极端降水条件下延河水沙特征对比分析及其影响因素

为探究延河流域在开展水土保持工程前后极端降水条件下水沙特征变化情况,采用统计学方法对比分析了延河流域1977年和2013年7月两次极端降水条件下的水沙特征变化情况。结果表明:1977年7月极端暴雨具有降雨强度大和降雨量峰值大、降雨强度空间分布极不均匀的特征;2013年7月极端暴雨具有降雨总量和时段降雨量大、暴雨频率高、降雨强度空间分布较均匀的特征。2013年7月洪水洪峰流量、洪水总径流量、洪峰含沙量等特征值较1977年7月显著减小,输沙量随径流量的减小而显著减小。1977年7月洪水表现为陡涨陡落,洪水历时较短;2013年7月洪水表现为缓涨缓落,洪水历时明显延长。与1977年相比,2013年泥沙颗粒明显细化。该研究表明1990年代以来水土保持高水平的规模化治理改变了流域产、汇流的下垫面条件,是导致1977年和2013年7月极端降水条件下的水沙特征表现迥异的主要原因。该研究为应对极端降水引发的洪灾和防治水土流失提供可靠的科学理论依据。

Comparative analysis of flow and sediment characteristics of the Yanhe River under extreme rainfall conditions and research on influence factors

To explore flow and sediment characteristics under extreme rainfall conditions before and after erosion and torrent control works in the Yanhe River basin, we used statistical methods to analyze flow and sediment characteristics under extreme rainfall conditions in July 1977 and 2013, including daily rainfall and precipitation at different times at 30 weather stations, flow and sediment discharge at two hydrologic stations, and grain composition at the Ganguyi station. The results showed that extreme rainfall in July 1977 had the characteristics of high average rainfall intensity and peak rainfall, and uneven spatial distribution of rainfall intensity. Extreme rainfall in July 2013 had the characteristics of high total precipitation and hourly rainfall intensity, high rainstorm frequency and relatively uniform spatial distribution of rainfall intensity. Precipitation in July 2013 was approximately twice as high as precipitation in July 1977; however, flood peak flow, total runoff and sediment concentration in July 2013 were significantly decreased compared with July 1977, and there was a significant decrease in sediment discharge corresponding to the decrease in runoff. Flooding in July 1977 was characterized by a steep rise and fall of water and a short flood duration; in contrast, flooding in July 2013 was characterized by a slow rise and fall of water and a significantly longer flood duration. Compared with 1977, there was a decrease in the total flood runoff in July 2013, and the proportions of runoff before and after the peak decreased and increased, respectively. Compared with 1977, sand grain size was clearly smaller in 2013; Furthermore, the weight of sediment with smaller size had increased, whereas the weight of sediment with larger size had decreased. This study reveals that a series of high-level erosion and torrent control works, such as returning farmland to forest (grass) engineering, has changed the underlying surface conditions in the Yanhe River basin since the 1990s, which contributed to changes in rainfall and sediment characteristics under extreme rainfall conditions between July 1977 and 2013. The findings of this study provide a reliable theoretical basis for measures to control flooding caused by extreme rainstorms and for prevention of water loss and soil erosion.