Hydrologic Connectiviti Properties Of Microtopographyic Surface On The Loess Tilled Siope

The tiled slope is a major agricultural farming sites in the Chinese Loess Plateau,and it is also the area where soil erosion occurs most easily.As soil erosion has been severely constraining the level of agricultural production and economic sustainability in Chinese Loess Plateau,its hydrologic connectivity can affect sediment deposition and runoff migration processes,thereby affecting the further development and evolution of soil erosion.So,the hydrologic connectivity is a major factor for understanding the spatial changes of runoff.However,almost all existing studies are at the basin scale,few research on hydrologic connectivity has been done at a micro-topographic terrain scale,especially on loess tilled slope.It has seriously affected people's understanding about the important role of microtopography.In order to have a deep understanding of the slope runoff process and mechanism at a micro-topographic scale,analyze the process of runoff and sediment source,express the complexity of the runoff process and the effects of surface roughness,the properties of hydrologic connectivity of microtopographic slope surfaces?measures of contour tilage and artificial digging,at gradient of 5°,10°,15°,20°and 25°?under simulated rainfall?at rain intensity of90mm/h and 60mm/h?were exlpored.The results showed that:?1?The accuracy of point cloud data will affect the numerical simulation of microtopographic surface,thus affecting the total river length,river network threshold,flowlength and surface roughness.In this paper,The best accuracy of elevation point cloud data pumping is 6 mm,and can be used for the Kriging interpolation method to building high-precision DEM,which is an important data base for the study of surface hydrologic connectivity.?2?There was a strong correlation between the river network threshold and the total river length.The optimum threshold was 0.9.The fitting degree of the river network threshold and the total length of the river was as follows:AD_90mm/h>CT_90mm/h>AD_60mm/h.?3?The flowlength of runoff can be used as an important indicator to describe the structural connectivity of hydrology on the surface of microtopography.The ratio of the number of grids of runoff length can express the formation of the runoff source area.Runoff source in Loess tiled slope were mainly made up of flowlength of 6-10mm.As the rain continued,constantly converged into larger runoff source areas,increased hydrologic connectivity path and promoted the development of hydrologic connectivity.?4?Slope gradient,rainfall intensity and surface roughness were the main factors affecting the structural connectivity of the hydrology.On the whole,the greater the slope and rainfall intensity,the greater the flowlength,the better the hydrologic connectivity,while the increased surface roughness hinders the development of hydrologic connectivity.In addition,farming measures had a certain influence on the structural connectivity of hydrology,under the same slope gradient and rainfall intensity,AD is more conducive to the development of hydrologic connectivity than CT.?5?Simplified hydrograph and relative surface connection function can vividly reflect the functional connectivity of hydrology of these microtopographic slopes,and express runoff production processes and mechanisms.That is,the ratio of surface connected to the outlet to the total surface of the soil tank?C,m²/m²?peaked quickly and then became stable under continuous rainfall.However,when the infiltration rate on the slope is consistent with the surface water storage speed,the average of C was as follows:AD_90mm/h>CT_90mm/h>AD_60mm/h.?6?Slope and rainfall intensity were the main factors affecting the hydrologic connectivity.The greater the slope and rainfall intensity,the smaler the cumulative precipitation corresponding to the peak value of C in simplified hydrograph and the ratio of depress storage.And minimum depress storage corresponding to the peak value of C in relative surface connection function,shorter time it took for C to reach its peak,the greater the degree of fitness of the simplified hydrograph and the relative surface connection function,the better the hydrologic connectivity.At the same time,farming practices also had a certain influence on the functional connectivity of hydrology.Under the same slope and rainfall intensity conditions,AD is more conducive to the development of hydrological connectivity than CT.Exploration into microtopographic hydrological connectivity can facilitate scale conversion from microtopography defined by a limited area with a smaler grid unit to mesotopographic defined by administrative district,slope,plots etc.and to macrotopographic defined by basin area.Due to high precise data and information,,the result of this dissertation can increase the precision of hydrologic modeling of slope surface undoubtedly,and is useful for scientific decision to promote sustainable management of water and land resources in the Loess Plateau.