尾巨桉人工林小流域降水产流特征分析

研究尾巨桉(E.urophylla×E.grandis)生长阶段(林龄3.5—5.5 a)所处小流域的降水产流特征,有助于了解桉树生长过程的生态水文效应,对修订桉树人工林经营方案中注重提高生态系统的水源涵养能力有重要参考意义。以广西南宁桉树森林生态系统定位观测研究站(南宁桉树生态站)的闭合尾巨桉林小流域为试验区,在小流域出水口建设1个测流堰,在测流堰附属房的测定池安放1个自动水位计,定位观测小流域2013年5月—2015年4月的地表径流,使用生态站的自动气象观测系统观测降水量和土壤体积含水量,建立降水、土壤含水量和径流的函数关系,分析土壤前期含水量对径流形成和持续的影响。小流域年均降水量1300 mm,以小雨为主,两个年度小雨共计191场,占降水强度等级总场数74%;降水年内分布不均,雨季集中在季夏,占全年降水量的60%以上,冬季降水最少,属于干旱季节;降水产流现象在降水集中的月份才可能出现,2013年5月—2014年4月的径流深为81 mm,径流系数6%,2014年5月—2015年4月的径流深只有9 mm,径流系数仅为0.7%;径流初始时间明显滞后于降水初始,滞后时间与前期土壤含水量密切相关;径流递增率与降水历时呈线性函数关系,径流递减率与径流消退时间呈对数函数关系;降水产流过程经历径流递增期、稳定期和递减期3个阶段。

Analysis on Rainfall-runoff of E. urophylla×E. grandis Plantationin Small Catchment

To explore hydrologic process of eucalypt plantation ecosystem based on artificial interference of management measures,researching rainfall-runoff characteristics of a small catchment at the period from 3.5-year-old to 5.5-year-old of eucalypt plantation growth which were in favour of enhancing capacity of water storage and water conservation of eucalypt plantation ecosystem when formulated or corrected forest management plan.This study was on the basis of Guangxi Nanning forest ecosystem observation and research station(NEES)as a platform where a small closed catchment of E.urophylla×E.grandis plantation was selected to be a trial region.We built a flow weir at the place of outlet of the catchment and a small house beside the flow weir.In the house we established a measuring pool where a nilometer was put into the bottom of the pool for monitoring the data of water level change from May 2013 to April 2015 which could be used to calculate the quantify of runoff,plus the data of rainfall and soil water volume content which were monitored by automatic weather station installed at the water divide of small catchment.A relationship between rainfall and runoff was established and we also analyzed the impact of previous soil water on runoff beginning and the lag and extended time of runoff.The annual mean rainfall was 1300 mm,the rain was mainly light rain,the sum of light rain were 191 times within these two years which occupied 74%of the total of all different rainfall intensity levels.It was uneven of rainfall distribution between months in one year.Rainfall concentrated in the summer which accounted for 60%of the total of rainfall in one year.Rainfall was the fewest in the autumn which belonged to arid season.Runoff phenomenon was likely to be observed in the rainy season.The depth of runoff was 81 mm and the coefficient of runoff was 6%from May 2013 to April 2014,likewise,the depth of runoff was only 9 mm and the coefficient of runoff was low to 0.7%from May 2014 to April 2015.The time of runoff generation was lagged behind rainfall and hysteretic time was closely related to previous soil water content.Increasing rate of runoff showed a linear relationship with the time of rain duration,declining rate of runoff presented an exponentially functional relationship with the time of runoff duration.The whole runoff process had three stages which were increasing period,stable period and declining period.