The Relation Of Soil Surface Roughness And Runoff Characteristic On Slope Farmland

Runoff generation and confluence on slope surface is an important form of runoff runoffyield and concentration in watershed, and is also one of main subjects of hydrology. Due tolimits of tools and computing technologies, the existing researches mainly focus on themechanism of runoff generation and confluence in small watershed, calculation of runoffyield and the build of runoff-conflux model as well as the calibration of parameters. Whilerunoff generation and confluence on slope surface is often ignored. In view of this, wecarried out an experiment about characteristics of runoff generation and confluence on slopesurface in sloping fields with three tillage practices including contour tillage, artificialdigging and artificial hoeing widely used on cultivated farmland of loess plateau, and thelinear slope was taken as the control measure. The study was conduct based on somesimilarities between the network of slope concentration and the river network on the basinscale with an indoor stimulated rainfall experiment, and structural characteristics of thenetwork of runoff generation and confluence on slope surface were measured according toconfluence density and runoff frequency. Characteristics of slope runoff and sediment on asmall scale and the evolvement confluence network properties were also explored underinfluence of surface roughness, which will be a help to enhance insights into slope erosionprocess and provide basis for the establishment of the runoff-conflux model. Results wereshowed as follows:1. The accuracy of four interpolation methods under different tillage measures wascompared. Results showed that, under different tillage measures, the disjunctive kriginginterpolation was appropriate for the micro-DEM establishing in the contour tillage treatment;the local polynomial interpolation was appropriate for the micro-DEM establishing in theartificial digging treatment; the radial basis function interpolation was appropriate for themicro-DEM establishing in the artificial hoeing treatment; while the accuracy of fourinterpolation methods on the linear slope was not differed significantly.2. The evolvement of surface roughness during rainfall was analyzed, which showed:the surface roughness was first decreased and then increased on the whole under differenttillage measures as the rainfall continued. When other conditions were same, the bigger ofslope gradient was, the greater of the variation of surface roughness was; the bigger ofrainfall intensity was, the greater of the variation of surface roughness was. 3. The relationship between initial runoff production time and surface roughness as wellas slope gradient showed that, the delay of initial runoff production time on slope surfacecaused by surface roughness was related to the rainfall intensity and slope gradient. Whenother conditions were same, the bigger of surface roughness was, the greater of the delayedaction on the initial runoff production time was. Otherwise this action was smaller.Meanwhile, effects of surface roughness on the delay of initial runoff production timedecreased as the rainfall intensity and slope gradient increased. The relationship between theinitial runoff production time and surface roughness as well as slope gradient presented as theformulas showed: T60=0.544×R-0.090×S+2.520；T120=0.431×R-0.148×S+1.307.4. Effects of surface roughness on the slope runoff and sediment showed that, sloperunoff yields on the whole trended to increase and finally to be stable under different tillagemeasures with the rainfall going on; the sediment yields first increased and then decreased,but finally became stable. The increase of surface roughness could reduce slope runoff andsediment yields. Effects of surface roughness on the slope runoff and sediment yieldsdecreased with the rainfall intensity increasing. There were different effects of slope gradienton the runoff and sediment yields due to different micro-reliefs. On the whole, when otherconditions were same, the bigger of slope gradient was, the greater of slope runoff andsediment yields were.5. The evolvement of characteristics of runoff pathway during rainfall was analyzed,which showed, the runoff pathway changed and turned to downslope. Runoff at all levelsbecame systematical and the confluence regularly changed direction to the main runoffpathway. The network of slope confluence was few and scattered on the roughed slopes underthe artificial digging and hoeing treatments compared with the control treatment. Theintensive of slope confluence network increased under different tillage practices as the slopegradient increased, especially on the linear slope.6. The relationship between confluence density,runoff frequency and surface roughnessas well as slope gradient showed that,when the rainfall condition was same,the confluencedensity on slope surface on the whole tended to increase, while the runoff frequency firstincreased and then decreased. The confluence density and runoff frequency obviouslydecreased on the roughed slope. The increasing degree of confluence density and runofffrequency declined significantly in the case of big rainfall intensity. The confluence densityand runoff frequency on slope surface both increased as the slope gradient increased, andespecially the increase was the most significant on the linear slope. The relationship presentedas the formula showed: D=0.276×S-1.96×R+11.19与Cf=1.15×S-2.90×R+59.22。...