| Soil and water loss of loess plateau is one of main reasons for the destruction of resource, deterioration of environment and reduction of crop output. Thus the research for soil loss law has also being highly paid attention, on the basis of it, this thesis mainly discusses runoff and its role in sloping farming land of loess plateau, which has been completed by simulative rainfall experiment at south(Chunhua) region, central-north(Ansai) region of this district, and by employing hydrographic, hydraulic, statistical theories.The effect of factors on runoff generation of loess plateau is: To starting runoff time, it is highly positive correlated with farming measure and decreases with rain intensity, soil moisture before rainfall-, slope, but the role of rain intensity is bigger. To runoff modulus, rain intensity is the first influential factor, farming measure and soil moisture before rainfall are respectively the second and third factor, while slope is at least significant?Not only the optimal mathematical mould is given, but integrated model is produced.The effect of factors on sediment is different. In south area, rain intensity, slope are main factors and have accelerating impact; In central-north area, unit depth runoff yield is highly pertinent to it, the following factor is soil moisture before rainfall, other factors' role is confined by grotto erode. A erode predicting model is concluded after giving regressive relationship formula between every factor and erode modulus.In theory, differential equations of instantaneous and cumulative runoff yield are deduced by integral to unit area. The runoff yield equation, which can calculate runoff volume after knowing the curve of sloping runoff to time, is trial-calculated, compared with other known academic modulus, the result is it the highest in precision and best in effect.At first, runoff is analysed from its form , while flow of ridge along contour line in a field has obvious unsticking flow's characteristic, other flow, which is in the case of linear slope. hoe-cultivated slope, farming along slope has so-called 'agitated laminar' flow. second, runoff is taken into account from its flowing kind, in Chunhua, south region of loess plateau, hoe-cultivated land is not likely to occur rapids or limited flow; Farming along slope has the biggest frequency to farm them; Linear slope is between hoe-cultivated land and Farming along slope, and is mainly slow flow. But Ansai, whatever farming measures, always appears rapids.When slope starts to runoff, a thin topsoil, which is 2-5mm, is saturated by water, The way of runoff generation belongs to runoff generation over infiltration under thin topsoil.The limited value of runoff and sediment generation are tested by experiment in indoor. About runoff generation, the average limited rain intensity is 0.121 mm/min, the average limited rain volume is 9.325mm and the average limited moment is 77.8min; About sediment generation, the average limited rain intensity is 0.412mm/min, the averagelimited rain volume is 19.850mm. these numerical value are similar to other research outcome in other regions .A statistical work is done about natural rainfall data from runoff stations of soil and water conservation in loess region. The folio wings are concluded: to runoff generation, the average limited rain intensity is 0.064mm/min, the average biggest rain intensity is 0.470mm/min; to sediment generation, the average limited rain intensity is 0.072mm/min, the average biggest rain intensity is 0.325mm/mino Because natural precipitation is variable in strength with time, these result are smaller than those from experiment, but the average biggest rain intensity about sediment is near to experimental value, thus explains soil erode is mainly formed during the biggest rain intensity under nature .In the same circumstance, runoff and sediment yield of Ansai are smaller than those in Chunhuao runoff and sediment yield process varies significantly with rain intensity and have a increasing trend with slope At... |
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