| The sandy area of Yulin was located in the north of the Loess Plateau region, which wasTransition Zone from the Loess hilly gully region to the Mu Us Slandland. And the soil waspoor, the resisting erosion capacity was weak, which belonged to the wind and water erosionarea region alternately, so the soil erosion was severe. The Kuyehe River belongs to highstrength erosion center of the the Yellow River basin, and serious soil erosion led towatercourse deposition and land degradation. In "Eleventh five-year" period, most slopefarmland in sandy area had already dropped out of cultivating, which had protected andimproved the local ecological environment, and the surface coverage was improved obviously.In recent years, the runoff and sediment relationship of the middle reaches of the YellowRiver river produced big change, and how to correctly understand and evaluate the effectionof sandy area vegetation on the runoff and sediment relationship was one of key problems tobe solved.Therefore, this study set up field experiment plot at Yulin sandy area, using the methodof artificial runoff scouring experiment, carring out the research of runoff and sedimentrelationship of different underlying slope surface, revealling the influence of slope vegetationcover change on the runoff and sediment relationship. This test set up40experiment plot,including three kinds of site conditions which included bare slope, artificial vegetation slopeand the natural vegetation slope, four coverage degrees including four artificial slope of0%,35%,50%,65%, five slope degree including natural vegetation slope of10°,15°，20°,25°,30°. The scouring test was carried out respectively in the different treatment conditions,through analyzing the test data, revealling the relationship between slope runoff and slopesediment and the influence of slope vegetation cover change on the runoff and sediment relationship, the conclusions were shown as follows:(1) In different site conditions, the overall trend of runoff and sediment was accordance,which was: bare slope>artificial grass>natural grass, which showed that vegetationrecoverment could reduce runoff effectively and achieve the benefits of water reduction. Thedata showed that, the runoff reduction benefits of the natural slope was the best, and thesediment reduction benefits reached above98%, which was remarkable. Thus, in themeasures of controlling water loss and soil erosion, closing hillsides to foster afforestationand grass was a more effective method than the manual sowing grass vegetation restoration.(2) In different vegetable coverage degree conditions, along with the increas of coveringdegree the runoff quantity of artificial plot increased while the sediment decreased. Whichshowed that in artificial vegetation restoration measures, the sediment reduction benefits wasnot by decreasing slope runoff. So the slope of artificial vegetation restoration can effectivelyreduce soil erosion, but can not achieve good benefits of water reduction.(3) In different slope conditions, the runoff and sediment of natural slope will increasealong with the increase of the terrain slope. From the analysis of test data can be seen, alongwith the slope decreases, the benefits of sediment reduction and water reduction bothincreased, when the slope of the terrain reduced to15°, the benefits of water reductionreached above20%, and the benefits of sediment reduction achieved above90%, so theadminister of the steep slope of Yulin was the keypoint of the performance of the water andsoil containment.(4) In the condtions of different site, different coverage degree, different slope, thefitting relationship between accumulated runoff and sediment of different slope showed:except natural slope of25°, there were good power function relationship between sloperunoff and sediment, and the interaction relation of accumulated sediment and runoff could beexpressed using the power function equation as y=axb(a, b were constants). From differentpower function curves can be seen, the slope accumulated sediment yield trends can bedivided into three stage including rapid increase, slowly increase and tending to steady.(5) In different flow and different coverage degree conditions, there were goodexponential function relationship between slope runoff and sediment, and the interactionrelation of accumulated sediment and runoff can be expressed using the exponential functionequation as y=aebx(a, b were constants). From different fitting curves can be seen, underthe same flow conditions, the slope sediment gradually decreased along with the increase ofcovering degree, and under the same covering degree conditions, the slope sedimentgradually increased along with the increasing of the scouring flow.(6) In different flow and different coverage degree conditions, the fitting relationship ofslope runoff quantity and coverage degree could be represented by polynomial function as y =ax2+bx+c (a, b, c were constants), and the results showed: under the same flow conditions,the slope runoff presented the first decreases and then increases along with the increase ofcoverage degree. From different fitting curves can be seen, when the scouring flow were4L/min,6L/min,9L/min, if the slope runoff reached the minimum the relevant coveragedegree were16.5%,30%,52%. Thus, when scouring flow terned bigger, the demand washigher for covering degree.(7) In the different slope and the same coverage degree conditions, the slope sedimentand runoff would increase along with the increasing of the terrain slope. Through regressionanalysis, the correlation relationship between slope sediment and runoff and terrain slopeshowed good power function relation, the fitting regression equations were: ysediment=0.0094x3.227, yrunoff=40.966x0.479, and the correlation coefficient R2were0.9799and0.9259.The results showed that: the sediment content was small when the grade was small, and theslope sediment increased along with the increase of slope, and the increased speed faster andfaster. The slope runoff showed a trend of increase gradually along with the increase of slope,but its increasing speed was relatively more slowly compared with the slope sediment. |
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