Multiple soil and water conservation measures applied together perform better at reducing runoff and sedimentation than individual measures, which can be attributed to their synergistic effects on water erosion. However, whether these synergistic effects are always effective at reducing water erosion remains unclear. In this study, a series of physical models representing a slope-gully system were tested to quantify the trend of synergistic effects of multi-measure over time through simulated rainfall. The tested scenarios included four vegetation patterns on the slope—Pattern A: no grass, Pattern B: grass on the up-slope, Pattern C: grass on the middle-slope and Pattern D: grass on the down-slope—and five levels of runoff path length decrease (RPLD) in the gully caused by sedimentation of a check dam (0, 1, 2, 3 and 4 m). Synergistic effects on runoff and sediment yields were influenced by vegetation patterns and RPLDs. Under the same vegetation patterns, synergistic effects increased with increase of RPLD. Under the same RPLD, the mean value of synergistic effects on runoff was in the following order: Pattern D (0.10%) > Pattern C (0.09%) > Pattern B (0.06%), and synergistic effects on sediment yields had a similar order: Pattern D (0.60%) > Pattern C (0.42%) > Pattern B (0.22%). Under Pattern B, based on the Mann–Kendall trend test, the synergistic effects on the runoff yields decreased over time. Contrastingly, under Patterns C and D, the synergistic effects on the runoff yields increased over time. The results show that the synergistic effect has time effect, and its change trend is related to vegetation patterns. Additionally, the results suggest that the middle- and lower-slopes should be prioritized when restoring vegetation as the synergistic effects on runoff tend to increase when these have good vegetation cover.

中文翻译：

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植被格局和沉积作用之间的协同作用对坡沟系统中的水侵蚀具有时间影响

多种水土保持措施联合应用在减少径流和沉积方面比单独采取措施效果更好，这可以归因于它们对水土流失的协同作用。然而，这些协同效应是否始终能有效减少水土流失仍不清楚。在本研究中，测试了代表坡沟系统的一系列物理模型，通过模拟降雨来量化多措施随时间的协同效应趋势。测试场景包括斜坡上的四种植被模式——模式A：无草、模式B：上坡有草、模式C：中坡有草、模式D：下坡有草——以及五个级别淤积坝（0、1、2、3 和 4 米）沉积引起的沟渠径流路径长度减少（RPLD）。径流和产沙量的协同效应受到植被格局和 RPLD 的影响。相同植被格局下，协同效应随着RPLD的增加而增强。在相同的RPLD下，径流协同效应的平均值如下：模式D（0.10%） >模式C(0.09%)>>模式B(0.06％)和对沉积物产量的协同效应具有相似的顺序：模式D(0.60％) >模式B(0.06％)。模式C(0.42%)>>模式 B (0.22%)。在模式 B 下，根据曼-肯德尔趋势检验，径流产量的协同效应随着时间的推移而减少。相比之下，在模式 C 和 D 下，径流产量的协同效应随着时间的推移而增加。结果表明，协同效应具有时间效应，其变化趋势与植被格局有关。此外，研究结果表明，在恢复植被时应优先考虑中坡和下坡，因为当这些坡地植被覆盖良好时，对径流的协同效应往往会增加。