坡面径流过程流量自动观测方法

Automatic approach to the measurement of low flow in the slope runoff processes

坡面径流过程中的流量自动观测是目前野外实验的难点问题。通过室内试验和野外人工模拟降雨径流场试验,分析了翻斗式雨量计与20°和30°三角堰中自记水位计在测量15l/min以下的小流量上的差异。获得了不同流量条件下20°和30°堰角的流量系数。以该系数的计算结果与实测流量对比表明,随水头的减小和堰角的增大而误差增加。野外实验结果表明,自记水位计测定小流量的结果偏低约15%,在流量很小时无法记录到数据,不能完整记录整个退水过程。依据试验结果,实现了以翻斗式流量计与自记水位计相结合的组合式流量监测方法的设计,为精确测量低含沙的小流量和变化流量的流域水文实验提供了监测手段。

Low flow is a main pattern in surface runoff, subsurface runoff and base flow in arid and semi-arid region. It＇s most important to keep the stability of regional eco-environment. However, it＇s hard to measure precisely this kind of low flow using the available instruments. The difference of low flow less than 15l/min between tipping bucket rain gauge and automatic water level recorders immerging into triangle weir box with outlets of 20 degrees and 30 degrees were discussed by the outdoor experiments at runoff plot with rainfall simulator and the indoor supplement experiments. Indoor experiments results showed that, when water level at outlet of weir box was lower than 10 mm, the mean measured discharge by tipping bucket rain gauge was 2 % higher than the real amount measured by cylinder. The discharge coefficients for 20 degree and 30 degree weir box could be expressed with individual piecewise function at 10 mm and 15 mm headwater, respectively. The discharge coefficient of 20 degree weir box tended to be a constant by 0. 289 if headwater was up to 55 mm. That of 30 degree weir box tended to be a constant by 0. 449 at headwater up to 15 mm. Compared the calculating results with parameters from indoor experiments to the real amount, the error of simulating method increased with the decline of headwater and with the enlargement of weir box degree. Field experiments showed that the measuring result of automatic water level recorder was 15% lower than the real amount in low flow. When the headwater was lower than 0. 5 mm, the variation of flow was so weak that the data for automatic water level recorder failed to be measured. Therefore, the recession process could not be recorded entirely. With the experiments, a low flow measurement system integrated the tipping bucket flow meter and automatic water level recorder was presented. It will provide a precise approach for low flow and various flows with sediment concentration up to 1 kg/m^3 for catchment hydrologic experiments.