| The Karst Trough Valley not only has a special surface/underground double geological structure,but also has a typical rock strata dip:dip/anti-dip slope.A Karst landscape,which formes surface and underground double-layer structures under the influences of tectonism and long-term karst processes is characterized by degraded and rocky surface landscape with desertification,and the underground layer contains a complex hydrological system.Because of the great difficulty of directly determining the underground fissure flow,the surface loss and underground leakage on dip/anti-dip slope remains unknown.There are two key scientific questions to be solved in the comprehensive rehabilitation measures for land rocky desertification in Karst Trough Valley as follows:reveal the relationship between geological characterstic and the space distribution of runoff sediment.Therefore,carrying out the research about the characteristics of the Karst Trough Valley containing dip/anti-dip slope and understanding the impact of rock strata dip on the mechanism of surface loss and underground leakage have extremely important significance,which would promote the develop high efficient techniques on the prevention of the surface loss and underground leakage in Karst Trough Valley.This paper selected karst bedding/inverse slope as the research object in Karst Trough Valley area.It applied soil science,water hydrology,soil erosion theory.Basis on the field surveying,the spatial distribution of bedding/inverse slope was inverstigated in Karst Trough Valley area and analyzed the physical properties of the Karst Trough Valley.First,field sampling methods were used to survey the soil physical-chemical properties,spatial variation characteristics and the environmental impact factors on dip/anti-dip slope of the Karst Trough Valley.Secondly,an indoor artificial simulation of rainfall experiment,designed to dip/anti-dip slopes?10°,20°,30°,40°and 60°?,5treatments in rainfall intensities?0.25,0.5,0.75,1.0 and 1.5 mm/min?and 5 treatments in underground pore fissures?1%?2%?3%?4%and 5%?in nearest dwell angle?25°?was carried out to study characteristics of surface loss and underground leakage and hydrodynamic parameters and their relationships on dip/anti-dip slopes in Typical Karst Valley.The results could provide valuable information for the establishment of empirical soil erosion model and a theory foundation for controlling surface erosion and underground leakage in Karst Trough Valley on a national scale.The main results were as follows:1.Revealing the spatial variability of soil physical-chemical properties and its environmental impact factors on dip/anti-dip slope in Karst Trough Valley preliminary.?1?Based on the geostatistical analysis,the optimal model for describing the spatial distribution characteristics of soil physical-chemical properities on dip/anti-dip slope is Gaussian model.For the dip slope,most of the structural ratio?C/?C+C0??of the soil physical properties were more than 75%,and its spatial correlation were significant.For the anti-dip slope,the structural ratio?C/?C+C0??of the soil physical properties were lower than that of the dip slope,and its spatial correlation were weak.In addition,the fitting degree of soil physical-chemical properties on anti-dip slope were higher than that on dip slope.?2?According to the comparision of semi-variance model range,the ranges of the dip/anti-dip slope were larger than the sampling interval?20 m?,which indicated that the actual soil sampling number in this study can meet the requirements for the analysis of the spatial variability of soil properties.Meanwhile,the spatial differentiation characteristics of soil physical-chemical properities on dip/anti-dip slope were different by the GIS geostatistics.The spatial variability of surface soil physical-chemical properities is relatively strong,varies from each other,and is mainly affected by natural factors.In addition,the actual research area can be well predicted by the spatial predicted distribution map through the ordinary interpolation.?3?Based on the comprehensive correlation analysis of environmental factors,the environmental factors take significant effect on the spatial distribution of soil physical-chemical properities.For dip slope,the incidence of environmental factors are in the order of slope position?-0.8008?>bedding dip and rock strike?-0.6514?>slope aspect?-0.4933?>vegetation coverage?-0.4783?>farming level?0.4366?>bedrock bare rate?0.3831?>slope?0.3302?>vegetation type?0.3063?>rock dip?-0.2122?>slope shape?-0.0681?.For the anti-dip slope,the incidence of environmental factors are in the order of slope position?-0.9142?>slope shape?-0.4165?>vegetation type?0.3829?>vegetation coverage?-0.3698?>slope aspect?0.322?>bedrock bare rate?0.2743?>farming level?0.2572?>bedding dip and rock strike?0.1454?>rock dip?-0.0395?>slope?0.0161?.In general,the slope position is the most important environmental constraint factor for the spatial variation of the dip/anti-dip slope in Karst Trough Valley at small scale.2.Figuring out the threshold of rainfall intensity,underground pore fissures and bedding dip on the runoff and sediment yield,and understanding the mechanism of surface loss and underground leakage on dip/anti-dip slope of Karst Trough Valley.?1?The study on the change law of surface/underground runoff and its influencing factors in Karst Trough Valley.The application of light rainfall?0.25 and 0.5 mm/min?for 60 min did not generate surface runoff on the slope.The surface runoff occurred on the slope when the rainfall intensity was 0.75 mm/min.When the rainfall intensity was1.5 mm/min,the surface runoff exceeds the underground runoff.For the dip slope,the 3%underground pore fissure is the critical value of surface/underground runoff,the 40°bedding dip is the critical value of surface runoff,and the 20°bedding dip is the critical value of underground runoff.For the anti-dip slope,the surface runoff is the major component when the underground pore fissure is 1%,while the underground runoff exceeded the surface runoff when the underground pore fissure over the 1%.When the bedding dips were the 30°and 40°,the surface runoff is the major part of the runoff,while the underground runoff is the main compont for other bedding dip.There is an extremely significant negative correlation between surface runoff and underground runoff,and the coefficient of the partial correlation is r=-0.903.?2?The study on the change law of surface/underground sediment yield and its influencing factors in Karst Trough Valley.The dip/anti-dip sloep is dominated by underground sediment yield when the rainfall intensity is 0.25 and 0.5 mm/min,while it is dominated by surface sediment yield when the rainfall intensity is over the 0.75mm/min.For the dip slope,the soil was lost mainly along the soil surface,the surface sediment yield first increase and then decrease,and the maximum sediment yield appeared at the 30°bedding dip.However,the underground sediment yield varied with a bedding dip peak about 30°.For the anti-dip slope,the the underground sediment yield exceeded the surface sediment yield when the underground pore fissure was 1%.When the bedding dips were the 10°and 60°,the surface runoff is the major part of the runoff,while the underground sediment yield is the main compont for other bedding dip.There is an extremely significant negative correlation between surface runoff and underground runoff,and the coefficient of the partial correlation is r=-0.786.?3?The study on the change law of surface/underground flow-sediment and its influencing factors in Karst Trough Valley.There was only underground suspended load generate on dip/anti-dip slope when the rainfall intensity is small?0.25and0.5mm/min?.The 0.75 mm/min is the critical value of the surface bed load generate on dip/anti-dip slope.For the dip slope,the maximizing surface suspended mass appeared at the 3%underground pore fissures.The surface bed load was the main component when the bedding dip is 30°,while the surface suspended mass is the major part of the soil for other bedding dip.For the anti-dip slope,the underground suspended mass was higher than surface suspended mass when the bedding dip were the 10°and 60°,while the surface suspended mass exceeded the underground suspended mass for the other bedding dip.There was a highly significant correlation between surface/underground runoff and sediment,the relationships were as follows:U=aQ+b.3.Determining the relationship between the flow-sediment and hydrodynamic parameter under the different conditions with rainfall intensity,underground pore fissures and bedding dip,and establishing the model of surface runoff and sediment yield in Karst Trough Valley.?1?The flow velocity,runoff depth,Reynolds number?Re?,Froude number?Fr?,shear stress and flow power increased with the increasing of rainfall intensity,while the flow resistance coefficient and manning roughness decreased.For the dip slope,the maximum flow rate and flow power generate at the 3%underground pore fissure,and the maximum runoff depth,flow resistance,manning roughness and shear stress appeared at the 4%underground pore fissures.However,when the bedding dip was 60°,the minimum Fr value was less than 1,shear stress and retardation reached the maximum.For the anti-dip slope,the maximum Fr value appeared at the 3%underground pore fissures,the maximum shear stress?0.0059Pa?appeared at 1%underground pore fissures,and the minimum flow power?0.00037N/ms?appeared at 5%underground pore fissures.In addition,the runoff depth,Re,shear stress and flow power reached the maximum at the 30°bedding dip,while the maximum Fr value appeared at the 40°bedding dip.?2?Significant negative correlation was found between Resistance coefficient?f?and Reynolds number?Re?on the dip/anti-dip slope,and it can be described by a linear equation:f=aRe+b.Meanwhile,significant negative correlation was also found between Resistance coefficient?f?and Froude number?Fr?,and it can be described by a power function equation:f=aReb.?3?For a single hydrodynamic parameter,the fitting degree of unit energy of cross section was highest with the runoff on dip/anti-dip slope,while the fitting degree between flow power and runoff of the anti-dip slope and sediment yield of the dip/anti-dip slope were the highest.Each single hydrodynamic parameter had a quadratic function relationslip with the runoff and sediment yield on dip/anti-dip slope.For the multiple hydrodynamic parameters,the fitting degree of each combination of dip/anti-dip slope was high and its influence on runoff is extremely significant,except for the cross section energy and shear stress had lower fitting degree with the runoff of anti-dip slope.In conclusion,this study took the dip/anti-dip slope of Karst Trough Valley of Youyang County,Chongqing Province as the research object.First,by the methods of geostatistics and GIS spatial analysis methods,the spatial variation characteristics of soil properties on dip/anti-dip were recognized,and the influence of environmental factors on the spatial variation of soil physical-chemical properties was revealed.The results showed that the correlation of spatial distribution of soil physical-chemical properties on dip slope was higher than that on anti-dip slope,and the slope position is the most critical influenced environmental factor for the spatial variation of soil physical-chemical properites.Secondly,based on the field survey,indoor simulated rainfall experiments were used to exam the effect of rainfall intensity,underground pore fissure and bedding dip on the surface loss and underground leakage and determine the best hydrodynamic parameters of the model.Overall,Acrodding to the combination of field observation and indoor simulation,the process and characteristics of surface loss and underground leakage were studied by the methods of classical statistics,geostatistics and simulated rainfall.The research methods and techniques have been innovated,the mechanism of the surface loss and underground leakage on dip/anti-dip slope is advanced,which provides scientific and technological support for the comprehensive control of rocky desertification in Karst Trough Valley. |
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