integratedly the theory knowledges of multi-disciplinary. And several control measures used for rills and drop pit were proposed, which were of great importance to reducing the threat of storm runoff erosion to the safety ofthe dikes in the lower reaches of Yellow River, and to improving the flood control capacity of the dikes and the standard management of the dike engineering. The main study results were as follows:(1)The effect of the storm on soil erosion. Under the same design experiment conditions including rainfall intensity, rainfall duration and soil water content, the soil erosion increased nonlinearly with the rain intensity. And the soil erosion increased with the increasing rainfall duration and soil water content, respectively.(2) The effect of runoff on the erosion. With the same rainfall intensity, the soil erosion on the dike slope caused by the runoff mainly depended on the factors such as the runoff amount, on the other words, the up-slope drainage area of dike slope. In addition, the soil erosion caused by the combination of rainfall and the upslope-discharged runoff was more apparently than that caused by only the simulated rainfall.(3)The formation mechanism of rill and drop pit. The rill and drop pit on the dike slope were both the results of storm rainfall runoff erosion. The results of field and laboratory simulated rainfall experiments showed that there were many differences in the formation mechanism and development process between the rill and drop pit. On the formation mechanism, the rill was mainly formed by the concentrated action of the excess rain, i. e. surface runoff, on the dike slope surface, while the formation of drop pit could be explained by the soil erosion process under the soil surface, which was the result of the combination of overland flow, subsurface flow caused by the infiltration of the saturated surface runoff and the existing defects within the dikes such as crack, mousehole, fox and brock dens. On the development process, the rill could formed in a storm rainfall with high rainfall intensity, but the drop pit was the result of the combination actions of rainfall, runoff and subsurfaceflow of several storm rainfall events . In addition, the critical conditions for the formation of the rills including the rainfall intensity, rainfall duration and drainage area were analyzed in the paper. And the development process of drop pit, which was divided into three stages, i.e. leakage flow or pore flow stage, pressure pore flow stage, free pore flow stage in the paper, was analyzed, too.(4)The control measures of the rill and drop pit. According to the formation characteristics of the rill and drop pit respectively, several control measures were proposed in the paper. In addition, the parameters for the design of drainage ditches on the dike in the lower reaches of Yellow River, including runoff coefficient and sediment concentration were presented too.(5)According to the basic theories of design storm of small watershed and the underlying surface conditions and the characteristic of runoff generation and flood routing of the dike crest of the dikes in the lower reaches of Yellow River, the dike crest of the dike was simulated by a parallelogram area, by applying the wave theory of overland flow, the runoff generation duration and runoff concentration time were calculated and the calculation formula for design peak discharge of drainage ditch on the dike crest was deduced in the paper. The relationships between the optimum section, interval and peak discharge of drainage ditches and its investment were analyzed, and as a result, the optimization method and result of drainage ditches were proposed.