黄丘区小流域暴雨径流动力特征对淤地坝配置的响应

为定量揭示淤地坝措施配置对黄丘区小流域暴雨径流形成及演进过程的影响，采用室内小流域人工模拟降雨试验，对不同淤地坝措施布设情景下（无坝、单坝、双坝）小流域不同断面径流的水动力、侵蚀动力特征进行研究。结果表明：径流量与含沙量整体均随时间推移而增大，无淤地坝布设情景下径流量增幅为114.60 cm3/s，双坝情景的径流量增幅仅有70.11 cm3/s；淤地坝对小流域暴雨径流演进过程的影响显著，淤地坝布设后径流流态由主要的紊流-缓流变为以层流-缓流为主，雷诺数Re减小幅度达到12.04%～85.85%；动力参数中径流功率ω和雷诺数Re可以被认为是能够较好描述不同淤地坝布设下侵蚀产沙的动力因子。研究结果对于揭示流域暴雨径流过程及成灾机理具有重要现实意义，可为科学评价水土保持措施调控径流过程的效应提供理论依据。

Response of rainstorm runoff dynamic characteristics to check dam configuration in the small watershed of loess hilly regions

Abstract: Rainstorm has been one of the key factors causing runoff and soil erosion in the Yellow River Basin of China. The check dam can serve as one of the most important engineering measures for soil and water conservation during soil erosion control in the Loess Plateau. However, the check damn has posed a great impact on the formation, evolution, and development of the rainstorm runoff process via the changing runoff, erosion dynamics, and energy distribution in the watershed. Therefore, it is crucial to reveal the various elements nexus in the erosion system of the watershed, in order to explore the disaster mechanism of rainstorm runoff under the action of soil and water conservation measures. This study aims to quantitatively reveal the influence of the check dam configuration on the formation and rainstorm runoff evolution in small watersheds of loess hilly regions. An indoor experiment of artificial simulated rainfall was carried out to analyze the hydrodynamics and erosion dynamic characteristics of runoff at different sections in small watersheds with the different measures (no dam, single, and double dam) and the rainfall intensity as 60 mm/h, according to scale relationship. The results showed that: 1) The sediment concentration of runoff increased significantly, as the time and erosion increased the most in the case of a no-check dam. The maximum increase of erosion (runoff) was more than 114.60 cm3/s (only 70.11 cm3/s) in the case of no (double) dam. The sediment concentration values under the No. 1 single dam, No. 2 single and double dam were reduced by 0.14, 0.14, and 0.19 g/cm3, respectively, compared with that without the dam. 2) The check dams posed a significant impact on the evolution process of rainstorms and runoff in small watersheds. The double dam was the most effective to restrain the increase of velocity, while the limited control effect, compared with the single dam. The check dam had also a great influence on the runoff flow state, where the increasing resistance coefficient determined the runoff flow and sediment transport capacity. There was a time-delayed runoff from the laminar to a turbulent state, which increased the stability of flow state change. The runoff state started to change in 10-15 min without the dam, but without change in the check dam until 50 min later. 3) The check dam reduced the runoff power and runoff erosion power, further delaying the growth trend of runoff erosion power. The runoff power under the no-dam scenario was 1.42-2.45 (1.59-2.64) times that under the No.1 (double) dam scenario. More importantly, the flow pattern changed from the turbulent to laminar slow flow, where the Reynolds number decreased 12.04%-85.85% after the construction of the check dam. 4) The runoff process depended mainly on the runoff power, Reynolds number, runoff erosion power, and average velocity in small watersheds. The dominant parameters were ranked in the descending order of the runoff power, Reynolds number, runoff erosion power, and average velocity. The erosion dynamic parameters also posed a much greater impact on the evolution of runoff than the hydrodynamic force parameters. Consequently, the runoff power and Reynolds number can be expected to serve as the dynamic factors for the erosion sediment yield under different siltation dam configurations. The findings can offer practical implications for the pregnant environment and the disaster mechanism of rainstorms and runoff in the basin. A theoretical basis can also be used to evaluate the effect of soil and water conservation engineering measures on the regulation of the runoff process.