集水区降雨径流晌应的环境同位素实验研究

Experimental Research on Catchment Runoff Responses Traced by Environmental Isotopes

利用环境同位素氚和氧-18对实验集水区进行降雨和径流响应的研究表明:(1)地面径流必源于本次降雨的概念不确,其中往往有非本次降雨的水量。经对1986年～1989年各次降雨估算表明,非本次降雨贡献最高可达50.5％。(2)非饱和带壤中流和饱和带地下水径流中必有非本次降雨的水量,并与地面径流一样,在次降雨径流过程中有时程变化。(3)对不同径流组成的流量过程,非本次降雨所占的比重不同。通过分析,可知降雨径流相关关系中的一一对应假定不确切,认为:传统的降雨径流经验关系和单位线概念需重新考虑;传统的过程线经验划分方法和现行同位素划分方法的有关基本假定不完全符合实际.

The isotopic composition(T,18O)of rainfall and various runoff components including interflow from unsaturated zone and grouadwater flow from saturated zone was monitored during the rainfall events of 1986-1989 in a special designed experimental catchment with all the runoff components are measurable. The contribution of preveni-ent water (old water) to surface runoff is identified and the portion of old water ranged from 0% to 50.5% is estimated. It implies that the current concept which considers surface runoff is always orginated from event rainfall is very likely a misconception. The different contributions of old water in interflow and groundwater flow are identified and estimated, too. The existance of temporal isotopic variability of runoff components during rainfall events demonstrates the temporal variations of old water composition in these components. For the four patterns of hydrograph with different combinations of runoff components, different compositions of old water are found ranged from 0% to 77%. As a comparison, several natural basins were sampled. From these results, it is shown that the current method of hydrograph separation up to now used widely in this country is, unrealistic in generally. These results also pose questions about the concepts related to rainfall-runoff relationships and to the UH analyses.