| Soil relates to human survival and development, and Karst Areas system which is one of the most serious soil erosion areas is typical of the ecologically fragile area because of high sensitivity, low catastrophe capacity and small environmental capacity.Karst is widespread in China and distributional area of carbonate rocks is up to3,463,000km2including buried karst. Additionally, the area in exposed stratum of carbonate rocks is2.06million km2, while the area of explosed carbonate rocks is907,000km2.The variation of runoff and sediment yield of surface and underground runoff with rainfall duration affected by different pore fissure degree, exposed bedrock rate and rainfall intensity were studied through artificial rainfall simulation. Artificial rainfall simulation has contributed to provide a theoretical basis for evaluation and assess of soil erosion in karst areas and control measures of rocky soil erosion in future.The results showed:1The impacts of each factor on the slope runoff(1) Surface and subsurface cumulative runoff increased with the increase of the rainfall intensity;the fluctuation range of surface runoff is great,the fluctuation range is from146.5to685L;the fluctuation range of subsurface runoff is smaller than surface,the fluctuation range is from119.5to327.3L.With the rainfall duration,the fluctuation range of surface runoff is2L and the fluctuation range of subsurface runoff is2.5L in rainfall intensity with30mm/h; the fluctuation range of surface runoff is6L and the fluctuation range of subsurface runoff is5.5L in rainfall intensity with50mm/h;the fluctuation range of surface runoff is13L and the fluctuation range of subsurface runoff is6L in rainfall intensity with150mm/h; the fluctuation range of surface and subsurface runoff increased with the increase of the rainfall intensity; the variation of surface and subsurface runoff fluctuated with rainfall duration.(2) In smaller rainfall intensity with30mm/h and50mm/h and the larger bare rock rate with50%, the infiltration rate is greater,all of rainfall is infiltration and the surface did not produces runoff; surface and subsurface cumulative runoff increased with the increase of the rainfall intensity in the same bare rock rate;the variation of surface and subsurface runoff fluctuated with bare rock rate in the same rainfall intensity.(3) The surface runoff is the largest for758.8L in the largest rainfall intensity with150mm/h and the smallest underground cracks holes with l%;The surface runoff is the smallest for98L in the smallest rainfall intensity with30mm/h and the largest underground cracks holes with5%;The subsurface runoff is the smallest for68.1L in the smallest rainfall intensity with30mm/h and the smallest underground cracks holes with1%;The subsurface runoff is the smallest for345.2L in the largest rainfall intensity with150mm/h and the largest underground cracks holes with5%;Surface and subsurface cumulative runoff increased with the increase of the rainfall intensity in the same underground cracks holes,Surface cumulative runoff decreased with the increase of the underground cracks holes in the same rainfall intensity,but the subsurface is reversed.(4) Surface and subsurface cumulative runoff has little change and the variation is fluctuating within the range of10L;In the same rainfall intensity,the variation range of surface runoff is from143.5L to629.5L,the variation range of subsurface runoff is from95L to367L,so surface cumulative runoff is larger than subsurface.the variation of surface and subsurface runoff fluctuated with rainfall duration.The fluctuation range of surface runoff is the largest in the rainfall intensity with150mm/h and the slope is84.658;The fluctuation range of subsurface runoff is the smallest in the rainfall intensity with30mm/h and the slope is84.658.2The impacts of each factor on the surface soil loss(1) When the rain intensity is smaller(30mm/h), the ground surface did not loss bed load,only loss suspended sediment,It can be seen that the loss of ground surface to produce bed load have critical rainfall intensity;with the rainfall intensity increases, the loss of bed load and suspended sediment generated from ground surface are increased,the changes of suspended sediment loss generated from ground surface is larger,and soil loss mainly through suspended sediment,the soil loss that through suspended load is2/3of the ground surface soil total loss;When rainfall intensity is unchanged,bed load and suspended load is generated ground surface loss is fluctuated along rainfall duration,and at the same rainfall intensity,with rainfall duration,the changes of bed load loss generated from ground surface is larger than suspended sediment loss.(2) When the rain intensity is smaller (30mm/h), the ground surface did not generate bed load loss;In the exposed bedrock was50%,When the rain intensity is30mm/h and50mm/h,ground surface did not have bed load and suspended sediment loss;In the same bare rock,bed load and suspended load loss that generated from ground surface is rainfall intensity increasing;at the same rainfall intensity,soil erosion from ground surface is fluctuated with exposed bedrock rate increases;Soil loss mainly through the suspended sediment.(3) When the rain intensity is smaller (30mm/h) and underground holes and fissures is larger (3%,4%and5%), ground surface did not have bed load loss,have only suspended sediment loss; At the same degree of underground fissures holes,soil loss generated from ground surface is increases with rainfall intensity increasing;at the same rainfall intensity,Soil loss generated from surface ground is increases with the degree of underground holes and fissures decreasing;The soil loss mainly through suspended sediment,When the rain intensity is150mm/h, the maximum loss of soil is199.94g/min.(4) When the rainfall intensity is smaller (30mm/h), the Ground surface did not have bed load loss,have only suspended sediment loss;surface ground soil loss is fluctuated with rainfall duration; With the rainfall intensity increasing, the loss variation of surface ground soil is increases,When the rain intensity is30mm/h, the suspended sediment loss of ground surface is changed4.1345, When the rain intensity is150mm/h, the suspended load loss of ground surface is changed102.499; When the rain intensity is150mm/h, the suspended load loss of ground surface is changed largest,K190.3,When the rain intensity is30mm/h, the suspended load loss of ground surface is changed smallest,K=0.0817,When the rain intensity is30mm/h, did not have bed load loss, so the relationship between the bed load cumulative and rainfall duration is a parallel line:y=0.3The effects of various factors on the subsurface erosion(1) Subsurface loss drained through suspension, without a loss of over, so it produced suspended sediment, no load. Soil loss increases with the rainfall intensity. There was fewer changes of soil loss when the rainfall intensity was30-50mm/h, greater changes of soil loss when the rainfall intensity was50-80mm/h varies widely, and the small changes in the rainfall intensity which was120-150mm/h.(2) The amount of soil loss increased with rainfall intensity when rock exposed rate was stable; soil loss in surface and subsurface were volatility with rock exposed rates increasing when the rainfall intensity was constant.(3) Soil loss amount increased with the rainfall intensity when underground hole fracture was stable. Soil erosion amount increased with the underground hole fracture when the rainfall intensity was stable. Variation of soil erosion was the greatest when rainfall intensity increased from50mm/h to80mm/h.(4) Subsurface loss was greater with rainfall intensity. Soil loss fluctuated with rainfall duration and the variation of soil loss was large with rainfall intensity. Variation of surface suspended sediment (K=23.443) was the largest when rainfall intensity was150mm/h while variation of surface suspended sediment (K=6.0077) was the lest when rainfall intensity was30mm/h.The degree of correlation between soil erosion and each factor was rainfall intensity>rain time>degrees of underground holes and fissures>ratios of uncovered rocks. |
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