森林小流域的降雨出流机制的探讨

本文简述了森林小流域中降雨—截流—下渗—地中水—地表水各个环节的作用。作者认为,在降雨出流过程中,下渗和土壤中的快速流是非常重要的部分,而地表出流所占的比例是比较小的。一般来说,森林土壤的下渗率比较大,森林流域的贮水能力也是很可观的。这些就决定了森林流域的产流不是霍顿产流,也不同于现在流行的许多产流理论和模式。在湿润地区形成产流区时的特点并非是表层土壤首先饱和,而是地下水位或被地下水支持的饱和毛细管带上升到表面附近使该区发生饱和,因而产生以及维持这种饱和状态所需的垂直下渗和地中水的侧向补给是流域是否发生产流的先决条件之一,而地表流可认为是回归流。此外,流域地中水产流对降雨响应过程可认为是由作用在毛细管带中的水的压力平衡受破坏而引起的,这个压力通过毛细管带传递到饱和带。作用在毛细管带中的水的压力平衡受破坏的原因可以是封存在土壤中的被瞬间压缩的空气压力作用,也可以是降雨直接接触到已发展至地表的非饱和毛细管带的上缘。

THE MECHANISM OF STORMFLOW GENERA TON IN THE SMALL FORESTED WATERSHED

The paper explains the role of precipitation, infiltration, subsurface water and surface water in the small forested watershed. The authors consider the infiltration and the rapid flow in soil were very important in stormflow generation processes, in, which the subsurface water contributed more than surface water did.Generally speaking, the infiltration rate and the capacity of water storage in forested watershed are very large, which implied the Horton's theory or other current models of stormflow ' generation do not work there,In the contribution area, the saturated state was resulted from the rising of groundwater or the development of saturated zone above the groundwan ter.Therefore, the generation and maintenance of the contribution area depended on the infiltration and lateral flow and the surface water could be considered as the "return flow" .The quick response of the subsurface water discharge to the rainfall is considered to be caused by the break of an equilibrium of forces acting on air and water in the capillary fringe, that is, by the quick conversion of the tension-saturated capillary fringe into the pressure-saturated zone. The equilibrium of forces acting on water in the capillary fringe can be broken either by the increase of the pneumatic pressure of the entrapped air with successive rainfall or by the rainfall directly when the capillary fringe just near to the groundwater surface.