Runoff Process In A Typical Small Permafrost Watershed At The Headwaters Of Yangtze River

For the severe natural environment in alpine regions especially permafrost regions, the research of hydrological process in these area is very weak, especially for the hydrological cycle and seasonal characteristics in alpine meadow-marsh wetland. The basic features of elements and mechanism of hydrological cycle was not very clearly in alpine permafrost regions. Paying more attention to the hydrological cycle and influenced mechanism in typical permafrost regions at the headwaters of Yangtze River has obvious significance. Principal findings are concluded as follows:(1) In permafrost region, there have two obviously flood season, with spring flood and summer flood. And the peak value of summer flood is larger than spring flood. Components about the two stage are inconsistency, precipitation and thawing actives frozen soil layer forming spring flood; And precipitation accounting mostly for the summer flood. Annual average runoff coefficient is 0.47, runoff modulus is 7.7 L·S^-1·Km², runoff coefficient changes greatly in different monthes. Furthermore the runoff coefficient in May, June, September and October is larger than the annual average, even exceed 1.0, and summer flood runoff coefficient is small.(2) Typical thawing-ice snow flood is the main type floods in spring flood stage, mixed flood and precipitation flood are main type in summer floods stage, but the last one is the mainly forms. As the temperature increased Runoff increased in spring flood, but decreased in summer flood stage. As the temperature increased, the annual average runoff decreased.(3) The recession processes is relatively rapidly in spring flood, the duration was less than 7.5 days, the first and third of the spring recession processes are longer than the second stage. Runoff are mainly influenced by snowmelt, precipitation, permafrost thawing at spring flood stage, precipitation and snow melting accounting for main composition; At summer flood stage, the first recession process affected byprecipitation, and interflow is the mainly forms at the second recession stage.(4) Analyzing the factors that controlled the runoff shows that at different stages the impact factor is different. For instance, soil temperature and soil moisture above 65cm plays a leading role in spring flood; in summer dry stage, correlation between soil temperature and moisture above 40cm and runoff is negative, and the deeper soil temperature and soil moisture plays a leading role; temperature and precipitation plays a leading role in summer flood; in autumn dry stage, the impact factors are soil temperature, soil moisture and temperature.(5) Compared non-degraded marsh wetland runoff field, interflow is then mainly type runoff yield in 400m², reached 85% about all the water quantity, and responded obviously on precipitation and little surface current; and interflow and surface flow have the same tendency in 200m², and the amount of interflow still larger than surface flow; but appeared contrary tendency in degraded marsh runoff field. Surface flow is obviously larger than interflow and response significantly to precipitation; Compared the result flow about the two types vegetation runoff field: surface flow dramatic increased in degraded runoff field while decraesed in non-degraded runoff field, the former is three times bigger than the latter, interflow appears as the former five times bigger than the latter; runoff yield with area increased has the inverse ratio relationship.