黄土丘陵沟壑区吕二沟流域水沙关系变化分析

Variation in the rainfall-runoff-sediment delivery relationships of Lu'ergou Watershed in the hilly-gully region on the Loess Plateau

流域水沙关系的研究可为流域水土流失模型构建和水土保持效益评价提供科学依据。根据黄土丘陵沟壑区第三副区的吕二沟流域在1982—2010年间的74场次洪水事件水文泥沙数据,对降雨、径流和输沙的关系进行分析,并用Mann-Kendall法检验流域次洪水事件径流系数和平均含沙量的变化趋势和显著性。结果显示,降雨量和降雨历时是流域径流和输沙的主要影响因素,前期降雨量中前7天降雨量与径流系数的相关性最显著。吕二沟流域具有较好的水沙关系。通过Mann-Kendall法检验得到1985年8月24日发生的洪水事件是流域径流系数时间序列的突变点,突变点之后径流系数呈显著减小趋势,植被覆盖面积的增加是流域降雨-径流关系发生变化的主要原因。流域次洪水事件平均含沙量时间序列没有发生显著变化,表明以植物措施为主的水土流失综合治理没有显著影响吕二沟流域的水沙关系。

Rainfall-runoff-sedimentation relationships are of great importance for predicting watershed soil erosion and evaluating the benefits of soil and water conservation in the watersheds. The hydrological data of 74 flood events of Lu＇ergou Watershed on the Loess Plateau from 1982 to 2010 were used to investigate the relationships among rainfall, runoff and suspended sediment transport. The variations of event-based runoff coefficients and mean suspended sediment concentrations and their significance were identified using the Mann-Kendall test method. The results indicated that the precipitation and duration of rainfall event were the most relevant factors controlling the hydrological response. The most significant correlation was observed between runoff coefficient and 7-day antecedent precipitation. Sediment yield was closely related to runoff in Lu＇ergou Watershed. The jump point for the sequence of the event-based runoff coefficient was the flood event on 24 August 1985. Afterwards, there was a significant decreasing trend in the sequence of event-based runoff coefficient. The increase in the vegetation cover area in Lu＇ ergou Watershed was the main cause for the change of the rainfall-runoff relationship. There was no significant change for the sequence of event-based mean suspended sediment concentration, which indicated that the soil and water conservation based on vegetation measures had no significant effect on the runoff- sedimentation relationship of Lu＇ ergou Watershed.