Effects Of Up-slope Runoff And Sediment On Shallow Gully Erosion Process At Loess Hillslopes

Quantifying ephemeral gully erosion process may enhance to deeply understand soil erosion process on steep hillslope, and provides important theory support to establish erosion prediction model. This thesis is used a dual-box system (one is test box located down-slope and the other is feeder box located at up-slope) to simulate the ephemeral gully development and to quantify impacts and mechanism of up-slope runoff and sediment on ephemeral gully erosion process. Ephemeral gully erosion processes affected by different sediment concentrations in upslope runoff and its mechanism were illuminated. The relationship between ephemeral gully developing processes and surface erosion topography was also analyzed. The main results are as follows 1. The development of ephemeral gully erosion was studied after the beginning ephemeral gully form was shaped. The change of ephemeral gully headward erosion, gully-wall collapsing and deep-cutting erosion were quantified in the three stages of initial-phase, metaphase and anaphase. In the initial-phase, headward erosion and gully-wall collapsing were dominant; in the metaphase, gully-wall collapsing and deep-cutting erosion were main erosion forms; and gully-wall collapsing was dominant in the stable phase, but the speed of gully-wall collapsing was lower than that in other two stages. 2. The contributions of ephemeral gully erosion development in different stages to sediment delivery were analyzed. The sediment yield in the three different stages accounts for 59.2%, 58.4% to 59.7%, and 26.6% of the total sediment yield in ephemeral gully catchment, respectively. 3. The ephemeral gully erosion processes affected by different sediment concentration in up-slope runoff were quantitative described. Detachment-transport was dominant in ephemeral gully erosion process. Up-slope runoff and sediment has important impacts on ephemeral gully erosion process. The sediment delivery process was not equilibrium when up-slope runoff with different sediment concentrations discharged into the test box; sediment from up-slope were totally transported and the up-slope runoff caused net sediment yield at the test box. The net sediment yield induced by up-slope runoff was decreased with the increase of sediment concentration in up-slope runoff. The net sediment yield caused by up-slope runoff was affected by the up-slope runoff rate, sediment concentration, rainfall intensity, slope gradient, slope length and ephemeral gully developing process. The net sediment yield caused by the up-slope runoff accounts for 4.7% to 94.4% of the total sediment yield in whole ephemeral gully catchment. And the sediment delivery process of ephemeral gully erosion was homologous with ephemeral gully development. 4. The impacts of up-slope runoff rate on ephemeral gully sediment delivery were analyzed. The results showed that the sediment yield caused by up-slope runoff increased as rainfall intensity, slope gradient and slope length increased. The increment of sediment yield caused by up-slope runoff accounted for 15% to 70% of the total sediment delivery, which was affected by rainfall intensity, slope gradient and slope length. 5. The surface erosion topography in different experimental treatments was measured and DEM was made through probe method. The effect of ephemeral gully erosion process on surface topography was analyzed. By the analysis on erosion topography after rain, the difference in ephemeral gully erosion process under different rainfall intensity and slope gradient conditions was understood, and the difference in hillslope erosion types was studied too. The results also directly inflected the soil erosion intensity under different rainfall intensity and slope gradient conditions.