渭河华县段漫滩洪水变异特征及其生态效用探析

以渭河华县段漫滩洪水为研究对象,首先运用ToB(Top of Bank)方法确定不同历史大断面下的河道漫滩水位,采用水位流速法计算并统计渭河华县段1965-2010年间漫滩洪水发生的次数、淹没持续时间及漫滩期最大流量,并进一步分析其演变趋势。其次,以漫滩洪水发生次数和淹没持续时间为评估指标,应用变化范围法(RVA)对漫滩洪水的变异程度进行评估,从侧面探讨漫滩洪水变化对滨河生态系统的潜在影响。计算结果显示,渭河华县段1965-2010年间累计发生漫滩洪水34次,年均仅0.74次,且漫滩洪水次数、淹没持续时间、漫滩最大流量在时域上均呈显著下降趋势。尤其是20世纪90年代以后,受来水量减少和渭河下游泥沙淤积的共同影响,漫滩洪水多为小流量洪水,较以前其流速和流量都有所减弱,生态效果有限。而RVA评价结果则表明渭河华县段漫滩洪水的淹没次数和持续时间两个指标均发生了高度变异,缩减严重,对滨河生态环境有较大的潜在威胁。建议管理部门制定相应措施,适时人造漫滩洪水,以保障滨河湿地、滩地的生态平衡与安全。

Change in overbank flood at Huaxian Section of the Wei River and its potential impact on riparian ecosystem

In this paper, we investigated the overbank flood at the Huaxian section of the Wei River. First, we employed the top of bank (ToB) method to calculate the overbank flood level corresponding to different historical large profiles, and employed hydraulic methods to calculate the frequency, duration, and maximum flow of overbank floods at Huaxian section from 1965 to 2010. Moreover, with the frequency and duration of overbank floods as evaluation indexes, we used the range of variability approach ( RVA ) to evaluate the variation of the overbank flood time series and discussed its potential impact on the riparian ecosystems. The results showed that the overbank flood occurred 34 times at the Huaxian section of the Wei River in 1965-2010, that is 0.74 times a year. The frequency, duration, and maximum flow of overbank floods all showed a significant decreasing tendency over time. Especially since the 1990s, the over bank floods were mostly small floods due to flow reduction and sediment deposition in the lower reaches of the Wei River, and they had slower flow speed, smaller quantity, and limited ecological effects. Meanwhile, the evaluation results by RVA showed the frequency and duration of the overbank floods at Huaxian section both changed significantly , which would posegreat potential threat to the riparian environment. Thus, we suggest that the administration should take more measures such as artificial overbank floods to protect the ecological balance and security of riparian wetlands and beaches.