喀斯特坡地裸露心土层产流产沙模拟研究

通过人工降雨探索表土剥离后喀斯特坡地侵蚀产沙特征及机制,为该地区开展地下水土流失研究及指导水土流失防治工作具有重要的理论和现实意义。试验采用钢槽装填土石模拟喀斯特地区表土剥离后坡地的"二元结构",通过人工模拟降雨揭示了雨强(30、50、80mm h~(-1))、坡度(10°、15°、20°、25°)和地下孔(裂)隙度(1%、2%、3%、4%、5%)对坡地土壤侵蚀的影响,并在此基础上进一步讨论了各因子对剥离表土后的坡地造成的影响。结果表明:(1)表土剥离后地下漏失的隐蔽性增强,小雨强的坡地土壤侵蚀容易被忽视,30、50 mm h~(-1)雨强条件下,仅当坡地坡度≥15°时地表出现径流,坡地侵蚀产沙以地下流失为主,地下产流量、产沙量随雨强先增大后减小。(2)喀斯特地区坡地土壤侵蚀治理不应只重视地表水土流失,更应关注垂直方向上的土壤侵蚀——地下漏失,低坡度(坡度≤15°)条件下,地表近乎无产流产沙,坡地侵蚀产沙集中在地下孔(裂)隙,而坡度为20°、25°的坡地,其地下产沙比重仍分别高达0.85~0.97、0.59~0.84。剥离表土后的坡地水土保持应从地表、地下两个方向进行,避免由地下漏失引起的岩溶塌陷。增大地下孔(裂)隙度能显著提高地下产流量和产流系数,并促进地下孔裂隙产沙量和产沙比重的增加。

Simulation Study on Bare Subsoil Runoff and Sediment Yield on Karst Slope

Objective]The unique"dualistic structured"(land surface and underground) hydrologic system in the karst areas of Southwest China has the areas subjected to two types of soil erosion simultaneously,i.e. surface erosion and underground erosion. Relevant researches show that soil erosions on the land surface and in the underground crevices are the two pathways for and components of the soil and water loss in the karst region. In recent years,with the intensified development in the karst region of Southwest China,construction of industrial parks and urbanization has become a hot spot. Consequently large areas of forest land and/or cultivated land have or are being stripped of topsoil for construction projects,thus depriving the land of its vegetation protection and topsoil cover,and making it completely nude and exposed to rainfall erosion. Currently,though much effort has been done studying underground soil and water loss in karst area,almost nothing has been reported about characteristics of the soil erosion on slope land with topsoil stripped of,and the researches,done or being carried on,fail to illustrate either characteristics of the spatial distribution of runoff and sediment in the surface and underground of slopes or effects of affecting factors,like rainfall,slope,underground fissure porosity,etc. of slope soil erosion on characteristics and mechanisms of runoff and sediment generation on stripped slopes in the areas. Therefore,this study is oriented to illustrate and analyze distribution characteristics of runoff and sediment in the surface and underground along stripped slopes,and further to explore effects of rainfall,slope,underground fissures, pores and holes on soil erosion. Method]An indoor experiment was carried out using steel troughs filled up with rocks and soil to simulate the"dualistic structure"of stripped slopes the karst area. In the experiment, troughs were adjusted to slope gradient,10°,15°,20° and 25°,separately,and rainfalls different in intensity(30,50 and 80 mm h-1)were simulated on troughs of artificial slopes,different in fissure porosity (10°,15°,20° and 25°),to explore how the three factors affecting soil erosion on the slopes.Result]Results show that:(1)On stripped slopes,underground erosion became more elusive and tended to be neglected when the rainfall event was low in intensity. When rainfall intensity rose up to 30 and 50 mm h-1, underground soil and water loss turned to be in dominancy and surface runoff was observed only on slopes ≥15°in gradient. With rainfall rising in intensity,underground soil and water loss varied in a curve of saddle shape,and the variation with rainfall intensity displayed an order of 80<30<50 mm h-1 in magnitude.(2)On gentle slopes,≤15°,soil and water loss occurred mainly in the fissures and pores underground,and was not observed on the surface,while on slopes,20° or 25°ingradient,the underground sediment yield accounted for 85%~97% and 59%~ 84% of the total on the slope.(3)The effect of underground holes and porosity on underground soil and water loss was significant,and a positive relationship was observed of underground runoff and runoff coefficient with underground fissure porosity. The higher the fissure porosity,the bigger the channels for soil and water loss and the more soil and water lost underground,and hence the higher the proportion of the underground soil and water loss to the total.Conclusion]To control soil erosion in karst areas,it is not wise to pay attention only to surface soil erosion. Downwards erosion or underground soil and water loss should be the focus of attention in the karst region. In development and construction projects,it is crucial to control underground leakage,so as to avoid leakage-triggered collapse of underground karst caves. All the findings in this study are expected to be of some theoretical and practical significance to future studies on underground soil and water loss as well as guidance of soil erosion prevention and control in the karst areas.