林火前后坡面覆盖类型对产流产沙影响的模拟试验

Simulation Experiment on the Influence of Slope Cover Types on Runoff and Sediment Yield Before and After Forest Fire

通过室内模拟降雨试验,设置3种降雨强度(30,60,90 mm/h)和3种地表覆盖类型(裸土坡面、1 cm马尾松枯落物覆盖、1 cm马尾松灰烬覆盖),研究林火发生前后不同地表覆盖下的坡面产流产沙过程,明确枯落物和植物灰烬覆盖的减流减沙效益。结果表明:(1)相比裸坡,枯落物和灰烬覆盖下的坡面初始产流时间分别延长33%~80%和51%~200%,灰烬覆盖对延缓产流的效果更为明显;(2)相比裸坡,枯落物覆盖的减流效果稳定在12%~36%,而灰烬覆盖在中小雨强的减流效果高于70%,在90 mm/h雨强时减流效果降低至7%;(3)裸土坡面产流呈现先快速升高后稳定的趋势,而枯落物和灰烬覆盖坡面产流效果呈现“阶梯”形上升趋势;(4)枯落物覆盖能够减小径流携沙量和总产沙量,在3种雨强下减沙效益均高于85%,且高于同雨强下灰烬覆盖的减沙效益。枯落物覆盖的减流减沙效果在不同雨强下表现较为稳定,而灰烬覆盖的减流减沙效果受降雨强度的影响显著,且枯落物覆盖的减沙效益在3种雨强下均优于灰烬覆盖,说明在林火发生后地表覆盖改变是引起土壤侵蚀增加的重要因素之一。

Through indoor simulated rainfall experiment, three kinds of rainy intensity(30, 60 and 90 mm/h) and three types of slope cover(bare slope, 1 cm Masson’s pine litter cover, and 1 cm Masson’s pine ash cover) were set up to study the process of runoff and sediment yield of slope under different ground cover before and after forest fire, and to clarify the benefits of runoff and sediment reduction under pre-fire litter cover and post-fire ash cover. The results showed that:(1) Compared with the bare slope, the initial runoff yield time was extended by 33%~80% and 51%~200% on litter-covered slope and ash-covered slope, respectively, and the ash cover had a more obvious ability in delaying runoff generation.(2) Compared with the bare slope, the runoff reduction benefit of litter cover was stable at 12%~36% under three rain intensities, while the runoff reduction benefit of ash cover was larger than 70% under 30 mm/h and 60 mm/h rain intensities, and reduced to 7% when the rain intensity was 90 mm/h.(3) The runoff yield on the bare slope showed a trend of rapid increase at first and then stable, while on the slope covered by litter and ash exhibited “stepwise” upward trend.(4) Litter cover could reduce runoff sediment carrying capacity and total sediment yield, and the sediment reduction benefits were all over 85% under the three rain intensities, and higher than that of the ash-covered slope under the same rainfall intensity. The runoff and sediment reduction benefits of the litter cover were relatively stable under different rainfall intensities, and the runoff and sediment reduction benefit of the ash cover was significantly affected by rainfall intensity. Moreover, the sediment reduction benefits of the litter cover was superior to the ash cover under three rain intensities, indicating that the change of land cover after forest fire was one of the critical factors causing the increase of soil erosion.