植被覆盖下黄土凸型复合坡面水流特征

针对黄土凸型复合坡面侵蚀产沙规律研究现状的薄弱问题,该文通过对野外凸型复合坡面进行不同流量(14、18、22 L/min)、不同植被覆盖度(30%、50%、70%)和不同植被覆盖坡位(凸型复合坡面的上坡坡底和下坡坡底)的放水冲刷试验,对黄土凸型复合坡面径流侵蚀发生过程中的水流特征进行了深入研究。结果表明,当植被覆盖度为70%,且植被布设在凸型复合坡面上坡坡底时,复合坡面的水流流态属于缓流过渡流,其他情况下凸型复合坡面的水流流态属于急流过渡流。植被布设在凸型复合坡面下坡坡底时的雷诺数和佛罗德数大于植被布设在凸型复合坡面上坡坡底时相应的雷诺数和佛罗德数。用达西阻力系数和曼宁糙率系数这2个参数表达径流阻力结果一致。植被布设在凸型复合坡面上坡坡底时的达西阻力系数和曼宁糙率系数大于植被布设在凸型复合坡面下坡坡底时相应的达西阻力系数和曼宁糙率系数。研究结果可为植被覆盖下黄土凸型复合坡面侵蚀产沙过程机理的研究和植被措施在黄土凸型复合坡面中的合理配置提供科学参考。

Flow characteristics of convex composite slopes of loess under vegetation cover

Abstract: Convex composite slopes are the common and natural slopes in the Loess Plateau. But researches on loess convex composite slope are limited. To explore sediment yield laws of the loess convex composite slopes in the present erosion situations, the field runoff scouring experiments were conducted, and the effects of vegetation cover on the flow pattern and flow resistance in the process of the runoff erosion occurrence of the loess convex composite slopes were studied. Three water inflow rates with 14, 18 and 22 L/min were involved in this scouring experiment. Three vegetation coverage degrees, 30%, 50%, 70% and two kinds of vegetation spatial locations, the bottom of the up-slope of the loess convex composite slopes and the bottom of the down-slope of the loess convex composite slopes were taken into consideration in the experiment design. Results showed that when the vegetation coverage degree was equal to 70%, and the vegetation was laid in the bottom of the up-slope of the loess convex composite slopes, the flow pattern of the loess convex composite slopes belonged to the slow transition flow. In other cases, the flow pattern of the loess convex composite slope belonged to the turbulent transitional flow. When the vegetation coverage was laid in the bottom of the down-slope of the loess convex composite slopes, the values of Reynolds number of runoff and the Froude numbers of the runoff were relatively large compared to the values when the vegetation coverage was laid in the bottom of the up-slope of the loess convex composite slopes. There are two kinds of runoff resistance representations, one is Darcy-Weisbach friction coefficient, and the other is Manning roughness coefficient. Runoff resistance expressed by Darcy-Weisbach friction coefficient was consistent with that expressed by Manning roughness coefficient in this study. When vegetation coverage was laid in the bottom of the up-slope of the loess convex composite slopes, the parameters of Darcy-Weisbach friction coefficient and Manning roughness coefficient were larger than that when vegetation coverage was laid in the bottom of the up-slope of the loess convex composite slopes. The results of this paper can provide a scientific reference for the research on the erosion and sediment yield mechanism of the loess convex composite slopes under vegetation cover as well as the rational allocation of the vegetation cover in the loess convex composite slopes.