关键词: 黄土高原, 流域, 特性指标, 径流模量, 产沙模量, 相关系数

Abstract: On the basis of extensive field investigation, the paper incorporates and analyses over 4000 observation data including 21 variables in 1954- 1982, which come from 58 small watersheds with basin area from 0.193km² to 329km² located in three pro-vinces (Figure 1.). A few findings are obtained:1. An effect of runoff and its rate on sediment yield is much more obvious than that of rainfall and its intensity. Analysis indicates that the relation between mo-ludus of total volume of runoff M_w (m³/km²) and that of sediment yield M_s(m³/ km²) during a single flood may be expressed as M_s~M_w^1.5 and that the relation between modulus of total volume of runoff during all of annual flood series producing sediment and that of annual sediment yield Msa(m³/km²) may also be expressed as M_sa~M_wa^1.5Considering runoff rate, i. e. the modulus of peak discharge during a minute M_q (m³/km²) and the annual mean modulus of peak discharge during a minute for each of annual flood series M_q(m³/km²), the relations between modulus of sediment yield M_s, Msa and the composite factors (M_w + M_q), (M_wa + M_q) may respectively be expressed as M_s~(M_w+M_q)^1.5 M_sa~(M_wa+M_q)^1.5 And they all have better correlation coefficients.2. Characteristic factors of watersheds surface influencing sediment yield are mainly relief ratio R_h, ruggedness number D_h, basin elongation R_e, regulation range (including the amount of vegetative cover) R_p and resistance of ground layer to erosion and permeability Rs. With the observation data from 58 of small catchmentbasins of loess region in China (Table 4.), two regression equations can therefore be derived, in which M_sa/M_wa1.5=0.26772R_h^0.586*R_e^-0.560*D_h^-1.418*R_p^-0.703*R_s^-3.864 M_sa/M_wa=16.6188R_h^0.548*R_e^-0.486*D_h^-0.719*R_p^-0.809*R_s^-4.509 3. In view of the fact that basin elongation R_e is directly related to relief ratio of catchment basin R_h, the variable R_e may therefore be omitted. And the exponent values in regression equations can suitably be modified. Thus, a composite index of basin surface characteristics is given as follows:I=R_h^0.6*D_h^0.2*R_p^-0.8*R_s^-3.5 In order for both sides of equation to be nondimensional number, and from the data of 58 small catchment basins shown in table 4, an equation may be expressed as follows:M_sa/M_wa=31.8291^0.83 It is, in effect, a model of sediment yield, which represents the general relationship among the regime of runoff, basin surface characteristics and sediment yield. It is possible that as quantitative basis classifying erosion regions and as a model predicting sediment yield in small watershed with macroscopic approach, it can be employed.4. From Figure 4 it may roughly be seen that the composite index I values of surface characteristics for various basins with different erosion intensity can be given as follows: I value‰ Erosion intensity >20 Very high 4-2 0 High 1-4 Medium 0.5一1 Low <0.5 Very low

Key words: Loess Plateau, Drainage basin, Characteristic index, Runoff modulus, Sediment yield modulus, Correlation coefficent